Host Density Research Articles

Abundance assessment of Sulawesi Banded Swallowtail, Papilio gigon gigon and availability of resource plants in Bantimurung Bulusaraung National Park, South Sulawesi, Indonesia

Abstract. Ismail T, Maulany RI, Ngakan PO. 2024. Abundance assessment of Sulawesi Banded Swallowtail Papilio gigon gigon and availability of resource plants in Bantimurung Bulusaraung National Park, South Sulawesi, Indonesia. Biodiversitas 25: 673-682. The Sulawesi Banded Swallowtail (Papilio gigon gigon Felder & Felder, 1864) is an endemic butterfly species of Sulawesi, Indonesia currently under threat from hunting and trade activities and habitat degradation. This study aims to examine the abundance of P. gigon gigon and resource plants' availability and to analyze the relationship between resource host and nectar plant density with the abundance of the butterfly species in Bantimurung Bulusaraung National Park, South Sulawesi, Indonesia. Data were collected using the line transect method in two habitat types: settlement and forest located in three observation sites (Bantimurung, Leang-leang, and Pattunuang). The data were analyzed with Spearman's correlation test. The results showed a significant positive correlation in Bantimurung between the host plant densities (r = 0.258; p = 0.010) and nectar plants (r = 0.211; p = 0.036) with the abundance of P. gigon gigon. In Pattunuang, the host plants had indicated an insignificant correlation (r = 0.061; p = 0.548) with the abundance of P. gigon gigon, and in contrast, the nectar plants showed a significant positive correlation (r = 0.487; p = 0.000). Only in Leang-leang the correlation between the abundance of P. gigon gigon showed no significant correlation with both host (r = 0.152; p = 0.132) and nectar plants (r = 0.041; p = 0.686). Differences between the observation areas were suspected to be influenced by human activities such as tourism and hunting. Therefore, management interventions by the national park are required to support the conservation of P. gigon gigon in the area.

Preferential ordering of incommensurate-length guest particles in a smectic host.

Using density functional theory, we study the preferential ordering of rod-like guest particles immersed in a smectic host fluid. Within a model of perfectly aligned rods and assuming that the guest particles do not perturb the smectic host fluid, simple excluded-volume arguments explain that guest particles that are comparable in length to the host particles order in phase with the smectic host density layering, whereas guest particles that are considerably shorter or longer order in antiphase. The corresponding free-energy minima are separated by energetic barriers on the order of the thermal energy kBT, suggesting that guest particles undergo hopping-type diffusion between adjacent smectic layers. Upon introducing a slight orientational mismatch between the guest particles and the perfectly aligned smectic host, an additional, smaller free-energy barrier emerges for a range of intermediate guest-to-host length ratios, which splits the free-energy minimum into two. Guest particles in this range occupy positions intermediate between in-phase ordering and in-antiphase ordering. Finally, we use Kramers' theory to identify slow, fast, and intermediate diffusive regimes for the guest particles as a function of their length. Our model is in qualitative agreement with experiment and simulation and provides an alternative, complementary explanation in terms of a free-energy landscape for the intermediate diffusive regime, which was previously hypothesized to result from temporary caging effects [M. Chiappini, E. Grelet, and M. Dijkstra, Phys. Rev. Lett. 124, 087801 (2020)]. We argue that our simple model of aligned rods captures the salient features of incommensurate-length guest particles in a smectic host if a slight orientational mismatch is introduced.

Mutualism at the leading edge: insights into the eco-evolutionary dynamics of host-symbiont communities during range expansion.

