Technical feasibility of the mechanical release of predator insects
to control the Colorado potato beetle, Leptinotarsa decemlineata
(Say)
Mémoire
Saad Almady
Maîtrise en génie agroalimentaire
Maître ès sciences (M. Sc.)
Québec, Canada
© Saad Almady, 2013
Résumé
Le doryphore de la pomme de terre (DPT), Leptinootarsa decemlineata (Say) (Coleoptera: Chrysomelidae) est l’insecte ravageur qui cause le plus de dommage aux plants de pommes de terre, de tomate et d’aubergine en se nourrissant de leur feuillage. Le DPT est devenu un phénomène inquiétant vu sa présence dans presque 16 millions de km² répartis à travers l’Amérique du Nord, l’Europe et l’Asie et il continue par sa grande capacité de se propager. Actuellement, les insecticides chimiques représentent le moyen le plus efficace pour lutter contre le DPT. Malheureusement, l’utilisation excessive des produits chimiques pour lutter contre le DPT devient inefficace après quelques années puisque cet insecte nuisible réussit à développer une résistance envers ces produits. Aussi, l’utilisation excessive et incontrôlée des insecticides chimiques est coûteuse pour les producteurs de pommes de terre et pourrait résulter en de sérieux problèmes environnementaux et de santé humaine. Compte tenu de ce qui précède, les chercheurs scientifiques ont redoublé d’efforts pour trouver des alternatives intéressantes aux produits chimiques afin de lutter contre le DPT. Une des alternatives consiste à utiliser le contrôle biologique en procédant à un lâcher massif d’ennemis naturels du DPT. Cette alternative qui ne fait recours à aucun produit chimique est très avantageuse puisqu’elle permet de produire des produits biologiques tout en préservant l’environnement. L’efficacité de cette alternative à contrôler le DPT a été prouvée à petite échelle. Toutefois, le lâcher manuel des insectes prédateurs à grande échelle est inconcevable. Pour remédier à ce problème, quelques récents travaux de recherche ont mis l’emphase sur le lâcher mécanique des prédateurs pour lutter contre les insectes nuisibles. L’objectif de ce travail de recherche
était de tester un distributeur mécanique de larves de deuxième, troisième et quatrième stades de Podisus maculiventris dans un champ de pommes de terre. Les résultats obtenus ont démontré que le prototype de distribution mécanique est efficace en ce qui a trait au lâcher de prédateurs dans les parcelles de pommes de terre. Aussi, le contrôle du DPT dans les parcelles de lâcher mécanique est aussi efficace que celui dans les parcelles de lâcher manuel et ce par comparaison aux parcelles témoins sans aucun contrôle.
Abstract
The Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae) is a pest insect that can cause real damage to potato, tomato, and eggplant crops by consuming their leaves if left uncontrolled. The CPB is becoming an alarming phenomenon because of its presence in about 16 million km² spread across North America, Europe, and Asia, and it is still spreading. Currently, chemical insecticides are the most effective mean to control the CPB. Unfortunately, the exclusive use of chemicals to control the CPB becomes ineffective after few years because this pest insect succeeds to develop resistance to such chemicals. Also, excessive and uncontrolled use of chemical insecticides is costly for potato growers and could lead to serious human health and environmental problems. Therefore, scientists have been trying to find interesting alternatives to control the CPB. One of these alternatives consists of using the biological control by massive release of natural enemies of the CPB. This chemical free alternative has several significant advantages as it allows producing organic food while preserving the environment. The effectiveness of this alternative in controlling CPB populations has been proven at small scale. However, hand release of predator insects at large scale is unconceivable. To remedy to this problem, some recent studies carried out in the last few years have focused on the mechanical release of predators to control pest insects. The objective of this research study was to test a mechanical distributor of second, third, and forth-instar nymphs of Podisus
maculiventris in a potato field. Obtained results showed that the mechanical release system
is efficient in releasing predators in potato plots. Also, the control of CPB in the mechanical release plots is as efficient as that in the manual release plots compared the check plots with no control.
Table des matières
Résumé ... i
Abstract ...iii
Table des matières ... v
Liste des tableaux ... vii
Liste des figures ... ix
Dédicaces ... xi
Remerciements ...xiii
Avant-propos ... xv
INTRODUCTION ... 1
CHAPITRE I: REVUE DE LITTÉRATURE ... 3
1.1 Colorado potato beetle ... 3
1.2 Management of the Colorado potato beetle ... 5
1.2.1 Cultural control ... 5
1.2.2 Physical control of Colorado potato beetle ... 6
1.2.3 Chemical control ... 7
1.2.4 Biological control ... 9
1.2.4.1 Natural enemies of the Colorado potato beetle ... 10
1.2.4.2 Storage conditions of the natural enemies ... 11
1.3 Mechanical release of natural enemies ... 11
CHAPITRE II: HYPOTHÈSE ET OBJECTIFS ... 16
Hypothèse ... 16
Objectifs ... 16
CHAPITRE III: PARTIE EXPÉRIMENTALE, RÉSULTATS ET DISCUSSION ... 17
Résumé ... 18
Abstract ... 19
3.1 INTRODUCTION AND LITERATURE REVIEW ... 20
3.2 MATERIALS AND METHODS ... 22
3.2.1 Predators ... 22
3.2.2 Description of the mechanical release system ... 23
3.2.3 Experimental design and procedure ... 25
3.2.4 Statistical analyses ... 27
3.3 RESULTS AND DISCUSSION ... 28
3.3.1 Predator release efficiency on the adult stage of the CPB ... 28
3.3.2 Predator release efficiency on the L3-L4 stage of the CPB ... 29
3.3.3 Predator release efficiency on the L1-L2 CPB populations ... 30
3.4 CONCLUSIONS AND RECOMMENDATION ... 34
Acknowledgements ... 34
References ... 34
CHAPITRE IV: CONCLUSION GÉNÉRALE ET RECOMMANDATIONS ... 38
4.1 Conclusion générale ... 38
4.2 Recommandations ... 39
Références ... 40
Liste des tableaux
Table 1.1: Common names of insecticides to which the Colorado potato beetle has
developed resistance (Whalon et al., 2008)………. ... 8
Table 3.1 ANOVA results for the predator release efficiency on the CPB adult population. 28
Table 3.2 ANOVA results for the predator release efficiency on the L3-L4 stage of CPB. ... 29
Table 3.3 ANOVA results for the predator release efficiency on the L1-L2 stage of CPB. ... 31 Table 3.4 ANOVA results for the predator release efficiency on the CPB egg masses. ... 32
Liste des figures
Figure 1.1: Colorado potato beetle larvae feeding on potato plant leaves ... 3
Figure 1.2: A Colorado potato beetle larva feeding on a tomato (http://www.omafra.gov.on.ca/ IPM/english/tomatoes/insects/colorado-potato-beetle.html) ... 5
Figure 1.3: Overview of trenches covered by plastic rolls (Boiteau and Vernon, 2001) ... 6
