Eleanor Groden

Evaluation of Synergistic Interactions Between the Colorado Potato Beetle (Coleoptera: Chrysomelidae) Pathogen Beauveria bassiana and the Insecticides, Imidacloprid, and Cyromazine

Abstract Laboratory studies investigated the interaction between the fungal entomopathogen Beauveria bassiana (Balsamo) Vuillemin and sublethal doses of the insecticides imidacloprid and cyromazine when applied to larvae of the Colorado potato beetle, Leptinotarsa decemlineata (Say). When second instars were fed potato leaf discs treated with sublethal doses of imidacloprid and a range of doses of B. bassiana, a synergistic action was demonstrated. Similar results were observed when larvae were sprayed directly with B. bassiana conidia and immediately fed leaf discs treated with imidacloprid. No synergistic interaction was detected when larvae were fed leaf discs treated with sublethal doses of imidacloprid 24 h after application of B. bassiana conidia to larvae. However, a synergistic interaction was detected when larvae were fed leaf discs treated with imidacloprid and sprayed with B. bassiana conidia 24 h later. Although sublethal doses of both imidacloprid and the triazine insect growth regulator (IGR) cyromazine prolonged the duration of the second instar, only imidacloprid interacted with B. bassiana to produce a synergistic response in larval mortality. In leaf consumption studies, the highest dose of B. bassiana tested promoted feeding in inoculated second instars. Feeding was inhibited when larvae were fed foliage treated with sublethal doses of imidacloprid and significantly reduced when fed foliage treated with a sublethal dose of cyromazine. Starvation of larvae for 24 h immediately after B. bassiana treatment produced a similar result to the combined treatment of B. bassiana and imidacloprid and increased the level of mycosis when compared with B. bassiana controls. Imidacloprid treatment affected neither the rate of germination of B. bassiana conidia on the insect cuticle nor the rate at which conidia were removed from the integument after application. The statistical analysis used to detect synergism and the possible role of starvation-induced stress factors underlying the observed synergistic interactions are discussed.

Starvation induced stress and the susceptibility of the Colorado potato beetle, Leptinotarsa decemlineata, to infection by Beauveria bassiana.

Starvation of second instar Colorado potato beetle larvae for 24h immediately after treatment with Beauveria bassiana conidia increased susceptibility to the pathogen and subsequent sporulation of cadavers but decreased time to larval death. In feeding studies, B. bassiana-treatment had no effect on subsequent larval development, and mortality occurred 5-6 days after treatment. Twenty-four hours of starvation alone retarded subsequent larval development but did not affect mortality. Mortality of B. bassiana-treated starvation stressed larvae occurred 4-5 days after treatment. Both B. bassiana treatment and 24h starvation significantly reduced total foliage consumption and daily weight gains. On the day of treatment, B. bassiana had no effect on the efficiency with which food was converted to biomass (ECI). ECI was not affected by B. bassiana or starvation alone on the day following treatment but was significantly affected by a combination of both. When larvae were exposed to a range of limited food quantities, ECI decreased with decreasing food availability but only extreme stress (starvation for 24h) increased susceptibility to B. bassiana. Topical application of Dacryodes excelsa resin (an antifeedant) to potato leaves caused a concentration dependent reduction in foliage consumption and weight gain by second instar larvae but did not affect larval mortality. When larvae were exposed to a fixed concentration of B. bassiana and a range of antifeedant concentrations there were significant linear relationships between 24h larval weight gain and mortality and 24h larval weight gain and sporulation. The interaction between starvation stress and the susceptibility to B. bassiana infection is discussed and its possible implications in pest management considered.

Intercolony aggression within and among local populations of the invasive ant, Myrmica rubra (Hymenoptera: Formicidae), in coastal Maine

Abstract Myrmica rubra L. was introduced into New England in the early 20th century, and at present, has a patchy distribution in parts of northeastern North America, including records from 31 communities in Maine. M. rubra is highly polygynous, and colonies reproduce vegetatively, forming dense local populations where conditions are favorable. Using mobile nests and baited arenas in a series of field aggression bioassays, we tested patterns of internest tolerance within and among local populations on Mt. Desert Island, ME. We found that foragers originating from fragments of the same colony or from neighboring nests retained a high level of intraspecific tolerance over several months, whereas significant intercolony aggression among workers was present between colonies within the same local patch separated by ≈10 m. Within populations, aggression score values were found to increase linearly with internest distance within a site. Aggression was highest between colonies from spatially different populations on the island and was higher still when nests were assayed against colonies at an off-island site 70 km away in Castine, ME. These data strongly suggest a multicolonial organization within and among local populations of M. rubra in parts of its introduced range. These findings contradict the loss of intraspecific aggression and unicolonial social structure over large geographic areas that have previously been observed in other invasive ant species, particularly Linepithema humile Mayr.