The evolution of mutualism between host and symbiont communities plays an essential role in maintaining ecosystem function and should therefore have a profound effect on their range expansion dynamics. In particular, the presence of mutualistic symbionts at the leading edge of a host-symbiont community should enhance its propagation in space. We develop a theoretical framework that captures the eco-evolutionary dynamics of host-symbiont communities, to investigate how the evolution of resource exchange may shape community structure during range expansion. We consider a community with symbionts that are mutualistic or parasitic to various degrees, where parasitic symbionts receive the same amount of resource from the host as mutualistic symbionts, but at a lower cost. The selective advantage of parasitic symbionts over mutualistic ones is increased with resource availability (i.e. with host density), promoting mutualism at the range edges, where host density is low, and parasitism at the population core, where host density is higher. This spatial selection also influences the speed of spread. We find that the host growth rate (which depends on the average benefit provided by the symbionts) is maximal at the range edges, where symbionts are more mutualistic, and that host-symbiont communities with high symbiont density at their core (e.g. resulting from more mutualistic hosts) spread faster into new territories. These results indicate that the expansion of host-symbiont communities is pulled by the hosts but pushed by the symbionts, in a unique push-pull dynamic where both the host and symbionts are active and tightly-linked players.

On–Off Intermittency and Long-Term Reactivity in a Host–Parasitoid Model with a Deterministic Driver

Bursting behaviors, driven by environmental variability, can substantially influence ecosystem services and functions and have the potential to cause abrupt population breakouts in host–parasitoid systems. We explore the impact of environment on the host–parasitoid interaction by investigating separately the effect of grazing-dependent habitat variation on the host density and the effect of environmental fluctuations on the average host population growth rate. We hence focus on the discrete host–parasitoid Beddington–Free–Lawton model and show that a more comprehensive mathematical study of the dynamics behind the onset of on–off intermittency in host–parasitoid systems may be achieved by considering a deterministic, chaotic system that represents the dynamics of the environment. To this aim, some of the key model parameters are allowed to vary in time according to an evolution law that can exhibit chaotic behavior. Fixed points and stability properties of the resulting 3D nonlinear discrete dynamical system are investigated and on–off intermittency is found to emerge strictly above the blowout bifurcation threshold. We show, however, that, in some cases, this phenomenon can also emerge in the sub-threshold. We hence introduce the novel concept of long-term reactivity and show that it can be considered as a necessary condition for the onset of on–off intermittency. Investigations in the time-dependent regimes and kurtosis maps are provided to support the above results. Our study also suggests how important it is to carefully monitor environmental variability caused by random fluctuations in natural factors or by anthropogenic disturbances in order to minimize its effects on throphic interactions and protect the potential function of parasitoids as biological control agents.

Resource asynchrony and landscape homogenization as drivers of virulence evolution: The case of a directly transmitted disease in a social host.

Throughout the last decades, the emergence of zoonotic diseases and the frequency of disease outbreaks have increased substantially, fuelled by habitat encroachment and vectors overlapping with more hosts due to global change. The virulence of pathogens is one key trait for successful invasion. In order to understand how global change drivers such as habitat homogenization and climate change drive pathogen virulence evolution, we adapted an established individual-based model of host-pathogen dynamics. Our model simulates a population of social hosts affected by a directly transmitted evolving pathogen in a dynamic landscape. Pathogen virulence evolution results in multiple strains in the model that differ in their transmission capability and lethality. We represent the effects of global change by simulating environmental changes both in time (resource asynchrony) and space (homogenization). We found an increase in pathogenic virulence and a shift in strain dominance with increasing landscape homogenization. Our model further indicated that lower virulence is dominant in fragmented landscapes, although pulses of highly virulent strains emerged under resource asynchrony. While all landscape scenarios favoured co-occurrence of low- and high-virulent strains, the high-virulence strains capitalized on the possibility for transmission when host density increased and were likely to become dominant. With asynchrony likely to occur more often due to global change, our model showed that a subsequent evolution towards lower virulence could lead to some diseases becoming endemic in their host populations.

Monitoring urban biological invasions using citizen science: the polyphagous shot hole borer (Euwallacea fornicatus).

The online version contains supplementary material available at 10.1007/s10340-024-01744-7.