Figure 1.4: Perillus bioculatus adult (http://www.omafra.gov.on.ca/IPM/english/tomatoes/inse) ... 9
Figure 1.5: Podisus maculiventris adult (http://greenmethods.com/biocontrols/podisus/) ... 10
Figure 1.6: Manual release of predator insects using a small brush ... 12
Figure 1.7: View of a specially designed container for predator release (Khelifi et al., 2011) .. 12
Figure 1.8: Plastic device specifically designed to open the containers filled with a mixture of predators and popcorn ………... ... 13
Figure 1.9: Predator release system designed by Khelifi et al. (2011) ... 14
Figure 1.10: Overview of the field mechanical release prototype ... 15
Figure 1.11: New version of the containers used in the field mechanical release prototype: the containers are filled with a mixture of predators and popcorn ... 15
Figure 3.1: Predators mixed with popcorn as a carrier material. ... 23
Figure 3.2: The mechanical release system connected to the three-point hitch of the tractor 24 Figure 3.3: Close view of the mechanical release system. ... 25
Figure 3.4: Dimensions and random arrangement of the plots. ... 26
Figure 3.5: Evolution of the CPB adult populations under the three treatments: control, mechanical, and manual………. ... 29
Figure 3.6: Evolution of the L3-L4 CPB populations under the three treatments: control, mechanical, and manual………. ... 30
Figure 3.7: Evolution of the L1-L2 CPB populations for the three treatments: control, mechanical, and manual………. ... 32
Figure 3.8: Evolution of the number of CPB egg masses for the three treatments: control, mechanical, and manual………. ... 33
Dédicaces
I dedicate this thesis to my parents, my wife, and my
Remerciements
I would like first to gratefully acknowledge my supervisor Professor Mohamed Khelifi for his unlimited help and support. He gave me from his experience and time a lot, which makes me never gives him real word.
I gratefully acknowledge the financial support from the Ministère de l’agriculture, des pêcheries et de l’alimentation du Québec (MAPAQ) and the technical support from Yannick de Ladurantaye, Sylvain de Ladurantaye, and Marie-Ève Lemieux. I also thank la Ferme Daniel Bolduc et fils 1980 Inc. for providing the necessary plots to carry out the experiments as well as a tractor to operate the mechanical distributor.
I would like also to thank the Saudi Arabian Cultural Bureau and King Saud University for funding and providing me with a source of income, which has enabled my dream to come true.
Finally, I am gratefully thankful to my family in Saudi Arabia for their help and support.
Avant-propos
This M. Sc. thesis contains four chapters. The first chapter is dedicated to the literature review including Colorado potato beetle (CPB), alternative methods to control the CPB, and the mechanical release system designed and built at the Department of Soils and Agri-Food Engineering of Université Laval. The second chapter presents the hypothesis and objectives of the research study. The third chapter mainly contains the paper « Control of the Colorado potato beetle, Leptinotarsa decemlineata (Say), using predator insects released by a mechanical prototype », which was published in 2012 in the Journal of Environmental Science and Engineering. The fourth chapter represents a general conclusion and some recommendations for future work.
INTRODUCTION
La pomme de terre (Solanum tuberosum) est, sans aucun doute, un des aliments les plus consommés au monde (Agyours International, 2013). Une forte diminution dans la production de cette culture peut alors affecter la sécurité alimentaire et l'économie agricole. En outre, certains pays misent sur la pomme de terre comme aliment principal au lieu du riz et du pain. Pour ces raisons, les producteurs de pommes de terre essaient d'augmenter le rendement de cette culture en contrôlant les ennemis qui peuvent y causer de réels dommages. Le véritable ennemi de la culture de pommes de terre est le doryphore de la pomme de terre (DPT), Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), qui est le principal insecte ravageur en Amérique du Nord, en Europe et en Asie (Hare, 1980; Jolivet, 1991; Boiteau et al., 1992; Radcliffe et al., 1993; Howard et al., 1994).
Le DPT est un ravageur difficile à contrôler en raison de sa capacité à résister à la plupart des moyens de lutte chimique. Aux États-Unis, plus de 30 ingredients actifs sont enregistés pour contrôler le doryphore (Alyokhin et al., 2008). Jusqu’à présent, le DPT a réussi à développer une résistance envers la plupart des pesticides chimiques commerciaux homologués. La résistance à l’imidacloprid est déjà rapportée dans plusieurs états américains, notammnent le Michigan, New York et le Maine (Mota-Sanchez et al., 2006; Alyokhin et al., 2007, 2008). Aussi, l'utilisation excessive et incontrôlée de moyens chimiques pour lutter contre cet insecte ravageur peut engendrer des problèmes environnementaux et de santé humaine.
Compte tenu de ce qui précède, les chercheurs scientifiques n’ont cessé de déployer des efforts pour trouver d’autres alternatives aux pesticides chimiques. Depuis plusieurs décennies, la lutte biologique utilisant des prédateurs entomophages a été explorée comme alternative aux insecticides chimiques pour contrôler les insectes nuisibles (Le Berre et Portier, 1963). Toutefois, cette alternative est la moins développée en Amérique du Nord pour le contrôle du doryphore en particulier. L’utilisation d’un prédateur naturel du ravageur tel que la punaise prédatrice Perillus bioculatus ou Podisus maculiventris, seule ou en combinaison avec d’autres approches biocompatibles, est une alternative efficace
pour le contrôle à long terme du doryphore (Cloutier et al., 2002). Cette efficacité a été prouvée à petite échelle en procédant au lâcher des insectes prédateurs sur le feuillage des plants de pommes de terre à l’aide d’un petit pinceau. Cependant, cette façon de faire est inconcevable à grande échelle vu le grand nombre d’insectes prédateurs requis pour un contrôle adéquat du DPT. Il est alors impératif de mécaniser l’opération de lâcher d’insectes prédateurs dans les champs de pommes de terre.
L’équipe de recherche du Dr Mohamed Khelifi, professeur au Département des sols et de génie agroalimentaire de l’Université Laval, a réussi au fil du temps à concevoir et fabriquer un prototype de distribution mécanique d’insectes prédateurs (de Ladurantaye et al., 2010; Khelifi et al., 2011; de Ladurantaye et Khelifi, 2012). Ce prototype pourrait effectuer un lâcher massif d'insectes prédateurs tout en préservant leur intégrité physique. Il a été conçu pour être couplé à n'importe quel tracteur et activé par son système hydraulique. L'objectif de cette étude était alors de tester ce prototype en conditions réelles dans un champ de pommes de terre.
