Composition of the Spruce Budworm (Choristoneura fumiferana) Midgut Microbiota as Affected by Rearing Conditions

The eastern spruce budworm (Choristoneura fumiferana) is one of the most destructive forest insect pests in Canada. Little is known about its intestinal microbiota, which could play a role in digestion, immune protection, communication and/or development. The present study was designed to provide a first characterization of the effects of rearing conditions on the taxonomic diversity and structure of the C. fumiferana midgut microbiota, using a culture-independent approach. Three diets and insect sources were examined: larvae from a laboratory colony reared on a synthetic diet and field-collected larvae reared on balsam fir or black spruce foliage. Bacterial DNA from the larval midguts was extracted to amplify and sequence the V6-V8 region of the 16S rRNA gene, using the Roche 454 GS-FLX technology. Our results showed a dominance of Proteobacteria, mainly Pseudomonas spp., in the spruce budworm midgut, irrespective of treatment group. Taxonomic diversity of the midgut microbiota was greater for larvae reared on synthetic diet than for those collected and reared on host plants, a difference that is likely accounted for by several factors. A greater proportion of bacteria from the phylum Bacteroidetes in insects fed artificial diet constituted the main difference between this group and those reared on foliage; within the phylum Proteobacteria, the presence of the genus Bradyrhizobium was also unique to insects reared on artificial diet. Strikingly, a Bray-Curtis analysis showed important differences in microbial diversity among the treatment groups, pointing to the importance of diet and environment in defining the spruce budworm midgut microbiota.     

Next‐generation sequencing sheds light on intricate regulation of insect gut microbiota

Next‐generation sequencing (NGS) technologies are getting cheaper and easier and hence becoming readily accessible for many researchers in biological disciplines including ecology. In this issue of Molecular Ecology, Sudakaran et al. (2012) show how the NGS revolution contributes to our better and more comprehensive understanding of ecological interactions between gut symbiotic microbiota and the host organism. Using the European red firebug Pyrrhocoris apterus as a model system, they demonstrated that the gut microbiota consists of a small number of major bacterial phylotypes plus other minor bacterial associates. The major bacteria are localized in a specific anoxic section of the midgut and quantitatively account for most of the gut microbiota irrespective of host's geographic populations. The specific gut microbiota is established through early nymphal development of the host insect. Interestingly, the host feeding on different food, namely linden seeds, sunflower seeds or wasp larvae, scarcely affected the symbiont composition, suggesting homoeostatic control over the major symbiotic microbiota in the anoxic section of the midgut. Some of the minor components of the gut microbiota, which conventional PCR/cloning/sequencing approaches would have failed to detect, were convincingly shown to be food‐derived. These findings rest on the robust basis of high‐throughput sequencing data, and some of them could not be practically obtained by conventional molecular techniques, highlighting the significant impact of NGS approaches on ecological aspects of host–symbiont interactions in a nonmodel organism.     

Impact of non‐pathogenic bacteria on insect disease resistance: importance of ecological context

1. The aerial surface of plants is a habitat for large and diverse microbial communities; termed the phyllosphere. These microbes are unavoidably consumed by herbivores, and while the entomopathogens are well studied, the impact of non‐pathogenic bacteria on herbivore life history is less clear. 2. Previous work has suggested that consumption of non‐entomopathogenic bacteria induces a costly immune response that might decrease the risk of infection. However, we hypothesised that insect herbivores should be selective in how they respond to commonly encountered non‐pathogenic bacteria on their host plants to avoid unnecessary and costly immune responses. 3. An ecologically realistic scenario was used in which we fed cabbage looper, Trichoplusia ni Hübner, larvae on cabbage or cucumber leaves treated with the common non‐entomopathogenic phyllosphere bacteria, Pseudomonas fluorescens and P. syringae. Their constitutive immunity and resistance to a pathogenic bacterium (Bacillus thuringiensis; Bt) and a baculovirus (T. ni single nucleopolyhedrovirus) were then examined. 4. While feeding on bacteria‐treated leaves reduced the growth rate and condition of T. ni, there was no effect on immunity (haemolymph antibacterial and phenoloxidase activities and haemocyte numbers). Phyllosphere bacteria weakly affected the resistance of T. ni to Bt but the direction of this effect was concentration dependent; resistance to the virus was unaffected. Host plant had an impact, with cucumber‐fed larvae being more susceptible to Bt. 5. The lack of evidence for a costly immune response to non‐entomopathogenic bacteria suggests that T. ni are probably adapted to consuming common phyllosphere bacteria, and highlights the importance of the evolutionary history of participants in multi‐trophic interactions.     