How does parasite environmental transmission stage concentration change before, during, and after disease outbreaks?

Outbreaks of environmentally transmitted parasites require that susceptible hosts encounter transmission stages in the environment and become infected, but we also know that transmission stages can be in the environment without triggering disease outbreaks. One challenge in understanding the relationship between environmental transmission stages and disease outbreaks is that the distribution and abundance of transmission stages outside of their hosts have been difficult to quantify. Thus, we have limited data about how changes in transmission stage abundance influence disease dynamics; moreover, we do not know whether the relationship between transmission stages and outbreaks differs among parasite species. We used digital PCR to quantify the environmental transmission stages of five parasites in six lakes in southeastern Michigan every 2 weeks from June to November 2021. At the same time, we quantified infection prevalence in hosts and host density. Our study focused on eight zooplankton host species (Daphnia spp. and Ceriodaphnia dubia) and five of their parasites from diverse taxonomic groups (bacteria, yeast, microsporidia, and oomycete) with different infection mechanisms. We found that parasite transmission stage concentration increased prior to disease outbreaks for all parasites. However, parasites differed significantly in the relative timing of peaks in transmission stage concentration and infection outbreaks. The "continuous shedder" parasites had transmission stage peaks at the same time as or slightly after the outbreak peaks. In contrast, parasites relying on host death for transmission ("obligate killers") had transmission stage peaks before outbreak peaks. For most parasites, lakes with outbreaks had higher spore concentrations than those without outbreaks, especially once an outbreak began; the exception was for a parasite, Pasteuria ramosa, with very strong genotypic specificity of infection. Overall, our results show that disease outbreaks are tightly linked to transmission stage concentration; outbreaks were preceded by increases in transmission stage concentration in the environment and then were fueled by the production of more transmission stages during the outbreak itself, with concentrations decreasing to pre-outbreak levels as outbreaks waned. Thus, tracking transmission stages in the environment improves our understanding of the drivers of disease outbreaks and reveals how parasite traits may affect these dynamics.

Variable prevalence of diseases and compromised health conditions on hard corals around Mauritius Island, Western Indian Ocean

Although coral diseases and compromised health conditions (CHCs) are one of the most prominent threats to coral reefs globally, they have yet to be thoroughly investigated in the Western Indian Ocean. This study aimed to assess the prevalence and spatial distribution of coral diseases and CHCs around Mauritius. Six coral diseases [Growth Anomaly (GA), Skeletal Eroding Band (SEB), Brown Band (BrBD), Porites White Patch Syndrome (PWPS), White Syndromes (WSs), and Yellow Band (YB)] and four CHCs [Pink Patches (PP), Pink Spots (PS), Pink Line Syndrome (PLS), and Focal Bleaching (FB)] were spatially variable in prevalence among the 17 studied sites. The average prevalence for Mauritius was 4.88% (SD 0.52%), almost half of what has been documented from Caribbean and Pacific reefs (about 10%). Total coral colony density (R = −0.585, P < 0.001) and diseases/CHCs-affected host density (R = −0.249, P > 0.05) were negatively correlated while human population density (R = 0.085, P < 0.05) and coral cover (R = 0.045, P < 0.05) were positively correlated with coral diseases/CHCs prevalence. The prevalence of diseases/CHCs significantly differed between the reef-flat and fore-reef zones, with the latter exhibiting higher prevalence. Cluster analyses revealed that PLS, YB, and FB were mostly distributed in the fore-reef zone, while the other diseases/CHCs were mostly predominant on the reef-flats. However, coral disease/CHCs prevalence did not differ significantly (F = 2.613, P > 0.05) between protected and nonprotected zones. These findings have important implications for informing appropriate coral reef conservation and management strategies for Mauritius.

Host movement dominates the predicted effects of climate change on parasite transmission between wild and domestic mountain ungulates.