CHAPITRE I
REVUE DE LITTÉRATURE
1.1 Colorado potato beetle
The Colorado potato beetle (CPB) is one of the complex pests because of its ability to relatively rapidly develop resistance against chemical insecticides, as well as the large number of eggs, which CPB females can lay after each mating. Thomas Nuttal discovered this pest insect in 1811. In 1824, Thomas Say described the specie as Doryphora
decemlineata (Casagrande, 1985). The CPB is originated from Mexico (Hare, 1990; de
Oliveira, 1992). It can destroy the whole potato plants by consuming their leaves in few days if not controlled. This insect has four development stages (instars). The worst stage in terms of potato leaves consumption is stage four (Figure 1.1). At this stage, one larva consumes around 40 cm² of potato leaves per day (Logan et al., 1985; Ferro et al., 1985). Compared to a fourth stage larva, an adult of CPB only consumes 10 cm² potato leaves per day (Ferro et al., 1985). The CPB female can lay 20 to 30 eggs each time and 300 to 800 eggs during its life period (Harcourt, 1971). The high number of the eggs reflects the quick proliferation of this pest if left without control.
Figure 1.1 Colorado potato beetle larvae feeding on potato plant leaves
The Colorado potato beetle needs 14 to 56 days to complete its life cycle from egg to adult (De Wilde, 1948; Walgenbach and Wyman, 1984; Logan et al., 1985; Ferro et al., 1985). The temperature is one of the most important factors affecting the pace of growth of CPB, and its fastest development occurs when the temperature is between 25 and 32oC (Alyokhin et al., 2008; Alyokhin, 2009). In spring, CPB adults emerge from the soil where they spent the whole winter season. They start walking and feeding for 5 to 10 days after which they could fly (Voss and Ferro, 1990; Yang, 1994; Weber and Ferro, 1996). Two major factors affect adult flight: air temperature and solar insulation (Caprio and Grafius, 1990). In the presence of wind, the CPB adult could fly long distances up to more than 100 km (Wiktelius, 1981). CPB adults normally take 50-250 degree-days (DD10 , 10oC base temperature) before emerging from the soil (Yang, 1994; Ferro et al., 1999). Males and females need 60-80 DD10 before mating (Ferro et al., 1999). The survival of the beetle in the soil varies from one country to another. In Ukraine for example, between 0.4 and 6.5% of the beetles remained in the latency period in sandy soils for two years. On the other hand, all of them emerged from the soil after the first winter in clay soils (Ushatinskaya, 1962, 1966). Comparing with Washington State, 16 to 21% of hibernating adults emerged after two winters, and more than 2% emerged after three winters (Biever and Chauvin, 1990). The CPB females do not usually start producing eggs until they accumulate at least 51 DD10 since their appearance from chrysalises (Alyokhin and Ferro, 1999a). Also, females can lay eggs using sperm from the last fall mating after diapause (Ferro et al., 1991; Baker et al., 2005). Eggs hatch within 4 to 9 days. Larvae go through four stages before reaching the adult stage, and this usually takes from two to four weeks. During the four stages or instars, larvae consume 3, 5, 15, and 77% of potato plants leaves, respectively (Ferro et al., 1985; Logan et al., 1985). At the end of the fourth stage, larvae drop themselves from the leaves into the soil for the pupa stage (5 to 10 days). Thereafter, the life cycle of a new generation of CPB adults starts. The CPB can have one to three generations per year.
The CPB prefers potatoes, Solanum tuberosum. However, it can survive by feeding on all of the Solanaceae family such as tomato (Figure 1.2) and eggplant crops (Casagrande, 1987).
Figure 1.2: A Colorado potato beetle larva feeding on a tomato
(http://www.omafra.gov.on.ca/IPM/english/tomatoes/insects/colorado-potato-beetle.html).
1.2 Management of the Colorado potato beetle
There are several alternatives to control the CPB including cultural, physical, chemical, and biological means.
1.2.1 Cultural control
The cultural control is used to reduce or prevent the population of CPB. Usually, this kind of control is used with other control means such as chemical and biological control. The most successful technique of such a control is the crop rotation by growing different crops in succession in the same field each season. This technique to manage this pest insect was first used in 1872 (Bethune, 1872). The distance between the rotated fields should be from 300 to 900 m because of the high mobility of the beetles (Weisz et al. 1994; Hough-Goldstein and Whalen 1996; Weisz et al. 1996; Sexson and Wyman 2005).
Delay of planting time is another cultural control method. This technique is adequate with overwinter CPB adults (first generation) because potato plants emerge after the declination of CPB population.
1.2.2 Physical control of Colorado potato beetle
Several methods in physical control could be used to control the CPB. One of these methods consists of using trenches of at least 25 cm furrow depth with an angle of 50 degrees or greater (Boiteau et al., 1994). These trenches must surround potato fields and must be covered with plastic rolls (Figure 1.3). After winter, CPB adults emerge from overwintering soil sites and walk looking for food. They drop into trenches when they try to reach potato fields.
Figure 1.3: Overview of trenches covered by plastic rolls (Boiteau and Vernon, 2001).
This technique is successful after winter because CPB adults cannot fly due to cold weather. Indeed, CPB adults require a temperate of 70oF (21oC) to fly. To better benefit from this control technique, the plastic-lined trench must be placed between the CPB adults
and the new potato field before their emerging. Research studies indicated that trenches with an angle of 46° or greater could result on an average of 84% of captured beetles under field conditions (Boiteau et al., 1994). For small number of potato plants such as in small greenhouses or in house backyards, plants handpicking of CPB adults and egg masses can be very successful.
The thermal control using heat in plant protection to burn the CPB is another physical method to control the CPB. It is associated with the use of propane equipment. This method involves passing a propane flame over the potato plants to kill or disable the adult potato beetles that are feeding on the leaves. Often, the exposure of CPB adults to a propane flame results in quick sublethal injuries to their legs due to the small size of these latters. These injuries prevent CPB adults from climbing back up on potato plants to feed and they eventually die of starvation or infection. Duchesne et al. (1992) indicated that the propane flamer could also reduce CPB egg hatching by 15 to 30% but its effect on CPB larvae is minimal.
The effectiveness of using thermal control against spring CPB adults was demonstrated for the first time in 1989 in the United States (Duchesne et al., 2001). The main research studies related to thermal control of CPB were conducted by two research groups between 1991 and 1995: one in the state of New York, USA (Moyer et al., 1992) and the other in the province of Quebec, Canada (Gill et al., 1994). Since the thermal control technique has an impact only on CPB adults and egg masses, it could not be used alone to control the populations of CPB. It should be therefore integrated with other control strategies.