Potential role for gut microbiota in cell wall digestion and glucoside detoxification in Tenebrio molitor larvae

Tenebrio molitor larvae were successfully reared free of cultivatable gut lumen bacteria, yeasts and fungi using two approaches; aseptic rearing from surface sterilized eggs and by feeding larvae with antibiotic-containing food. Insects were reared on a rich-nutrient complete diet or a nutrient-poor refractory diet. A comparison of digestive enzyme activities in germ free and conventional insects containing a gut microbiota did not reveal gross differences in enzymes that degrade cell walls from bacteria (lysozyme), fungi (chitinase and laminarinase) and plants (cellulase and licheninase). This suggested that microbial-derived enzymes are not an essential component of the digestive process in this insect. However, more detailed analysis of T. molitor midgut proteins using an electrophoretic separation approach showed that some digestive enzymes were absent and others were newly expressed in microbiota-free larvae. Larvae reared in antibiotic-containing refractory wheat bran diet performed poorly in comparison with controls. The addition of saligenin, the aglycone of the plant glucoside salicin, has more deleterious effects on microbiota-free larvae than on the conventionally reared larvae, suggesting a detoxifying role of midgut microbiota. Analysis of the volatile organic compounds released from the faecal pellets of the larvae shows key differences in the profiles from conventionally reared and aseptically reared larvae. Pentadecene is a semiochemical commonly found in other beetle species. Here we demonstrate the absence of pentadecene from aseptically reared larvae in contrast to its presence in conventionally reared larvae. The results are discussed in the light of the hypothesis that microbial products play subtle roles in the life of the insect, they are involved in the digestion of refractory food, detoxification of secondary plant compounds and modify the volatile profiles of the insect host.     

Contributions of gut bacteria to Bacillus thuringiensis-induced mortality vary across a range of Lepidoptera

Background  

Gut microbiota contribute to the health of their hosts, and alterations in the composition of this microbiota can lead to disease. Previously, we demonstrated that indigenous gut bacteria were required for the insecticidal toxin of Bacillus thuringiensis to kill the gypsy moth, Lymantria dispar. B. thuringiensis and its associated insecticidal toxins are commonly used for the control of lepidopteran pests. A variety of factors associated with the insect host, B. thuringiensis strain, and environment affect the wide range of susceptibilities among Lepidoptera, but the interaction of gut bacteria with these factors is not understood. To assess the contribution of gut bacteria to B. thuringiensis susceptibility across a range of Lepidoptera we examined larval mortality of six species in the presence and absence of their indigenous gut bacteria. We then assessed the effect of feeding an enteric bacterium isolated from L. dispar on larval mortality following ingestion of B. thuringiensis toxin.     

Effects of entomopathogenic bacterium Photorhabdus temperata infection on the intestinal microbiota of the sugarcane stalk borer Diatraea saccharalis (Lepidoptera: Crambidae)

