Demographic characteristics of Cadra cautella on brown rice at different temperatures: 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 un-derstanding 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 degrees C) using the age-stage, two-sex life table program. At 15 degrees C, the majority of larvae failed to reach the 2nd instar. At 35 degrees 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 degrees C), while a dramatic decline occurred at 35 degrees 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 degrees C, respectively, with significant difference between all values. Approximately 16.0% of late instar almond moth larvae showed signs of diapause induction at 20 degrees C, i.e., wandering behavior and delayed pupation. The developmental 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 and 15.47 d). At 20 degrees C, the offspring of the diapausing in-dividuals 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 degrees C can effectively limit the damage caused by C. cautella population due to their inability to develop into later instars at this temperature.