Pheromones are semiochemicals that are produced and received by members of the same species. A range of behaviors and biological processes are influenced by pheromones, but pest management programs most often use compounds that attract a mate (sex pheromones) or call others to a suitable food or nesting site (aggregation pheromones). |
Other pheromones regulate caste or reproductive development in social insects (honey bees and termites for example), signal alarm (in honey bees, ants, and aphids), mark trails (ants), and serve other functions.
Attractant-baited traps are used instead of (or in addition to) other sampling methods for two major reasons. First, these traps are very sensitive and may capture pest insects that are present at densities too low to detect with a reasonable amount of effort using other inspection methods. This attribute can be extremely important when the goal of a sampling program is to detect foreign or "exotic" pests as soon as they enter an area so that control measures can be initiated immediately. Second, traps baited with chemical attractants capture only one species or a narrow range of species. This specificity simplifies the identification and counting of target pests. Sensitivity and specificity make attractant-baited traps efficient, labor-saving tools.
Attractant-baited traps are used in monitoring programs for at least three purposes: (1) to detect the presence of an exotic pest (an immigrant pest not previously known to inhabit a state or region); (2) to estimate the relative density of a pest population at a given site; and (3) to indicate the first emergence or peak flight activity of a pest species in a given area, often to time an insecticide application or to signal the need for additional scouting. The use of traps to detect exotic pests has been demonstrated in widely publicized efforts to detect and eradicate pests such as the gypsy moth and the Mediterranean fruit fly whenever infestations are detected in new areas.
Although attractant-baited traps give an indication of pest density, several factors make the interpretation of density estimates complex and difficult. First, environmental factors affect trap catches. Temperature, rainfall, and wind speed and direction influence attractant release (from lures) and insect flight. Many insects fly and respond to semiochemicals only at certain time (dawn, midday, dusk, night, etc.), and then only if temperatures at that time exceed a minimum level (often 50 to 60° F). Wind speed and direction determine the extent of insect movement from surrounding areas to traps within a field or orchard.
Further complication can result from the fact that almost all attractant-baited traps are used to capture adult insects. Damage to crops, however, is caused not by the adult male moths attracted to the traps but by the subsequent generation of caterpillars that female moths produce. Because variable environmental conditions and variable densities of natural enemies greatly influence pest survival between the time trapping data are collected and the time pest damage occurs, establishing a precise economic threshold (the pest population level that warrants control) based on trap counts is difficult. Where counts from traps are used to estimate pest density and determine control needs, guidelines are usually conservative or somewhat vague.
Attractant-baited traps can be used to signal the need for additional sampling efforts or to time insecticide applications and eliminate unnecessary spraying. One example of the use of pheromone traps to trigger further sampling involves the black cutworm, a common but sporadic pest of seedling corn in the Midwest. Pheromone traps baited with a specific sex attractant are used in a statewide sampling program to monitor the annual spring migration of black cutworm moths from southern states into Illinois. In area where counts of male moths in traps indicate the potential for damaging infestations of cutworm larvae, producers are urged to check for cutworm density and crop damage in fields of seedling corn. For pests that cause unacceptable levels of damage even at low population densities, such as the codling moth or apple maggot in commercial apple orchards, traps can be used as the only sampling method for determining the dates to begin and end insecticide application programs.
For all programs that use traps of any type, trap design and trap placement are important factors. For example, common paper sticky traps are ineffective for monitoring corn earworm moths. Male corn earworm moths that are attracted to a chemical lure seldom enter these box- or tentlike traps. Instead, a much larger, cone-shaped trap must be used to capture this insect. Similarly, placing traps at the correct height and in the correct portion of a field (edge or center) or building is sometimes the key to detection or interpretation.
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