Imre S. Otvos

Recovery of nontarget Lepidoptera on Vancouver Island, Canada: one and four years after a gypsy moth eradication program.

The gypsy moth (Lymantria dispar) is a destructive defoliator that is not established in British Columbia, Canada, because of successful eradication programs involving the microbial insecticide Bacillus thuringiensis var. kurstaki (Btk). In 1999, three aerial applications of Btk were made over two areas, totaling 12,805 ha, on southern Vancouver Island, Canada. The impacts of these Btk applications on nontarget Lepidoptera were studied from 1999 to 2004 on Garry oak (Quercus garryana) and common snowberry (Symphoricarpos albus). In 1999, lepidopteran larvae were collected from S. albus foliage at 24 urban parks and from Q. garryana foliage at 28 oak-dominated habitats. The initial impacts (i.e., 1999 data) were published previously, and the present paper is a continuation of the same study. We tested two hypotheses: Reductions of nontarget Lepidoptera would be more severe at 12 to 13 months postspray than at one to two months postspray, and recovery would be significant, though not necessarily complete, at four years postspray. The total number of nontarget Lepidoptera on S. albus and Q. garryana was significantly reduced in the treatment sites in each year of the study: the reduction was greatest in 2000. Relative to the reference sites, each of 11 species that were initially reduced by the Btk applications showed an increase in the treatment sites between 2000 and 2003, by which time only four species remained significantly reduced in the treatment sites. The uncommon species were significantly reduced in 1999 and 2000 but not in 2003, indicating that some recovery had occurred. Limitations and economic implications of the present study are discussed.

Field Testing Chinese and Japanese Gypsy Moth Nucleopolyhedrovirus and Disparvirus Against a Chinese Population of Lymantria Dispar Asiatica in Huhhot, Inner Mongolia, People's Republic of China

ABSTRACT The activity of three geographic isolates of the gypsy moth nucleopolyhedrovirus (LdMNPV) was evaluated in field trials against larvae of the Chinese population of Lymantria dispar asiatica Vnukovskij in Inner Mongolia, Peoples Republic of China, in 2004, 2005, and 2006. Although the Chinese isolate of the virus, LdMNPV-H, was the most pathogenic of the isolates tested, having the lowest mean lethal concentration causing 50% and 95% larval mortality, the increase in efficacy that would be obtained by incorporating this isolate into a commercial product does not justify the time or expense required to register it for use in the United States or Canada. The commercially available North American isolate, LdMNPV-D, was moderately pathogenic, whereas the Japanese isolate, LdMNPV-J, was the least pathogenic. The slopes of the dose—response regression lines for the three virus isolates indicated that the Chinese gypsy moth larvae were more homogenously susceptible to LdMNPV-H and LdMNPV-D than to LdMNPV-J. Time-response data showed that LdMNPV-J was significantly more virulent, but at a much higher dose, than the other two isolates, causing 50% mortality in the shortest time, followed by LdMNPV-H and LdMNPV-D. Rainfall immediately after the application of LdMNPV-D in 2005 resulted in significantly reduced gypsy moth larval mortality.

Development and evaluation of methods to detect nucleopolyhedroviruses in larvae of the Douglas-fir tussock moth, Orgyia pseudotsugata (McDunnough).

ABSTRACT Various molecular methods are used to detect pathogenic microorganisms and viruses within their hosts, but these methods are rarely validated by direct comparison. Southern hybridization, enzyme-linked immunosorbent assay (ELISA), and a novel DNA extraction/PCR assay were used to detect Orgyia pseudotsugata multiple nucleopolyhedrovirus (OpMNPV) in Douglas-fir tussock moth larvae. PCR was more sensitive than Southern hybridization and ELISA at detecting semipurified virus. ELISA, however, was the most accurate method for detecting virus within larvae, given that Southern hybridization and PCR produced false-negative results (31% and 2.5%, respectively). ELISA may be preferable in some applications because virus infections can be quantified (r2 = 0.995). These results may be applicable to both applied and academic research that seeks to accurately identify the incidence of viruses and microorganisms that regulate insect populations.

Monitoring Nontarget Lepidoptera on Ribes cereum to Investigate Side Effects of an Operational Application of Bacillus thuringiensis subsp. kurstaki

Abstract The abundance of nontarget Lepidoptera on the shrub Ribes cereum Douglas was monitored from 1997 to 2000 in an Interior Douglas-fir forest in British Columbia to assess potential side effects of an operational program to control the western spruce budworm, Choristoneura occidentalis Freeman. The treatment was a single application of Bacillus thuringiensis subsp. kurstaki (Btk) (Foray 48B) at the rate of 30 BIU/ha in 2.4 liter/ha. The guild of leaf-feeding Lepidoptera on R. cereum was dominated by Gelechia ribesella Chambers, and Euhyponomeutoides gracilariella Busck, which made up 24 and 62% of the guild, respectively. The remaining 14% of the guild comprised numerous sparsely distributed species (at least 45 different species based on morphotypes). Total larval abundance was significantly lower on plants that were sprayed with Btk than on plants that were covered to exclude Btk. Covering the plants was a novel approach that enabled us to replicate the treatment within a single spray area. G. ribesella and E. gracilariella were significantly reduced by Btk, but a modest reduction of ‘sparsely distributed species’ was not significant. Both G. ribesella and E. gracilariella appeared to make a full recovery within 2 yr of the Btk spray, but as a group the abundance of the sparsely distributed species was lowest in the year 2000 in both the Btk sprayed area and an untreated comparison area. This suggests a general decline independent of the treatment. Microscopic examination of cadavers of the two major nontarget species showed the presence of Btk in some of the larvae reared from the treated plot, but Btk was absent in larvae from the reference plot.

