Linda Butler

Population synchrony within and among Lepidoptera species in relation to weather, phylogeny, and larval phenology

Abstract.  1. The population dynamics of native herbivore species in central Appalachian deciduous forests were studied by analysing patterns of synchrony among intra‐ and interspecific populations and weather.

Association Between Ants (Hymenoptera: Formicidae) and Habitat Characteristics in Oak-Dominated Mixed Forests

Abstract The relationship between ants and their habitats was examined in oak-dominated mixed forests in the central Appalachian mountains. Ants were sampled using pitfall traps over the summers of 1995, 1996, and 1997. Principal component and correlation analysis indicated that ant diversity (Shannon’s H′), species richness, and abundance were closely correlated with habitat principal components. Fewer ants, lower number of species, and lower ant diversity were found at sites with higher elevation and soil moisture. Diversity (H′) of ants and species richness decreased by 0.1 (R2 = 0.75) and 2.2 (R2 = 0.57) when the elevation increased 100 m, respectively. As the elevation increased, there were relatively less Formica neogagates Emery and more Aphaenogaster rudis (Emery). More ant species and individuals were found on ridges than in valleys.

Occurrence of Lepidoptera on Selected Host Trees in Two Central Appalachian National Forests

Abstract In 1995 and 1996, Lepidoptera larvae of 13 families were sampled by pruning foliage from canopies of maple, hickory, red oak group, white oak, and chestnut oak. The families were Arctiidae, Geometridae, Hesperiidae, Lasiocampidae, Lycaenidae, Lymantriidae, Noctuidae, Notodontidae, Nymphalidae, Papilionidae, Saturniidae, Sphingidae, and Thyatiridae. Samples were collected from 18 plots (each 200 ha), nine in the George Washington National Forest in Virginia and nine in the Monongahela National Forest in West Virginia. Sampling seasons were from May to mid-August; foliage samples were collected each week. The occurrence of Lepidoptera on host trees within the two forests was compared. A total of 131 species of caterpillars representing 13 families was collected. Most larvae were Noctuidae (47 species) and Geometridae (44 species). Of 6,743 larvae collected over both years, 57% were gypsy moth, Lymantria dispar (L.). The population of this species collapsed during the second year of the study because of the fungus Entomophaga maimaiga. Other particularly abundant species in both forests were Acronicta ovata Grote, Hyphantria cunea (Drury), Polia latex (Guénée), Melanolophia canadaria (Guénée), Alsophila pometaria (Harris), and Nadata gibbosa (J.E. Smith). Some species were found only in one forest. Larval richness and abundance were higher in May and August and the lowest numbers occurred in June and July. Abundance and richness were different for the 2 yr. Population shifts may be directly related to weather conditions or indirectly related through the effects of temperature or rainfall patterns on natural enemies, foliage chemistry, or other factors. The number of species of caterpillars collected from the host tree groups was 62 on maple, 77 on hickory; 76 on the red oak group, 75 on chestnut oak, and 66 on white oak. The abundance of larvae ranged from 14.8% collected on maple to 25.4% collected on the red oak group.

A Comparison of Pitfall Traps with Bait Traps for Studying Leaf Litter Ant Communities

Abstract A comparison of pitfall traps with bait traps for sampling leaf litter ants was studied in oak-dominated mixed forests during 1995–1997. A total of 31,732 ants were collected from pitfall traps and 54,694 ants were collected from bait traps. They belonged to four subfamilies, 17 genera, and 32 species. Bait traps caught 29 species, whereas pitfall traps caught 31 species. Bait traps attracted one species not found in pitfall traps, but missed three of the species collected with pitfall traps. Collections from the two sampling methods showed differences in species richness, relative abundance, diversity, and species accumulation curves. Pitfall traps caught significantly more ant species per plot than did bait traps. The ant species diversity obtained from pitfall traps was higher than that from bait traps. Bait traps took a much longer time to complete an estimate of species richness than did pitfall traps. Little information was added to pitfall trapping results by the bait trapping method. The results suggested that the pitfall trapping method is superior to the bait trapping method for leaf litter ant studies. Species accumulation curves showed that sampling of 2,192 ± 532 ants from six plots by pitfall traps provided a good estimation of ant species richness under the conditions of this study.

Abundance, Diversity, and Activity of Ants (Hymenoptera: Formicidae) in Oak-Dominated Mixed Appalachian Forests Treated with Microbial Pesticides

Abstract This study is part of a long-term analysis of nontarget effects of microbial pesticide application in the George Washington (Augusta County, VA, USA) and Monongahela National Forests (Pocahontas County, WV, USA). Ants were collected using pitfall traps to assess the effect of Bacillus thuringiensis Berliner variety kurstaki (Foray 48 F) and gypsy moth nuclear polyhedrosis virus (Gypchek) application on ant communities. Ant samples were also compared by sampling years. Pitfall traps were operated for 45 wk during summers of 1995–1997. A total of 31,732 ants was collected from pitfall traps; they belonged to four subfamilies, 17 genera, and 31 species. The ant species richness, diversity, abundance, and species composition did not change as a result of the treatments. Further tests of ant abundance were suggested because the test power was low. Comparisons between sampling years showed a very similar species composition and species evenness. There was a significant decrease in ant abundance in the third year of sampling, which might have been caused by over-trapping. Some rare species did not appear in the second and third year of sampling.

