Investigation of diapause induction in Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae) larvae

The larvae of the Mediterranean flour moth, Ephestia kuehniella (Zeller), are widely used, as an alternative host, to rear some biocontrol agents such as Habrobracon hebetor (Say) for biological control programs. To enhance the quality of mass production, it is necessary to optimize the rearing of natural enemies on alternative hosts. The aim of this study was to investigate the possibility of diapause induction in the Iranian population of E. kuehniella larvae for optimizing the mass production of biocontrol agents such as H. hebetor.

To study the diapause induction in E. kuehniella larvae, the insect eggs (0.04 g) were released on 200 g of wheat flour and kept under optimal rearing conditions (25 ± 1°C, 65 ± 5% relative humidity, and 16:8 (L:D) h). After the emergence of each larval instar, they were divided into two groups. The first group included larvae that had already been reared in each instar (first to fifth instars) at 15 ± 1°C and total darkness for one week and the second group under the same conditions for two weeks. Then, the larvae of both groups were transferred to the optimal rearing conditions. After the emergence of fifth (final) instar, the percentage of larvae entered the diapause where the duration of diapause was evaluated. The control group consisted of larvae that were reared in the optimal rearing conditions.

The results revealed that 8 to 45% of the fifth instar larvae from the first group and 100% of the fifth instar larvae from the second group entered the diapause. The percentage of diapausing larvae from the first group was the highest when they were reared in the fourth or fifth instars at 15°C and total darkness. The duration of diapause in the larvae from the second group (19.41 to 20.56 days) was significantly longer than those from the first group (15.20 to 16.92 days).

The present study is the first attempt showing diapause induction in Iranian population of E. kuehniella. By increasing the availability of host larvae by inducing diapause, the efficiency of mass production of biocontrol agents such as H. hebetor can be enhanced.