Design and placement of synthetic sex pheromone traps for cacao mirids in Ghana

Abstract

Cacao mirids (Sahlbergella singularis,Distantiella theobromaandBryocoropsis laticollis) were captured in pheromone traps releasing a 2:1 blend of the sex pheromone components of the two first named species in a series of five experiments on cacao (Theobroma cacao) plantations in Ghana. A total of 835 cacao mirids were caught, all male, 95% of which wereS. singularis, 3%D. theobromaand 2%B. laticollis.Two sticky trap and two water trap designs made from locally available materials were as effective for capturingS. singularisand total mirids as the best sticky trap from previously reported studies. Coating the outer surface of a large water trap with sticker increased the catch 4.4×, and 2.7× for a cylindrical sticky trap. Sticker on the outside of the water trap also increased the inside catch ofS. singularisby 76% and total mirids by 71%. The numbers ofS. singularisandD. theobromatrapped increased with increasing trap elevation and were highest around canopy level. Those traps caught an average 12× more mirids than traps at 1.8 m, the height recommended currently. Therefore, large water traps coated with sticker and aligned with the cacao canopy should raise the current capture rates of pheromone traps for cacao mirids about 50×, which may be sufficient for effective pest management by mass trapping without synthetic insecticides.

Optimal pheromone trap density for mass trapping cacao mirids

“…Here, D. theobroma was the most abundant species in searches to hand height (96%) and by insecticide knockdown (71%) which suggests that its much lower representation than S. singularis in pheromone trap catches (23%) may reflect either a lower response to the sex pheromone, as numbers caught per trap showed no decline with increasing trap density, and/or a higher percentage failing to enter the traps, confirming Sarfo et al. (). Both, insecticide knockdown and searches to hand height produced similarly low estimates of mirid population density.…”

“…Our results suggest that the optimal density for mass‐trapping S. singularis , the dominant cacao mirid in most West Africa countries (Entwistle, ; Collingwood, ; Idowu, ; Babin et al., ; Mahob et al., ; Yede et al., ; Anikwe & Makanjuola, ), and often at sites in Ghana (Owusu‐Manu, ; Antwi‐Agyakwa, ; Adu‐Acheampong et al., ; Sarfo et al., ), is 150 traps ha −1 , but in order to offer a viable alternative to insecticides (Baker, ) trap efficiency needs improvement. Coating the outside of traps with a killing agent and raising traps to canopy level are easily deployable measures that would potentially improve capturing efficiency by about 50× (Sarfo et al., ). At a meeting in 2016, Guillon (unpubl.…”

“…() placed their traps at 2.7 m. Sarfo et al. () also demonstrated that only ca. 23% of mirid males that responded to the pheromone entered the trap, which suggests that traps at 1.8 m probably trapped out ca.…”

“…However, Sarfo et al. () demonstrated that traps at 1.8 m caught 8% of the numbers of male S. singularis caught in traps positioned just beneath the canopy. Similarly low‐trap heights had been used in earlier pheromone trapping studies in cacao (Padi et al., ; Ayenor et al., ; Mahob et al., ), although, in response to the results of Sarfo (), Awudzi et al.…”

“…In terms of application of the pheromone for control of mirids there is no gain in using densities higher than 150 traps ha −1 for mass trapping or attract‐and‐kill of S. singularis , although a density above 300 traps ha −1 may be optimal for D. theobroma . Such high densities may be unrealistic for a practical wide‐scale mass trapping programme, particularly when traps have to be deployed in the upper canopy (Sarfo et al., ). El‐Sayed et al.…”