Climate change is shifting the transmission of parasites, which is determined by host density, ambient temperature and moisture. These shifts can lead to increased pressure from parasites, in wild and domestic animals, and can impact the effectiveness of parasite control strategies. Understanding the interactive effects of climate on host movement and parasite life histories will enable targeted parasite management, to ensure livestock productivity and avoid additional stress on wildlife populations. To assess complex outcomes under climate change, we applied a gastrointestinal nematode transmission model to a montane wildlife-livestock system, based on host movement and changes in abiotic factors due to elevation, comparing projected climate change scenarios with the historic climate. The wildlife host, Alpine ibex (Capra ibex ibex), undergoes seasonal elevational migration, and livestock are grazed during the summer for eight weeks. Total parasite infection pressure was more sensitive to host movement than to the direct effect of climatic conditions on parasite availability. Extended livestock grazing is predicted to increase parasite exposure for wildlife. These results demonstrate that movement of different host species should be considered when predicting the effects of climate change on parasite transmission, and can inform decisions to support wildlife and livestock health.

Prevalence of tick-borne bacterial pathogens in Germany-has the situation changed after a decade?

Tick-borne pathogens, such as Borreliella spp., Rickettsia spp., and Anaplasma spp., are frequently detected in Germany. They circulate between animals and tick vectors and can cause mild to severe diseases in humans. Knowledge about distribution and prevalence of these pathogens over time is important for risk assessment of human and animal health. Ixodes ricinus nymphs were collected at different locations in 2009/2010 and 2019 in Germany and analyzed for tick-borne pathogens by real-time PCR and sequencing. Borreliella spp. were detected with a prevalence of 11.96% in 2009/2010 and 13.10% in 2019 with B. afzelii and B. garinii as dominant species. Borrelia miyamotoi was detected in seven ticks and in coinfection with B. afzelii or B. garinii. Rickettsia spp. showed a prevalence of 8.82% in 2009/2010 and 1.68% in 2019 with the exclusive detection of R. helvetica. The prevalence of Anaplasma spp. was 1.00% in 2009/2010 and 7.01% in 2019. A. phagocytophilum was detected in seven tick samples. None of the nymphs were positive for C. burnetii. Here, observed changes in prevalence were not significant after a decade but require longitudinal observations including parameters like host species and density, climatic factors to improve our understanding of tick-borne diseases.

Seasonal trends in lysogeny in an Appalachian oak-hickory forest soil.

Since 1989, investigations into viral ecology have revealed how bacteriophages can influence microbial dynamics within ecosystems at global scales. Most of the information we know about temperate phages, which can integrate themselves into the host genome and remain dormant via a process called lysogeny, has come from research in aquatic ecosystems. Soil environments remain under-studied, and more research is necessary to fully understand the range of impacts phage infections have on the soil bacteria they infect. The aims of this study were to compare the efficacy of different prophage-inducing agents and to elucidate potential temporal trends in lysogeny within a soil bacterial community. In addition to mitomycin C and acyl-homoserine lactones, our results indicated that halosulfuron methyl herbicides may also be potent inducing agents. In optimizing chemical induction assays, we determined that taking steps to reduce background virus particles and starve cells was critical in obtaining consistent results. A clear seasonal trend in inducible lysogeny was observed in an Appalachian oak-hickory forest soil. The average monthly air temperature was negatively correlated with inducible fraction and burst size, supporting the idea that lysogeny provides a mechanism for phage persistence when temperatures are low and host metabolism is slower. Furthermore, the inducible fraction was negatively correlated with both soil bacterial and soil viral abundance, supporting the idea that lysogeny provides a mechanism for temperate phage persistence when host density is lower. The present study is the first of its kind to reveal clear seasonal trends in inducible lysogeny in any soil.IMPORTANCELysogeny is a relationship in which certain viruses that infect bacteria (phages) may exist within their bacterial host cell as a segment of nucleic acid. In this state, the phage genome is protected from environmental damage and retains the potential to generate progeny particles in the future. It is thought that lysogeny provides a mechanism for long-term persistence for phages when host density is low or hosts are starved-two conditions likely to be found in soils. In the present study, we provide the first known evidence for a seasonal trend in lysogeny in a forest soil. Based on clear relationships observed between lysogeny, temperature, and soil microbial abundance, we find support for previous hypotheses regarding the factors governing lysogeny.

