REARING OF RED WEAVER ANT (OECOPHYLLA SMARAGDINA F.) FOR THE MANAGEMENT OF HELOPELTIS ANTONII SIGN. (HEMIPTERA: MIRIDAE) IN CASHEW (ANACARDIUM OCCIDENTALE L.)

Abstract

Helopeltis antonii Sign. is the most serious pest of cashew in all cashew-growing areas of Sri Lanka. It feeds on the tender succulent shoots, inflorescences, immature nuts and apples resulting in drying of shoots, blighting of inflorescences and immature nut fall. In large scale cashew growing, insecticide spraying for the management of Helopeltis is the only effective method that has been practiced by many cashew growers. However, high cost of insecticides and insecticide application, chemical residues in cashew nut, reduction of beneficial organism like pollinators and other natural enemies of pests, development of pests’ resistance to pesticides and environmental pollution are major disadvantage of that method. On the contrary, biological control would be of high importance for the pest management in cashew as more sustainable and eco-friendly method. Several natural enemies of Helopeltis antonii were recorded in cashew plantations. Among them red weaver ant Oecophylla smaragdina F. (Hymenoptera: Formicidae) was observed with relatively higher population densities. Therefore, an experiment was conducted to ascertain the feasibility to use red weaver ant as effective biological control agent for the management of H. antonii in cashew lands. A red weaver ant (Oecophylla smaragdina F.) population was maintained during four consecutive years in an experimental site at Kamandoluwa cashew plantation. The experimental site was divided into two separate blocks. One block was introduced with red weaver ants and the other one was kept without ants. Ant nests were used for introduction of red weaver ants into the site for successful colonization. Data on yield, severity of the damage at different flushing stages of the trees were recorded during the experimental period (2005-2008). Yield data of the four years were analyzed by ‘Pool t’ test. A preliminary study was carried out to assess the predatory action of red weaver ant on Helopeltis under laboratory conditions and results were analyzed by Chi-Square test. Predatory action, nesting and foraging behaviour of ants were observed under field and laboratory conditions. A significant yield reduction was observed (P<0.05) in the block where red ants were not introduced compared to the block with red ants introduction. Chi-Square on predation were 72.78 (P<0.0001) and 97.63 (P<0.0001) for adult and nymphs of Helopeltis, respectively. Results revealed that the red weaver ants (Oecophylla smaragdina F.) are efficient predators on Helopeltis antonii Sign. having potential for the management of that pest in cashew plantations.