Andrew Reeson

Baculovirus resistance in the noctuid Spodoptera exempta is phenotypically plastic and responds to population density

Parasite resistance mechanisms can be costly to maintain. We would therefore predict that organisms should invest in resistance only when it is likely to be required. Insects that show density–dependent phase polyphenism, developing different phenotypes at high and low population densities, have the opportunity to match their levels of investment in resistance with the likelihood of exposure to pathogens. As high population densities often precipitate disease epidemics, the high–density form should be selected to invest relatively more in resistance. We tested this prediction in larvae of the noctuid Spodoptera exempta. Larvae reared at a high density were found to be considerably more resistant to a nuclear polyhedrosis virus than those reared in isolation. A conspicuous feature of the high–density phase of S. exempta and other phase–polyphenic Lepidoptera is cuticular melanization. As melanization is controlled by the phenoloxidase enzyme system, which is also involved in the immune response, this suggests a possible mechanism for increased resistance at high population densities. We demonstrated that melanized S. exempta larvae were more resistant than non–melanized forms, independent of rearing density. We also found that haemolymph phenoloxidase activity was correlated with cuticular melanization, providing further evidence for a link between melanization and immunity. These results suggest that pathogen resistance in S. exempta is phenotypically plastic, and that the melanized cuticles characteristic of the high–density form may be indicative of a more active immune system.

Density‐dependent prophylaxis: evidence from Lepidoptera–baculovirus interactions?

Insects from a range of taxa use early larval density as a cue to the future deterioration of their current habitat (Dingle, 1996). Their response to this cue is often to redirect resources away from activities favouring immediate reproduction at the natal site (e.g. egg maturation) towards those that favour reproduction in a different location or at a different time (e.g. the development of wings and flight muscles or the deposition of lipid reserves). As well as predicting a decline in the quality or quantity of the larval food resource, early larval density may also predict the risk of exposure to pathogens, which often increases in a predictable manner with population density. Under such circumstances, natural selection will favour those individuals that use early larval density to predict the optimal level of resources to allocate to pathogen resistance later in life. Such an adaptive prophylactic response to larval density may explain the results of several recent studies of moth caterpillars and their baculoviruses. Kunimi & Yamada (1990) reared caterpillars of the Oriental armyworm moth ( Mythimna separata ) at densities ranging between one and twenty larvae per container. They then orally inoculated newly emerged fourth-instar caterpillars with various concentrations of nuclear polyhedrosis virus (NPV) and recorded the number of deaths. They found that NPV-induced mortality declined gradually from 95% for insects reared solitarily to 37% for those reared at a density of twenty larvae per container. The LC 50 value for caterpillars reared at the highest density was about tenfold that for individuals reared solitarily. In a second experiment, Kunimi & Yamada (1990) allowed second-instar caterpillars to feed for 2 days on artificial diet contaminated with a granulosis virus (GV) before rearing them for a further 36 days under either solitary or crowded conditions. They found that larvae reared at high densities (twenty per container) were about fourfold more resistant to GV than those reared singly. Thus, in this species at least,

Agent-based modeling in ecological economics.

Interconnected social and environmental systems are the domain of ecological economics, and models can be used to explore feedbacks and adaptations inherent in these systems. Agent‐based modeling (ABM) represents autonomous entities, each with dynamic behavior and heterogeneous characteristics. Agents interact with each other and their environment, resulting in emergent outcomes at the macroscale that can be used to quantitatively analyze complex systems. ABM is contributing to research questions in ecological economics in the areas of natural resource management and land‐use change, urban systems modeling, market dynamics, changes in consumer attitudes, innovation, and diffusion of technology and management practices, commons dilemmas and self‐governance, and psychological aspects to human decision making and behavior change. Frontiers for ABM research in ecological economics involve advancing the empirical calibration and validation of models through mixed methods, including surveys, interviews, participatory modeling, and, notably, experimental economics to test specific decision‐making hypotheses. Linking ABM with other modeling techniques at the level of emergent properties will further advance efforts to understand dynamics of social‐environmental systems.

APPLICATION OF 16S RDNA-DGGE TO EXAMINE THE MICROBIAL ECOLOGY ASSOCIATED WITH A SOCIAL WASP VESPULA GERMANICA

Invertebrates host numerous bacteria, with interactions ranging from pathogenesis to symbiosis. While certain symbiotic relationships have been well studied, little is known about the dynamics of these bacterial communities. Denaturing gradient gel electrophoresis (DGGE) was used to examine the bacterial microflora associated with the eusocial wasp Vespula germanica. DGGE profiles of larval guts revealed a variable microflora, suggesting that V. germanica is not dependent on a particular suite of mutualists. The variation in profiles was not related to season, nest size or macrohabitat. Sequences corresponding to Lactococcus, Lactobacillus, a novel Leuconostoc and two Rickettsiella grylli strains were obtained. DGGE proved to be a useful technique for characterizing the wasp microflora. Given the importance of microbial communities to invertebrates, there is much to be gained from the application of such techniques.