1.2.3 Chemical control
The use of chemicals to control the CPB started in 1864 (Gauthier et al., 1981). It is
the most effective way to control the CPB on a short-term basis. However, there are several problems resulting from this kind of control on a long-term basis. One of these problems is that the CPB has a notable ability to develop resistance to a wide range of chemical pesticides used for its control (Table 1.1). For instance, the average effective period for new pesticides to resist from CPB is about 3.5 years (Hunt and Vernon, 2001). Moreover, CPB
eggs and pupae are not susceptible to chemical pesticides, which leaves no choice to growers than to apply more chemicals.
Table 1.1: Common names of insecticides to which the Colorado potato beetle has
developed resistance (Whalon et al., 2008)
Chemical group
Common names
Carbamates Aldicarb, carbary, carbofuran, cloethocarb, dioxacarb, oxamy1, propoxur
Organophosphates
Azamethiphos, azinphosethy1, azinphosmethy1, chlorfenvinphos,
malathion, methamidophos, methidathion, monocrotophos, parathion, parathion-methy1, phorate, phosmet, phoxim, quinalphos, tetrachlorvinphos, trichlorfon
Organochlorines DDT, methoxychlor
Cyclodiene Organochlorines Aldrin, chlordane, dieldrin, endosulfan, endrin, HCH-gamma, toxaphene
Organotins Azocyclotin
Inorganics Hydrogen cyanide
Pyrethroids, Pyrethrins Cypermethrin, deltamethrin, esfenvalerate, fenvalerate, permethrin
Isoflavones Rotenone
Neonicotinoids
Thiamethoxam, acetamiprid, clothianidin, dinotefuran, imidacloprid,
desmethylthiamethoxam,
N-methylimidaclopridnitenpyram, thiacloprid
Macrocyclic lactones Abamectin
Nereistoxin analogues Cartap
Spinosyns Spinosad
Bacillus thuringiensis subsp.tenebrionis
endotoxins Bt
The first resistance to chemical insecticides was noticed in 1952. It was against dichlorodiphenyltrichloroethane (DDT), one of the popular insecticides efficiently used by potato producers to control CPB populations (Quinton, 1955). Excessive and uncontrolled use of chemicals to control the CPB can lead to many serious problems such as human
health and environmental contamination. According to Giroux (2003), 49% of wells in Quebec used for drinking water were contaminated by the regular use of chemical insecticides, with 35% of them polluted by the imidacloprid insecticide, Admire, which is mainly used to control the CPB. The use of chemical insecticides also negatively affects the biological control because it kills CPB natural enemies.
1.2.4 Biological control
The biological control is an interesting alternative to chemical means to control the
CPB as it preserves the environment while allowing growers to produce chemical free potatoes. This biological alternative consists on using natural enemies that mainly feed on CPB. Scientists have identified many species of natural enemies of CPB (e.g. Hough-Goldstein et al., 1993). The predaceous stink bugs Perillus bioculatus (Heteropterera: Pentatomidae) (Figure 1.4) and Podisus maculiventris (Hemiptera entatomidae) (Figure 1.5) have been reported to have noticeable effect on CPB populations. Massive release of these predators prevents the development of the beetle density by 62%, and increases potato crops by 65% (Biever and Chauvin, 1992a). The two-spotted stink bug, Perillus
bioculatus, is one of the specialized predators, which preys on all of CPB stages (Saint-Cyr
and Cloutier, 1996; Hough-Goldstein et al., 1993; Cloutier et al., 2002). The lady beetle
Coleomegilla maculata (Coleoptera: Coccinellidae) feeds on eggs and small larvae (Groden
et al., 1990; Hazzard et al., 1992).
Figure 1.5: Podisus maculiventris adult (http://greenmethods.com/biocontrols/podisus/).
Studies showed that releasing the natural predator, the two-spotted stink bug,
Perillus bioculatus at rate of 3 per plant, reduces the CPB populations by 60% (Biever and
Chauvin, 1992a). However, the use of CPB natural predators is not very common compared to chemical insecticides (Campbell et al., 1985; Hajek et al., 1987). Existing natural predator populations are not able to decrease the CPB populations below the economically damaging threshold and have to be used in combination with other control means (Ferro, 1994).
1.2.4.1 Natural enemies of the Colorado potato beetle
The two-spotted stink bug, Perillus bioculatus (Heteroptera: Pentatomidae), is one of the most specialized insect predators with the possibility to attack eggs, all larval stages, and adults (Saint-Cyr and Cloutier, 1996; Hough-Goldstein et al., 1993; Cloutier et al., 2002). Releasing P. bioculatus on a small-scale plot and in a greenhouse to control the CPB has been proven to be one of the most effective alternative solutions to chemical insecticides (Bellows, 1993). According to Cloutier and Bauduin (1995), the best time to
release P. bioculatus nymphs is early in spring because CPB-egg-mass density is at its
highest level.
The spined soldier bug Podisus maculiventris (Say) is however a generalist predator. It feeds not only from CPB, but also from other species. This predator also attacks all CPB development stages without damaging the plants (Saint-Cyr and Cloutier, 1996; Hough-Goldstein et al., 1993; Cloutier et al., 2002).
Both predators are resistant to the harsh North American climate. Indeed, they are native to North America. Since Perillus bioculatus is a specialist predator, i.e., it feeds exclusively from CPB; it is mostly documented in controlling CPBs. It has been shown that three Perillus bioculatus/plant can reduce 60% of the population of CPB in a potato field (Ferro, 1994).
1.2.4.2 Storage conditions of the natural enemies
Knowledge of the storage conditions of the natural enemies is important to keep them in good conditions until their release in potato fields. Second instar nymphs are known to be more convenient compared with eggs and first instar because they have the ability to spread in the whole field (Lanchance and Cloutier, 1997; Cloutier, 1997). However, older nymphs and adults in particular can rapidly leave the release area searching for preys. For these reasons, research scientists focused more on studying the second P.
bioculatus nymphs’ storage conditions. There are three factors affecting the second P. bioculatus nymphs’ storage conditions: air temperature, photoperiod, and period of storage.
A recent study by de Ladurantaye et al. (2010) dealt with the most appropriate short-term storage and transport conditions of the stink bug P. bioculatus nymphs from their production site to the organic farm. This study showed that the photoperiod had no significant effect on the survival of young nymphs with a storage period of 8 days at any of the three tested experimental temperatures (9, 12, and 15oC). However, for 10 days of storage under the same conditions, nymphs’ survival was reduced by about 20%.
1.3 Mechanical release of natural enemies
Manual release of predators in potato fields using a small brush as shown in figure 1.6 is time consuming and costly at small scale. It is even not feasible at large scale.
