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 infectivi ty of A. pisum by P. neoaphidis as a function of time and dose, and calcula te the LC50. The likelihood ratio test based on the CLL model was used to t est for differences in levels of aphid infectivity by P. neoaphidis over di fferent photoperiod regimes. Differences in the LC50 values from CLL modell ing over different time periods were found among the two regimes of 11- and 16-h photophases at a constant temperature of 20 degrees C, and two regime s at daily fluctuating temperatures from 5.4 to 18.9 degrees C (with half-h ourly changes of 0.56 degrees C the mean temperature was 12.12 degrees C). The LC50 for the same time period was lower under the higher temperature co nditions than under lower fluctuating temperature conditions. The likelihoo d test ratio statistics showed no significant difference in the slope param eter for three out of four treatments (two from the constant temperature of 20 degrees C, and one from 5.4 to 18.9 degrees C, irrespective of photopha se conditions). This suggests that different temperatures and photophases m ay change the temporal characteristics of P. neoaphidis, and result in high er 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.