FACTORS INFLUENCING SURVIVAL OF CITRUS THRIPS (THYSANOPTERA, THRIPIDAE) PROPUPAE AND PUPAE ON THE GROUND

Survival of citrus thrips, Scirtothrips citri (Moulton), propupae and pupae was investigated by seeding emergence traps with known numbers o f larvae and recovering emerging adults. Results from traps in the fie ld and undisturbed soil cores in the laboratory suggest that frequent irrigation and some autoclave-excludable factors suppress survival of citrus thrips. The autoclave-excludable factors exhibited a more prono unced suppression at 20 and 25 degrees C than at 18 or 30 degrees C, b ut the effect appeared to be relatively independent of gravimetric wat er content. Adding Berlese extracts, or water-leaches from suppressive soils to autoclaved soils did not result in reduced survival. Exposin g citrus thrips larvae in screen cages to the soil microflora and faun a did not yield any evidence of virulent pathogens. Adding decollate s nails, Rumina decollata (L.), to autoclaved soil cores resulted in sig nificant suppression. Assuming that adult migration from adjacent grov es contributes only marginally to the population increase in a particu lar orchard, citrus thrips levels may be reduced through frequent irri gation and inoculative releases of decollate snails. However, large-sc ale field studies remain to be carried out to judge the practical feas ibility of such tactics.