Entomology

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Ground-dwelling beetles as bioindicators in transgenic corn
(2009) Lepping, Miles; Shrewsbury, Paula M; Dively, Galen P; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Ecological risk assessment for transgenic crops requires identification of appropriate biological indicator organisms for use in laboratory and field biomonitoring studies. Ground-dwelling predatory beetles in the families Carabidae and Staphylinidae comprise a diverse and abundant group of nontarget organisms in field corn systems where rootworm-resistant transgenic varieties are deployed. First, the utility of two sampling methods (pitfall trapping and suction-based litter extraction) was assessed for estimating ground beetle (Coleoptera: Carabidae) population parameters in Maryland cornfields. Sampling bias was established for pitfall trapping, confirming the limitations of this semi-quantitative method for capturing a representative portion of the epigeal community. Litter extraction data conformed to predictions for abundance in relation to trophic identity, body size and biomass. Litter extraction identified smaller bodied carabid omnivores and carnivores as numerically dominant over larger bodied species that have received focus in risk assessment studies. A small-bodied carabid, Elaphropus xanthopus (Dejean), was identified as the dominant carnivore, and therefore selected for nontarget exposure and toxicity studies. Second, in choice and no-choice experiments, corn pollen was identified as a realistic, direct exposure pathway to transgenic proteins for E. xanthopus. Third, organism-level exposure to Cry34Ab1 rootworm-resistant protein was demonstrated for E. xanthopus in the laboratory and field during corn pollen shed. Field studies also revealed contamination across transgenic and non-transgenic test plots, indicating experimental design must account for the movement of study organisms and/or transgenic plant tissues. Finally, a toxicity study examined the effects of dietary exposure to rootworm-resistant Cry34/35Ab1 corn pollen for two beetle species, a carabid, E. xanthopus, and a staphylinid, Strigota ambigua (Erichson). Transgenic pollen exposure did not affect longevity or sub-lethal behaviors for either species. Small-bodied, predatory ground beetles are recommended as candidate bioindicator organisms in risk assessment studies designed to optimize field monitoring, exposure detection, and bioassay for transgenic pesticides.
Nutrient regulation by an omnivore and the effects on performance and distribution
(2009) Pearson, Rachel Estelle Goeriz; Gruner, Daniel S; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Omnivores have a unique interaction with their nutritional environment because they have adapted to consume food from different trophic levels. To successfully navigate their variable resources, omnivores must maintain some level of nutrient regulation. To explore the effects of nutrient regulation by an omnivore, I used a salt marsh katydid, Conocephalus spartinae. To first address the ability of Conocephalus to perform on a wide range of diets and to regulate their nutritional intake, I used artificial diets that differed in relative amounts of protein and carbohydrate (Chapter 1). I found that Conocephalus survival decreased on a high protein diet due in part to a decrease in lipid stores but growth was not affected by diet. In a second experiment Conocephalus showed a degree of nutrient regulation as evidenced by the difference in what they actually ate and the predicted consumption if they had been feeding equally on the diets presented in each treatment. However, I did not find evidence for tight macronutrient regulation. Next I explored capacity of Conocephalus to regulate their nutrient intake (nitrogen and lipid) when fed naturally co-occurring prey (Chapter 2). I first established that the prey differed in their protein and lipid content and that these differences were related to the size of the prey species. When Conocephalus were fed different prey species individuals showed no differences in either growth or survival. In the final experiment, I found that Conocephalus did show evidence of a degree of nitrogen and lipid regulation because they did not feed equally on all of the prey species offered. Lastly, I documented the relationship between the ability of Conocephalus to locate plant and prey resources and the effect that these resources have on omnivore performance (Chapter 3). I found that Conocephalus aggregates in areas of high plant quality but that their numbers do not correspond to areas of high prey density. However, I found that katydid growth and survival was enhanced by prey availability but not plant quality. Overall, I documented how an organism like an omnivore relates to its nutritional environment and how nutrient regulation might affect performance and distribution. Last, I documented the relationship between the ability of katydids to locate plant and prey resources and the effect that these resources have on omnivore performance (Chapter 3). I found that katydids aggregate in areas of high plant quality but that their numbers do not correspond to areas of high prey density.