Horizontal transmission of Beauveria bassiana (Bals.) Vuill

1 Factors influencing horizontal transmission of the entomopathogen Beauveria bassiana in the Colorado potato beetle (CPB) were examined through a series of laboratory studies.

Abundance of carabid beetles and other ground-dwelling arthropods in conventional versus low-input bean cropping systems

Abstract The abundance and seasonal dynamics of carabid beetles and other ground-dwelling arthropods in conventional and low-input dry bean ( Phaseolus vulgaris L.) cropping systems were investigated over two field seasons in Maine, USA. In 1988, carabids and staphylinids were significantly greater in number in the low-input plots. Staphylinids and arachnids were significantly more abundant in the low-input plots in 1989. Elaterid adults were abundant in 1988, and the number in the conventional plots was 23 times higher than in the low-input plots. Multivariate analysis showed that compositions of major ground-dweling arthropods differed significantly between the two cropping systems from the early to middle season of plant growth. Individual carabid species differed between the two cropping systems. Harpalus rufipes, Pterostichus melanarius, Agonum muelleri, Clivina fossor, Carabus memoralis, Carabus auratus , and Loricera pilicornis were dominant carabid species in this study. In 1988, Pterostichus melanarius, Carabus auratus , and L. pilicornis were significantly more abundant in the low-input plots, while A. muelleri and Clivina fossor were significantly more abundant in the conventional plots. In 1989, however, only A. muelleri was significantly different between cropping systems and a significantly higher number was trapped in the low-input plots.

Beauveria bassiana horizontal infection between cadavers and adults of the colorado potato beetle, Leptinotarsa decemlineata (say)

Abstract The behavior of adult Colorado potato beetles (Leptinotarsa decemlineata) in the presence of Beauveria bassiana sporulating on cadavers was studied to determine the likelihood of disease infection as beetles emerge from the soil and colonize host plants. In 2001, the movement of single adult Colorado potato beetles was monitored in arenas containing infective cadavers in differing spatial patterns between four potato plants. In 2002, a similar design was used, but was under the more natural conditions of a potato field. In both experiments, direction, time, and directness of beetle travel was not significantly affected by the presence or absence of infective cadavers, showing no avoidance of these cadavers by adult Colorado potato beetles. The likelihood that emerging adults would contact infective cadavers on the soil surface was quantified at different cadaver densities. A curvilinear relationship (y = 4.8313x0.4459) best describes the frequency of encounters of adults as a factor of increasing density of cadavers on the soil surface. Mortality of adults and production of conidia on cadavers after encounters with increasing densities of infective cadavers had similar relationships that show the decreased susceptibility of adults to B. bassiana compared with prepupae. These relationships were used to model horizontal infection to emerging adults in the summer months, subsequent to a conidial spray targeted at larvae. The model indicates that horizontal infection of adults may potentially be significant (30–70% of horizontal infection), and that simulated early sprays targeted at first-instar larvae resulted in the maximum levels of predicted horizontal infection.

Ant Diversity and Distribution in Acadia National Park, Maine

ABSTRACT Exotic ant species are a primary threat to ant biological diversity, posing a negative impact to native ant communities. In this study, we examine species richness of ants (family Formicidae) in Acadia National Park, ME, as a fundamental step toward understanding the present impact of the exotic species Myrmica rubra on native ant species. Twelve habitat types were sampled, along six transects, with pitfall traps, visual searching, bait traps, and leaf litter extraction, and the aid of 34 volunteers. We report 42 species of ants in Acadia National Park, comprising five subfamilies (Amblyoponinae, Dolichoderinae, Formicinae, Myrmicinae, and Ponerinae) and 15 genera; the cataloged species represents 75% of the species originally recorded in the area by Procter (1946). Our findings suggest M. rubra is currently not a dominant species throughout the entire island. However, where this species has invaded locally, few competing native species coexist. The species Lasius alienus, Formica subsericea, Myrmica detritinodis, Camponotus herculeanus, Formica argentea, Formica aserva, and Tapinoma sessile occurred most often in our survey. We report the ant species Amblyopone pallipes and Dolichoderus mariae as two new records for the state of Maine.

