Environmental effects on the development and survival of the scale insect Abgrallaspis cyanophylli (Signoret) (Homoptera : Diaspididae) with reference to its suitability for use as a host for rearing biological control agents

Developmental and survival rates of the locally important diaspidid pest, A bgrallaspis cyanophylli (Signoret) reared on Solanum tuberosum L. tubers we re examined under light and dark conditions; humidities of 33, 53, 62 and 7 5% relative humidity (RH); varying population densities; constant temperatu res in the range of 20 to 30 degreesC and at cycling temperatures of 12 h a t 14 degreesC and 12 h at 30 degreesC Developmental rare was slightly lower under constant light conditions but mortality was higher in the dark, part icularly amongst the males. At 26 degreesC, there were no differences in de velopmental rate in relation to the various humidity levels. However; survi val was significantly lower at 33% RN, with females suffering higher mortal ity than males. Population density was found to have no effect on developme ntal rate or size of the females Overall mortality increased in line with p opulation density although the result was poorly correlated. Within the ran ge 20-28 degreesC developmental rate increased with rising temperature but decreased at 30 degreesC. Thermal summation and polynomial regression data show a theoretical lower thermal threshold for development of 12.47 degrees C. The thermal constant was 541.7 degree days. Survival was lowest at 20 de greesC and 30 degreesC and highest at temperatures in the median range and under cycling conditions. Male survival was significantly higher than that of the females at 30 degreesC and under the cycling regime of 14/30 degrees C. The results suggest that the optimum conditions for rearing A. cyanophyl li on potatoes would be at temperatures in the range 24-26 degreesC and hum idities of 55-65% RH.