AN ECOLOGICAL STUDY OF THE DAMAGE DONE TO AVOCADO FRUITS BY CITRUS-LEAFHOPPER PENTHIMIOLA-BELLA (CICADELLIDAE) AND COCONUT-BUG PSEUDOTHERAPTUS-WAYI (COREIDAE) IN SOUTH-AFRICA

Feeding on young avocado fruit by citrus leafhopper Penthimiola bella (Still (Homoptera: Cicadellidae) causes protrusions on the surfaces of the maturing fruits, rendering them unacceptable for export. In the p resent study it was found that the incidence of protrusions on Hass av ocados (10%) was five times greater than on Fuerte (2%) avocados. The damage was inflicted during early fruit development and did not increa se above 11% (average 9%) during the study period. Protrusions were di stributed throughout the study site with no edge effect. Feeding was s trongly linearly density-dependent, and fruits with protrusions were n ot aborted (i.e. the trees utilize resources to mature fruit that are lost to the grower). A technique for monitoring the incidence of fruit bearing protrusions is described. In contrast, feeding by coconut bug Pseudotheraptus wayi (Brown) (Heteroptera: Coreidae) was exponentiall y density-dependent, but did enhance fruit drop. The mass of indented fruit was 28% lower than that of healthy fruit and those bearing protr usions, indicating that these fruits are less energy-expensive than th ose bearing protrusions whose mass did not differ from that of healthy fruits.