For these reasons, Khelifi et al. (2011) have designed an innovative mechanical release system to release pre-counted insect predators at once. This was based on the research studies of Cloutier and Jean (1998) and Cloutier and Bauduin (1995). Specifically designed containers were used in the release system. These containers were designed for source-point release of predators in potato fields (Figure 1.7). At one end of the containers,
a trap held closed with a hinge spring was fixed. The trap opens when the containers cross the plastic device shown in figure 1.8, letting the predators falling on the ground.
Figure 1.6: Manual release of predator insects using a small brush.
Figure 1.7: View of a specially designed container for predator release (Khelifi et al.,
Figure 1.8: Plastic device specifically designed to open the containers filled with a mixture
of predators and popcorn.
The laboratory test bench of Khelifi et al. (2011) mainly consisted on a vertical chain conveyor mounted on two vertical shafts activated by an electric motor (Figure 1.9). Predators are mixed with wood chips or popcorn as a neutral carrier material to allow them freely moving inside the containers, and to release all of them. The reason for using wood chips and popcorn is that both of them are biodegradable, light, and non-compact.
Khelifi et al. (2011) used that predator release system for their experimental design to explore the survival rate of the dropped predators after releasing them. The results showed that (1) there was no significant effect of using thin wood chips or popcorn to release second-instar P. maculiventris nymphs, and (2) for both release techniques (mechanical and manual release by using a small brush), only the time after release noticeably affected the survival of nymph predators. After one day of release, the average survival rate with both carrier materials was 98.6%. After seven days, the survival rate dropped to 92.9%. This study showed that the predator mechanical release technique is very interesting and promising for commercial potato production.
Figure 1.9: Predator release system designed by Khelifi et al. (2011).
Based on the laboratory predator release system, a field mechanical release prototype was designed and built. This mechanical release prototype is intended to be connected to the three-point hitch of the tractor and can be activated by any tractor equipped with a hydraulic system. It consists of four containers installed on two horizontal chains driven by two sprockets. The two sprockets are installed on two vertical shafts driven by a hydraulic motor (Figure 1.10). The containers have been carefully designed to ensure the safety of the predators and the successful release of all of them (Figure 1.11). This mechanical release prototype has been tested in a potato field by Almady et al. (2012) and allowed obtaining better results compared to the manual release process.
Figure 1.10: Overview of the field mechanical release prototype.
Figure 1.11: New version of the containers used in the field mechanical release prototype:
CHAPITRE II
HYPOTHÈSE ET OBJECTIFS
Hypothèse
Considérant que l’efficacité biologique du lâcher manuel d’insectes prédateurs dans des parcelles de pommes de terre a fait ses preuves à petite échelle et que la lutte biologique représente une meilleure alternative à la lutte chimique, il serait donc possible de mécaniser l’opération de lâcher dans des champs de pommes de terre pour une lutte biologique efficace à grande échelle contre le doryphore de la pomme de terre (Taking into account
that the biological efficiency of the manual release of predator insects in potato plots has been proven at small scale and that the biological control represents a better alternative to chemical control, it would be therefore possible to mechanize the release operation in potato fields for an efficient biological control against the Colorado potato beetle at large scale).
Objectifs
L’objectif principal de ce travail de recherche était de tester un distributeur mécanique de deuxième, troisième et quatrième stades de Podisus maculiventris en conditions réelles dans un champ de pommes de terre pour lutter contre le doryphore de la pomme de terre. Les objectifs spécifiques étaient de tester le fonctionnement du distributeur mécanique au champ et de vérifier l’efficacité biologique du lâcher mécanique des prédateurs (The main
objective of this research study was to test a mechanical distributor of second, third, and fourth instar nymphs of Podisus maculiventris under real conditions in a potato field to control the Colorado potato beetle. The specific objectives were to test the operation of the mechanical distributor in the field and to check the biological effectiveness of the mechanical release of predators).
CHAPITRE III
PARTIE EXPÉRIMENTALE, RÉSULTATS ET DISCUSSION
Le présent chapitre est constitué d’un article intitulé « Control of the Colorado
Potato Beetle, Leptinotarsa decemlineata (SAY), using predator insects released by a mechanical prototype ». Son objectif principal est d’examiner l’efficacité de la distribution
mécanique d’insectes prédateurs dans un champ de pommes de terre pour lutter contre le doryphore de la pomme de terre.
La réalisation de cette partie expérimentale ainsi que la publication scientifique qui en a découlé ont été effectués par le candidat à la maîtrise, monsieur Saad Almady, avec son directeur de recherche, le professeur Mohamed Khelifi, et la collaboration de Madame Marie-Pascale Beaudoin, agronome au Ministère de l’agriculture, des pêcheries et de l’alimentation du Québec (MAPAQ). Monsieur Saad Almady a activement participé à la planification des essais, à l’exécution du protocole de recherche au champ et à la compilation et l’analyse des données expérimentales. Il a rédigé et révisé l’article qui compose le présent chapitre. Cet article a déjà été publié et il est référencé comme suit : Almady, S., M. Khelifi, M.-P. Beaudoin. 2012. Control of the Colorado Potato Beetle,
Leptinotarsa decemlineata (SAY), using predator insects released by a Mechanical
Control of the Colorado Potato Beetle, Leptinotarsa decemlineata
(SAY), using predator insects released by a mechanical
prototype
Saad Almady, Mohamed Khelifi, Marie-Pascale Beaudoin
The authors are Saad Almady, Graduate Student, Department of Soils and Agri-Food Engineering, Université Laval, Quebec City, QC, Canada, and Agricultural Engineering Department, College of Food and Agriculture Sciences, King Saud University, Riyadh, Saudi Arabia, Mohamed Khelifi, Associate Professor, Department of Soils and Agri-Food Engineering, Université Laval, Quebec City, QC, Canada, Marie-Pascale Beaudoin, Agronomist, Ministry of Agriculture, Fisheries, and Food, Québec, QC, Canada.
Corresponding author: Mohamed Khelifi, Associate Professor, Ph.D., main research
field: Power and Machinery, E-mail: mohamed.khelifi@fsaa.ulaval.ca.
