Incidence of natural enemies of Planococcoides njalensis Laing and Planococcus citri Risso in researcher-managed and farmer-managed cocoa farms

Abstract

Studies were carried out at Tafo in researcher (CRIG)-managed farms and farmer-managed farms to assess the incidence of natural enemies in colonies of Planococcoides njalensis Laing and Planococcus citri Risso, the two most important vectors of the Cocoa Swollen Shoot Virus disease in Ghana. The CRIG farms were sprayed four times with either lindane or propoxur per mirid season, using motorised knapsack sprayers, and weeded at least twice annually, mostly by slashing with cutlass and occasionally by applying herbicides. Control of black pod disease caused by Phytophthora palmivora (Butl.) Butl. was by a combination of cultural practices and chemical control. The peasant farmers partially adopted the CRIG recommendations, spraying unspecified dosages of any available insecticides once or twice annually against mirids, and rarely spraying against the black pod disease. Most weeded once or twice annually while others waited till harvesting time, only to make tracks to trees carrying ripped pods. Mealybug colonies were sampled monthly in both farm types by examining cocoa trees from the base to hand height, brushing observed colonies within this range into glass vials and taking them to the laboratory. Unparasitized adults (females), third instar nymphs and mummies were separated and counted to give an estimate of the colony size. Mummies were kept in vials and observed for the emergence of parasitoids. The monthly incidence of both P. njalensis and P. citri colonies on the farmers' farms and the CRIG farms did not differ significantly. Similarly, the percentages of their colonies free from natural enemies in the two farm types did not differ significantly, and the differences in the incidence of parasitoids, and also of predators, in colonies of the two vectors in the two farm types were not significant. These results are discussed in terms of agrochemical usage and the efficiency of the natural enemies in the control of mealybug vectors of CSSV.


(Journal of the Ghana Science Association: 2001 3(3): 45-51)