Differential expression of the vitellogenin gene in the spruce terminal weevil feeding on resistant versus susceptible host trees.
Reproductive maturation and oviposition of the spruce terminal weevil (Pissodes strobi, Peck) are inhibited by resistant Sitka spruce (Picea sitchensis (Bong) Carr.). Vitellogenin is an egg yolk protein precursor which accumulates during the maturation of eggs. We describe the molecular cloning and characterization of a fragment of the vitellogenin gene from the spruce terminal weevil. The DNA sequence of this fragment has high identity to vitellogenin sequences from other insects and less to nematode and vertebrate vitellogenins. It hybridizes on Northern blots to a single 6.0 kb mRNA that is expressed only in females, and only after they have commenced reproductive development. Vitellogenin gene expression is induced by treatment with juvenile hormone, and is differentially regulated in insects feeding on resistant or susceptible trees. The effects of resistance on vitellogenin gene expression were studied to confirm our earlier findings and to provide a sensitive bioassay for identifying resistance factors.