Zixin Liu

Diapause enables insect survival in unfavorable environments. The parasitic wasp A. japonicus, a natural enemy of several fruit-tree pests, undergoes larval diapause. Previous work has shown that larval diapause in A. japonicus can be induced by medium temperatures in combination with short-day photoperiods; however, the molecular functions associated with this response remain poorly understood. Here, integrated transcriptomic and proteomic approaches were employed to investigate the molecular signatures associated with larval diapause in A. japonicus. The identification of 3399 differentially expressed genes and 3112 differentially expressed proteins was carried out between diapause and non-diapause larvae. Among these, five gene–protein pairs showed consistent differential expression, including farnesol dehydrogenase, crystallin (associated with longevity-related pathways), forkhead-associated (FHA) domain-containing proteins, and the detoxification enzyme cytochrome P450. These findings show that larval diapause in A. japonicus is accompanied by extensive physiological and biochemical remodeling, and juvenile hormone-related signaling is likely involved in this process. In summary, these results provide insights into future gene function research, especially with regard to the mechanism of larval diapause in A. japonicus.

Chinese silkworm (Antheraea pernyi) eggs are used as factitious hosts of Anastatus fulloi, and refrigeration of these eggs is essential for large-scale rearing of A. fulloi. We studied the effects of cold storage of A. pernyi eggs on egg quality and the fitness of A. fulloi reared on the eggs. Four cold storage treatments and two cold storage periods were assessed. The 0–3 °C refrigerator treatment was unsuitable for long-term (>70 days) storage. Cold storage at −5 °C and −18 °C increased the loss rate of A. pernyi eggs, but there was no significant difference between the control and 0–3 °C water bath treatment. The parasitism rate of A. fulloi was reduced when A. pernyi eggs were refrigerated for 6 or 12 months. There were no obvious differences in eclosion rate and percentage of females between control and eggs subjected to 6-month storage in 0–3 °C, −5 °C, and −18 °C water bath treatments. However, the eclosion rate and percentage of females decreased sharply when the storage period was 12 months. The overall eclosion rate of A. fulloi was reduced at the prolonged refrigeration time. Cold storage reduced host egg quality and their fitness suitability for A. fulloi. To minimize losses in the large-scale rearing of A. fulloi, A. pernyi eggs should be refrigerated in a 0–3 °C or −5 °C water bath treatment, and the storage period should not exceed 6 months.

Anastatus japonicus Ashmead is a widely used biological control agent against stink bugs that can be successfully reared using the large eggs of the Chinese silkworm. In this study, environmental factors responsible for the induction of diapause in A. japonicus were investigated on host eggs of the Chinese silkworm. A. japonicus exhibited a facultative, mature larval diapause within its host eggs. Second–third instar larva are the most sensitive stages to diapause stimuli. The accumulation of diapause stimuli during all the larval stages maximized the diapause response. A short photoperiod of 10L:14D and temperature of 17 °C led to the occurrence of the highest diapause response, while a long photoperiod (14L:10D) and low temperatures (11 and 14 °C) prevented the diapause. A specific exposure period was required to reach high diapause incidence. Diapausing mature larvae had a significantly higher survival rate after 180 days storage at 10 °C than that of nondiapausing mature larvae. Taken together, results suggest methods that could be exploited in the developmental regulation, field-release pretreatment technology, and long-term storage of A. japonicus.