Vincent D'Amico

Virus transmission in gypsy moths is not a simple mass action process

We used the nuclear polyhedrosis virus (LdNPV) of the gypsy moth, Ly- mantria dispar (Lepidoptera: Lymantriidae), to test one of the basic assumptions of most models of disease dynamics, that the rate of horizontal transmission is directly proportional to the product of the densities of healthy larvae and virus. To do this we made measurements of virus transmission, using small-scale experiments in bags on red oak (Quercus rubra) foliage and field data on naturally occurring populations from a previous study. We observed a decline in the transmission constant as the densities of both healthy larvae and pathogen increased, indicating that the rate of disease transmission is not directly proportional to the product of these variables.

Pathogen clumping: an explanation for non-linear transmission of an insect virus

Abstract.  1. Previous work has shown that transmission of some insect pathogens is a non‐linear process. A number of hypotheses have been put forward as explanations for this phenomenon; however, none have proven wholly satisfactory. Here we test the effects on transmission of spatial distribution of an insect virus by testing whether or not experimental manipulations of pathogen clumping lead to different values of a clumping parameter. The gypsy moth nucleopolyhedrovirus (LdMNPV) was used, which is transmitted when larvae consume virus released from previously infected larvae that have died on foliage.

Quantifying horizontal transmission of Nosema lymantriae, a microsporidian pathogen of the gypsy moth, Lymantria dispar (Lep., Lymantriidae) in field cage studies

Nosema lymantriae is a microsporidian pathogen of the gypsy moth, Lymantria dispar that has been documented to be at least partially responsible for the collapse of L. dispar outbreak populations in Europe. To quantify horizontal transmission of this pathogen under field conditions we performed caged-tree experiments that varied (1) the density of the pathogen through the introduction of laboratory-infected larvae, and (2) the total time that susceptible (test) larvae were exposed to these infected larvae. The time frame of the experiments extended from the early phase of colonization of the target tissues by the microsporidium to the onset of pathogen-induced mortality or pupation of test larvae. Upon termination of each experiment, the prevalence of infection in test larvae was evaluated. In the experiments performed over a range of pathogen densities, infection of test larvae increased with increasing density of inoculated larvae, from 14.2+/-3.5% at density of 10 inoculated per 100 larvae to 36.7+/-5.7% at 30 inoculated per 100 larvae. At higher densities, percent infection in test larvae appeared to level off (35.7+/-5.5% at 50 inoculated per 100 larvae). When larval exposure to the pathogen was varied, transmission of N. lymantriae did not occur within the first 15 d post-inoculation (dpi) (11 d post-exposure of test larvae to inoculated larvae). We found the first infected test larvae in samples taken 20dpi (16 d post-exposure). Transmission increased over time; in the cages sampled 25dpi (21 d post-exposure), Nosema prevalence in test larvae ranged from 20.6% to 39.2%.

Bacteria associated with larvae and adults of the Asian longhorned beetle (Coleoptera: Cerambycidae)

Abstract Bacteria representing several genera were isolated from integument and alimentary tracts of live Asian longhorned beetle, Anaplophora glabripennis (Motschulsky), larvae and adults. Insects examined were from infested tree branches collected from sites in New York and Illinois. Staphylococcus sciuri (Kloos) was the most common isolate associated with adults, from 13 of 19 examined, whereas members of the Enterobacteriaceae dominated the isolations from larvae. Leclercia adecarboxylata (Leclerc), a putative pathogen of Colorado potato beetle, Leptinotarsa decemlineata (Say), was found in 12 of 37 larvae examined. Several opportunistic human pathogens, including S. xylosus (Schleifer and Kloos), S. intermedius (Hajek), S. hominis (Kloos and Schleifer), Pantoea agglomerans (Ewing and Fife), Serratia proteamaculans (Paine and Stansfield) and Klebsiella oxytoca (Flugge) also were isolated from both larvae and adults. One isolate, found in 1 adult and several larvae, was identified as Tsukamurella inchonensis (Yassin) also an opportunistic human pathogen and possibly of Korean origin.. We have no evidence that any of the microorganisms isolated are pathogenic for the Asian longhorned beetle.

