Semiquinone and ascorbyl radicals in the gut fluids of caterpillars measured with EPR spectrometry

The biological activity of phenolic compounds ingested by caterpillars is commonly believed to result from their oxidation, although the products of oxidation have been well-characterized in only a few cases. The initial oxidation products of phenols (semiquinone or phenoxyl radicals) can be measured with electron paramagnetic resonance (EPR) spectrometry. In this study semiquinone radicals formed from tannic acid and gallic acid in the gut fluids of two species of caterpillars were measured. In Orgyia leucostigma, in which ingested phenols are not oxidized, semiquinone radicals were absent or at very low intensities. By contrast, in Malacosoma disstria, in which ingested phenols are oxidized, high semiquinone radical intensities were measured. In the absence of detectable levels of semiquinone radicals, ascorbyl radicals were detected in the EPR spectra instead. High molar ratios of ascorbate to phenols in an artificial diet produced ascorbyl radicals in the midgut fluids of both species, while diets containing low molar ratios produced semiquinone radicals. Similar results were obtained in M. disstria fed the leaves of red oak or sugar maple. The results of this study provide further evidence that ascorbate is an essential antioxidant that prevents the oxidation of phenols in the gut fluids of caterpillars, and demonstrate that EPR spectrometry is a valuable method for determining the degree of oxidative activation of phenols ingested by herbivorous insects.     

Influence of food and larval age on the defensive chemistry of Saturnia pyri

Scolus secretions and hemolymph of caterpillars of Saturnia pyri fed with two different foodplants (Crataegis monogyna, Prunus spinosa) were chemically analyzed and their chemical similarities determined. The secondary-compound patterns obtained for the two body fluids showed no significant differences when compared between the two groups of alternatively fed last-instar larvae. Thus, the composition of these fluids of full-grown caterpillars is not influenced by the larval diet. However, younger larvae on P. spinosa revealed a diversity of compounds differing significantly from that of larger caterpillars fed with either C. monogyna (both body fluids) or P. spinosa (hemolymph only). This indicates that, on the one hand, the hemolymph composition is adapted to the changing physiological requirements of the given instars whereas, on the other hand, the defensive mixtures remain unaltered in the late larval instars due to a constant spectrum of potential enemies.     

Fenton-type reactions and iron concentrations in the midgut fluids of tree-feeding caterpillars

Peroxides are formed in the midgut fluids of caterpillars when ingested tannins and other phenolic compounds oxidize. If these peroxides broke down in the presence of redox-active metal ions, they would form damaging free radicals (Fenton-type reactions). Elemental iron is present in relatively large amounts in leaves and artificial diets, but little is known about its concentration and redox state in midgut fluids, or the extent of Fenton-type reactions in these conditions. This study compared the levels of hydroxyl radicals and iron in the midgut fluids of two species of caterpillars: Orgyia leucostigma, in which phenol oxidation is limited, and Malacosoma disstria, in which phenol oxidation is more extensive. We tested two hypotheses: (1) higher levels of hydroxyl radicals are formed in M. disstria (consistent with the higher concentrations of hydrogen peroxide in this species), and (2) lower concentrations of iron are present in O. leucostigma (providing greater protection of its midgut fluids from oxidative damage). Hydroxyl radical levels increased greatly in M. disstria, but not in O. leucostigma, when they consumed a tannin-containing diet, supporting the first hypothesis. Protein oxidation was also significantly increased in the midgut fluids of M. disstria that ingested tannic acid, consistent with hydroxyl radical damage. Contrary to the second hypothesis, similar concentrations of iron (70 microM) remained in solution or suspension in both species of caterpillars on an artificial diet. Over 90% of this iron appeared to be in the reduced (catalytically active) state in both species. We conclude that tree-feeding caterpillars protect their midgut fluids from oxidative damage caused by Fenton-type reactions by limiting the formation of peroxides, rather than by limiting the availability of reduced iron.     

Competition between the gypsy moth, Lymantria dispar, and the northern tiger swallowtail, Papilio canadensis: interactions mediated by host plant chemistry, pathogens, and parasitoids

