Gypsy moth flight study

The partner agencies that make up the Minnesota Cooperative Gypsy Moth Program are launching a pilot project this summer to study detection trap capture rates as a function of the effect of temperature on male moth flight. The pilot project, which involves releasing sterilized male moths, will take place near Cloquet Valley State Forest, NE of Duluth. Additional work will be done in future years along the North Shore and in central Minnesota.

The purpose of the project is to determine the capture rates of male moths across the range of summer temperatures typically found in Minnesota. Currently, gypsy moth introductions are monitored using detection traps baited with the female moth sex attractant. Baited sticky traps are placed in grids of varying densities based on the risk of introduction. So for instance, the Twin Cities, which are at high risk of new gypsy moth introductions because of the volume of people movement, is trapped at a density of one trap per one square mile. Where the risk of introduction is lower, traps are placed at a density of one trap per four square miles, or none at all.

Male moths are strongly attracted to the bait and are thus caught in the grid of detection traps. The rate of capture helps indicate the status of any potential gypsy moth populations. For instance, a single moth most likely means a single introduction very unlikely to become established. While sites with single moth catches are monitored the following year, there is little concern of an infestation. Ten moths or more in a trap indicate a possible infestation. Whether or not such an infestation becomes established depends on site conditions, weather patterns and how soon we detect its presence. The sooner we catch it the more easily the infestation can be eradicated. Hence the use of detection traps.

The work done to establish the relationship between male moth capture rates and gypsy moth population numbers was done mostly back east. While the current trapping techniques have worked well in areas where the moth currently resides, the moth is beginning to move into areas where capture rates have not been studies in depth. Phenology models that indicate predicted flight periods based on daily temperatures also use eastern data, so may or may not accurately predict what will happen in Minnesota. Using eastern standards, Minnesota cooperators risk misinterpreting trap data from northern Minnesota where average summer temperatures are considerably lower than areas previously studied.

This study consists of three 9-square mile plots trapped at densities of 36, 16 and 1 trap per square mile respectively. These are the densities commonly used by the MN Department of Agriculture, the lead agency in gypsy moth trapping, to determine if there is an infestation and where the boundaries of the population are. Male moths (which do not feed and only live a few days to a week) will be released on a weekly basis from the center of each plot. Traps will be checked, capture data recorded and correlated with weather data taken on each plot. Released moths can be distinguished from wild moths through the ingenious use of colored dyes. Gypsy moth caterpillars are fed on a diet laced with an oil-soluble red dye. The dye colors their hemolymph or ?blood?. Once the caterpillars pupate, the female pupae, which are nearly twice the size of males, are discarded. Male moth pupae are irradiated to sterilize them before they emerge as moths. The male pupae are placed in small pint-sized cartons filled with an iridescent colored external dye. The cartons are opened and hung from trees near plot center. When the moths emerge, they dry their wings, now covered in the external dye, and take off in search of a female. The external dye comes in four colors, distinguishing one batch of moths from another. The date of each release is recorded along with the color of that batch. That way, if a moth emerges late and gets caught along with moths from a later release, scientists can tell which batch they came from. If no external dyes are found, the moth can be crushed to display the internal dye that distinguishes wild from sterilized moths.

Nearby residents are not likely to notice the gypsy moths because the number being released is relatively small and the plots are in wooded areas away from towns. Unless there is a resident population of gypsy moths in the area that we don?t know about, the released males are unlikely to find a female. Even then, they will not be able to fertilize her eggs. Those interested in the study can contact one of the Regional DNR Forest Health Specialists (see the DNR website for contact information).

As with all gypsy moth projects there are a number of cooperators involved. The Natural Resource Research Inst. (NRRI) stationed in Duluth and affiliated with the University of Minnesota is overseeing the field work with radios contributed by the MN Dept of Transportation. Funding has been provided by USDA Animal & Plant Health Inspection Service (APHIS) and Forest Service (USFS). Project coordination and support is being provided by MN Departments of Agriculture (MDA) and Natural Resources (DNR) ? all in the name of cooperative gypsy moth management.