Abstract: The interaction between the aphid-specific entomophthoralean fungus, Pandora neoaphidis, and the pea aphid, Acyrthosiphon pisum, was investigated in computercontrolled growth chambers at regimes of varying temperature and photoperiod simulating different seasonal patterns in an attempt to reveal the potential preadapting behaviorof the fungus for overwintering. Based on the fitting of the time-dose-mortality model to the experimental data, the time-dose effect pattern was found to be similar between the photoperiods of 16 ∶ 8 and 11: 13 (L ' D) at 20℃, but was significantly different between the constant and daily varying temperatures (5.4-18.9℃ at the rate of 0.56℃per 30 min) and also between the above photoperiods at the same varying temperature.With the varying temperature treatment, the mean incubation time of the fungus on the host (I. E. , mean lethal time postinoculation) was 15.14 d for 8 h of light, 15.19 d for 9.5 h, 11.79 d for 11 h, 13.33 d for 11.5 h, 11.73 d for 12 h, and 9.21 d for 16 h, respectively. This displayed a significantly negative correlation (a=15.58, b=- .93,r²=0.78,p＜0.01). However, the mean incubation periods were nearly identical for 11and 16 h of light at 20℃ (5.85 d and 5.97 d). Abnormal hyphal bodies of the fungus were not found during microscopic examination of all cadavers from all the regimes of temperature and photoperiod. The fungus maintained its infectivity to the host at all theregimes considered and had no preadapting behavior to overwintering. However, the short photoperiods were found to decrease the mean incubation time at the varying temperature that simulated a late autumn or early winter pattern.