RÉSUMÉ: Le doryphore de la pomme de terre (DPT) est sans doute le principal insecte
ravageur des cultures de pommes de terre en Amérique du Nord, en Europe et en Asie. L’utilisation des insecticides chimiques pour contrôler cet insecte nuisible a commencé dans les années 1860. Jusqu’à présent, aucun produit chimique commercial n’a été capable de contrôler efficacement ce ravageur. De plus, le DPT a développé, au fil des années, une résistance à la majorité des insecticides chimiques commerciaux. La lutte biologique via le lâcher manuel d’ennemis naturels du DPT a connu un succès à petite échelle. Toutefois, le lâcher manuel de ce prédateur à grande échelle n’est pas réaliste. L’objectif de cette étude était d’examiner l’efficacité de lutter contre le DPT à l’aide d’un lâcher mécanique d’insectes prédateurs sous des conditions réelles dans un champ de
pommes de terre. Les résultats obtenus indiquent que le lâcher mécanique d’insectes prédateurs a résulté en un meilleur contrôle des populations de DPT et des masses d’œufs que le lâcher manuel. Le succès de ce lâcher mécanique d’insectes prédateurs dans les champs de pommes de terre sera très utile pour la lute biologique contre les insectes prédateurs dans de nombreuses autres cultures en rangs comme la fraise, la laitue, etc.
Mots clés: Doryphore de la pomme de terre, insecticides chimiques, lute biologique, lâcher
mécanique, ennemis naturels, Perillus bioculatus, Podisus maculiventris.
ABSTRACT: The Colorado potato beetle (CPB) is unquestionably the major insect pest
of potato crops in North America, Europe, and Asia. The use of chemical insecticides to control this insect pest started in the 1860s. To date, no registered chemical has been capable of effectively managing this agricultural pest. Moreover, the CPB has developed over the years a resistance to most of the registered chemical insecticides. The biological control through manual release of natural enemies of the CPB has been successful at small
scale. However, hand release of these predators at large scale is not realistic. The objective
of this study was to investigate the effectiveness of controlling the CPB through mechanical release of predator insects under real conditions in a potato field. Obtained results indicate that the mechanical release of predator insects resulted in a better control of the CPB populations and egg masses than the manual release. The success of this mechanical release of predator insects in potato fields will be highly valuable for the biological control of insect pests in many other row crops such as strawberry, lettuce, etc.
Keywords: Colorado potato beetle, chemical insecticides, biological control,
3.1INTRODUCTION AND LITERATURE REVIEW
The ability of the world to produce sufficient food is being affected by global climate change and a fast increase in the demand for food. Recent experience indicates that plant genetic resources, genomic research, and genomic-assisted breeding could have a major effect on potato breeding in the future. The Colorado potato beetle (CPB),
Leptinootarsa decemlineata (Say) (Coleoptera: Chrysomelidae) is one of the serious
problems, which causes real damage to potato, tomato, and eggplant crops by consuming their leaves if left uncontrolled. The CPB has a complicated and diverse life history, which is well suited to agricultural environments, and makes it a complex and challenging pest to control (CPB resistance). Temperature is one of the most important factors affecting the pace of growth of CPB and its fastest development occurs when the temperature is 28oC [1]. In spring, CPB adults emerge from the soil where they spent the whole winter season. They start walking and feeding for 5 to 10 days after which they could fly [2, 3, 4]. The CPB is one of the most important pests in Eurasia and North America and represents an appreciated model for insect behavioral studies. Moreover, CPB lives in association with potato crops or other solanaceous plants where feeding and oviposition occur [5].
Unfortunately, the use of chemical insecticides to control the CPB becomes ineffective after few years because this pest insect succeeds to develop resistance to more than 50 active ingredients belonging to all major insecticide classes [6]. Resistance levels vary greatly among different populations and between beetle life stages, but in some cases can be very high (up to 2,000-fold). The first resistance to insecticides was noticed in 1952. It was against DDT, one of the popular insecticides to most of potato’s producers [7]. Also, excessive and uncontrolled use of chemical insecticides is costly for potato growers and
could lead to serious human health and environmental problems. According to Giroux [8], 49% of wells in Quebec, Canada, used for drinking water were polluted by the regular use of chemical insecticides, with 35% of them polluted by the imidacloprid insecticide, Admire, which is normally used to control the CPB. The mechanisms of CPB resistance to insecticides include enhanced metabolism involving esterases, carboxylesterases and monooxygenases, and target site insensitivity, as well as reduced insecticide penetration and increased excretion. These resistance mechanisms are sometimes highly diverse even within a relatively narrow geographical area. It is usually inherited as an incompletely dominant or incompletely recessive trait, with one or several genes involved in its determination. However, insecticide resistance in this insect will likely remain a major challenge to the pest control practitioners.
Still limited understanding of the beetle biology, its flexible life history, and grower reluctance to adopt some of the resistance management techniques create impediments to successful resistance management. Overcoming these obstacles is not an easy task, but it will be crucial for sustainable potato production. Therefore, scientists have been trying to find interesting alternatives to control the CPB. First, development of new insecticides is increasingly expensive, which affects their market price paid by growers [9]. Secondly, available alternatives may be less convenient and more environmentally damaging than the failed insecticides they have to replace [6]. Third, a threat of insecticide failure due to resistance development increases the already high real and perceived risks of potato farming. In the field, insecticide resistance can be observed as little or no reduction in the density of beetle populations and their damage to potato plants following insecticide application. Another alternative consists of using biological control by massive release of
natural enemies of the CPB. The two-spotted bug, Perillus bioculatus (Heteroptera: Pentatomidae), is one of the most specialized insect predators with the possibility to attack eggs, all larval stages, and adults [10, 11, 12]. Releasing P. bioculatus on a small scale plot and in a greenhouse to control the CPB has been proven to be one of the most effective alternatives to chemical insecticides [13]. According to Cloutier and Bauduin [14], the best time to release P. bioculatus nymphs is early in spring because CPB-egg-mass density is at its highest point. Podisus maculiventris (Say), also known as spined soldier bug is another predator of CPB. P. maculiventris is however a generalist predator, i.e., it feeds not only from CPB, but also from other species. P. bioculatus and P. maculiventris are resistant to the harsh North American climate. They are native to North America and attack all CPB development stages without damaging the plants.
This chemical free alternative has several significant advantages as it allows producing organic food while preserving the environment. The effectiveness of this alternative in controlling CPB populations has been proven at small scale. However, hand release of predator insects at large scale is unconceivable. To remedy to this problem, some recent studies carried out in the last few years have been focused on the mechanical release of predators to control pest insects. This research study focuses on the mechanical distribution of second and third -instar nymphs of P. maculiventris to control CPB in potato crops.
3.2 MATERIALS AND METHODS 3.2.1 Predators
The spined soldier bug P. maculiventris was used as predator. Based on the recommendation of Cloutier and Jean 15, the required number of 2nd and 3rd -instar
nymphs of P. maculiventris were ordered in small containers of 50 specimens for a total of 24 containers (1200 predators) from the Bug Factory (Nanoose Bay, British Columbia, Canada). Upon arrival at the laboratory of the Department of Soils and Agri-Food Engineering, Université Laval, Quebec City, Quebec, Canada, nymphs of P. maculiventris were placed at a temperature of 15 ± 1oC. The larvae were then transferred to larger containers (Fig. 3.1) in order to release them in the field located in Lac St-Jean, Quebec, Canada. These predator larvae were mixed with popcorn as a carrier material to enhance their release. Indeed, preliminary tests showed that most of the predators clung firmly to the walls of the container and hence remained inside 17.