Comparison of Sampling Techniques Used in Studying Lepidoptera Population Dynamics

Abstract Four methods (light traps, foliage samples, canvas bands, and gypsy moth egg mass surveys) that are used to study the population dynamics of foliage-feeding Lepidoptera were compared for 10 species, including gypsy moth, Lymantria dispar L. Samples were collected weekly at 12 sites during a 15-wk period in 1995–2001. For each non–gypsy moth species, light trap and canvas band estimates were regressed against foliage sample to determine how well they predict population abundance. Gypsy moth estimates obtained from foliage and under canvas bands were compared with counts of egg masses using a similar linear model. All comparisons were made on three spatial scales: plot (200 ha), forest (2,000–3,000 ha), and study site (200,000 ha). Abundance of moths collected by light traps were good predictors of population size compared with counts of larvae on foliage, whereas mixed results were obtained for canvas bands. Both foliage samples and canvas band samples proved to be good predictors of gypsy moth population size on the plot and forest scale, although only foliage samples provided good estimates at the study site scale. For all comparisons, predictability of light traps and canvas bands increased with increasing spatial scale.

Predicting the Host Range of Entomopathogenic Fungi

For many years the development and use of natural enemies to control insect pests has primarily focused on entomophagous insects that are predators and parasitoids. As it has become easier to work with microbes and increasing numbers of scientists have cross-trained in studies of microorganisms as well as entomology, the number of programs evaluating use of pathogens to control insect pests has increased. Among the diverse groups of microbes pathogenic to invertebrates, there are >700 species of entomopathogenic fungi. Fungi are unique among invertebrate pathogens because the major site of infection is through the cuticle, while most other pathogens must be ingested and subsequently invade through the gut (Hajek and St. Leger 1994). Because fungi invade through the cuticle, fungal pathogens are especially important for control of insects that suck plant sap and therefore would not ingest other types of entomopathogens. However, entomopathogenic fungi are being investigated for control of virtually all groups of pestiferous arthropods

Risk of Infection by the Fungal Pathogen Entomophaga maimaiga Among Lepidoptera on the Forest Floor

Abstract The entomopathogenic fungus Entomophaga maimaiga causes epizootics in gypsy moth, Lymantria dispar (L.), populations and persists in forests as a reservoir of spores in soil at the bases of trees. To investigate whether E. maimaiga infects Lepidoptera living in leaf litter, we collected and reared larvae in leaf litter, understory vegetation, and on tree boles within a 200-cm radius around trunks of red oak, Quercus rubra L., trees. Among the 358 lepidopteran larvae reared, only one gelechiid larva (out of 84 collected) and one larva of the noctuid Sunira bicolorago (out of 20 individuals from this species) were infected by E. maimaiga. Our collections included 67 gypsy moth larvae, of which 25 (37%) were infected by E. maimaiga. The majority of infected gypsy moth larvae were collected during the second half of June, when few nontarget Lepidoptera were present in the oak leaf litter. A bioassay of Zanclognatha laevigata Grote, a herminiine noctuid whose larvae spend their entire lives in leaf litter, yielded no infection. Because laboratory host specificity studies had demonstrated high levels of infection only in lymantriid larvae, we also caged larvae of the lymantriid Orgyia leucostigma (J. E. Smith) over soil at the bases of trees or in understory vegetation. Levels of infection for O. leucostigma remained consistently lower than among caged gypsy moth larvae, and infection was always higher in the soil than on the understory vegetation. We conclude that, aside from gypsy moth larvae, E. maimaiga infections among litter-dwelling lepidopteran larvae were rare, and we hypothesize that infection of other lymantriids in the field will depend on whether they visit the ground level for a significant period of time.

New Tachinidae (Diptera) Host Records of Eastern North American Forest Canopy Lepidoptera: Baseline Data in a Bacillus thuriengiensis Variety kurstaki Nontarget Study

Abstract Macrolepidopteran caterpillars collected in 1995 and 1996 in the Monongahela National forest, Pocahontas County, WV, and the George Washington National forest, Augusta County, VA, yielded 60 previously unreported tachinid host associations. Most associations were between native species, but the introduced polyphagous tachinid Compsilura concinnata (Meigen) produced eight new associations with native hosts. The tachinids collected were slightly broader in their host preferences than associated Braconidae and Ichneumonidae, illustrating their potential importance in regulating foliage-feeding macrolepidopteran populations in the region studied. The sample years reported herein are the pretreatment baseline portion of a long-term study on the effects of Lymantria dispar (L.) defoliation, efficacy of applied Bacillus thuringiensis variety kurstaki Berliner, and the natural occurrence of the L. dispar pathogen Entomophaga maimaiga Humber, Shimazu & Soper on nontarget organisms.

Lethal Effects of Biological Insecticide Applications on Nontarget Lepidopterans in Two Appalachian Forests

Abstract Eighteen 200-ha study plots were established in the Monongahela National Forest, West Virginia, and in the George Washington National Forest, Virginia. The overall purpose of the study was to determine nontarget effects of biological insecticides used to control gypsy moth, Lymantria dispar (L.). From 1995 through 1998 blacklight traps, foliage pruning, and canvas bands were used to collect lepidopteran adults and larvae to determine population abundance 2 yr before and during two consecutive years of treatment applications. During 1997 and 1998, six plots were each aerially treated with nucleopolyhedrosis virus Gypchek (GC) (US Forest Service, Ansonia, CT) and Bacillus thuringiensis variety kurstaki (Btk). The remaining six plots were left untreated (control). Counts of adults and larvae of 19 species from five families were tallied to assess treatment effects. Both spring- and summer-defoliating larvae were sampled. Analysis of variance indicated a significant interaction between pretreatment/treatment years and the three treatment groups for the adults of two species and the larvae of three species. Fewer larvae were collected from Btk plots than from GC and control plots during treatment years, but not during pretreatment years. Gypchek was not determined to adversely affect nontarget species. Adults of 10 species and larvae of four species were more numerous during treatment years than pretreatment years. Adults of four species and larvae of five species were more numerous during pretreatment years than during treatment years.