Photorhabdus temperata is an entomopathogenic bacterium that is associated with nematodes of the Heterorhabditidae family in a symbiotic relationship. This study investigated the effects of P. temperata infection on the intestinal microbiota of the sugarcane stalk borer Diatraea saccharalis. Histopathology of the infection was also investigated using scanning electron microscopy. Groups of 20 larvae were infected by injection of approximately 50 bacterial cells directly into the hemocoel. After different periods of infection, larvae were dissected and different tissues were used for bacterial cell quantification. P. temperata was highly virulent with an LD₅₀ of 16.2 bacterial cells at 48 h post-infection. Infected larvae started dying as soon as 30 h post-infection with a LT₅₀ value of 33.8 h (confidence limits 32.2–35.6) and an LT₉₀ value of 44.8 h (CL 40.8–51.4). Following death of the larvae, bacteria from the midgut did not invade the hemocoel. In the midgut epithelium, P. temperata occupied the space underneath the basal lamina. The cultivable intestinal bacterial populations decreased as soon as 1 h post-infection and at 48 h post-infection, 90% of the gut microbiota had died. The role of P. temperata in control of the midgut microbiota was discussed.     

Chemical modulators of the innate immune response alter gypsy moth larval susceptibility to <Emphasis Type="Italic">Bacillus thuringiensis</Emphasis>

Background  

The gut comprises an essential barrier that protects both invertebrate and vertebrate animals from invasion by microorganisms. Disruption of the balanced relationship between indigenous gut microbiota and their host can result in gut bacteria eliciting host responses similar to those caused by invasive pathogens. For example, ingestion of Bacillus thuringiensis by larvae of some species of susceptible Lepidoptera can result in normally benign enteric bacteria exerting pathogenic effects.     

Strategy for orchard use of Bacillus thuringiensis while minimizing impact on Choristoneura rosaceana parasitoids

Trials were conducted to study how spring Bacillus thuringiensis Berliner subsp. kurstaki treatments on apple may be timed to maximize the survival of parasitoids of the obliquebanded leafroller, Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae), found in the southern interior of British Columbia, Canada. Orchard collections verified that second through fourth instar obliquebanded leafrollers were found in varying proportions from pink through the petal fall stage of apple development when spring B. thuringiensis treatments are applied vs. lepidopteran pests. Laboratory‐reared second through fourth instar obliquebanded leafrollers, unparasitized and parasitized by one of three native parasitoid species, were fed untreated apple leaves or leaves treated with B. thuringiensis. The highest mortality of unparasitized obliquebanded leafrollers occurred when fourth instars were exposed to B. thuringiensis‐treated leaves; B. thuringiensis‐induced mortality in the unparasitized second and third instars was less than 50%. The consumption of B. thuringiensis‐treated leaves by host larvae significantly increased the percentage of dead host larvae in all parasitized and unparasitized treatments. However, because of the low susceptibility of this leafroller species to B. thuringiensis, relatively high numbers (38–43%) of three obliquebanded leafroller parasitoid species were able to survive the consumption of B. thuringiensis by second and third instar host larvae. Fourth instar obliquebanded leafrollers were found at the full bloom and petal fall stage of apple development in the orchard, at which time B. thuringiensis treatments are recommended for optimal leafroller control. The highest parasitoid mortality due to host mortality was recorded in Apophua simplicipes Cresson (Hymenoptera: Ichneumonidae) and Macrocentrus linearis (Nees) (Hymenoptera: Braconidae), when the hosts were treated as fourth instars. Both of these parasitoids emerge from fifth and sixth instar obliquebanded leafrollers. Bacillus thuringiensis did not have as negative an impact on Apanteles polychrosidis Viereck (Hymenoptera: Braconidae), which emerges when the host is in the fourth instar. When leafroller mortality and parasitism were combined, the B. thuringiensis treatment did not significantly increase host elimination above that of parasitism alone, except for larvae parasitized by A. simplicipes that were in the fourth instar. The consumption of B. thuringiensis by unparasitized larvae was shown to slow larval development.     