Biological Activity of Bacillus thuringiensis and Associated Toxins against the Asian Longhorned Beetle (Coleoptera: Cerambycidae)

Bacillus fhuringiensis Berliner var. tenebrionis and 5. thuringiensis toxins were as- sayed against larval and adult Asian longhorned beetles, Anoplophora glabripennis (A. glabrip- ennis). Preliminary in vitro assays showed some toxins to be active on whole midgut prepara- tions in voltage clamp assays and in assays on brush border membrane vesicles formed from midgut epithelial cells. For in vivo tests, a commercially-available product (Novodo@) was incorporated into artificial diet, upon which larvae were allowed to feed ad lib. In other tests, droplets of solubilized B. thuringiensis toxins were fed to larval and adult beetles using a mi- cropipette. None of the in vivo assays showed significant negative effects on either larvae or adults. We believe that some aspect of A. glabripennis midgut chemistry may be incompatible with toxin activation or mode of action. The Asian longhorned beetle, Anoplophora glabripennis (Motschulsky), is a large wood-boring cerambycid native to parts of mainland China and Korea. Anoplophora glabripennis is a polyphagous feeder with a marked preference for poplar, maple and willow. Adult beetles feed and mate on the leaves, branches, and bole of trees, and female beetles chew slits in the bark in which to deposit a single egg. After hatching, larvae burrow and consume wood under the bark surface, eventually penetrating deeply into trees. The damage resulting from larval feeding can be sufficient to render large trees unsound, creating hazardous conditions in populated areas. Anoplophora glabripennis was accidentally introduced into the United States in solid wood packing material from China, discarded in areas adjacent to airports. There were likely a number of such introductions in the 1980s and 1990s. Populations of A. glabripennis now exist in and near New York City, NY and Chicago, IL. These populations have been the targets of intense efforts aimed at eradication, usually in the form of removal and burning of infested trees. Less intrusive methods of control are currently being sought, especially biological control methods using parasites and microbial pesticides. Bacillus thuringiensis Berliner, an aerobic soil-dwelling bacterium, has a long his- tory of use in biopesticides. Bacillus thuringiensis and its subspecies produce insec- ticidal proteins during sporulation, the primary of which is S-endotoxin. Because the 6-endotoxins are derived from bacterial Cry genes, they are also known as Cry toxins (e.g., Cryl or Cry Ma). Some Cry toxins, notably Cryl b, have been shown to have

Deletion of v-chiA from a Baculovirus Reduces Horizontal Transmission in the Field

ABSTRACT Nucleopolyhedroviruses (NPVs) can initiate devastating disease outbreaks in populations of defoliating Lepidoptera, a fact that has been exploited for the purposes of biological control of some pest insects. A key part of the horizontal transmission process of NPVs is the degradation of the larval integument by virus-coded proteins called chitinases, such as V-CHIA produced by the v-chiA genes. We used recombinant and naturally occurring strains of the Lymantria dispar NPV (LdMNPV) to test horizontal transmission in the field, release of virus from dead larvae under laboratory conditions, and cell lysis and virus release in cell culture. In the field, strains of LdMNPV lacking functional v-chiA genes showed reduced horizontal transmission compared to wild-type or repaired strains. These findings were mirrored by a marked reduction in released virus in laboratory tests and cell culture when the same strains were used to infect larvae or cells. Thus, this study tests the pivotal role of liquefaction and the v-chiA gene in field transmission for the first time and uses complementary laboratory data to provide a likely explanation for our findings.

Comparison of aerially-applied Gypchek strains against gypsy moth (Lepidoptera: Lymantriidae) in the presence of an Entomophaga maimaiga epizootic

The standard strain (LDP-226) of Gypchek®, a nucleopolyhedrovirus product registered by the USDA Forest Service against the gypsy moth, Lymantria dispar (L.), was compared against a strain, LdMNPV-203NL (NL = nonliquefying), that was developed for production in cell culture. Both strains were applied by air to U.S. government property in Prince Georges Co., MD, in early May 2003 at the rate of 1 x 1012 occlusion bodies per ha. The two goals of the study were (1) to compare the first and second wave effects of the two strains against gypsy moth populations; and (2) to delineate the combined effects of the applied virus and the expected epizootic of the gypsy moth specialist fungal entomopathogen Entomophaga maimaiga Humber, Shimazu, and Soper. Heavy rainfall in May and June preceded a massive epizootic of E. maimaiga, whose effects did not mask the first wave of viral mortality. When the effect of application sequence was considered, it was concluded that the two strains were equivalent in their first-wave impacts. High fungal-induced mid and late-season gypsy moth larval mortality suppressed the second wave of virus at all evaluation sites. There were no obvious differences in the second waves engendered by the two LdNPV strains in the greatly reduced late-instar larval population.

