Active Space of Pheromone Plume and its Relationship to Effective Attraction Radius in Applied Models

Abstract

The release rate of a semiochemical lure that attracts flying insects has a specific effective attraction radius (EAR) that corresponds to the lure's orientation response strength. EAR is defined as the radius of a passive sphere that intercepts the same number of insects as a semiochemical-baited trap. It is estimated by calculating the ratio of trap catches in the field in baited and unbaited traps and the interception area of the unbaited trap. EAR serves as a standardized method for comparing the attractive strengths of lures that is independent of population density. In two-dimensional encounter rate models that are used to describe insect mass trapping and mating disruption, a circular EAR (EAR c ) describes a key parameter that affects catch or influence by pheromone in the models. However, the spherical EAR, as measured in the field, should be transformed to an EAR c for appropriate predictions in such models. The EAR c is calculated as (π/2EAR2 )/F L , where F L is the effective thickness of the flight layer where the insect searches. F L was estimated from catches of insects (42 species in the orders Coleoptera, Lepidoptera, Diptera, Hemiptera, and Thysanoptera) on traps at various heights as reported in the literature. The EAR c was proposed further as a simple but equivalent alternative to simulations of highly complex active-space plumes with variable response surfaces that have proven exceedingly difficult to quantify in nature. This hypothesis was explored in simulations where flying insects, represented as coordinate points, moved about in a correlated random walk in an area that contained a pheromone plume, represented as a sector of active space composed of a capture probability surface of variable complexity. In this plume model, catch was monitored at a constant density of flying insects and then compared to simulations in which a circular EAR c was enlarged until an equivalent rate was caught. This demonstrated that there is a circular EAR c , where all insects that enter are caught, which corresponds in catch effect to any plume. Thus, the EAR c , based on the field-observed EAR, can be used in encounter rate models to develop effective control programs based on mass trapping and/or mating disruption.

Estimating Insect Flight Densities from Attractive Trap Catches and Flight Height Distributions

“…Currently, there are no methods and equations that use trap catch data to estimate insect flight densities, a crucial factor in the success of mass trapping and mating disruption programs (Shorey, 1977;Cardé, 1990;Cardé and Minks, 1995;Miller et al, 2006a, b;El-Sayed et al, 2006, 2009Byers, 2007Byers, , 2008. In order to develop methods and equations for determining flight densities from trap catch data, several parameters need to be estimated and understood.…”

“…In mass trapping for control of insects, the most effective lure is that with the largest EAR ascertained by field-testing the semiochemical at increasing release rates. The EAR has been used in simulation models of mass trapping and mating disruption (Byers, 2007) that are important tools of integrated pest management (Shorey, 1977;Cardé, 1990;Cardé and Minks, 1995;Miller et al, 2006a, b;El-Sayed et al, 2006, 2009Byers, 2008). These and other studies, however, have relied upon subjectively testing densities of lures/traps by trial and error until some negative effect on mating success was observed.…”

“…These and other studies, however, have relied upon subjectively testing densities of lures/traps by trial and error until some negative effect on mating success was observed. This approach would be more efficient with a better knowledge of flight densities, EAR of attractants, and use of simulation models to determine the trap density most likely to succeed in control measures (Byers, 2007(Byers, , 2008.…”

“…The circular EAR (termed EAR c ), used in encounter-rate simulations of mass trapping in two dimensions (2D), is not identical to the spherical EAR obtained from insect catches in the field (Byers, 2008(Byers, , 2009. A transformation of EAR is necessary ( Fig.…”

“…This conversion equation requires an estimation of the effective flight layer (F L ), which reflects the vertical layer where the particular insect species flies in search of mates and host plants. Essentially, if the vertical flight density distribution described by the standard deviation (SD) is squeezed into a layer of uniform density equal to that at the mean flight height, then the thickness of this layer is the F L (Byers, 2008(Byers, , 2009. However, the F L does not describe a real layer, so hereafter to avoid confusion the F L will be replaced with its equivalent, which is SD Á ffiffiffiffiffiffiffiffi ffi 2 Á p p .…”