Bacterial larvicides for vector control: mode of action of toxins and implications for resistance

Vector control can be an effective strategy to interrupt disease transmission and biolarvicides based on the entomopathogenic bacteria Bacillus sphaericus, and Bacillus thuringiensis serovar israelensis (Bti) have been successfully used to control species of public health relevance from the genera Aedes, Culex, Anopheles and Simulium. The most important feature of these agents is their ability to produce insecticidal proteins with selective action on the larval midgut. These protoxins are produced as crystals that, once ingested by larvae, are processed into active toxins, interact with receptors in the midgut epithelium and trigger cytopathological effects leading to larval death. B. sphaericus and Bti toxins share the initial steps of the mode of action; however, they interact with different midgut molecules. B. sphaericus presents a single larvicidal factor, the binary (Bin) toxin, whose action relies on the binding to one class of midgut receptors, while Bti crystals contain four protoxins (Cry4Aa, Cry4Ba, Cry11Aa and Cyt1Aa), which display interactions with multiple midgut receptors. The mode of action of B. sphaericus displays a greater potential for resistance selection, compared to Bti, and, to date, there is no record of insect resistance to the latter, contrarily to B. sphaericus. The set of mosquitocidal toxins and their interaction with midgut target sites are described in this review, as well as the implications for the potential to select resistance amongst exposed populations. These biolarvicides have specific mode of action that rely on unique interactions and make them the most selective agents to control Diptera insects actually available.     

Diadegma insulare development is altered by Plutella xylostella reared on water‐stressed host plants

Natural enemies of herbivores function in a multitrophic context, and their performance is directly or indirectly influenced by herbivores and their host plants. Very little is known about tritrophic interactions between host plants, pests and their parasitoids, particularly when the host plants are under any stress. Herbivores and their natural enemies’ response to plants under stress are diverse and variable. Therefore, in this study we investigated how diamondback moth, Plutella xylostella (L.), reared on water‐stressed host plants (Brassica napus L. and Sinapis alba L.) influenced the development of its larval parasitoid, Diadegma insulare (Cresson). No significant differences were observed in development of P. xylostella when reared on water‐stressed host plants. However, all results indicated that water stress had a strong effect on developmental parameters of D. insulare. Development of D. insulare was delayed when the parasitoid fed on P. xylostella, reared on stressed host plants. Egg to adult development of D. insulare was faster on non‐stressed B. napus than non‐stressed S. alba followed by stressed B. napus and S. alba. Female parasitoids were heavier on non‐stressed host plants than stressed counterparts. Furthermore, the parasitoid lived significantly longer on stressed B. napus. However, body size was not affected by water treatment. Most host plant parameters measured were significantly lower for water‐stressed than non‐stressed treatments. Results suggest that development of this important and effective P. xylostella parasitoid was influenced by both water stress and host plant species.     

Interactions between Bacillus thuringiensis subsp. kurstaki HD-1 and midgut bacteria in larvae of gypsy moth and spruce budworm

We examined interaction between Bacillus thuringiensis subsp. kurstaki HD-1 (Foray 48B) and larval midgut bacteria in two lepidopteran hosts, Lymantria dispar and Choristoneura fumiferana. The pathogen multiplied in either moribund (C. fumiferana) or dead (L. dispar) larvae, regardless of the presence of midgut bacteria. Inoculation of L. dispar resulted in a pronounced proliferation of enteric bacteria, which did not contribute to larval death because B. thuringiensis was able to kill larvae in absence of midgut bacteria. Sterile, aureomycin- or ampicillin-treated larvae were killed in a dose-dependent manner but there was no mortality among larvae treated with the antibiotic cocktail used by [Broderick et al., 2006] and [Broderick et al., 2009]. These results do not support an obligate role of midgut bacteria in insecticidal activity of HD-1. The outcome of experiments on the role of midgut bacteria may be more dependent on which bacterial species are dominant at the time of experimentation than on host species per se. The L. dispar cohorts used in our study had a microflora, that was dominated by Enterococcus and Staphylococcus and lacked Enterobacter. Another factor that can confound experimental results is the disk-feeding method for inoculation, which biases mortality estimates towards the least susceptible portion of the test population.     

