Diapause Induction, Color Changes, and Supercooling Point of Diapause Larvae of Tetrastichus septentrionalis Yang (Hymenoptera: Eulophidae)

Abstract

The chalcid wasp Tetrastichus septentrionalis Yang (Hymenoptera: Eulophidae) is one of the dominant pupal parasitoids of Hyphantria cunea (Drury) (Lepidoptera: Erebidae). In this study, the photoperiod’s effect on diapause induction in T. septentrionalis using the alternative host Tenebrio molitor was measured, revealing that T. septentrionalis is of the long-day type. The critical photoperiods for diapause induction in T. septentrionalis were estimated to be between photoperiods of 13:11 and 14:10 (L:D) h at 18 °C, and between photoperiods of 12:12 and 13:11 (L:D) h at 21 °C and 24 °C. We also found that T. septentrionalis diapausing larvae were grey-brown, while normally developed (non-diapausing) individuals were light yellow. The diapause-sensitive insect state was the larval stage, and the short light exposure treatment had a significant cumulative effect on diapause induction. The least squares method was used to calculate a lower developmental threshold of 13.34 ± 0.50 °C and an effective cumulative temperature of 184.46 ± 11.46 d·°C for post-diapause development. The average supercooling point of diapausing mature larvae was significantly lower than that of non-diapausing ones. Our research on T. septentrionalis provides a reference for the biological control of H. cunea and other leaf-eating pests.

Transcriptomics Provide Insights into the Photoperiodic Regulation of Reproductive Diapause in the Green Lacewing, Chrysoperla nipponensis (Okamoto) (Neuroptera: Chrysopidae)

“…During the induction process of diapause in insects, notable changes in physiological characteristics and gene expression often occur. Diapause is sometimes accompanied by changes in body coloration; for example, the chalcid wasp Tetrastichus septentrionalis has two body colors, light yellow in the non-diapause state and gray-brown in the diapause state [11]. For instance, there is an initiation of yolk deposition, an accumulation of lipids in the fat body, and the activation of genes involved in fatty acid synthesis [12][13][14].…”

“…This implies that the photoperiod not only causes physiological changes in adults but also has potential effects on larvae. Environmental factors inducing diapause have been widely studied, but there are few reports on the sensitive period of diapause induction [10,11,38]. It has been observed that third-instar larvae and pre-pupae exhibit greater sensitivity compared with other stages of preimaginal development in C. nipponensis [32].…”