Fig. 3.1: Predators mixed with popcorn as a carrier material. 3.2.2 Description of the mechanical release system
The mechanical release system, proposed by Khelifi et al. [16], was designed for a source-point release of predators in potato fields. As shown on Fig. 3.2, the release system consists on four containers installed on horizontal chains. Two sprockets installed on two
vertical shafts driven by a hydraulic motor drive the chains. The release system is connected to the three-point hitch of a John Deere tractor (model 6430, 95 PTO hp) and driven by its hydraulic system.
Fig. 3.2: The mechanical release system connected to the three-point hitch of the tractor.
Since the predators are very small and fragile, they were placed in a specially designed container to preserve their physical integrity. At one end of the container, a trap held closed with a hinge spring was fixed. The trap opens when the container crosses a plastic rail (in yellow in figure 3.3), which contains meanders. These meanders allow shaking the containers, thus helping to shoot down all the predators (Fig 3.3). The required
number of predator larvae per container and the distance between the release points in the field have to be adjusted in advance based on a field monitoring.
Fig. 3.3: Close view of the mechanical release system. 3.2.3 Experimental design and procedure
A randomized complete block design was used to carry out the experiments. The field was split into experimental plots (4 row large and 3.5 m long, Fig. 3.4). Rows are spaced 1.21 m apart for a total of 3.64 m large. The total area of a plot was 12.74 m2 (0.001274 ha). Potato plants were seeded every 0.194 m, i.e. 18 plants/row or 72 plants/plot. The following treatments were considered: (1) mechanical distribution of predators (Mec), (2) manual distribution of predators on the foliage (Man), and (3) control plots (C).
There were 9 plots (3 plots per treatment) with a space equal to four rows (3.64 m) to separate them in width and the equivalent of 18 plants (3.5 m) to separate them in length (Fig. 3. 4). The total area of the experimental site (including buffer zones) was 318.5 m2 (0.03185 ha).
The rate of predators recommended by Cloutier and Bauduin 14 is 2 L2-L3 predators per plant, i.e. a minimum of 150 predators per plot. For our trials, a rate of 3 predators per plant was considered. Predators were released at the peak of egg lying of
Con (1) Mec (8) Man (5) Mec (2) Man (7) Con (6) Man (3) Mec (4) Con (9) 3.64 m 3.5 m 17.5 m 18.2 m 3.5 m 3.64 m (4 rows) Total area = 318.5 m2 = 0.03185 ha
CPB, i.e. towards the end of June. Predators were released at the L2-L3 stages. An expert agronomist carried out field monitoring.
For the mechanical distribution of predators (Mec), four containers containing 50 predators each were used per plot. Based on the recommendations of Cloutier and Jean [15], a first release was made 0.75 m away from the beginning of the 2nd row and a second one 2.75 m away from the previous release on the same row (2 m between both releases and 0.75 m from the beginning or the end of a row). Both releases were replicated two rows further using the same procedure.
In the plots of manual distribution (Man), predators were directly released on the plant foliage using a small brush according to Cloutier and Bauduin [14] and Cloutier and Jean [15]. The number of P. maculiventris per plot was 200.
In the control plots (Con), no treatment was applied. These plots were used to determine the CPB population trends throughout the trial period. They also served to check whether it is appropriate or not to proceed with chemical control (depending on the presence or absence of CPB).
After releasing the predators, masses of eggs and the number of L1-L2, L3-L4, and adults were counted on ten randomly plants per plot twice a week from 22 July until 5 September. This was usually done on Monday and Thursday at 10:00 am when the conditions are appropriate.
3.2.4 Statistical analyses
The data were analyzed using the Statistical Analysis System software package (SAS program, version 9.2). Data were analyzed using the Proc Mixed repeated
measurement of SAS. The smaller Akaike’s information criterion (AIC) and Bayesian information criterion (BIC) model of the covariance structures were used because the smaller AIC and BIC numbers, the better fit of covariance model.
3.3 RESULTS AND DISCUSSION
3.3.1 Predator release efficiency on the adult stage of the CPB
Obtained results showed a significant main effect of the predators on CPB adults (p = 0.0019) while the interaction between the treatments and the days had no effect (p = 0.2925) (Table 3.1). Also, a significant difference between control and manual treatments (p = 0.0054), and between mechanical and manual treatments (p = 0.0007) was found while there is no significant difference between control and mechanical treatments (p = 0.3297).
Table 3.1 ANOVA results for the predator release efficiency on the CPB adult population.
Source of variation D.F. F-values Pr > F[a]
Treatments 2 10.09 0.0019 **
Day 12 17.63 < 0.0001 **
Treatments × Day 24 1.27 0.2925 NS
[a] ** = Significant at the 0.01 level; NS = not significant.
At the beginning of the trials, the population of CPB adult was less than 0.13 adults per plant for all the treatments during the first two weeks because the CPB was at the L3-L4 stage (Fig. 3.5). On August 11, the number of CPB adults sharply increased in the manual treatment compared to the control and mechanical treatments. On August 23, the population of CPB adults gradually decreased to 0.73 adults per plant for the manual treatment indicating that the predators did a good control on the adult stage of CPB. Thereafter, CPB adult populations increased to 2 and fluctuated around this number until the end. In contrast, the number of CPB adults in the control and mechanical treatments decreased to 0.5 adults.
Fig. 3.5: Evolution of the CPB adult populations under the three treatments: control, mechanical, and manual.
3.3.2 Predator release efficiency on the L3-L4 stage of the CPB
The results showed a significant effect of the treatments on the CPB L3-L4 populations (p = 0.0044) while the interaction between the treatments and the days had no significant effect (p = 0.1035) (Table 3.2). A significant difference between control and mechanical treatments (p = 0.0313) and between mechanical and manual treatments (p = 0.0012) was also found whereas there is no significant difference between control and manual treatments (p = 0.1857).
Table 3.2 ANOVA results for the predator release efficiency on the L3-L4 stage of CPB.
Source of variation D.F. F Values Pr > F[a]
Treatments 2 6.75 0.0044 **
Day 13 17.33 < 0.0001 **
[a] ** = Significant at the 0.01 level; NS = not significant.