Galleria mellonella infected with Bacillus thuringiensis involves Hsp90

Insects are good models for studying the innate immune response. We report that Galleria mellonella larvae infected with entomopathogenic bacteria Bacillus thuringiensis kurstaki show changes in the level of Hsp90. Our experimental approach was to pre-treat larvae with the Hsp90-binding compound, 17-DMAG, before infection with B. thuringiensis. We show that pre-treated animals display a higher level of immune response. This was mainly manifested by enhanced action of their hemolymph directed toward living bacteria as well as lysozyme activity digesting bacterial peptidoglycan. The observed phenomenon was due to the higher activity of antimicrobial peptides which, in contrast to healthy animals, was detected in the hemolymph of the immunestimulated larvae. Finally, the physiological significance of our observation was highlighted by the fact that G. mellonella pre-treated with 17-DMAG showed a prolonged survival rate after infection with B. thuringiensis than the control animals. Our report points to a role for Hsp90 in the immune response of G. mellonella after infection with B. thuringiensis at the optimal growth temperature.     

Characterization of the bacterial microbiota of Biomphalaria glabrata (Say, 1818) (Mollusca: Gastropoda) from Brazil

Roughly 200 000 000 people in 74 countries infected with schistosomes all share the fact that they came in contact freshwater harbouring infected snails. The aim of the study is to characterize the microbiota of wild and laboratory‐reared snails of Biomphalaria glabrata from Pernambuco, Brazil. The microbiota of these molluscs was identified biochemically by the VITEK 2 automated microbiological system. Antimicrobial susceptibility testing was carried out by the disc diffusion method with ß‐lactam antibiotics, aminoglycosides, quinolones, folate pathway inhibitors, fenicols and tetracyclines. The results showed that all bacteria identified were gram‐negative, including 11 bacterial genera: Aeromonas, Citrobacter, Enterobacter, Cupriavidus, Rhizobium, Stenotrophomonas, Pseudomonas, Klebsiella, Acinetobacter, Vibrio and Sphingomonas. Regarding the antimicrobial susceptibility, all the isolates exhibited resistance to amoxicillin and sensitivity to meropenem (beta‐lactam antimicrobials). The microbiota of the wild snails consisted predominantly of Enterobacter cloacae, while the laboratory‐reared snails predominantly showed Citrobacter freundii and Aeromonas sobria.

Significance and Impact of the Study

Biomphalaria glabrata is a Brazilian freshwater Planorbidae of great medical relevance as an intermediate host of Schistosoma mansoni. About a month after being infected by one or more miracidia larvae of a compatible schistosome, B. glabrata sheds thousands of cercariae into the water where they seek human skin and, if successful, penetrate to establish infection, eventually taking up residence and maturing in blood vessels of the small intestine. Results obtained from this study aim at targeting novel biological control strategies for schistosomiasis such as paratransgenesis. This is the first study on the microbiota of B. glabrata from Brazil.     

Patterns of temporal and enemy niche use by a community of leaf cone moths (Caloptilia) coexisting on maples (Acer) as revealed by metabarcoding

The diversity of herbivorous insects is often considered a function of host plant diversity. However, recent research has uncovered many examples of closely related herbivores using the same host plant(s), suggesting that partitioning of host plants is not the only mechanism generating diversity. Herbivores sharing hosts may utilize different parts of the same plant, but such resource partitioning is often not apparent; hence, the factors that allow closely related herbivores to coexist are still largely undetermined. We examined whether partitioning of phenology or natural enemies may explain the coexistence of leaf cone moths (Caloptilia; Gracillariidae) associated with maples (Acer; Sapindaceae). Larval activity of 10 sympatric Caloptilia species found on nine maple species was monitored every 2–3 weeks for a total of 13 sampling events, and an exhaustive search for internal parasitoid wasps was conducted using high‐throughput sequencing. Blocking primers were used to facilitate the detection of wasp larvae inside moth tissue. We found considerable phenological overlap among Caloptilia species, with two clear peaks in July and September–October. Coexisting Caloptilia species also had largely overlapping parasitoid communities; a total of 13 chalcid and ichneumon wasp species attacked Caloptilia in a nonspecific fashion at an overall parasitism rate of 46.4%. Although coexistence may be facilitated by factors not accounted for in this study, it appears that niche partitioning is not necessary for closely related herbivores to stably coexist on shared hosts. Co‐occurrence without resource partitioning may provide an additional axis along which herbivorous insects attain increased species richness.     