Soldier neotenics of Zootermopsis nevadensis (Hagen) and Archotermopsis sp. (Isoptera: Termopsidae): Morphology, Development, Behavior, and Evolution
(2009) Johnson, Susan Elaine; Thorne, Barbara L; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
I: The relictual reproductive soldier neotenics of primitive Termopsid termites may offer insights into the evolution of eusociality and sterile castes in termites. II: Soldiers and helpers in a new Thai species of Archotermopsis do not display unusually complete gonad development. The first neotenic pair ever reported for this genus is described. III: Morphological differences between soldiers and soldier neotenics in the head and gonads are quantified in Z. nevadensis. There is not necessarily a clear delineation in morphology between soldiers and soldier neotenics. IV: Colony age and size do not significantly influence the differentiation or survival of male replacement reproductives in colonies of Z. nevadensis. Soldier neotenics' development is not significantly influenced by the presence of normal soldiers. V: Soldier neotenics and related female neotenics tend to have greater initial survival after interactions with colonies with only normal neotenics. Mostly helpers are aggressors, never soldier neotenics or neotenics.
EFFECTS OF ABIOTIC STRESS AND PREDATOR REFUGE ON TERRESTRIAL PREDATOR-PREY INTERACTIONS
(2009) Lewis, Danny; Denno, Robert F.; Gruner, Daniel; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
A major goal of ecology has been to understand how abiotic stress modifies species interactions, including predation. In marine habitats, a well-supported hypothesis holds that stress reduces the importance of predation because predators are more vulnerable to stress than prey, but this hypothesis has not been well-tested in terrestrial systems. The effect of refuge from stress on predation level has been studied even less, particularly in terrestrial systems. My research examines the effects of two types of stress, and refuge from them, on predation in a terrestrial salt-marsh food web. I investigated the stress of winter weather and asked first, whether the top predator used a particular marsh habitat as a winter refuge, second, how inter-year variation in winter severity affected refuge use, and third, how refuge use affected the predator's spatial distribution later in the year (Chapter 1). I found that spring predator density was higher within the refuge than outside, a difference that increased following colder winters. Consequently, predators were forced to re-colonize the rest of the marsh from the winter refuge, creating a long-lasting density gradient with lower densities farther from the refuge. In contrast, prey densities were not affected by winter temperatures, and were higher outside the refuge. This prey distribution may have facilitated predator colonization of non-refuge habitats. I investigated the stress of tidal inundation on marsh predators and prey, and their use of vegetation above water as a refuge from submersion. I found that densities of two key predators were more highly correlated with refuge availability than with tidal intensity. Notably, this correlation with refuge increased during the highest tides of the month. In contrast, distribution of the most abundant herbivore was not correlated with refuge availability (Chapter 2). These results suggested that tides impacted predators more than herbivores, but that refuge negated tidal effects on predators. To test these hypotheses, I eliminated tidal inundation from experimental field mesocosms while allowing control mesocosms to experience normal tides (Chapter 3). I found that tides caused substantial mortality at all trophic levels, but affected predators significantly more than herbivores and decreased predation levels.
Ecological dynamics of macrolepidoptera feeding on box elder (Acer negundo L.)
(2008-08-29) Lind, Eric; Barbosa, Pedro; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Understanding species abundances and distributions is a major goal of ecology. Although manipulative experiments can reveal mechanistic properties of interactions among a small number of species, and macroecological studies can draw fundamental insights from patterns at a large scale, inference about local communities as a whole requires a combination of these approaches. I used a suite of techniques to better understand the ecological dynamics of a group of insect herbivores, the assemblage of moth caterpillars feeding on box elder, a common riparian tree. I examined the landscape ecology of the assemblage to determine the degree of turnover at multiple scales, and how diversity of the assemblage depended on host plant context. I found apparent homogeneity of caterpillar diversity masked important differences in co-occurrence even at small scales, though the expected influence of host plant diversity was not observed. Examining the species through time, I investigated how species abundance was related to body size, intrinsic population growth rate, and diet breadth. Whereas body size did not scale significantly with abundance in this group of species, and diet breadth had a complex relationship with abundance, the population growth rate developed in association with the host plant explained the differential abundance of species on the plant quite well. Finally, I quantified elemental content of species in the group, to determine how stoichiometric constraints related to size and growth rates of caterpillars in the assemblage. I found some support for a theory connecting elemental composition to ecological interactions, though the results were species-dependent. Throughout these investigations I explicitly considered the evolutionary relatedness of co-occurring species using phylogenetic methods. By merging ecological and phylogenetic data, a more unified picture of the important mechanisms underlying species properties can be obtained. Through tests of theory at the landscape, community, and individual level, I have presented a clearer picture of the forces structuring this assemblage of caterpillars, and provided a template for investigations of community dynamics at a similar scale.
