Juvenile hormone and a protein associated with the larval diapause of the southwestern corn borer, Diatraea grandiosella

Abstract

Pre-diapausing larvae of the southwestern corn borer, Diatraea grandiosella, were found to store an electrophoretically discrete protein fraction which makes up about 20% of the soluble proteins of the fat body of newly diapaused individuals. This fraction appears to be restricted to the larval fat body and haemolymph. It accumulates in the fat body of pre-diapausing larvae and reaches a maximum titre in newly diapaused individuals. The protein is utilized gradually during diapause so that only traces of it remain after diapause has terminated. The protein fraction was found to accumulate in the fat body of non-diapausing larvae which had been treated with a juvenile hormone (JH) mimic. This treatment induces a diapause-like state. The involvement of JH in the accumulation and utilization of the protein was investigated by examining the proteins of the fat body after larvae had been allatectomized, or had received a JH mimic application, or had received both treatments. The results showed that non-diapausing larvae began to accumulate the protein fraction within 8 days of receiving a single application of JH mimic. Allatectomy of pre-diapausing larvae was shown to suppress the accumulation of the protein. This suppression was partially reversed by a topical application of JH mimic. JH mimic treatments and allatectomy of diapausing larvae were also shown to cause a decrease in the titre of most of the proteins of the fat body including the diapause-associated protein. The diapause-associated protein has a molecular weight of about 41,000, and contains 15–17 different amino acid residues, of which aspartate, leucine, lysine, and glutamate predominate, comprising about 43, 37, 35 and 32 residues per molecule, respectively. We suggest that diapauselin is a suitable name for this protein. Our findings provide the necessary framework for undertaking a more detailed analysis of the hormonal regulation of diapauselin synthesis and utilization.