Factors regulating lipophorin synthesis by the larval fat body of the southwestern corn borer, Diatraea grandiosella

Abstract

The effects of starvation, dietary lipid restriction, topical methoprene treatment, and diapause termination on the synthesis of lipophorin by larval fat bodies of the southwestern corn borer, Diatraea grandiosella, were examined. Excised larval fat bodies were labeled in vitro with [ 3H]leucine and the synthesis and release of [ 3H]lipophorin were measured using immunochemical methods. When 9 day old larvae were transferred from control diet on to a nonnutritive agar medium, protein synthesis, including lipophorin synthesis, was inhibited two and four days later. Larvae returned to control diet regained their capacity to synthesize lipophorin. Larvae transferred to a lipid-depleted diet at 10 days of age showed no decrease in lipophorin synthesis two, 8 or 14 days later. When non-diapause 5th instar larvae were treated with methoprene to induce a diapause-like state, lipophorin synthesis and release by the fat body was intermediate between that of non-diapause and pre-diapause larvae. Late diapause larvae, immediately after being transferred to conditions that accelerated diapause termination, showed an increase in lipophorin synthesis over that of controls retained under diapause-sustaining conditions. Thus, the resumption of lipophorin synthesis precedes the onset of the pupal molting cycle, thereby making lipophorin available for lipid transport upon resumption of morphogenesis.