Abstract: The cotton-melon aphid, Aphis gossypii Glover,
an extremely polyphagous pest insect, comprises of sympatric populations
specialized on deferent host plants. The life history of A.
gossypii infesting cucurbit crops remains elusive because oviparous
aphids from overwintering hosts (often hibiscus) cannot colonize
cucurbit crops. We verified that the hibiscus-specialized lineage (HI)
suffered high mortality and gave birth to very few nymphs developing
into yellow dwarfs when transferred to fresh cucumber because the HI
lineage was unable to ingest phloem sap from fresh cucumber. However,
the HI lineage ingested phloem sap successfully when cucumber leaves
were pre-infected with Pseudoperonospora cubensis , a biotrophic
phytopathogen, accompanied by significant fitness improvement. More
surprisingly, the HI lineage with feeding experience on pre-infected
cucumber for two generations performed as well as the
cucumber-specialized lineage (CU) did on fresh cucumber, and inflicted
typical damage symptom to healthy cucumber plant. This phytopathogen
mediated host plant adaptation may be widespread in polyphagous aphids.
Keywords : host specialization; host race; phytopathogen
mediated host adaptation of insect; transcriptional adaptation; host
range expansion; polyphagous aphid; biotrophic phytopathogen