Monitoring of the European Corn Borer (Lepidoptera: Crambidae) in Central Maine

Abstract Pheromone trap types and within-field trap locations were compared for their effectiveness in monitoring the flight activity of European corn borer, Ostrinia nubilalis (Hübner), and its relationship to egg mass density and crop damage in sweet corn in central Maine from 1995 to 1996. The use of both 3:97 Z:E-11-tetradecenyl acetate and 97:3 Z:E-11tetradecenyl acetate pheromone blends confirmed that European corn borer in central Maine is attracted to both pheromone lure types. European corn borer moths were captured predominantly with the E-lure type than with the Z-lure type in both years. The Scentry Heliothis trap was more effective than the Multi-Pher trap, but similar to the pheromone-baited water pan trap for monitoring European corn borer flights. With the Scentry Heliothis trap, the grassy border and 1st corn rows were the best locations for moth capture during the early flight period, but during the peak flight period, traps located in the middle of the field caught the most moths. Corn damage was recorded before moth captures in some sites and before egg mass counts in others, indicating poor efficacy of traps for early flights. Significant and positive correlations were found between moth captures in the midfield location and egg mass counts, and corn leaf damage, and between egg mass counts and corn leaf damage. However, low coefficients of variation suggest that pheromone trap captures were not good predictors of European corn borer leaf damage in sweet corn.

Phylogeny of Hirsutella species (Ophiocordycipitaceae) from the USA: remedying the paucity of Hirsutella sequence data

Hirsutella (Ophiocordycipitaceae: Hypocreales) is a genus of insect, mite, and nematode pathogens with an asexual morph, which generally produce a mucilaginous cluster of one or several conidia on phialides that are basally subulate and taper to a fine neck. The generic name Hirsutella has been proposed for suppression in favour of Ophiocordyceps as a consequence of the ending of dual nomenclature for different morphs of pleomorphic fungi in 2011. Though the generic name is well established, geographically dispersed, and speciose, exceptionally few sequences are available in online databases. We examined 46 isolates of 23 Hirsutella species from the USA, curated by the USDA-ARS Collection of Entomopathogenic Fungal Cultures (ARSEF Culture Collection), that previously had not been molecularly characterized and produced a phylogeny of these organisms; we included previously published Hirsutella and Ophiocordyceps taxa. In producing the largest phylogeny of Hirsutella isolates so far, we provide: (1) context for discussing previously-hypothesized relationships; (2) evidence for revisions as taxonomic transitions move forward; and (3) available molecular data to be incorporated into further evolutionary studies of Ophiocordycipitaceae.

Wild Bumblebee (Bombus) Diversity and Nosema (Microsporidia: Nosematidae) Infection Levels Associated with Lowbush Blueberry (Vaccinium angustifolium) Production and Commercial Bumblebee Pollinators

The primary objective was to determine if the prevalence of Nosema bombi infection is higher for wild bumblebees (Bombus spp.) caught in lowbush blueberry growing areas with a history of commercial bumblebee use than for bumblebees caught in areas without a history of commercial bumblebee use. Additionally, we wished to determine relative Bombus species abundances and diversity in blueberry growing regions. Over two years we caught, identified to species, and dissected 767 bumblebees. Light microscopy revealed overall infection levels of 5.48%. The history of commercial bumblebee use had no relation to infection levels. Bumblebee species diversity and field location had significant relationships to infection ( adjusted = 0.265; species diversity , ; field region , ). The absence or presence of one species, Bombus terricola, appears to determine the relationship between species diversity and infection. The data show B. terricola decline in sampled regions and almost half of the collected B. terricola were infected with Nosema. The commercial species, B. impatiens, shows an increase in abundance, but with a 6.9% proportion infection. Molecular confirmation of the infecting species was ambiguous, suggesting a need for future clarification of the infecting species.