The gypsy moth, Lymantria dispar, and the northern tiger swallowtail, Papilio canadensis, overlap geographically as well as in their host ranges. Adult female swallowtails are incapable of distinguishing between damaged and undamaged leaves, and the opportunities for competition between these two species are numerous. We designed field and laboratory experiments to look for evidence of indirect competition between P. canadensis and L. dispar larvae. Swallowtail caterpillars were reared in the laboratory on leaves from gypsy-moth-defoliated and undefoliated trees to explore host-plant effects. We tested for pathogen-mediated interactions by rearing swallowtail larvae on both sterilized and unsterilized leaves from defoliated and undefoliated sources. In addition, we measured the effects of known gypsy moth pathogens, as well as gypsy moth body fluids, on the growth and survival of swallowtail larvae. Field experiments were designed to detect the presence of parasitoid-mediated competition, as well: we recorded parasitism of swallowtail caterpillars placed in the field either where there were no gypsy moth larvae present, or where we had artificially created dense gypsy moth populations. We found evidence that swallowtails were negatively affected by gypsy moths in several ways: defoliation by gypsy moths depressed swallowtail growth rate and survival, whether leaves were sterilized or not; sterilization significantly reduced the effect of defoliation, and gypsy moth body fluids proved lethal; and swallowtail caterpillars suffered significantly increased rates of parasitism when they were placed in the field near gypsy moth infestations.     

The Ancient Chemistry of Avoiding Risks of Predation and Disease

Illness, death, and costs of immunity and injury strongly select for avoidance of predators or contagion. Ants, cockroaches, and collembola recognize their dead using unsaturated fatty acids (e.g., oleic or linoleic acid) as “necromone” cues. Ants, bees, and termites remove dead from their nests (necrophoric behavior) whereas semi-social species seal off corpses or simply avoid their dead or injured (necrophobic behavior). Alarm and avoidance responses to exudates from injured conspecifics are widespread. This involves diverse pheromones, complex chemistry and learning. We hypothesized that necromones are a phylogenetically ancient class of related signals and predicted that terrestrial Isopoda (that strongly aggregate and lack known dispersants) would avoid body fluids and corpses using fatty acid “necromones.” Isopods were repelled by crushed conspecifics (blood), intact corpses, and alcohol extracts of bodies. As predicted, the repellent fraction contained oleic and linoleic acids and authentic standards repelled several isopod species. We further predicted a priori that social caterpillars (lacking known dispersants) would be repelled by their own body fluids and unsaturated fatty acids. Both tent caterpillars and fall webworms avoided branches treated with conspecific body fluid. Oleic and linoleic acids were also strongly avoided by both species. Necromone signaling appears widespread and likely traces to aquatic ancestors pre-dating the divergence of the Crustacea and Hexapoda at least 420 million years ago.     

黄野螟群体大小对幼虫个体生存和发育的影响

幼虫聚集取食是一些鳞翅目昆虫提高幼虫生长和存活的手段。通过对聚集取食的黄野螟Heortia vitessoides Moore幼虫在室内条件下进行饲养,探究黄野螟幼虫的群体数量大小(分别为30、60、90头幼虫)对幼虫体长、发育速度、达末龄(5龄)时的存活率的影响。分析发现在排除天敌捕食和食物缺乏的前提下,从3龄开始,大群体(90头)的体长显著大于小群体(30头),大群体的幼虫发育速度显著快于小群体,大群体对幼虫前4个龄期时的成活率没有显著提高,尽管大群体的存活率在均值上高于小群体,但是幼虫总体存活率在不同群体中差异不显著。黄野螟幼虫的聚集取食对幼虫的生长的促进作用明显,显著促进了幼虫的生长,加快了幼虫的发育。     

Pyrrolidonyl and pyridyl alkaloids in Lymantria dispar

The occurrence and metabolism of nicotine and related N-containing compounds in body fluids of the gipsy moth were addressed. Thin layer chromatographic studies clearly showed the simultaneous presence of GABA and 2-pyrrolidone but not of GABamide in the larval haemolymph and osmeterial secretion of Lymantria dispar as well as in the corresponding body fluids of the saturniids, Saturnia pavonia and Attacus atlas. Furthermore, feeding and injection experiments using alkylated precursors and combined gas chromatography/mass spectrometry gave evidence of the transformation of 2-pyrrolidone to nicotine and of nicotinic acid to nicotinamide in caterpillars of L. dispar. Based on these results, on the earlier described variation of the secondary-compound patterns of L. dispar during its development, and on literature data, metabolic pathways for the hitherto detected pyridyl and pyrrolidonyl alkaloids in Lymantriidae (and possibly Saturniidae) are proposed.     

Parasitism rate, parasitoid community composition and host specificity on exposed and semi-concealed caterpillars from a tropical rainforest

