Fruit flies have evolved mechanisms using olfactory and visual signals to find and recognize suitable host plants. The objective of the present study was to determine how habitat patterns may assist fruit flies in locating host plants and fruit. The tomato fruit fly, Neoceratitis cyanescens (Bezzi), was chosen as an example of a specialized fruit fly, attacking plants of the Solanaceae family. A series of experiments was conducted in an outdoor field cage wherein flies were released and captured on sticky orange and yellow spheres displayed in pairs within or above potted host or non-host plants. Bright orange spheres mimicking host fruit were significantly more attractive than yellow spheres only when placed within the canopy of host plants and not when either within non-host plants or above both types of plants. Additional experiments combining sets of host and non-host plants in the same cage, or spraying leaf extract of host plant (bug weed) on non-host plants showed that volatile cues emitted by the foliage of host plants may influence the visual response of flies in attracting mature females engaged in a searching behaviour for a laying site and in assisting them to find the host fruit. Moreover, the response was specific to mature females with a high oviposition drive because starved mature females, immature females and males showed no significant preference for orange spheres. Olfactory signals emitted by the host foliage could be an indicator of an appropriate habitat, leading flies to engage in searching for a visual image.

The role of various olfactory and visual stimuli was studied in host-plant finding by the asparagus fly Plioreocepta poeciloptera (Schrank), a monophagous monovoltine tephritid causing serious damage to asparagus spears. Volatiles released by asparagus plants were extracted by diethyl ether after cryotrapping concentration, and identified by gas chromatography–mass spectrometry. Twelve of the 13 compounds identified were tested using electroantennography to measure the response of the fly. Behavioural response was analysed using two different flight tunnels according to circadian rhythm, age and sex of adults, presence of the plant and of different coloured lures, presence of a male congener, or exposure to four pure asparagus odour compounds that elicited responses in electroantennography, i.e. hexanal, (E)-2-hexenal, (Z)-2-hexen-1-ol and decanal. Data showed that males locate the host plant more quickly than females. Females are attracted mainly by the blend of plant odour and male pheromone. Both sexes respond to a complex of stimuli only during the afternoon. These findings will be helpful in developing new and effective approaches to control this pest insect.

Mobility of tsetse flies is influenced by various factors including the search for a blood-meal. Field observations on the feeding behaviour of tsetse are difficult. The use of bait animals for experimental purposes may indicate food sources but not host selection under natural conditions. Availability and density of a particular potential host species in a tsetse habitat can influence the feeding habit of the latter. Flies are capable of adapting to new host species in the absence of the usual ones. Host selection might be due principally to availability of host(s) and not based on true preference. Tsetse flies respond to visual stimuli from moving objects. Their shape, colour and size are important factors eliciting visual response. Whether these factors are distinguished separately or in combinations is not clear. Odour emanating from live hosts causes up-wind olfactory response towards the source(s), resulting in actual landing on test targets even when the hosts are out of sight. The components of odour have not been isolated. It is therefore doubtful if host selection can be associated with odour, as this might imply that tsetse can differentiate the odours of the different potential hosts. The difficulties in ascertaining true host selection by tsetse are discussed to stimulate further investigations.