Managing the threat of infectious disease in fisheries and aquaculture using structured decision making

Fisheries and aquaculture provide food and economic security, especially in the developing world, but both face challenges from infectious disease. Here, we consider management of disease issues from a structured decision‐making perspective to examine how infectious disease can threaten seafood production and influence management decisions. For both wild fisheries and aquaculture, disease‐management objectives generally aim to mitigate the severity and economic burden of outbreaks. General management strategies include manipulating host densities, reducing system connectivity, conserving or improving habitat, and implementing direct treatments or some other biological interventions. To inform decisions, mathematical models can be used to explore disease dynamics and to forecast the potential effectiveness of alternative management actions. Developing and implementing disease‐management strategies also involve considering uncertainties and balancing competing stakeholder interests and risk tolerances. We conclude by outlining several steps for applying structured decision making that are broadly useful to decision makers facing issues related to disease.

Functional response of green lacewing, Chrysoperla zastrowi silemmi (Esben-Petersen) to its prey, cabbage aphid, Brevicoryne brassicae L.

Functional response influences the prey-predator interactions and hence is crucial for assessing the predatory potential of a given species. Laboratory studies were conducted at Dr. Y. S. Parmar University of Horticulture and Forestry, Solan, Himachal Pradesh, India during 2019-20 to assess the functional response of a generalist predator, Chrysoperla zastrowi sillemi (Esben-Petersen) (Neuroptera: Chrysopidae) against the cabbage aphid, Brevicoryne brassicae L. The feeding efficiency of larvae of C. zastrowi sillemi against varying densities of aphid i.e. 5, 10, 15, 20 and 30 was evaluated. The number of aphids consumed differed with prey densities and it was in direct proportion to the host density. All the three instars of C. zastrowi sillemi followed type II functional response. The attack rate (a) of the third instar larvae was maximum compared to first and second instars indicating the higher efficiency of later instar in prey consumption. Other parameters viz., the effectiveness of predator (a/th) and maximum predation rate (K) also followed similar trend while the prey handling time (Th) by the first instar took longer period (0.50 h) compared to second and third instars (0.46 h and 0.27 h, respectively). Searching efficiency was highest in the third instar which can be attributed to the higher mobility of fully grown larvae.

Functional response of green lacewing, <i>Chrysoperla zastrowi silemmi</i> (Esben-Petersen) to its prey, cabbage aphid, <i>Brevicoryne brassicae</i> L.

Functional response influences the prey-predator interactions and hence is crucial for assessing the predatory potential of a given species. Laboratory studies were conducted at Dr. Y. S. Parmar University of Horticulture and Forestry, Solan, Himachal Pradesh, India during 2019-20 to assess the functional response of a generalist predator, Chrysoperla zastrowi sillemi (Esben-Petersen) (Neuroptera: Chrysopidae) against the cabbage aphid, Brevicoryne brassicae L. The feeding efficiency of larvae of C. zastrowi sillemi against varying densities of aphid i.e. 5, 10, 15, 20 and 30 was evaluated. The number of aphids consumed differed with prey densities and it was in direct proportion to the host density. All the three instars of C. zastrowi sillemi followed type II functional response. The attack rate (a) of the third instar larvae was maximum compared to first and second instars indicating the higher efficiency of later instar in prey consumption. Other parameters viz., the effectiveness of predator (a/th) and maximum predation rate (K) also followed similar trend while the prey handling time (Th) by the first instar took longer period (0.50 h) compared to second and third instars (0.46 h and 0.27 h, respectively). Searching efficiency was highest in the third instar which can be attributed to the higher mobility of fully grown larvae.

