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

Abstract

Methods and equations have not been developed previously to estimate insect flight densities, a key factor in decisions regarding trap and lure deployment in programs of monitoring, mass trapping, and mating disruption with semiochemicals. An equation to estimate densities of flying insects per hectare is presented that uses the standard deviation (SD) of the vertical flight distribution, trapping time, the trap's spherical effective radius (ER), catch at the mean flight height (as estimated from a best-fitting normal distribution with SD), and an estimated average flight speed. Data from previous reports were used to estimate flight densities with the equations. The same equations can use traps with pheromone lures or attractive colors with a measured effective attraction radius (EAR) instead of the ER. In practice, EAR is more useful than ER for flight density calculations since attractive traps catch higher numbers of insects and thus can measure lower populations more readily. Computer simulations in three dimensions with varying numbers of insects (density) and varying EAR were used to validate the equations for density estimates of insects in the field. Few studies have provided data to obtain EAR, SD, speed, and trapping time to estimate flight densities per hectare. However, the necessary parameters can be measured more precisely in future studies.

Index of host habitat preference explored by movement‐based simulations and trap captures

“…However, trapping with pheromones in simulations of this type did not yield the appropriate HHP because catches were similar on traps inside and outside the host habitat area, giving HHP equal to zero. The reason catch was similar inside and outside the host habitat was that encounter rate models predict that catch is a function of speed and density (Byers, ; Byers & Naranjo, ; Levi−Zada et al., ). Thus, as speed decreased (smaller steps), a compensatory increase in density occurred as insects remained longer, which caused no differences in catch between the inside and outside areas.…”

“…Our results with catches of the monophagous lesser date moth on traps baited with sex pheromone inside and outside a date plantation used with Equation gave an HHP = 0.96. In most simulations, a correlated random walk of flight was assumed both inside and outside the host habitat as indicated in several studies of flying insects (Byers, ). This type of flight also was indicated from catches of lesser date moths on traps baited with female‐equivalent dispensers (FD) of 10 μg pheromone in a date plantation (Levi−Zada et al., ).…”

“…Movement-based models of habitat choice such as step-selection functions and resource selection functions have been developed for larger vertebrates that can be followed by GPS biotelemetry or by visual observations (Avgar, Potts, Lewis, & Boyce, 2016;Boyce et al, 2016;Gillies & St. Clair, 2010;Mason & Fortin, 2017;Patterson, Thomas, Wilcox, Ovaskainen, & Matthiopoulos, 2007;Thurfjell, Ciuti, & Boyce, 2014). In contrast, insects are small and essentially invisible in flight, thus their relative abundance, movements and spatial distributions can only be readily studied with traps that intercept or attract (Byers, 1999(Byers, , 2012a(Byers, , 2012bByers & Naranjo, 2014;Landolt & Phillips, 1997), or by conventional sampling methods (Kuno, 1991).…”

“…Olfactory mechanisms appear to aid moths, bark beetles, parasitoid wasps and many other insects in finding and staying in host habitat by means of attraction to pheromones and host plant volatiles (Byers, 1989;Byers et al, 1985;Cotes et al, 2015;El-Sayed et al, 2008Landolt & Phillips, 1997;Quilici & Rousse, 2012;Vet, 1983;Zhao & Kang, 2002). Many insects appear to have evolved behaviour to search in a random forward direction for host habitats until finding appropriate odour of host plants or insects (Byers, 1989(Byers, , 1991(Byers, , 1999(Byers, , 2012a(Byers, , 2012bLevi−Zada et al, 2018).…”

“…gave an HHP = 0.96. In most simulations, a correlated random walk of flight was assumed both inside and outside the host habitat as indicated in several studies of flying insects(Byers, 2012a). This type of flight also was indicated from catches of lesser date moths on traps baited with female-equivalent dispensers (FD) of 10 μg pheromone in a date plantation.…”