oa African Entomology - Biology of the Australian tortoise beetle Trachymela tincticollis (Blackburn) (Chrysomelidae: Chrysomelini: Paropsina). a defoliator of Eucalyptus (Myrtaceae). in South Africa



An Australian tortoise beetle, Trachymela tincticollis (Blackburn), was discovered near Cape Town in 1982 on severely defoliated Eucalyptus gomphocephala DC trees. By 1985 it had spread 800 kin to Port Elizabeth. Both adults and larvae feed on the new leaves of 13 Eucalyptus species cultivated in South Africa, including the important commercial species E. grandis Hill ex Maiden. Females laid an average of 11 eggs per day from mid-August to the end of December. Eggs were laid at dusk in fissures 0.5-1.0 mm wide in the bark of the host tree and the number of batches laid per day was largely determined by the amount of food available. Larvae hatched after four-and-a-half days and hid in fissures near their feeding sites during the day. They had a bimodal activity pattern, feeding just before sunrise (93 %) or after sunset (7 %). There were four larval instars before pupation in the soil below the host tree. Larvae were active from September to February with a peak in numbers in November which was synchronous with the annual leaf-flush of the host trees. Total development time from egg to adult emergence was 35 days. The sex ratio was approximately 1:1. Various traps were used to monitor the phenology of the different life stages. Adults flew at canopy height and dispersed mainly in February and March. This study formed part of a successful biological control programme in which the introduction of the egg parasitoid Enoggera reticulate Naumann (Hymenoptera: Pteromalidae) achieved a parasitism rate of 96 %.


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