A protein-level glimpse at the rapidly shifting physiology of male and female mountain pine beetles attacking lodgepole pine hosts

In order to successfully reproduce, adult mountain pine beetles must attack a host tree and overwhelm its defenses. The female is the first-attacking sex in this species. Arriving females, and the later-arriving males, produce aggregation pheromones as they invade the phloem tissue of host pines. Both sexes inoculate the tree with symbiotic, pathogenic fungi. Shifts in protein expression in both sexes during colonization are mainly related to energetics, reproduction, stress, and detoxification of secondary metabolites. In a proteomics experiment with females 757 proteins were quantitatively detected, 21 of which showed significant differences between starved and phloem-fed samples. Very rapidly (within 24 h) following initial feeding on host phloem, females express significantly higher levels of two vitellogenin-like lipid transporters but show a significant decrease in a proline biosynthetic protein. This is likely related to the shift from dispersal physiology to reproduction. In males 739 proteins were quantitatively detected, 28 of which showed significant differences between starved and phloem fed samples. Males begin to shut down energy metabolism after host colonization, but they show increases in calreticulin (a chaperone involved in protein folding) and a glutathione S-transferase (GST; potentially involved in detoxification of secondary metabolites). Both sexes show increases in heat shock proteins. And both sexes constitutively express, among other things, a variety of cytochromes P450, other GSTs, esterases, and proteins involved in DNA damage repair. The global protein expression observed in this insect relates well to its generally semelparous life cycle and its shifting host environment.