Macroinvertebrate predators and their role in shaping freshwater communities in constructed wetlands
(2008-07-29) Culler, Lauren Elizabeth; Lamp, William O; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The recent increase in the number of wetland construction projects has led to numerous studies investigating the response of the macroinvertebrate community in wetlands. Little is known, however, about the factors structuring these communities and how predation may shape community development. Here, I analyze two years of macroinvertebrate community data collected from 9 constructed wetlands at the Jackson Lane Preserve on the Eastern Shore of Maryland. Results suggest that abiotic factors may be less important than previously thought in structuring the macroinvertebrate community, and biotic factors such as predation may be more important. I then investigate the role of two larval dytiscid beetles in structuring the primary consumer community. These predators exert strong pressure on the community and, therefore, I conclude that predation is an important factor shaping freshwater communities in constructed wetlands. I offer several suggestions for wetland management with the goal of constructing wetlands with high ecological value.
Linking detritus and primary producer based communities
(2008-03-25) Hines, Jessica; Denno, Robert F; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Terrestrial food-web theory has been developed largely by examining species interactions in primary producer food webs. However, the decomposer subsystem can have strong influences on aboveground communities and ecosystem functioning. Here I examine, at several spatial scales, the complexity of terrestrial food-web interactions by considering interactions between species in detritivore and primary-producer food webs. I focused on Spartina alterniflora marshes and interactions among the numerically dominant herbivore Prokelisia dolus, its major spider predator Pardosa littoralis, and several detritivores (Littorophiloscia vittata, Orchestia grillus, Melampus bidentatus and Littoraria irrorata). I found that predator-detritivore interactions have weak indirect effects on plant growth and decomposition (Chapter 1). Furthermore, by serving as alternative prey, detritivores can influence the strength of predator-herbivore interactions. However, the strength of predator-herbivore-detritivore interactions was species-specific and depended on habitat structure (leaf litter - Chapter 1) and detritivore identity (Chapter 2). Although detritivore species are often functionally redundant in soil communities, changes in detritivore species composition can have divergent influences on aboveground predator-herbivore interactions (Chapter 2). Whereas some detritivores (Littorophiloscia vittatta) promote herbivore and predator survival, other detritivores (Littoraria irroratta) reduce predator and herbivore densities. Moreover, the geographic distribution of detritivores influences the relative strength of predator-herbivore interactions across broader spatial scales (Chapter 3). I found a shift in the relative abundance of dominant detritivore, herbivore, and predator species across a 1660 km latitudinal gradient. Detritivorous Littoraria snails that abound on low-latitude marshes modify Spartina vegetation structure and create an unfavorable habitat for Pardosa spiders. Pardosa exert stronger predation pressure on Prokelisia planthoppers on high-latitude marshes where spiders are abundant. Changes in global carbon cycles may influence the strength of linkages between primary production and decomposition food webs. I examined how changes in the detritivore food chain influenced the growth of two plant species (Scirpus olneyi and Spartina patens) under elevated and ambient CO2 conditions. I found limited and species-specific support for the increased importance of the decomposition pathway under elevated CO2 conditions. Overall, detritivores modified predator-herbivore interactions, live plant growth, and decomposition. The strength of these interactions changed with the composition of the detritivore community, latitude, and atmospheric CO2 conditions.