Pathways linking nutrient enrichment, habitat structure, and parasitism to host-resource interactions.

Human activities simultaneously alter nutrient levels, habitat structure, and levels of parasitism. These activities likely have individual and joint impacts on food webs. Furthermore, there is particular concern that nutrient additions and changes to habitat structure might exacerbate the size of epidemics and impacts on host density. We used a well-studied zooplankton-fungus host-parasite system and experimental whole water column enclosures to factorially manipulate nutrient levels, habitat structure (specifically: mixing), and presence of parasites. Nutrient addition increased infection prevalence, density of infected hosts, and total host density. We hypothesized that nutrients, mixing, and parasitism were linked in multiple ways, including via their combined effects on phytoplankton (resource) abundance, and we used structural equation modeling to disentangle these pathways. In the absence of the parasite, both nutrients and mixing increased abundance of phytoplankton, whereas host density was negatively related to phytoplankton abundance, suggesting a mixture of bottom-up and top-down control of phytoplankton. In the presence of the parasite, nutrients still increased phytoplankton abundance but mixing no longer did, and there was no longer a significant relationship between host density and phytoplankton. This decoupling of host-resource dynamics may have resulted from reduced grazing due to illness-mediated changes in feeding behavior. Overall, our results show that the impact of one human activity (e.g., altered habitat structure) might depend on other human impacts (e.g., parasite introduction). Fortunately, carefully designed experiments and analyses can help tease apart these multifaceted relationships, allowing us to understand how human activities alter food webs, including interactions between hosts and their parasites and resources.

The fleas of house mice (Mus musculus L.) and ship rats (Rattus rattus L.) in forest of the Orongorongo Valley, New Zealand

ABSTRACT The ectoparasites of introduced rodents in mainland New Zealand forests include several species of cosmopolitan flea that may be important in the population dynamics and future biocontrol of rodents. We describe a 2-rodent, 2-flea system that showed little change over 20 years. Ship rats (Rattus rattus) and house mice (Mus musculus) were snap trapped at fixed sites in the Orongorongo Valley, Wellington, for a study of their population ecology. The fleas Leptopsylla segnis and Nosopsyllus fasciatus were common on mice and rats respectively, and less common on the alternate hosts. Prevalence was described in relation to sex and age of the host, and to season and year. Male mice were more likely than females to carry L. segnis. Prevalence and intensity of infection mostly increased with age of host. Prevalence of both flea species showed modest seasonal variation, with a dip in autumn. Pregnant or lactating female rats and mice were less likely to have fleas than were non-breeding adult females. Prevalence did not vary positively with host density. We detected a slight overall increase in the prevalence of each flea species over the duration of the study. We conclude with some discussion of flea assemblages in New Zealand.

Small mammal community composition impacts bank vole (Clethrionomys glareolus) population dynamics and associated seroprevalence of Puumala orthohantavirus.

Rodents are important reservoirs for zoonotic pathogens that cause diseases in humans. Biodiversity is hypothesized to be closely related to pathogen prevalence through multiple direct and indirect pathways. For example, the presence of non-host species can reduce contact rates of the main reservoir host and thus reduce the risk of transmission ("dilution effect"). In addition, an overlap in ecological niches between two species could lead to increased interspecific competition, potentially limiting host densities and reducing density-dependent pathogen transmission processes. In this study, we investigated the relative impact of population-level regulation of direct and indirect drivers of the prevalence of Puumala orthohantavirus (PUUV) in bank voles (Clethrionomys glareolus) during years with high abundance. We compiled data on small mammal community composition from four regions in Germany between 2010 and 2013. Structural equation modeling revealed a strong seasonality in PUUV control mechanisms in bank voles. The abundance of shrews tended to have a negative relationship with host abundance, and host abundance positively influenced PUUV seroprevalence, while at the same time increasing the abundance of competing non-hosts like the wood mouse (Apodemus sylvaticus) and the yellow-necked field mouse (Apodemus flavicollis) were associated with reduced PUUV seroprevalence in the host. These results indicate that for PUUV in bank voles, dilution is associated with increased interspecific competition. Anthropogenic pressures leading to the decline of Apodemus spp. in a specific habitat could lead to the amplification of mechanisms promoting PUUV transmission within the host populations.

