Role of hormones in starvation-induced delay in larval hemolymph protein gene expression in Galleria mellonella

Summary

Developmental Northern analysis of larval hemolymph protein gene transcripts in Galleria mellonella showed that Lhp76 is expressed all through the larval life, while Lhp82 is expressed only during the last larval stadium. Neither transcript was detectable in pharate adults and adult moths. In addition, these transcripts were not detectable during the first 48 h of the last larval stadium. Experimental analyses of the effects of the nutritional state and the hormonal levels of the last instar larvae on LHP gene expression suggests that the nutritional state of the larva has no direct effect, but nutrition acts through its effect on the hormone titers. Larvae starved after the first 24 h of the stadium and those fed on a non-protein diet produced both the transcripts on schedule on day 3. However, starvation during the first 24 or 48 h or feeding them on agar caused a marked delay in activation of Lhp82. These starved larvae pupated 4 to 12 days later than controls. Furthermore, JH titers in the starved larvae remain high even 5 days after ecdysis into the last instar. Prothorax-ligation of the starved and the starved-refed larvae accelerated production of the transcripts, thereby suggesting that the nutritional state does not directly affect LHP gene expression. Application of JH 1 to the ligated preparations resulted in selective blocking of Lhp82, while 20-OH ecdysone affected both the genes, thereby supporting the view that the insect hormones play an important role in stage-specific expression of LHP genes.