Influence of dietary aconitine and nicotine on the gut microbiota of two lepidopteran herbivores

The gut microbiota plays an important role in pheromone production, pesticide degradation, vitamin synthesis, and pathogen prevention in the host animal. Therefore, similar to gut morphology and digestive enzyme activity, the gut microbiota may also get altered under plant defensive compound-induced stress. To test this hypothesis, Dendrolimus superans larvae were fed either aconitine- or nicotine-treated fresh leaves of Larix gmelinii, and Lymantria dispar larvae were fed either aconitine- or nicotine-treated fresh leaves of Salix matsudana. Subsequently, the larvae were sampled 72hr after diet administration and DNA extracted from larval enteric canals were employed for gut microbial 16S ribosomal RNA gene sequencing (338 F and 806 R primers). The sequence analysis revealed that dietary nicotine and aconitine influenced the dominant bacteria in the larval gut and determined their abundance. Moreover, the effect of either aconitine or nicotine on D. superans and L. dispar larvae had a greater dependence on insect species than on secondary plant metabolites. These findings further our understanding of the interaction between herbivores and host plants and the coevolution of plants and insects.     

Microbiome changes through ontogeny of a tick pathogen vector

Blacklegged ticks (Ixodes scapularis) are one of the most important pathogen vectors in the United States, responsible for transmitting Lyme disease and other tick‐borne diseases. The structure of a host's microbial community has the potential to affect the ecology and evolution of the host. We employed high‐throughput sequencing of the 16S rRNA gene V3‐V4 hypervariable regions in the first study to investigate the tick microbiome across all developmental stages (larvae, nymphs, adults). In addition to field‐collected life stages, newly hatched laboratory‐reared larvae were studied to determine the baseline microbial community structure and to assess transovarial transmission. We also targeted midguts and salivary glands due to their importance in pathogen maintenance and transmission. Over 100 000 sequences were produced per life stage replicate. Rickettsia was the most abundant bacterial genus across all sample types matching mostly the Ixodes rickettsial endosymbionts, and its proportion decreased as developmental stage progressed, with the exception of adult females that harboured a mean relative abundance of 97.9%. Laboratory‐reared larvae displayed the lowest bacterial diversity, containing almost exclusively Rickettsia. Many of the remaining bacteria included genera associated with soil, water and plants, suggesting environmental acquisition while off‐host. Female organs exhibited significantly different β‐diversity than the whole tick from which they were derived. Our results demonstrate clear differences in both α‐ and β‐diversity among tick developmental stages and between tick organs and the tick as a whole. Furthermore, field‐acquired bacteria appear to be very important to the overall internal bacterial community of this tick species, with influence from the host bloodmeal appearing limited.     

Ingested particles reduce susceptibility of insect larvae to Bacillus thuringiensis

Susceptibility to Bacillus thuringiensis of mosquito and lepidopteran larvae is affected by feeding behaviour and nutritional value of the available food. Reduced mortality is attributed to feeding inhibition and dilution of the pathogen in the presence of nutritional and inert particles, which limit the amount of ingested toxin. These reasons are, however, not sufficient to explain the data presented here. Values of LC₅₀ (the concentration that kills 50% of exposed population) of B. thuringiensis subsp. israelensis (Berliner) against Aedes aegypti (L.) larvae and of B. thuringiensis subsp. kenyae (Berliner) against Spodoptera littoralis (Boisduval) larvae were about 20–217 and 2.3–44‐fold higher, respectively, in the presence of nutritional or biologically inert (non‐nutritional) particles than without. The number of B. thuringiensis spores in carcasses of B. thuringiensis ‐killed A. aegypti and S. littoralis larvae were between 1.9 and 5.6‐fold and between 8.5 and 12‐fold higher, respectively, in the presence of particles than without. In all cases, non‐nutritional particles better protected the exposed larvae than nutritious particles. We propose that another basic mechanism exists, that ingested particles protect midgut epithelial cells by covering their surface and thus preventing availability of the toxin to the gut receptors. Understanding the defence mechanisms of insects against B. thuringiensis toxicity may lead to improved pest management methods.     

