Ecological Interactions

The abiotic environment and the presence of other organisms influence host-seeking behavior in nature. Among abiotic factors, temperature constraints and needs are probably the most important. For example, thermoregulating grasshoppers choose sites off the ground for cooling, and warm sunny substrates for basking. This can dictate the plants that are immediately available for feeding upon, so selection of thermoregulatory sites influences food selection. For example, the black lubber grasshopper, Taeniopoda eques, is highly polyphagous; when temperatures become very high in its desert environment in the middle of the day, however, it roosts as high off the ground as possible on mesquite or acacia bushes, and thus, any feeding is on these plants. During the cooler mornings and evenings it feeds only on plants at ground level. Many temperate butterflies seek out sunny or warm patches, and thus plants in those patches. For example, the meadow brown butterfly, Pararge aegeria, oviposits on various grasses but the actual choice depends on the temperature of the leaves, which in turn is influenced by whether the leaves are in sun or shade.

Wind is important for most insects. Wind speed and constancy influence odor plumes used by orienting insects. The wind speed also limits flight, with larger, stronger flying species remaining airborne at higher speeds. Very small insects are often carried by wind, and depending on the terrain, are deposited preferentially in certain places, such as the lee side of trees and hedges.

The presence of certain nonhost plants and the relative abundance or clumpiness of the host plant can alter the detailed behaviors involved in host seeking. For example, butterflies ovipositing in a habitat where two or more host plant species occur commonly tend to choose the species they laid eggs on previously, so that they land more often on the common host. In other insects, the host being selected for oviposition is dependent on factors such as the need for additional resources. In one example, the celery fly, Phylophylla heraclei, requires trees near to the celery host because this is where mating occurs and the adult food of aphid honeydew is available.

Insects that show odor-induced anemotaxis to their host plants presented alone in a wind tunnel in the laboratory do not always show the same behavior in field situations. For example, the Colorado potato beetle is attracted, at least from short distances, to its preferred host, potato. However, if nonhosts are also present, the response may be reduced or absent, and the host odor is said to be masked. Such interactions reduce the distance over which some host odors can be detected by phytophagous insects, and the phenomenon may be one of the mechanisms involved reduction of pest numbers in certain crop mixtures.

In addition, some insects are influenced by olfactory or visual evidence of prior occupation of a plant, competitors of the same or different species, and of the presence of natural enemies.

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