Diapause Induction, Color Change, and Cold Tolerance Physiology of the Diapausing Larvae of the Chouioia cunea (Hymenoptera: Eulophidae)

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Abstract
The chalcid wasp Chouioia cunea Yang (Hymenoptera: Eulophidae) is one of the most dominant pupal parasitoids of Hyphantria cunea (Drury) (Lepidoptera: Arctiidae), an invasive pest of many forestry trees and agricultural crops. For mass rearing C. cunea for biological control purposes, the pupae of Antheraea pernyi (Guérin-Méneville) (Lepidoptera: Saturniidae) have been widely used as a substitute host in China. In this article, photoperiodic effect on diapause induction in C. cunea within the pupae of A. pernyi was investigated, and the differences in cold tolerance physiology including supercooling point, water content, and activities of three protective enzymes (Peroxidase [POD], Catalase [CAT], and Superoxide dismuase [SOD]) between diapause and nondiapause mature larvae were comparatively determined. Our results revealed that C. cunea possess a short-day induced larval diapause. The critical photoperiods for diapause induction in C. cunea were estimated to be between a photoperiod of 13:11 and 14:10 (L:D) h at 18°C, or between a photoperiod of 12:12 and 13:11 (L:D) h at 21°C or 24°C. We also found that the color of C. cunea diapausing larvae was taupe, while the normally developed (nondiapausing) individuals were light yellow. This body color change can be used as an indicator of diapause entry of C. cunea larave. The average supercooling point of diapausing mature larvae were lower than those of nondiapausing ones. There were significant differences in the activity of three protective enzymes (POD, CAT, and SOD) between diapausing and nondiapausing mature larvae.

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