The relative abundance of the mealybug vectors (Hemiptera: Coccidae and Pseudococcidae) of cocoa swollen shoot disease in Ghana.
A census of the mealybug vectors of cocoa swollen shoot disease was made weekly on 238 Amazon cacao trees at Tafo, Ghana, between 1971 and 1976. The 6 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 4 species are more mobile than Planococcoides njalensis and could be more important in the spread of disease than has previously been supposed.