A short critical review is given on the literature of host plant finding in phytophagous insects with main emphasis on the Colorado potato beetle (Leptinotarsa decemlineata Say, col.: Chrysomelidae). The literature data are compared with the results of field experiments: (1) the foraging behaviour of adults was observed in a field arena on bare ground, and (2) adults were released in closed plant stands and recaptured by potted potato plants. It is concluded that host plant finding is a chance event in this species. The observed high directionality of move must be an adaptation increasing probability of host finding. Implications on population dynamics and agricultural practice are discussed.

ABSTRACT. Behavioural habituation† of Schistocerca gregaria Forskål fifth instar larvae to a feeding deterrent, nicotine hydrogen tartrate (NHT), is described. An attempt was made to differentiate between various factors possibly involved in the induction of this behavioural habituation. Sensory stimulation (through maxillary palp), cannulation of NHT into the crop, and its administration by gelatine capsules placed into the oesophagus each resulted in behavioural habituation, but in the latter two cases a sole induction via post‐ingestional input is not completely proven. Injection of NHT into the haemolymph did not induce habituation. It is concluded that habituation via sensory stimulation is a central phenomenon.

We have studied the relationship of bruchids and their legume hosts by extensive field sampling throughout Hungary over 17 years and by rearing the beetles from the samples in the laboratory. The value of the system lies in the accuracy of host affiliations. A total of 138 species and subspecies of plants were sampled, representing approximately 87% of the Leguminosae in Hungary. Only 51 legume species (37.0%) harboured bruchids (12 Bruchus spp. and 15 Bruchidius spp). Bruchids occurred in 38.3% of the host plant samples. Thirty‐seven plant species congeneric with bruchid host species were unoccupied by bruchids. The degree of host specificity ranged from monophagy (at least ecological monophagy) to oligophagy. On the basis of presence/absence data we tested the null hypothesis assuming that plant taxa and seed consuming bruchid species form congruent phyletic relations at the species level. We argue that the case for coevolution between the beetles and their hosts is weak. A comparison of the available taxonomic relationships (and presumed phylogenies) best fits a case of sequential evolution, with stronger phylogenetic conservatism in Bruchus species than in Bruchidius species. Bruchid and host plant taxa showed rough congruence only at the tribe level. We suggest that host shifts are best explained by the changes in the bruchids’ chemosensory system that determines the females’ host selection behaviour.

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.