Feature Article

Gypsy Moth Program Update

October, 2002

By Kimberly Thielen Cremers, MDA Gypsy Moth Program Coordinator, and, Susan Burks, DNR Forest Health Specialist

In spite of a long string of complications, the APPD unit and communication team of MN Dept. of Agriculture (MDA) put together a very success program for 2002. While there were a number of partners involved, along with some outside funding, MDA deserves to be congratulated for their efforts. Nearly 16,000 traps were hung, a record number of acres were treated and a massive PR campaign was launched, all with positive results. The increased public awareness alone will go along way toward delaying future establishment of the gypsy moth by reducing the number of new introductions.

2002 Treatment Results:

In 2002, two sites in the metro area (one in Minneapolis near Lake Harriet and one in Golden Valley, near Theodore Wirth Park) were treated with Bt, while a site in Houston County was treated with pheromone flakes.

Lake Harriet: Trapping following the 425 acre treatment found zero moths in spite of signs of early defoliation prior to the treatments and the recovery of two caterpillars found after the treatments were completed. The site was intensely trapped at 3-9 traps per acre for a total of 252 traps within the 50 acre core area. The remaining 375 acres within the treatment boundary were trapped at a density of 36 traps per square mile for a total of 104 traps. An additional 13 square miles were delimited around the treatment boundary. The delimit area was trapped at 16-36 traps per square mile. Ten single and one multiple trap of five were caught outside the treatment boundary. None of these finds appear to be related to the treatment site. The treatment boundary and the positive finds outside the treatment boundary will again be delimit trapped during the 2003.

Golden Valley Site: Burlap bands were also used to monitor caterpillar survival at this site, but none were found. The core area of 85 acres received 3 traps an acre. The remaining 1751 acres within the treatment block received 36 traps per square mile for a total of 169 traps. An additional 1679 acres outside the treatment area were delimit trapped at 16-36 traps per square mile. Six male moths were recovered, 1 within the mass trapping core, 2 within the treatment boundary, and 3 within the delimit boundary outside the treatment block. The catches were spread out geographically; suggesting the presence of a reproducing population is not likely.

Crooked Creek, Houston County: A 650 acre site, straddling part of the Dorr State Forest was treated with Disparlure (Disrupt II). The use of pheromone flakes is new to Minnesota but is becoming a common occurrence within the national Slow-the-Spread program. The primary advantage over Bt is the increased specificity. Disadvantages include the inorganic plastic chads used as a carrier and the one to two year residual that limits trapping following pheromone treatments. Pheromone flakes work by saturating an area with GM pheromone thus masking the presence of any female moths present (limiting, if not prohibiting mating). However, the flakes also mask the presence of any detection traps, which utilize the same pheromone to attract male moths. Although the area was intensively trapped this year (with no moths found) it will need to be trapped again next year before treatment results can be assessed. Catch history and limiting site factors made this an ideal candidate for the treatment. If the treatment is shown to be effective under MN conditions, it may prove useful in other situations.

A timber sale was conducted at this site in December 2001, with logging scheduled this winter. The Minnesota Department of Natural Resources will be working closely with the logger to inspect logs removed from the site. The receiving mills have already been notified and will be trapped this next season as a precautionary measure.

Trapping results:

Statewide numbers are down considerably. (See the map "2002 Gypsy moth survey moth catch by county") At this time, a total of 119 male moths have been caught statewide (note, traps along the North Shore were still being taken down at the time of this writing). This is the lowest number since 1993, when 93 male moths were caught. While North Shore trapping is not yet complete, the final numbers are not expected to climb dramatically. An additional 11 to 12 suspect moths (not yet confirmed) bring total of moths caught near Grand Portage up to 20 (3 traps had 2 moths and 14 were single finds), with 3 singles in Cook County, and 2 potential singles near Duluth.

2002 Minnesota gypsy moth survey North Shore areas of concern.

Nearly 80% of all the state parks were trapped for gypsy moth in the 2002 trapping season. A little fewer than 60% (39 parks) of these were within the standard MDA trapping grid. The remaining 19% (13 parks) were trapped by utilizing a roving trapper. Of the 52 state parks that were trapped only 2 male moths were recovered in one state park, Charles A. Lindbergh near Little Falls, Minnesota.

A total of 7 moths were trapped at nursery locations within the MDA trapping grid. Nurseries outside the standard trapping grid and all large-scale timber mills were trapped by USDA-APHIS, with no additional moths found.

2002 Sites of Concern:

2002 Minnesota gypsy moth survey southeast Minnesota areas of concern.

Money Creek, Houston/Winona County (treated in 2001): The site was intensively trapped in 2001, after the treatment and no male moths were recovered. The site was again intensely trapped in 2002 and again, not a single male moth was recovered. Because of 2 consecutive years of zero moth catches, the population is considered successfully eradicated. In 2003, the site will receive the standard trapping grid of 1 trap per square mile.

