Aphid-induced Defences in Chilli Affect Preferences of the Whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae)

Abstract

The sweetpotato whitefly (WF), Bemisia tabaci, is a major pest that damages a wide range of vegetable crops in Malaysia. WF infestation is influenced by a variety of factors, including previous infestation of the host plant by other insect pests. This study investigated the effects of previous infestation of host chilli plants by the green peach aphid (Myzus persicae) on the olfactory behavioural response of B. tabaci, using free-choice bioassay with a Y-tube olfactometer. We analysed volatile organic compounds (VOCs) emitted by non-infested and M. persicae-infested chilli plants using solid-phase microextraction and gas chromatography-mass spectrometry. Our results showed that female WFs preferred non-infested to pre-infested plants. Collection and analysis of volatile compounds emitted by infested plants confirmed that there were significant increases in the production of monoterpenes (cymene; 1,8-cineole), sesquiterpenes (β-cadinene, α-copaene), and methyl salicylate (MeSA) compared to non-infested plants. Our results suggest that host plant infestation by aphids may induce production of secondary metabolites that deter B. tabaci from settling on its host plants. These results provide important information for understanding WF host selection and dispersal among crops, and also for manipulating WF behaviour to improve IPM in chilli.

Figure 1. Mean (±SE) numbers of B. tabaci females settled on non-infested and pre-infested chilli plants at different times (1, 2, 3, 4 h) after WF release under free-choice bioassay, using two-way ANOVA.

Figure 2. Total mean (±SE) number of settled B. tabaci females in free-choice bioassay with non-infested and pre-infested chilli plants.

Different letters indicate a significant difference at (P < 0. 05). Each bar represents the mean of 5 replicates each assessed at 4 time intervals, using two-way ANOVA.

Figure 3. A schematic diagram of the Y-tube olfactometer, modified from Akol et al. (2003), used to test the effect of M. persicae feeding on behavioural response of B. tabaci.

Figure 4. Static headspace sampling with (SPME) device.

(A) The plant sample was enclosed in a glass container for 60 min, with a broad opening for easy removal of the plant. (B) The fiber is mounted on a SPME fiber holder. (C) The fiber was injected through the septum of the sample container by pushing the plunger of the SPME fiber holder, and extended from the needle and exposed to volatiles for 30 min. After collection VOCs, the fiber was retracted into the needle and the SPME device removed from the container for GC-MS analysis.