Integration of early virus treatment with a pheromone detection system to control Douglas-fir tussock moth, Orgyia pseudotsugata (Lepidoptera: Lymantriidae), populations at pre-outbreak levels

Abstract A naturally occurring virus often leads to the development of an epizootic late in the outbreak cycle of the Douglas-fir tussock moth, but not before significant damage occurs to the trees. This virulent virus can be mass-produced in the laboratory and, when applied early in the outbreak cycle, can prevent severe defoliation. This, however, requires that an early-warning system be integrated with a virus treatment. The development and integration of a pheromone monitoring system with a virus treatment is described. Stands susceptible to Douglas-fir tussock-moth outbreaks are defined by overlying maps of past outbreaks, forest and habitat types, and climatic zones. Pheromone-baited traps are placed and monitored annually at permanent locations in the susceptible areas. Measuring annual trends of moth density indicates the time and location of the next outbreak. Trap-catch data provide an early warning of impending outbreaks. This is confirmed by ground reconnaissance. Insect density and defoliation is predicted from egg-mass and larval sampling. The virus then can be applied from the air or from the ground into threatened stands to initiate an epizootic to prevent the development of an outbreak and to minimize tree damage. The virus appears to spread, and field tests with reduced dosages indicate that that small amount of virus applied can still decimate larval populations and prevent tree mortality, at considerably reduced cost.

Genotypic variation among Douglas-fir tussock moth nucleopolyhedrovirus (OpNPV) isolates in the western United States

Periodic outbreaks of the Douglas-fir tussock moth (Orgyia pseudotsugata) in forests of western North America generally end with a sudden collapse due primarily to an epizootic caused by a nucleopolyhedrovirus (NPV) that occurs naturally within O. pseudotsugata populations. We genotypically characterized NPV populations from Washington State, Oregon, Idaho, New Mexico and California for the first time. Of 159 infected tussock moth samples, restriction fragment length polymorphism (RFLP) analysis showed that 125 (78.6%) contained single nucleopolyhedrovirus (OpSNPV), 28 (17.6%) contained multiple nucleopolyhedrovirus (OpMNPV), and six (3.8%) contained both OpSNPV and OpMNPV. In comparison, our previous studies in the southern interior of British Columbia showed that all 298 samples examined were infected with OpMNPV, and none were infected with OpSNPV. More than half of the Washington OpSNPV samples shared the same genotype, but most OpSNPV genotypes were rare or unique: across the five states, 31 of the 43 different OpSNPV genotypes were each only found in a single sample. In contrast, only four different OpMNPV genotypes were found, and 29 of the 34 OpMNPV samples shared the same genotype, designated genotype AA. This strain of OpMNPV has been developed, registered and used in both Canada and the United States to control outbreaks of the Douglas-fir tussock moth. It is also the most common genotype in southern British Columbia. The estimated degree of genetic divergence ranged from 0% to 4.19% for the various OpSNPV genotypes and from 0% to 3.16% for the OpMNPV genotypes (based on number of shared bands). This is the first description of the genotypic diversity in a population of OpSNPV, and the first genotypic characterization of NPVs infecting O. pseudotsugata in the USA.

Effects of Long-Term Storage on Potency of TM Biocontrol-1, the Registered Viral Insecticide of Orgyia pseudotsugata (Lepidoptera: Lymantriidae)

Abstract The article presents the results of bioassaying 39 samples of TM Biocontrol-1, a viral insecticide, from 10 different lots and various sizes of vacuum-sealed packages that were stored at −10°C for 5–15 yr. This is the first study to present potency data for a registered virus product stored for this length of time. Laboratory bioassays in insects from the same colony from which the TM Biocontrol-1 was produced showed that the stored viral insecticide is still effective, although it lost ≈30% of its effectiveness during storage. A direct correlation of this loss with the length of time in storage is not apparent. Bioassays also showed that there are significant differences in the susceptibility of Douglas-fir tussock moth, Orgyia pseudotsugata (McDunnough), larvae from different geographic regions to OpMNPV (family Baculoviridae, genus Nucleopolyhedrovirus) infection. Package size did not affect the potency of stored TM Biocontrol-1. There were no clear, significant differences in the effectiveness among lots of TM Biocontrol-1 processed by different organizations.

Pupal sampling of the western hemlock looper, Lambdina fiscellaria lugubrosa (Hulst) (Lep., Geometridae) using burlap traps

Abstract: Three types of burlap traps were designed and tested for the western hemlock looper, Lambdina fiscellaria lugubrosa, in the interior of British Columbia from 1993 to 1994. While the first two trap types provided the means for examining the responses of pupating larvae to various layers of burlap band and pocket structure, the third trap type, which had the desirable burlap layers and structure, was used as a sampling tool for the insect. The effects of tree diameter, crown ratio, crown class, defoliation class and basal areas on trap capture appeared to vary with locations. However, a high correlation between trap capture and actual population density was consistently present. Therefore, trap capture can be used as an estimator of actual population density.

Forest roadside sampling of larvae and adults of the western hemlock looper, Lambdina fiscellaria lugubrosa

Abstract The roadside sampling method, in which sampling is conducted along a road has the advantage that large areas can be quickly surveyed. The method is particularly useful for forest areas where accessibility to trees within a stand can be a problem. In this study, larvae and adults of the western hemlock looper were sampled along forest roads and the data were examined with spatial statistics. The results indicated spatial continuity of insect counts along the forest roads, although the range and magnitude varied significantly between years and among sites. At Sugar Lake Forest Road, larvae and adults were spatially dependent within a distance of 7.25 km. In the three Vancouver watersheds, a significant spatial autocorrelation of male adult counts occurred when traps were up to 3 km apart. In addition, insect densities along the roads were closely related to those within the stands. The implications of these results to the management of the western hemlock looper are discussed.