Assessment of prey overlap between a native (Polistes humilis) and an introduced (Vespula germanica) social wasp using morphology and phylogenetic analyses of 16S rDNA

In newly invaded communities, interspecific competition is thought to play an important role in determining the success of the invader and its impact on the native community. In southern Australia, the native Polistes humilis was the predominant social wasp prior to the arrival of the exotic Vespula germanica (Hymenoptera: Vespidae). Both species forage for similar resources (water, pulp, carbohydrate and protein prey), and concerns have arisen about potential competition between them. The aim of this study was to identify the protein foods that these wasps feed on. As many prey items are masticated by these wasps to the degree that they cannot be identified using conventional means, morphological identification was complemented by sequencing fragments of the mitochondrial 16S rRNA gene. GenBank searches using blast and phylogenetic analyses were used to identify prey items to at least order level. The results were used to construct complete prey inventories for the two species. These indicate that while P. humilis is restricted to feeding on lepidopteran larvae, V. germanica collects a variety of prey of invertebrate and vertebrate origin. Calculated values of prey overlap between the two species are used to discuss the implications of V. germanica impacting on P. humilis. Results obtained are compared to those gained by solely ‘conventional’ methods, and the advantages of using DNA‐based taxonomy in ecological studies are emphasized.

Effects of phenotypic plasticity on pathogen transmission in the field in a Lepidoptera-NPV system

Abstract In models of insect–pathogen interactions, the transmission parameter (ν) is the term that describes the efficiency with which pathogens are transmitted between hosts. There are two components to the transmission parameter, namely the rate at which the host encounters pathogens (contact rate) and the rate at which contact between host and pathogen results in infection (host susceptibility). Here it is shown that in larvae of Spodoptera exempta (Lepidoptera: Noctuidae), in which rearing density triggers the expression of one of two alternative phenotypes, the high-density morph is associated with an increase in larval activity. This response is likely to result in an increase in the contact rate between hosts and pathogens. Rearing density is also known to affect susceptibility of S. exempta to pathogens, with the high-density morph showing increased resistance to a baculovirus. In order to determine whether density-dependent differences observed in the laboratory might affect transmission in the wild, a field trial was carried out to estimate the transmission parameter for S. exempta and its nuclear polyhedrosis virus (NPV). The transmission parameter was found to be significantly higher among larvae reared in isolation than among those reared in crowds. Models of insect–pathogen interactions, in which the transmission parameter is assumed to be constant, will therefore not fully describe the S. exempta-NPV system. The finding that crowding can influence transmission in this way has major implications for both the long-term population dynamics and the invasion dynamics of insect–pathogen systems.

Benefits of integrating complementarity into priority threat management.

Conservation decision tools based on cost-effectiveness analysis are used to assess threat management strategies for improving species persistence. These approaches rank alternative strategies by their benefit to cost ratio but may fail to identify the optimal sets of strategies to implement under limited budgets because they do not account for redundancies. We devised a multiobjective optimization approach in which the complementarity principle is applied to identify the sets of threat management strategies that protect the most species for any budget. We used our approach to prioritize threat management strategies for 53 species of conservation concern in the Pilbara, Australia. We followed a structured elicitation approach to collect information on the benefits and costs of implementing 17 different conservation strategies during a 3-day workshop with 49 stakeholders and experts in the biodiversity, conservation, and management of the Pilbara. We compared the performance of our complementarity priority threat management approach with a current cost-effectiveness ranking approach. A complementary set of 3 strategies: domestic herbivore management, fire management and research, and sanctuaries provided all species with >50% chance of persistence for

Mining Activity, Income Inequality and Gender in Regional Australia

4.7 million/year over 20 years. Achieving the same result cost almost twice as much (

Economic Behavior in the Face of Resource Variability and Uncertainty

9.71 million/year) when strategies were selected by their cost-effectiveness ranks alone. Our results show that complementarity of management benefits has the potential to double the impact of priority threat management approaches.

Priority threat management of invasive animals to protect biodiversity under climate change

Mining activity has been a significant driver of export growth as well as income and employment in parts of regional Australia. However, while income growth is an economic benefit, the high incomes associated with the mining sector may also lead to greater inequality. This paper describes an empirical analysis of mining activity and income inequality in regional Australia. The Gini coefficient (a measure of inequality) for personal income is found to be significantly associated with levels of mining employment. However, this relationship is not linear. Rather, income inequality initially increases with mining activity, before decreasing at medium to high levels of mining employment, following a Kuznets curve pattern. Segregating data for men and women reveals very different patterns. Among men, inequality initially increases as mining employment in a region increases, but then sharply decreases; at high levels of mining activity, income inequality among men is lower than is typically observed in non-mining areas. Among women, income inequality increases with mining activity throughout its range. This suggests that income inequality is most likely to be a problem in locales with intermediate levels of mining activity and that it affects men and women quite differently.