Investigations on Oecophylla longinoda (Latreille) (Hymenoptera: Formicidae) as a biocontrol agent in the protection of cashew plantations.
BACKGROUND: Cashew (Anacardium occidentale L.) has become a very important non-traditional tree crop in Ghana. The crop is, however, attacked by sap-sucking insects, particularly the mosquito bug, Helopeltis schoutedeni Reuter, the leaf-footed bug, Pseudotheraptus devastans (Dist.), and the coreid bug, Anoplocnemis curvipes (F.), which feed on shoots, panicles and fruits. Their damage is characterised by withering of the latter. In Ghana, Oecophylla longinoda Latr. occurs in large numbers on cashew and other native plants, but little is known about its relationship with insect pests. The relationship between O. longinoda and shoot and panicle damage by sap-sucking bugs and the effectiveness of O. longinoda as a biocontrol agent in the protection of cashew as compared with two chemical insecticides, lambda-cyhalothrin (Karate®) and cypermethrin+dimethoate (Cyperdim®), were therefore investigated at Bole in the northern region of Ghana. RESULTS: There was a negative correlation between numbers of O. longinoda nests and pest damage. Trees treated with cypermethrin+dimethoate (969 mg AI mL-1 tree-1) and lambda-cyhalothrin (100 mg AI mL-1 tree-1) recorded the smallest bug numbers, followed by O. longinoda. Trees infested by Oecophylla longinoda and trees treated with cypermethrin+dimethoate and with lambda-cyhalothrin had less than 6% pest damage to shoots, panicles and fruits, while water-sprayed trees recorded damage as high as 36.8% (shoots) in February, 32.9% (panicles) in February and 37.8% (fruits) in March. Cypermethrin+dimethoate again recorded the highest (485.0 kg ha-1) nut yield, followed by O. longinoda (431.0 kg ha-1), with water recording the lowest (93.0 kg ha-1) nut yield. CONCLUSION: The results indicate that O. longinoda can be used to control some sucking bugs as effectively as some insecticides.