Evaluation of the attractiveness of female sex pheromone formulations towards cocoa Mirids (Sahlbergella singularis Hagl and Distantiella theobroma (Dist.) Heteroptera: Miridae) at the IRAD-Nkoemvone research station; Field trapping experiments.

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Evaluation of the attractiveness of sex pheromone traps for the cocoa mirids

Sahlbergella singularis Hagl. and Distantiella theobroma Dist. (Hemiptera: Miridae)

Field trapping experiments at the IRAD-Nkoemvone research station

R. J. Mahob1_{, L. Dibog}2_{, C. F. Bilong Bilong}1_{, R. Babin}3_{, M. C. A. Downham}4_{, Yede}1_{, G. M. ten Hoopen}3

1_{Université de Yaoundé I, BP812, Yaoundé, Cameroun ;}2_{IRAD, BP2067, Yaoundé, Cameroun;}3_{CIRAD UR31, Montpellier, France;}4_{NRI, UK, England} Corresponding author: raymond.mahob@yahoo.fr

Cocoa mirids, Sahlbergella singularis Hagl. and Distantiella theobroma Dist. are the two major pests of cocoa in West Africa, causing 30 to 75% loss of production. Currently, in order to limit mirid damage, insecticide spraying is the preferred control method. However, there are many problems associated with insecticides, such as the high costs of chemicals, the development of pest resistance, the destruction of non targeted organisms and the pollution of the environment through an accumulation of pesticide residues in the soil, water and food chains. These constraints have led to the development of research towards a more Integrated Pest Management (IPM) approach for cocoa mirids.

The aim of our study was to contribute to the improvement of mirid control strategies, by using a synthetic female sex pheromone.

Study area: Nkoemvone (humid forest, southern Cameroon), 2°40’N and 11°20’E, altitude = 630m, T = 25°C, annual rainfall = 1700 mm.

Pheromones, traps and experimental design: we used 5 different blends of diester and/or alcohol, noted A, B, C, D and E, with the respective corresponding ratios (V:V): 1000:0, 1000:50, 1000:500, 1000:1000 and 0:1000.

Methodology:

Results

Table 1: Number (%) of S. singularis caught per pheromone traps including control traps for the duration of the study

A B C D E Control Total 22 (7.4%) 68 (22.7%) 72 (24.1%) 98 (32.8%) 27 (9.0%) 12 (4.0%) 299 (100%) Diversity of trapped insects

473 individuals / 20 families / 7 orders 299 out of 473 specimens were from the

species Sahlbergella singularis

0 1 2 3 4 5 6 7 8 Ja n-06 M a r-0 6 Ma y-0 6 Jul -06 Sep -06 No v-0 6 Ja n-07 M a r-0 7 Ma y-0 7 Jul -07 Sep -07 No v-0 7 Time (Months) N u m b e r o f m irid s at tract ed pe r ea ch phe ro m o n e t ra p s Phero A Phero B Phero C Phero D Phero E Control 0 10 20 30 40 50 A B C D E Control Phe romone N u m b e r o f m irid s c a u g h t/ tra p d e si g n s Delta trap Rectangular trap Sahlbergella singularis

The differential and selective attractiveness to S. singularis

(particularly the male adults) of the different compositions of

the pheromones tested were certainly due to differences in formulation. The pheromone compositions which contained both molecules (diester and alcohol) B, C and D were more efficient than those who possessed only one or none (A, E and the control) in terms of the attractiveness to mirids.

Rectangular traps caught more males (73.83% ) compared to Delta traps (26.17%), but this was likely due to its larger surface area (2.075 cm2 _{compared to 1.204 cm}2 _{for the delta}

trap).

A sex female pheromone formulation with both compounds (diester and alcohol) notably the pheromone compositions B, C and D and particularly D together with the Rectangular trap design have a good potential to lure and thus suppress mirid populations in cocoa, particularly the male adults of S. singularis. Pheromone composition and trap

design are important parameters to maximise efficiency of these components in an IPM approach for mirid control.

Fig. 1: Monthly number of S. singularis attracted/caught in pheromone traps

Fig. 2: Comparison of the numbers of mirids caught in both trap designs in function of the different pheromone compositions

c c bc ab ab a Université de Yaoundé I Institut de Recherche Agricole pour le Développement Centre de Coopération Internationale en Recherche Agronomique pour le Développement Acknowledgements

The authors specially thank the technical assistants of the Technician of Agriculture, EYENET Damien of the IRAD- Nkoemvone, for the field data collections.

I

ntroduction

Materials & Methods

Discussion & Conclusion

Field work

Plot 1: 1080 m2_{(36m X 30m)}

Prospecting and plot selection

Plot delimitation 6 m 6 m

Inspection of traps once a week Insect collection 6 m

6 m

18 delta traps 24 traps

12 delta + 12 rectangular A total of 42 traps hung in the trees

Laboratory

Plot 2: 1296 m2_{(36m X 36m)}

Statistical analysis: comparison of the average number of mirids per plot and per trap with an anova following by a Tukey’s post hoc test

6 m