Utilizing Fractional Artificial Neural Networks for Modeling Cancer Cell Behavior

In this paper, a novel approach involving a fractional recurrent neural network (RNN) is proposed to achieve the observer-based synchronization of a cancer cell model. According to the properties of recurrent neural networks, our proposed framework serves as a predictive method for the behavior of fractional-order chaotic cancer systems with uncertain orders. Through a stability analysis of weight updating laws, we design a fractional-order Nonlinear Autoregressive with Exogenous Inputs (NARX) network, in which its learning algorithm demonstrates admissible and faster convergence. The main contribution of this paper lies in the development of a fractional neural observer for the fractional-order cancer systems, which is robust in the presence of uncertain orders. The proposed fractional-order model for cancer can capture complex and nonlinear behaviors more accurately than traditional integer-order models. This improved accuracy can provide a more realistic representation of cancer dynamics. Simulation results are presented to demonstrate the effectiveness of the proposed method, where mean square errors of synchronization by applying integer and fractional weight matrix laws are calculated. The density of tumor cell, density of healthy host cell and density of effector immune cell errors for the observer-based synchronization of fractional-order (OSFO) cancer system are less than 0.0.0048, 0.0062 and 0.0068, respectively. Comparative tables are provided to validate the improved accuracy achieved by the proposed framework.

Scabies in the Amhara region of northern Ethiopia: a cross-sectional study of prevalence, determinants, clinical presentation and community knowledge

BackgroundThe WHO aims to prevent, eliminate or control neglected tropical diseases, including scabies, by 2030. However, limited epidemiological data presented a challenge to control efforts, especially in high burden countries....

Warmer temperatures reduce the transmission of a virus in a gregarious forest insect.

Understanding how climate warming will influence species interactions is a key question in ecology and predicting changes in the prevalence of disease outbreaks is particularly challenging. Ectotherms are likely to be more influenced by climatic changes as temperature governs their growth, feeding, development, and behavior. We test the hypothesis that pathogen transmission and host mortality will increase at warmer temperatures using a cyclic forest insect, the western tent caterpillar (WTC), Malacosoma californicum pluviale, and its baculovirus. The virus causes population declines at peak host density. WTC are gregarious and clustering is predicted to increase the risk of within family infection; however, how temperature influences this has not been examined. We investigated the impact of temperature on different components of the transmission process in order to pinpoint the possible mechanisms involved. In the laboratory, leaf consumption increased linearly with rising temperature between 15 and 30°C. Insects died more rapidly from virus infection as temperature increased, but this did not translate into differences in the production of viral transmission stages. To examine the influence of temperature on virus transmission, we created a temperature difference between two greenhouses containing potted red alder trees, Alnus rubra. The cooler greenhouse (mean 19.5°C) was roughly similar to ambient temperatures in the field, while the warmer greenhouse was 10°C higher (mean 29°C). As predicted, both larval movement and feeding were higher at the warmer temperature, while the likelihood of the preinfected, inoculum larvae dying on the tents was twice as high in the cooler greenhouse. This resulted in increased virus mortality and a higher transmission parameter under cooler conditions. Therefore, we suggest that, contrary to our prediction, the reduced movement of infected larvae at colder temperatures increased the risk of infection in these gregarious insects and had a greater impact on virus transmission than the increased activity of the susceptible larvae in warmer conditions. Long-term population data from the field, however, show no relationship between temperature and infection levels, suggesting that local changes in virus transmission might not scale up to population infection levels.