The relative abundance of the mealybug vectors (Hemiptera: Coccidae and Pseudococcidae) of Cocoa swollen shoot disease in Ghana

Abstract

A census of the mealybug vectors of cocoa swollen shoot disease was made weekly on 238 Amazon cocoa trees at the Cocoa Research Institute, Tafo, Ghana, between 1971 and 1976. The six species encountered were ranked in descending order of abundance: Planococcoides njalensis (Laing), Planococcus citri (Risso), Phenacoccus hargreavesi (Laing), Ferrisia virgata (Ckll), Pseudococcus concavocerarii James, P. calceolariae (Mask.). Planococcoides njalensis occurred at a much higher density on infested trees than other species but was found on fewer trees than either Planococcus citri or Phenacoccus hargreavesi. Over 13-week periods the probability of finding a mealybug on a particular tree was 0·87 for Planococcus citri, 0·77 for Phenacoccus hargreavesi, 0·36 for F. virgata, 0·32 for Pseudococcus concavocerarii, 0·23 for Planococcoides njalensis and 0·05 for Pseudococcus calceolariae. The results suggest that the first four species are more mobile than Planococcoides njalensis and could be more important in the spread of disease than has previously been supposed.