Differing Effects of Cabbage Defense Responses Induced by MEAM1 and MED Cryptic Species of Bemisia Tabaci on Later-Arriving Conspecifics and Heterospecifics

Two cryptic species of the Bemisia tabaci species complex, MEAM1 (Middle East-Asia Minor 1) and MED (Mediterranean), are highly destructive herbivores. Attack by herbivorous insects often induces defense responses in plants, including the accumulation of toxic secondary metabolites, the synthesis of herbivore-induced plant volatiles (HIPVs) and defensive proteins, and the release of volatile organic compounds that attract natural enemies. These defense responses, which often differ depending on the herbivore, may affect the preference and performance of later-arriving con- and heterospecific whiteflies that attack the same plant. In the present study, we found that MEAM1 whiteflies preferred settling and ovipositing on non-infested and MED-infested cabbage over MEAM1-infested cabbage plants, but that MED whiteflies showed no significant difference in settling or oviposition preference among non-infested, MEAM1-infested, and MED-infested plants. MEAM1 infestation increased the contents of total phenols and flavonoids in cabbage, which coincided with the increased expression of the following genes in the phenylpropanoid biosynthesis pathway: PAL2, C4H, and 4CL1. Soluble protein contents were also markedly higher in the MEAM1-infested cabbage plants than in the non-infested and MED-infested cabbage plants. Overall, these results demonstrate that previous infestation by MEAM1 and MED whiteflies induced defense responses in cabbage plants that had different effects on the host preference and performance of later-arriving con- and heterospecific whiteflies. Phenolic compounds may be the key factors influencing host choice by MEAM1 and MED whiteflies on cabbage plants.