Selection and characterization of Bacillus thuringiensis strains toxic against pyralid stored‐product pests

In this study, we present the selection and the characterization of Bacillus thuringiensis strains toxic against pyralid pests of stored products. Among 201 new B. thuringiensis strains isolated from different countries, two strains (BLB249 and BLB384) showed greater toxicity than the commercialized strain B. thuringiensis kurstaki HD1 against Ephestia kuehniella larvae. Morphological, molecular and biochemical investigations revealed that these strains were similar to HD1 but presented different cry gene content. Additional bioassays revealed that only strain BLB249 displayed higher toxicity than HD1 against Plodia interpunctella larvae. The study of Cry protoxin activation by midgut proteases of E. kuehniella and P. interpunctella larvae supported that higher toxicity of BLB249 and BLB384 strains compared to HD1 was not due to differential protoxin activation. Moreover, the toxic strains produced δ‐endotoxins and spores in similar amounts to HD1. Interestingly, the δ‐endotoxin production and the yield of BUPM26 strain were 32.87% and 35.12% greater than that of HD1. The potent insecticidal activities of BLB249 and BLB384 strains and the high level of δ‐endotoxin production by BUPM26 strain make them excellent candidates for use against E. kuehniella and P. interpunctella larvae.     

Survival of diverse Bacillus thuringiensis strains in gypsy moth (Lepidoptera: Lymantriidae) is correlated with urease production

Bacillus thuringiensis is an entomopathogenic bacterium that can kill a variety of pests, but seldom causes epizootics because it replicates poorly in insects. We have tested lepidopteran-toxic B. thuringiensis strains with diverse substrate utilization profiles for the ability to survive repeated passages through larvae of the gypsy moth, Lymantria dispar, without intervening growth on artificial media. These experiments have revealed a remarkable correlation between the production of urease by the bacteria and its ability to survive repeated passages through larvae. Of 26 urease-positive strains tested, 23 were capable of surviving five passages through gypsy moth larvae. In contrast, none of the 24 urease-negative strains tested survived to the 4th passage, with only three strains surviving to the 3rd passage. Selection of B. thuringiensis strains with phenotypic traits favoring replication in the environment, such as urease production, may improve their efficacy as biological control agents.     

Implications of a temperature increase for host plant range: predictions for a butterfly

Although changes in phenology and species associations are relatively well‐documented responses to global warming, the potential interactions between these phenomena are less well understood. In this study, we investigate the interactions between temperature, phenology (in terms of seasonal timing of larval growth) and host plant use in the polyphagous butterfly Polygonia c‐album. We found that the hierarchy of larval performance on three natural host plants was not modified by a temperature increase as such. However, larval performance on each host plant and temperature treatment was affected by rearing season. Even though larvae performed better at the higher temperature regardless of the time of the rearing, relative differences between host plants changed with the season. For larvae reared late in the season, performance was always better on the herbaceous plant than on the woody plants. In this species, it is likely that a prolonged warming will lead to a shift from univoltinism to bivoltinism. The demonstrated interaction between host plant suitability and season means that such a shift is likely to lead to a shift in selective regime, favoring specialization on the herbaceous host. Based on our result, we suggest that host range evolution in response to temperature increase would in this species be highly contingent on whether the population undergoes a predicted shift from one to two generations. We discuss the effect of global warming on species associations and the outcome of asynchrony in rates of phenological change.