Chilling results in failure of silk secretion by wandering larvae of Plodia interpunctella

Abstract

Silk production is an important part of the growth and development of many insects. However, the mechanism of its production is known to be vulnerable to various environmental stresses. We investigated whether chilling interrupts silk production by Plodia interpunctella, a serious pest of stored agricultural products. Wandering larvae were chilled at 4°C for 12h, after which the pupation rate of the larvae was determined by observing the number of corrugated cardboard cells that had been sealed with silk by pupating larvae. Less than 5% of cardboard cells were sealed after 3–12h of chilling, while 97.5% of the available cells in the non-chilled larvae group were sealed with silk. However, chilled larvae successfully eclosed, although emergence was delayed by 2–3d relative to that of non-chilled larvae. The silk glands of the chilled larvae were dissected and found to be less transparent than those of non-chilled larvae. However, real-time RT-PCR showed that the expression of both hsp70 and hsp90, but not hsp25 or grp78, was induced in the silk glands after chilling exposure. Our results suggest that silk secretion by P. interpunctella is highly susceptible to chilling stress, which may induce physical changes in unidentified components found within the silk glands.