The effect of background plant odours on the behavioural responses of Frankliniella occidentalis to attractive or repellent compounds in a Y-tube olfactometer

The western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), causes major losses in agricultural and horticultural crops worldwide. The volatile compounds methyl isonicotinate, p-anisaldehyde, eugenol, and linalool are known as olfactory attractants, and salicylaldehyde is known as a repellent for F. occidentalis under clean-air conditions in laboratory experiments. In the present study we assessed the responses of F. occidentalis to these compounds when presented alone, in combination, and in the presence of background odours emanating from cucumber (Cucumis sativus L., Cucurbitaceae), capsicum (Capiscum anuum L., Solanaceae), chrysanthemum (Chrysanthemum morifolium Ramat., Asteraceae), clove basil (Ocimum gratissimum L.), and lavender (Lavandula angustifolia L., both Lamiaceae) plants in a Y-tube olfactometer. In the presence of any background plant odour, the attractiveness of pure methyl isonicotinate to F. occidentalis proved to be consistently significant. Compared to clean-air conditions, a slightly lower percentage of thrips chose the Y-tube arm loaded with 10% p-anisaldehyde in the presence of cucumber leaf odour. With non-flowering clove basil plants in the background, F. occidentalis responses to 1% eugenol, a constituent of clove basil essential oil, were neutral, and the same applied to responses to pure linalool, a constituent of lavender essential oil, in the presence of flowering lavender plants. Also, thrips responses to pure or diluted salicylaldehyde were clearly influenced by plant background odours. We simulated a push-pull situation and found a trend indicating that the percentage of F. occidentalis choosing the airflow loaded with the attractant methyl isonicotinate was higher when the airflow in the other arm of the Y-tube was loaded with the repellent salicylaldehyde compared to clean air, and vice versa. We showed interactions between attractive or repellent volatile compounds and the environmental odours in the chemical ecology of F. occidentalis and the potential of a combined use of these compounds in thrips pest management.