Infectivity of Pandora neoaphidis (Zygomycetes: Entomophthorales) to Acyrthosiphon pisum (Hom., Aphididae) in response to varying temperature and photoperiod regimes

The infectivity of the pea aphid, Acyrthosiphon pisum , by the aphid-specific entomophthoralean fungus, Pandora neoaphidis , was studied in environmental chambers using computer simulated late-season temperature and photoperiod patterns and an excised fava bean leaf system. A complementary log-log (CLL) time–dose–mortality model was used to model time–dose trends in infectivity of A. pisum by P. neoaphidis as a function of time and dose, and calculate the LC₅₀. The likelihood ratio test based on the CLL model was used to test for differences in levels of aphid infectivity by P. neoaphidis over different photoperiod regimes. Differences in the LC₅₀ values from CLL modelling over different time periods were found among the two regimes of 11- and 16-h photophases at a constant temperature of 20°C, and two regimes at daily fluctuating temperatures from 5.4 to 18.9°C (with half-hourly changes of 0.56°C the mean temperature was 12.12°C). The LC₅₀ for the same time period was lower under the higher temperature conditions than under lower fluctuating temperature conditions. The likelihood test ratio statistics showed no significant difference in the slope parameter for three out of four treatments (two from the constant temperature of 20°C, and one from 5.4 to 18.9°C, irrespective of photophase conditions). This suggests that different temperatures and photophases may change the temporal characteristics of P. neoaphidis , and result in higher or lower infectivity to the pea aphid at certain dosage levels. However, changes in the photoperiod appear to be less important for the infectivity of P. neoaphidis to pea aphid than changes in temperature.