Evaluation of the toxicity of Actara 25 WG for the control of the cocoa mirid Sahlbergella singularis Hagl. (Hemiptera: Miridae) in Nigeria

In Nigeria, the brown cocoa mirid Sahlbergella singularis is responsible for over 30% yield loss in cocoa. Insecticides still remain a very important component among the strategies for effective controlof major insect pests of cocoa in Nigeria. The Cocoa Research Institute of Nigeria (CRIN) has the “National Mandate” to evaluate and recommend new insecticides for use on cocoa in Nigeria. Themortality rates of mirids on exposure to the various concentrations (0.01, 0.013, 0.015 and 0.02%) of Actara 25 WG increased with period of exposure of the mirids in the laboratory. Both Actara and theStandard Miricide were similar at 0.020% concentration as both gave a 100% kill of mirids at the 90th min. No mortalities were recorded in control cages throughout the exposure period. The insecticide didnot produce any adverse side effects on cocoa seedlings and mature plants sprayed with the various concentrations over the years. The relative toxicity of the insecticide at the four different concentrationsto adult mirids, 24 h after the first field treatment application, was 93.3, 82.4, 81.8 and 100% adult mortality, respectively. In the case of the nymphal mirids, percentage mortality was 89.6, 81.5, 86.8 and94.3% for the various concentrations, respectively. The population of both the adult and nymphal mirids crashed to almost zero (0) in most cases suggesting about 100% mortality 24 h after the secondspraying on the residual mirid populations. Mirid numbers remained so low until the third spray application after which it was unnecessary to spray the sub-plots, thereafter. Spraying of mature andfruiting cocoa farms at application rate of 0.015% was found adequate and recommended taking into consideration the impact of the product on the environment and for economic reasons