Effects of an aerial treatment of Bacillus thuringiensis kurstaki on non-target Lepidoptera caterpillars in Forest Park, Portland, Oregon DN Kearns, TE Valente, CS Hedstrom, and JJ Vlach Oregon Department of Agriculture, Salem, OR
Introduc on Methods
Bacillus thuringiensis kurstaki (Btk), a naturally occurring Four 100-m transects for sampling immature Lepidoptera soil bacterium, is widely used in aerial treatment were set up in treated (aerially sprayed with Btk) and programs for the European and Asian Gypsy Moth untreated sites in Forest Park in Spring 2016. Two (Lymantria dispar L.). In Spring 2016, the Oregon untreated transects were at an eleva on of 129 m, and Department of Agriculture Insect Pest Preven on and two treated transects were at an eleva on of 283 m. The Table 2. The number of caterpillar species collected post-spray Management Program (ODA IPPM) treated approximately distance between the transects within the spray block within the spray block is not significantly different from the 8000 acres in northwest Portland to eradicate an incipient and outside the spray block was approximately 5.2 km. number of species expected, based on the rela ve number popula on of the Asian Gypsy moth. Included in the collected pre-spray (X2c = 3.84, df = 2-1 = 1, p > 0.05) treatment area was Forest Park, a public municipal park We conducted the first sampling on April 13, 2016, two that covers over 5100 acres of second-growth and old days before the first aerial spray with Btk. We conducted Discussion growth forest. the second sampling on May 9, 2016, one week a er the third (final) aerial treatment was completed. Our analysis indicates that the aerial applica on of Btk was Public concerns about aerial spraying play a major role in successful in reducing caterpillar abundance within the spray planning an eradica on program. One focus of concern is All sampling was conducted using bea ng sheets. Two block (Table 1). The goal of the spray program was to eradicate the poten al for harming non-target species in an aerial teams of two people sampled along the transects, each any gypsy moth caterpillars in Forest Park. applica on of Btk. The bacterium is most effec ve as a going in opposite direc ons from the midpoint on the biological insec cide against leaf-feeding caterpillars in transect. Sampling effort consisted of tapping foliage of a Table 2 shows that there is no significant difference in the early instars, but it is not specific and may reduce chosen plant 12 mes (3 mes per quadrant) and number of Lepidoptera species before and a er the Btk popula ons of na ve Lepidoptera (Miller 1990). collec ng caterpillars that landed on the bea ng sheet. applica on within the spray block. This result indicates that the The most common host plants were chosen for sampling, treatment did not eradicate all na ve species and suggests that Here, we examine the effects of three aerial applica ons but some other plant species were included because recovery within the spray block may be rela vely rapid. For of Btk on na ve caterpillars in Forest Park. overall numbers of caterpillars were low. Common plants example, we collected a specialist on sword fern, Thallophaga included sword fern, Oregon grape, red huckleberry, taylorata, in the spray block a er the spray. Previous studies salmonberry, big leaf maple, vine maple, and hazelnut. have shown that na ve species recovery can occur two years a er a Btk treatment (Miller 1990). Dysstroma brunneata reared from flowering Transects within and outside of the spray block. currant. The caterpillar was collected outside Caterpillars were maintained on their host plant foliage in The blue line indicates the spray boundary. of the spray area and reared to the adult a sunroom in 16 ounce clear plas c cups. Fresh foliage Transects (in red) are labelled T1, T2, T3, and T4. stage. was placed in a floral pick filled with water and replaced as needed. The intent was to con nue rearing the caterpillars to later instars or adults so they could be iden fied.
Analysis Post-spray collec on: Cyclophora sp. Post-spray collec on: Geometrid (Geometridae) on vine maple inside species on vine maple inside spray area. There was naturally occurring variability outside and the spray area. inside the treatment block in caterpillar abundance and species diversity. Because sample sizes were rela vely low, we used simple Goodness-of-fit tests to examine post-spray effects. Total numbers of caterpillars per transect were compared to the numbers expected based on per-transect propor ons of pre-spray collec ons. Post-spray collec on: Noctuidae on Oregon grape inside spray area (reared Results to adult Diarsia rosaria).
Thallophaga taylorata (Geometridae) Orthosia hibisci (Noctuidae) collected Table 1. Based on a comparison with pre-spray collec ons, collected on sword fern outside spray on big leaf maple outside spray area. the number of caterpillars within the spray block was area. 2 significantly reduced a er the spray (Χ c = 6.63, df = 2-1 = 1, Acknowledgements p < 0.01). The general phenological development of some na ve Lepidoptera species that could be affected by an aerial We thank Jeffrey C. Miller (Oregon State University, Corvallis) for Literature cited advice on sampling methods, Kendra Petersen-Morgan (Portland Parks applica on of Btk in April and May is illustrated. It was developed as an educa onal tool for public mee ngs prior & Recrea on) for issuing the permit for the study in Forest Park, to the aerial Btk treatment. Not all species shown occur within the Forest Park study transects. Miller, J.C. 1990. Field assessment of the effects of a microbial Richard Worth (ODA IPPM) for iden fying adult specimens, Thomas pest control agent on nontarget Lepidoptera. American Shahan (ODA IPPM) for imagery, and Clint Burfi (ODA IPPM Manager) Entomologist 36:135-139. for suppor ng the study.