Sap Suckers

The cacao tree is host to some 1500 different insect species, though, mercifully, only a tiny fraction of these cause serious damage. One such group are sap-suckers known as capsids in West Africa, specifically Sahlbergella singularis and Distantiella theobromae, and mirids in Asia (Helopeltis species), and Central and South America (Monalonion species). These tiny insects are responsible for significant losses to cacao crops, resulting from direct damage through their feeding, as well as the ravages of opportunistic fungi that invade the tree via wounds caused by the mirids. This chapter looks at the biology and ecology of these sap-sucking pests and how this knowledge helps in devising control methods.

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

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.

Dieback of cocoa (Theobroma cacao L.) plant tissues caused by the brown cocoa mirid Sahlbergella singularis Haglund (Hemiptera: Miridae) and associated pathogenic fungi

The brown cocoa mirid,Sahlbergella singularisis the most important insect pest of cocoa for field damage has been classified into three categories that include blast, stagheadedness and mirid pocket. The mirid attack predisposes the cocoa plant to secondary infection by opportunistic pathogenic fungi. This study evaluated the dieback conditions associated with mirid damage due to associated fungi from lesions on pods, twigs and pin punctures. The relationship betweenPhytophthorablack pod infection and mirid infestation in the field was also established. The results indicated that dieback progression from the mirid lesions (8.5 mm) was significantly different (P< 0.05) from that of pin punctures (7.8 mm).Lasiodiplodia theobromaehad the highest proportion of isolates from pods (33%), twigs (47%), and pin punctures (38%).Fusarium decemcellulare(Albonectria rigidiuscula) accounted for 27.8% and 31.6% from pods and twigs; however, it was not recovered from pin punctures. Other isolated pathogens wereAspergillusspecies andRhizoctoniaspecies. There was a significantly strong positive correlation coefficient of 0.74 between the mirid population and the black pod disease infection in the field. The major fruit-bearing season of cocoa witnessed an increase in mirid infestation and blackpod infection. The effect of mirid–pathogenic fungi-associated damage could be ameliorated through effective crop husbandry practices to ensure that cocoa plant tissues are not unduly exposed to biological and mechanical injuries.