I-90, Winona Co: This site has a history of finds since 1999 when a single male moth was caught. In 2000, the site was delimited at 16 traps per acre and 2 moths were recovered in a single trap. In 2001, the site was again delimited at 16 traps per square mile and 11 moths were recovered in three traps. One trap alone had 9 moths. In 2002, the site was trapped at 36 traps per square mile with an increase in traps around the 2001 finds (traps were hiked into the woods to get a better grid layout). Only 2 moths were recovered in 2 traps. No egg mass survey is scheduled for this site, however it will again receive delimit traps and monitored very closely in 2003.

Wilson Twp Site, Winona Co: This is another site with a long history. In 1999, one trap caught 4 moths. In 2000, it was delimited at 16 traps per square mile and three single moths were caught. In 2001, the site was delimited at 16 traps per square mile and eight moths were recovered in four traps. In 2002, the site was trapped at 16 traps per square mile (with traps hiked into the woods), with more an intensive trapping around the 2001 finds. Only a single moth was recovered in one trap. This site will be monitored closely in 2003.

2002 Minnesota gypsy moth survey Twin Cities metro areas of concern.

Bass Lake (Plymouth) site: This site has seen low moth counts dating back to 1997. In 2001, 15 male moths were found in 9 traps, with no egg masses found. In 2002, the core site was trapped at 2 traps per acre with the remainder receiving 36 traps per square mile. Only 3 moths were recovered with 2 traps. The site will continue to be delimit trapped and monitored closely.

Sites of Concern for 2003:

Hugo, Ramsey/Washington County: This site was delimited for the first time during the 2002 trapping season at 16 traps per square mile (approx 3 square miles). Nine traps produced a total of 16 moths within the delimit site. Two additional traps just outside the delimit boundary caught 5 moths, for a total of 21 moths. This is the largest number of finds at a single site in 2002. In 2001, three standard detection traps within one square mile of each other caught 7 moths (1, 5, 1 moths). There were no finds in the area in during the 2000 season. The site, just south of Hugo, contains a relatively new development with a light industrial area surrounded by wet lowlands. No egg masses were found, so the site will be intensively trapped in 2003.

Southdale Mall, Hennepin County: This site is on the southwest corner of the Lake Harriet delimit site. n 2002, 5 traps caught 9 moths. In 2001, 2 delimit traps had 3 moths and 1 standard trap just outside the delimit boundary caught 3 moths, for a total of 6 moths. In 2000, two single moths were found in standard detection traps that were within 1 square mile of each other. The largest find was located near the Fairview Southdale Hospital. No egg masses were found, so again the site will be intensively monitored in 2003.

Rolling Stones, Winona County: One standard detection trap caught 8 moths in this wooded rural area. The site has no prior history of moth finds. An egg mass survey is scheduled.

Trapping plans for 2003 won?t be finalized until early spring. To a large extent, funding concerns will determine the extent of the program and how much is surveyed.

North Shore Temperature Study:

With federal funding, support from the OTIS lab of USDA APHIS, and field help from a number of local partners, NRRI, affiliated with the U of MN, placed traps in three 1 square mile plots at varying grid densities as a pilot project to assess the effect of temperature on moth flight and capture rates. At the center of each plot, sterile male moths were released on a weekly basis between July 18 and September 26. Colored external dyes were used to separate moths by release date. An internal dye (incorporated in the food on which the caterpillars were reared) was used to separate wild from reared moths (no wild moths were caught within the study area). Traps were checked regularly and the dye color recorded.

Moth emergence rates ranged between 5 and 78 % per release based on spent pupal cases. Recapture rates ranged between 4 and 7%. However, the largest challenge of the project (besides finding the traps among the alder bogs) was out-witting the chickadees. The birds quickly discovered the release cages and sat there picking the moths off as they emerged to dry their wings. Researchers had to devise mess bags to protect the moths until they were dry and strong enough to fly. Even then, the chickadees snagged a large number of the young male moths. The effect on moth recapture rates per plot won?t be known until the data is analyzed this winter.

If funding can be found, the plan is to expand the pilot to include two study areas, one north and one south, with three plots each to compare trap results across a temperature gradient. Again this year (three of the last four years), scattered singles were caught in the Grand Portage area in a pattern difficult to explain. Prediction models used to interpret data from the current system of detection trapping are based on results obtained in more southern latitudes. Because moth flight appears to decline when summer temperatures drop below 70 degrees, these models may not be reliable in far north MN. If moth flight is a relatively rare event in areas with cool summers, a single moth catch may be more likely to suggest an established population than a single moth in the metro area. With the proximity of gypsy moth populations in northern WI, it is important to determine how to interpret survey results in MN to ensure that an established population doesn?t escape detection to spread southward along the North Shore.