Influence of Dietary Experience on the Induction of Preference of Adult Moths and Larvae for a New Olfactory Cue

Abstract

In Lepidoptera, host plant selection is first conditioned by oviposition site preference of adult females followed by feeding site preference of larvae. Dietary experience to plant volatile cues can induce larval and adult host plant preference. We investigated how the parent's and self-experience induce host preference in adult females and larvae of three lepidopteran stem borer species with different host plant ranges, namely the polyphagous Sesamia nonagrioides, the oligophagous Busseola fusca and the monophagous Busseola nairobica, and whether this induction can be linked to a neurophysiological phenotypic plasticity. The three species were conditioned to artificial diet enriched with vanillin from the neonate larvae to the adult stage during two generations. Thereafter, two-choice tests on both larvae and adults using a Y-tube olfactometer and electrophysiological (electroantennography [EAG] recordings) experiments on adults were carried out. In the polyphagous species, the induction of preference for a new olfactory cue (vanillin) by females and 3rd instar larvae was determined by parents' and self-experiences, without any modification of the sensitivity of the females antennae. No preference induction was found in the oligophagous and monophagous species. Our results suggest that lepidopteran stem borers may acquire preferences for new olfactory cues from the larval to the adult stage as described by Hopkins' host selection principle (HHSP), neo-Hopkins' principle, and the concept of 'chemical legacy.'

Fig 1. Description of the different conditioning procedures used for the experiments.

(A) for mated female (B) for 3^rd instar larvae. Capital letters indicate for each cohort the type of diet on which they have been reared (C for the control diet; V for the same diet but enriched with vanillin). For 3^rd instar larvae, the last letter is in lower case because the insects were reared only up to the 3^rd instar on the control diet (c) or diet enriched with vanillin (v).

Fig 2. Response of mated female to odours of vanillin and control diets in a Y-tube olfactometer according to the different conditioning procedures CC, VC, CV and VV.

(A) S. nonagrioides (B) B. fusca (C) B. nairobica. Between parentheses, the number n of mated females tested. The number of mated females making a choice was set to 100% to calculate the percentage of responding females. Bars with the same letter indicate no significant differences at 5% level between treatments according to Fisher’s exact test.

Fig 3. Response of 3^rd instar larvae to odours of vanillin and control diet in a Y-tube olfactometer according to the different conditioning procedures CCc, CVc, VVc, CVv and VVv.

(A) S. nonagrioides (B) B. fusca (C) B. nairobica. Twenty 3^rd instar larvae were tested for each conditioning procedure. The number of larvae making a choice was set to 100% to calculate the percentage of responding larvae. Bars with the same letter indicate no significant differences at 5% level between treatments according to Fisher’s exact test.

Fig 4. Dose-response curves of electrophysiological activity of the female antennae according to the three conditioning procedures CC, CV and VV.

(A) S. nonagrioides (B) B. fusca (C) B. nairobica. Means (± SE) of EAG responses (maximum amplitudes of μV deflections) during the 0.5 s stimulation period with 1 to 1000μg of vanillin are given. For each species, repeated measures ANOVA was used to evaluate the effect of the conditioning procedure on the EAG dose-response curves from female antennae.