The influence of Dolichoderus thoracicus (Hymenoptera: Formicidae) on losses due to Helopeltis theivora (Heteroptera: Miridae), black pod disease, and mammalian pests in cocoa in Malaysia

Abstract

AbstractThe influence of the black cocoa ant Dolichoderus thoracicus (Smith) on losses due to the mirid Helopeltis theivora Waterhouse, black pod disease (caused by Phytophthora palmivora (Peronosporales)) and mammalian pests (rats, squirrels and civet cats) was studied over a two-year period in two separate fields of cocoa. Both fields initially had high D. thoracicus activity. In each field, ant-scarce plots were created by treating these plots with insecticides; ant-abundant plots existed where the plots were left untreated. An abundance of D. thoracicus clearly had a negative effect on numbers of mirids, with respectively 380 and 2222% more nymphs and adults being recorded in the ant-scarce than in the ant-abundant plots over the two-year period. An abundance of D. thoracicus did not increase black pod incidence: on the contrary it reduced incidence of the disease in both fields. The number of rat-damaged pods in ant-scarce plots was significantly higher than in ant-abundant plots in one of the fields but no significant difference was detected in the other. Regarding number of pods lost to squirrels and civet cats, no significant difference between ant-scarce and ant-abundant plots was obtained for both fields; the losses to either of these mammalian pests were extremely low. The number of healthy ripe pods in ant-abundant plots was 40.4 and 32.1% higher than in ant-scarce plots in the two fields, these increases being ascribed to protection from H. theivora damage by D. thoracicus.