Function of temperature on almond moth demographic characteristics: Do diapausing individuals contribute to population growth rate?

Abstract

The almond moth, Cadra cautella (Walker) (Lepidoptera: Pyralidae), is a recognized cosmopolitan pest of stored food products throughout its worldwide distribution. To enable effective control of this pest, a thorough understanding of the effect of temperature on their population growth is required. In this study, we investigated the population growth rate of group-reared C. cautella fed on brown rice at five different temperatures (15~35 °C) using the age-stage, two-sex life table program. At 15°C, the majority of larvae failed to reach the 2nd instar. At 35 °C, only 5 out of 150 individuals survived to the adult stage. There was no significant difference in fecundity between the three temperature groups (20, 25 and 30 °C), while a dramatic decline occurred at 35 °C (0.5 eggs/female). The intrinsic rates of increase of C. cautella were 0.0566, 0.1149, 0.1429, and -0.0901 d-1 at 20, 25, 30 and 35 °C, respectively, with significant difference between all values. Approximately 16.0% of late instar almond moth larvae showed signs of diapause induction at 20 °C, i.e., wandering behavior and delayed pupation. The development times of larvae (74.44 d) and pupae (17.13 d) were significantly longer in the diapausing cohort than in the non-diapausing cohort (54.89 d cv. 15.47 d). At 20 °C, the offspring of the diapausing individuals were still able to contribute 12.98% to the net reproduction rate of the entire cohort – an amount substantial enough to require attention when planning pest management programs. In conclusion, we suggest that 15 °C can effectively limit the damage caused by C. cautella population due to their inability to develop into later instars at this temperature.