On July 22, the population of L3-L4 larvae was 6.9 per plant for the control treatment against 5.8 per plant for the mechanical and manual treatments (Fig. 3.6). On July 28, the population of L3-L4 larvae rapidly decreased to less than 1 for all treatments. Thereafter, the population of L3-L4 larvae increased to 4.1 and 4.9 for the control and manual treatments, respectively, while it continued to decrease for the mechanical treatment. On August 12, the population of L3-L4 started to decline for all of treatments because the L3-L4 larvae moved to the adult stage. In the last two weeks, the population of L3-L4 larvae fluctuated between 0.1 and 0.8 L3-L4 larvae for all treatments.
Fig. 3.6: Evolution of the L3-L4 CPB populations under the three treatments: control, mechanical, and manual.
3.3.3 Predator release efficiency on the L1-L2 CPB populations
No significant effect on the L1-L2 CPB populations was observed among the three treatments (p = 0.0830). Also, the interaction between the treatments and the days was not significant (p = 0.8643) (Table 3.3).
Table 3.3 ANOVA results for the predator release efficiency on the L1-L2 stage of CPB.
Source of variation D.F. F Values Pr > F[a]
Treatments 2 3.43 0.0830 NS
Day 13 4.07 0.0027 **
Treatments × Day 26 0.64 0.8643 NS
[a] ** = Significant at the 0.01 level; NS = not significant.
At the beginning, the population of L1-L2 larvae per plant was 2.3 for the three treatments (Fig. 3.7). Thereafter, the number of L1-L2 peaked to 8.8 for the control treatment, 6.8 for the mechanical treatment, and 9.5 for the manual treatment because the eggs started to hatch on 23 July. The population of L1-L2 larvae per plant sharply decreased for the three treatments specially the mechanical treatment, which dropped to 1.1 L1-L2 larvae per plant. From 3 to 12 August, the population of L1-L2 larvae per plant continued decreasing because most larvae moved to the L3-L4 stage. By the end of September, the number of L1-L2 dropped to zero for all of the three treatments.
Fig. 3.7: Evolution of the L1-L2 CPB populations for the three treatments: control, mechanical, and manual.
3.3.4 Predator release efficiency on the CPB egg masses
No significant effect on the CPB egg masses was observed for all the treatments (p = 0.6188). Also, the interaction between the treatments and the days had no significant effect (p = 0.9864) (Table 3.4).
Table 3.4 ANOVA results for the predator release efficiency on the CPB egg masses. Source of variation D.F. F Values Pr > F[a]
Treatments 2 0.48 0.6188 NS
Day 13 7.47 < 0.0001 **
Treatments × Day 26 0.46 0.9864 NS
[a] ** = Significant at the 0.01 level; NS = not significant.
At the beginning of the trials, the number of CPB egg masses was high for all three treatments, particularly for the control treatment (Fig. 3.8). Then, this number gradually decreased because the eggs hatched.
Fig. 3.8: Evolution of the number of CPB egg masses for the three treatments: control, mechanical, and manual.
The mechanical treatment was the most efficient for all CPB stages as a gradual decrease of the populations of CPB was observed during the whole period of experimentation. Most of the predators successfully dropped from the containers along with the popcorn confirming the high release rate obtained in previous laboratory trials 17. It seems that the predators which were at the three and four stages spread out in the mechanical plots and achieved a good control. The manual treatment was the least efficient. This could be explained by the inaccuracy of the release process using a small brush as indicated by Cloutier and Bauduin 14. Also, some of the predators were too small (in the stage one and two) to succeed climbing on potato plants and doing efficient predation on CPB larvae and egg masses.
3.4 CONCLUSIONS AND RECOMMENDATION
Based on this research study, the following conclusions were drawn:
The mechanical distributer is efficient in releasing predator insects in the field; The mechanical release of predator insects resulted in a good control of CPB
populations and egg masses;
The mechanical release of predator insects is better than the manual release in terms of control of CPB populations and egg masses.
For a better control efficiency, it is recommended to release insect predators at the three and four stages and avoid releasing younger predators.
Acknowledgements
The authors gratefully acknowledge the financial support from the Ministère de l’agriculture, des pêcheries et de l’alimentation du Québec (MAPAQ) and the technical support from Yannick de Ladurantaye, Sylvain de Ladurantaye, and Marie-Ève Lemieux. They also thank la Ferme Daniel Bolduc et fils 1980 inc. for providing the necessary plots to carry out the experiments as well as a tractor to operate the mechanical distributor.
References
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CHAPITRE IV
CONCLUSION GÉNÉRALE ET RECOMMANDATIONS
4.1CONCLUSION GÉNÉRALE
Bien qu’il y ait plusieurs alternatives aux produits chimiques pour lutter contre le doryphore de la pomme de terre, aucune d’entre elles n’est capable de contrôler efficacement cet insecte nuisible. Les producteurs de pommes de terre utilisent principalement les insecticides chimiques pour lutter contre le doryphore de la pomme de terre. Toutefois, l’utilisation excessive des insecticides chimiques peut résulter en des problèmes de santé humaine et de pollution de l’environnement. Le contrôle biologique au moyen de prédateurs naturels du doryphore de la pomme de terre représente une solution concrète à cet insecte nuisible.
Quelques travaux de recherche scientifiques effectués au Département des sols et de génie agroalimentaire de l’Université Laval ont indiqué qu’un système innovateur et unique de lâcher mécanique d’insectes prédateurs a été conçu et fabriqué. Ce système de lâcher mécanique a été testé avec succès en laboratoire; mais devrait être mis à l’épreuve au champ pour évaluer sa performance dans des conditions réelles. L’objectif principal de ce travail de recherche était alors d’examiner la faisabilité technique de l’utilisation d’un tel système de lâcher mécanique au champ.
Les résultats des essais au champ ont indiqué que le distributeur mécanique testé est efficace dans le lâcher des insectes prédateurs au champ. Aussi, le lâcher mécanique des
insectes prédateurs est meilleur que le lâcher manuel en ce qui a trait au contrôle des populations de DPT et des masses d’œufs. Cela suggère que le lâcher mécanique des prédateurs à grande échelle est possible. Malgré que le distributeur mécanique ait été spécifiquement conçu pour lâcher les insectes prédateurs dans les champs de pommes de terre, il pourrait être utilisé pour lâcher d’autres types d’insectes prédateurs afin de contrôler d’autres insectes nuisibles dans certaines cultures en rangs comme les aubergines, les fraises, etc.
4.2RECOMMANDATIONS
Au terme de ce travail de recherche, il est recommandé :
de lâcher les insectes prédateurs aux stades trois et quatre et d’éviter de lâcher des prédateurs plus jeunes, car ils sont encore plus fragiles et peu mobiles.
d’appliquer le lâcher mécanique de prédateurs à une plus grande échelle.
de réaliser plusieurs autres essais au champ pour optimiser le prototype de distribution mécanique de prédateurs et tester davantage sa fiabilité.
