Identification, comparison, and functional analysis of salivary phenol-oxidizing enzymes in Bemisia tabaci B and Trialeurodes vaporariorum

The differences in the ability of the invading whitefly, Bemisia tabaci (Gennadius) (commonly known as biotype B and hereafter as B) and Trialeurodes vaporariorum (Westwood) (both Hemiptera: Aleyrodidae) to utilize salivary phenol-oxidizing enzymes polyphenol oxidase (PPO) and peroxidase (POD) to detoxify plant defensive phenolic compounds were explored. Polyphenol oxidase and POD were found in the saliva of both B and T.vaporariorum. For tomato colonies, the PPO and POD activities in the watery saliva of B were 2.27- and 1.34-fold higher than those of T.vaporariorum. The PPO activities against specific phenolic compounds commonly found in plants were compared. The activities of those from B were significantly greater than those from T.vaporariorum. We also measured PPO activity in both species after they had fed on plants that were undamaged or had been previously damaged with either a plant pathogen [Phytophthora infestans (Mont.) de Bary (Peronosporales)] infection, mechanical damage, B infestation, or exogenous salicylic acid. For B, PPO activities in watery saliva increased 229, 184, 152, and 139% in response to the four treatments, whereas those of T.vaporariorum only increased 133, 119, 113, and 103%, respectively. Biotype B infestation significantly increased the total phenolic content of tomato leaves. Meanwhile, feeding on tomato infestation with B had no significant effect on the survival rate of B, but decreased the survival rate of T.vaporariorum significantly. These results suggest that B has stronger ability utilizing PPO to detoxify high concentrations of phenolics than T.vaporariorum, and this contributes to a significant advantage for B to hold high fitness on plants with induced resistance. Possible roles of salivary PPO in the competition between B and T.vaporariorum are discussed.