Variable gene expression and fitness in a host-switching herbivore: assessing the cost of polyphagy

Insect herbivores that feed upon and colonize a wide range of plant species are among the most invasive and destructive agricultural pests worldwide, especially in mixed cropping systems. Although the capacity to utilize many plant species in different families offers distinct advantages for an herbivore, the comparative rarity of polyphagous species relative to mono- or oligophagous species suggests unique challenges that must be overcome. The whitefly Bemisia tabaci Gennadius (B-biotype) is a much studied insect with a host range >600 plant species that is exploited in both open and protected agriculture. Tandem studies conducted at the organismal and molecular levels examined potential changes in fitness and gene expression, respectively, as B. tabaci was experimentally switched among host plants, similar to its life cycle pattern in a mixed cropping system. Various life history components were measured on broccoli, cotton, and cantaloupe plants by either sustaining adult pairs on a single host or switching to an alternate host. Expression levels of a suite of cytochrome P450s and glutathione S-transferases were quantified by qRT-PCR with primers designed from published sequences. Fitness components were significantly highest when whiteflies were reared on cantaloupe plants irrespective of original source plants. Expression levels of select Cyp P450s were significantly highest on broccoli while corresponding fitness measures were lowest, suggesting possible biotic stresses associated with detoxification of glucosinolates present in broccoli.  By linking transcriptional processes of the genome to performance measures of the organism on various host plants, a better understanding of the functional genome of a highly invasive pest species in a mixed cropping environment will be possible.