Inducible plant responses linking above- and below-ground herbivory: ecological significance and underlying mechanisms
(2007-12-05) Kaplan, Ian; Denno, Robert F; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Above- and below-ground organisms can indirectly affect one another via several recently-described mechanisms, one such mechanism being herbivore-induced plant responses. Because plants leaves occur above-ground and roots below-ground, systemic plant responses to foliar- and root-feeding consumers can result in reciprocal interactions between above- and below-ground herbivory. To first address the broader theoretical context underlying plant-mediated herbivore interactions I conducted a meta-analytical review of interspecific interactions in phytophagous insects (Chapter 1). Using a data-set of 333 observations of interspecific herbivore interactions compiled from 145 independently published studies, I quantitatively assessed: (a) the overall importance of competition in the ecology of insect herbivores, and (b) whether plant-feeding insects conform to traditional competition paradigms. Despite finding frequent evidence for competition, I found very little evidence that phytophagous insects conform to theoretical predictions for interspecific competition. Notably, the strength of interactions between herbivores was largely unaffected by feeding guild, and occurred among distantly-related species that were spatially- and temporally-separated from one another. Moreover, in most cases plants mediated these indirect interactions. Next, I used the tobacco (Nicotiana tabacum) system to explore plant responses to foliar-feeding insects and root-feeding nematodes. I found that aboveground insect herbivores had limited impact on the secondary chemistry of roots, but belowground nematode herbivores strongly affected leaf chemistry (Chapter 2). However, the magnitude of leaf-root induction was also affected by vascular connectivity, with stronger induced responses among plant tissues that were more closely aligned (Chapter 3). Last, I assessed the impact of induced responses on the performance and abundance of foliar and root herbivores using manipulative greenhouse (Chapter 4) and field studies (Chapter 5). Overall, I documented that root-feeding nematodes positively affect leaf-chewing insects by interfering with aboveground nicotine dynamics, whereas aboveground insects benefit root-feeding nematodes via alteration of source-sink dynamics.
Consequences of omnivory and alternative food resources on the strength of trophic cascades
(2007-07-10) Frank, Steven David; Shrewsbury, Paula M; Denno, Robert F; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Omnivorous predators that feed on prey and plant resources are recognized as an important component of food webs but their impact on herbivore populations and trophic dynamics is unpredictable. Feeding on food items from multiple trophic levels increases the reticulate nature of food webs and the labile role of omnivores in promoting trophic cascades. Using carabid beetles in a corn agroecosystem, this research explored the interactive effects of predator guild (omnivore or carnivore) and the trophic origin of alternative food resources (seeds or fly pupae) on the control of herbivores (black cutworms) and plant survival. I demonstrated that the trophic guild and feeding performance of carabids can be predicted from their mandibular morphology. Carnivorous carabids, using mandibles with sharp points and a long shearing edge, kill and consume caterpillars more efficiently than omnivores that have mandibles with wide molar areas adapted for consuming prey and seeds. Omnivore preference for seeds and pupae further reduced their consumption of cutworms, which resulted in increased plant damage, ultimately dampening trophic cascades. In open field plots the abundance of omnivorous carabids and ants increased in response to seed but not pupae whereas neither subsidy affected the abundance of carnivorous predators. Pupae subsidies reduced predation of cutworms by carnivores and omnivores, consequently reducing seedling survival. However, in seed subsidized plots omnivorous predators switched from seeds to higher quality cutworm prey. Thus, predation of cutworms increased with cascading positive effects for seedlings. This research demonstrated that omnivorous carabids interacted more strongly with alternative food resources, particularly seeds, than carnivores. In addition, this difference can be linked to morphological differences that reduced omnivore efficiency as predators suggesting omnivores may be less effective agents of biological control. However, increased tenure time and aggregation to plant resources by omnivores helped restore trophic cascades, and should enhance biological control. Understanding the predacious behavior of omnivores in resource diverse environments is essential to predicting their role in trophic dynamics. I provide evidence that the trophic origin of alternative food drives the strength of this interaction and the extent to which omnivores promote trophic cascades.
The Influence of Predator Species Richness on Prey Mortality: Implications to Conservation Biological Control.
(2006-12-04) Lewins, Scott Asher; Barbosa, Pedro; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Understanding how changes in biodiversity affect the function of agroecosystems is paramount to conservation biological control. The Species Assemblage Control Hypothesis predicts increasing species richness of predator assemblages can increase the assemblages' ability to suppress pests. I hypothesized that an increase in species richness of a predator assemblage leads to an increase in prey mortality and predator species identity can alter the relationship. An assemblage of predators identified from an assessment of a collard agroecosystem was evaluated to find that only some predators fed on larval Pieris rapae, they did not differ in their per capita consumption, and some intraguild predation occurred. In testing the hypotheses I found a significant relationship between predator species richness and prey mortality; however, predator species identity altered the relationship. These findings highlight the importance in understanding predator assemblages before conservation decisions that effectively suppress pests can be made.

Entomology

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