Predicting Metapopulation Responses to Conservation in Human-Dominated Landscapes

Loss of habitat to urbanization is a primary cause of population declines as human-dominated landscapes expand at increasing rates. Understanding how the relative effects of different conservation strategies is important to slow population declines for species in urban landscapes. We studied the wood thrush Hylocichla mustelina, a declining forest-breeding Neotropical migratory species, and umbrella species for forest-breeding songbirds, within the urbanized mid-Atlantic United States. We integrated 40 years of demographic data with contemporary metapopulation model simulations of breeding wood thrushes to predict population responses to differing conservation scenarios. We compared four conservation scenarios over a 30-year time period (2014–2044) representing A) current observed state (Null), B) replacing impervious surface with forest (Reforest), C) reducing brown-headed cowbird Molothrus ater parasitism pressure (Cowbird removal), and D) simultaneous reforesting and cowbird removal. Compared to the Null scenario, the Reforest scenario increased mean annual population trends by 54 % , the Remove cowbirds scenario increased mean annual population trends by 38 %, and the scenario combining reforestation and cowbird removal increased mean annual population trends by 98 %. Mean annual growth rates (λ) per site were greater in the Reforest (λ = 0.94) and Remove cowbirds (λ = 0.92) compared to the Null (λ = 0.88) model scenarios. However, only by combining the positive effects of reforestation and cowbird removal did wood thrush populations stop declining (λ = 1.00). Our results suggest that independently replacing impervious surface with forest habitat around forest patches and removing cowbirds may slow current negative population trends. Furthermore, conservation efforts that combine reforestation and cowbird removal may potentially benefit populations of wood thrushes and other similarly forest-breeding songbird species within urbanized fragmented landscapes that typify the mid-Atlantic United States.

Is brood parasitism related to host nestling diet and nutrition

ABSTRACT Food and nutrient limitation can have negative effects on survival, fecundity, and lifetime fitness of individuals, which can ultimately limit populations. Changes in trophic dynamics and diet patterns, affected by anthropogenic environmental and landscape change, are poorly understood yet may play an important role in population regulation. We determined diets of Wood Thrushes (Hylocichla mustelina), a Neotropical migratory songbird species sensitive to urbanization, and explored how brood parasitism by Brown-headed Cowbirds (Molothrus ater) may be related to Wood Thrush nestling diets. Effects of brood parasitism on host nestling diets is an understudied stressor that may help explain observed population declines. We measured carbon (δ13C) and nitrogen (δ15N) stable isotopes of 7 invertebrate food sources (snails, spiders, isopods, earthworms, myriapods, insects, and caterpillars), blood plasma from adult male and female Wood Thrushes and from Wood Thrush nestlings in nests with and without Brown-headed Cowbird nestlings. Wood Thrush diet compositions were largely composed of high calcium (Ca) foods (51–62%, 95% highest density intervals [HDI]), including snails, isopods, and myriapods, as well as spiders (23–33%, 95% HDI). Caterpillars were the least common food item in Wood Thrush diets (0.01–3 %, 95% HDI). Wood Thrush nestling diets in nests without Brown-headed Cowbirds contained greater proportions of Ca-rich foods and spiders compared to the diet of nestlings in parasitized nests. Our data demonstrate that Wood Thrushes preferred Ca- and protein-rich foods, which may have important implications for adult survival and fecundity as well as nestling nutrition and development. Our results suggest that brood parasitism is related to host nestling diet, which could have potentially negative effects on developing nestlings through nutritional stress that may in turn affect survival, fecundity, and ultimately limit population growth.

Preferential edge habitat colonization by a specialist weevil, Rhinoncomimus latipes (Coleoptera: Curculionidae).

ABSTRACT Understanding the behavioral basis of dispersal and colonization is critical in biological control systems, where success of a natural enemy depends in part on its ability to find and move to new host patches. We studied behavior of the specialist weevil Rhinoncomimus latipes Korotyaev, a biological control agent of mile-a-minute weed, Persicaria perfoliata (L.) H. Gross, by releasing weevils at the forest edge and monitoring their colonization of potted host plants arrayed along the edge, out into the open field, and into the forest. Both distance from the release cage and habitat where plants were located affected colonization, with more than twice as many weevils found on plants at 2 m than at 6 or 14 m; at 14 m, 6–8 times as many weevils colonized plants along the forest edge compared with plants in the open field or within the forest. In a second experiment, weevils that were released in an open field 12 m from the forest edge initially flew in all directions, but again ultimately colonized more plants at the edge than out in the open field. This species may be adapted to seek host plants at the forest edge, because P. perfoliata generally is found in riparian corridors in its native range and along forest edges in North America. Results suggest that R. latipes will move successfully to new P. perfoliata patches along wooded edges, but may not readily locate isolated patches in the open or those embedded in forests.