The Role of Inhibitory Stimuli in the Choice of Oviposition Site by Phytophagous Insects

Abstract

The examination of substrate selection for oviposition behaviour by specialist phytophagous insects like Acanthoscelides obtectus, Bruchus pisorum, and Pieris brassicae, revealed that such processes were governed by information probably obtained through similar receptors to those taking part in feeding preference or rejection. The role of the ovipositor is assumed to be secondary or negligible. The receptors respond to a wide variety of inorganic or organic compounds of very dissimilar structure which inhibit oviposition on the most preferred host plants. Paradoxically, though females select the suitable ovipositi0n media for the progeny, oviposition stimuli still do not reflect the quality of the substrates as larval food. Oviposition preference of the adults seems to be narrower than the range of substrates suitable for larval development.Sign stimuli governing oviposition behaviour in phytophagous insects have been studied mostly from the point of view of host plant or substrate-specific stimuli (oviposition stimulants eliciting the egg-laying response.) Much less has been done to reveal the importance of inhibitory stimuli in determinating the host plant range in oviposition site selection~), or more generally, the possibility of inhibiting oviposition on the preferred substrate. This question is the more challenging since it could provide fundamental information for developing new selective pest control methods.On the basis of experiments and observations on the egg-laying behaviour of phytophagous insects which are highly specialised in their selection of oviposition sites, Jermy (1965) proposed a two-way specialization of chemoreceptors governing oviposition. As with food selection by phytophagous insects, the inhibitory stimuli were regularly determinants, i.e., the effect of the most potent stimuli or complex of stimuli inducing oviposition could be masked by inhibitory substances (antiovipositants) at an appropriate concentration. This assumption has been supported by the results of experiments carried out on various insect species indicating that egg-laying behaviour can be disturbed by the presence of various substances acting as contact chemical inhibitors (Gupta & Thorsteinson, 1960;Jermy, 1965;Terofal, ~) The notion "oviposition site selection" is used here in a narrow sense, i.e., it would not include orientation towards the substrate and refers only to the behavioural steps when contact has already been established between the insect and its oviposition substrate.

Assays for Insect Feeding

“…These have revealed that the palatability of a chemical or plant is relative to the available alternatives (Meisner and Ascher, 1972;Jermy and Szentesi, 1978;Richardson and Whitaker, 1982), and to the gustatory background against which the chemicals are presented. Measures of palatability based on choice tests between two concentrations may differ from ones based on tests between each concentration and a control.…”

“…In testing contact chemoreception and oviposition by Acanthoscelides obtectus, Jermy and Szentesi (1978) used glass slides and glass beads coated with test chemical in 2% starch solution. Woodhead and Bernays (1977) avoided substrates by presenting chemicals directly to the mouthparts with a syringe.…”

Contact Chemoreception

“…In many phytophagous insects the host plant spectrum is decisively determined by the botanical distribution of chemicals acting as feeding or oviposition deterrents (Dethier, 1980a;Jermy, 1966;Jermy and Szentesi, 1978;Schoonhoven and Jermy, 1977). Contact chemoreceptors sensitive to a wide variety of compounds have been identified in all species of Lepidoptera where such cells have been looked for (Schoonhoven, 1972a).…”

Oviposition stimulants and deterrents control acceptance ofAlliaria petiolata byPieris rapae andP. napi oleracea

“…Although the majority of insects can depend on plant chemistry to guide their selection of the most suitable site for development and survival of their progeny, plant chemistry may lead to 'mistakes' (Jermy & Szentesi 1978;Rodman & Chew 1980;Renwick 1989). Reported 'mistakes' by females laying eggs on plants that do not support larval development have been traced to chemical similarity of the plants to actual hosts (Chew 1977a;Rodman & Chew 1980;Renwick 1989;Jaenike 1990).…”