Insecticidal and repellent activities of Azadirachta indica A. (Juss) oil against fifth instar larvae and adults of Sahlbergella singularis (Hemiptera:Miridae)

Abstract

Sahlbergella singularis is one of the insects that causes the most damage to cocoa trees in Togo. The management of this pest is mainly based on chemical control, with its negative consequences for human health and the environment. In order to find an alternative to the use of synthetic pesticides, the insecticidal and repellent activities of neem oil were tested in vitro on fifth instar larvae and adults of S. singularis. Larvae were collected from a cocoa plot. The fifth instar larvae were separated from the other stages. Some of the larvae were reared in the laboratory until adult emergence. The concentrations of neem oil used were 0.5, 1, 1.5, 2 and 2.5 µl.ml-1. Insecticidal tests were carried out by spraying the solutions directly onto the insects. The repellency test was carried out using the preferential zone method on filter paper. The results showed an increasing mortality rate with increasing concentrations of neem oil for both fifth instar larvae and adults. The calculated LC50’s for larvae and adults were 0.89 and 0.98 µl.ml-1 respectively. Neem oil had a weak repellent effect on both fifth instar larvae and adults, with average repellency rates of 23.60% and 28.8% respectively. These results show that neem oil can be an alternative to the use of synthetic pesticides in the control of S. singularis.