The processes maintaining the enormous diversity of herbivore—parasitoid food webs depend on parasitism rate and parasitoid host specificity. The two parameters have to be evaluated in concert to make conclusions about the importance of parasitoids as natural enemies and guide biological control. We document parasitism rate and host specificity in a highly diverse caterpillar-parasitoid food web encompassing 266 species of lepidopteran hosts and 172 species of hymenopteran or dipteran parasitoids from a lowland tropical forest in Papua New Guinea. We found that semi-concealed hosts (leaf rollers and leaf tiers) represented 84 % of all caterpillars, suffered a higher parasitism rate than exposed caterpillars (12 vs. 5 %) and their parasitoids were also more host specific. Semi-concealed hosts may therefore be generally more amenable to biological control by parasitoids than exposed ones. Parasitoid host specificity was highest in Braconidae, lower in Diptera: Tachinidae, and, unexpectedly, the lowest in Ichneumonidae. This result challenges the long-standing view of low host specificity in caterpillar-attacking Tachinidae and suggests higher suitability of Braconidae and lower suitability of Ichneumonidae for biological control of caterpillars. Semi-concealed hosts and their parasitoids are the largest, yet understudied component of caterpillar—parasitoid food webs. However, they still remain much closer in parasitism patterns to exposed hosts than to what literature reports on fully concealed leaf miners. Specifically, semi-concealed hosts keep an equally low share of idiobionts (2 %) as exposed caterpillars.     

Material affects attack rates on dummy caterpillars in tropical forest where arthropod predators dominate: an experiment using clay and dough dummies with green colourants on various plant species

Predation can be one of the key factors that determine abundance in insect herbivore communities, and drive evolution of body size, and anti‐predator traits, including crypsis. Population dynamics and selection pressures will depend on the identity of dominant predators in the system, and these may vary substantially among habitats. Arthropods emerge as chief predators on caterpillars in the understorey of non‐montane tropical forest, whereas birds dominate elsewhere. In a tropical forest in Uganda, Africa, we evaluated marks on dummy caterpillars that differed in size, material (clay vs. dough), colourant, and plant species on which dummy caterpillars were exposed. We included live caterpillars to estimate the extent to which studies using artificial caterpillars reflect actual levels of predation. Ants and wasps were the most important damagers of dummy caterpillars, whereas bug and beetle damage was very rare, and no bird or small mammal damage was observed. Daily attack rates did not differ significantly from apparent mortality of live caterpillars (daily mortality = 12.1%), but dummy caterpillars made from dough were attacked more frequently (daily attack rate = 18.4%) than those from clay (daily attack rate = 6.9%). Caterpillars of different colour and size, and caterpillars exposed on different plant species had the same chances to be predated. This is in contrast to results from temperate area studies where birds dominate and are not affected by dummy caterpillar material, but prefer larger caterpillars. Our results are consistent with dominant predators on tropical forest caterpillars being invertebrates that are more chemically than visually oriented, so that: (1) material used for dummy caterpillars is important, (2) background matching is relatively unimportant, and (3) being large may have less of a cost. These patterns in predation might facilitate polyphagy and evolution of large body size in tropical Lepidoptera.     

Intraspecific variation in aspen phytochemistry: effects on performance of gypsy moths and forest tent caterpillars

Individual quaking aspen trees vary greatly in foliar chemistry and susceptibility to defoliation by gypsy moths and forest tent caterpillars. To relate performance of these insects to differences in foliar chemistry, we reared larvac from egg hatch to pupation on leaves from different aspen trees and analyzed leaf samples for water, nitrogen, total nonstructural carbohydrates, phenolic glycosides, and condensed tannins. Larval performance varied markedly among trees. Pupal weights of both species were strongly and inversely related to phenolic glycoside concentrations. In addition, gypsy moth performance was positively related to condensed tannin concentrations, whereas forest tent caterpillar pupal weights were positively associated with leaf nitrogen concentrations. A subsequent study with larvae fed aspen leaves supplemented with the phenolic glycoside tremulacin confirmed that the compound reduces larval performance. Larvae exhibited increased stadium durations and decreased relative growth rates and food conversion efficiencies as dietary levels of tremulacin increased. Differences in performance were more pronounced for gypsy moths than for forest tent caterpillars. These results suggest that intraspecific variation in defensive chemistry may strongly mediate interactions between aspen, gypsy moths and forest tent caterpillars in the Great Lakes region, and may account for differential defoliation of aspen by these two insect species.     

Comparative and experimental studies on the relationship between body size and countershading in caterpillars

Countershading is a gradient of colouration in which the illuminated dorsal surfaces are darker than the unilluminated ventral surface. It is widespread in the animal kingdom and endows the body with a more uniform colour to decrease the chance of detection by predators. Although recent empirical studies support the theory of survival advantage conferred by countershading, this camouflage strategy has evolved only in some of the cryptic animals, and our understanding of the factors that affect the evolution of countershading is limited. This study examined the association between body size and countershading using lepidopteran larvae (caterpillars) as a model system. Specifically, we predicted that countershading may have selectively evolved in large-sized species among cryptic caterpillars if (1) large size constrains camouflage which facilitates the evolution of a trait reinforcing their crypsis and (2) the survival advantage of countershading is size-dependent. Phylogenetic analyses of four different lepidopteran families (Saturniidae, Sphingidae, Erebidae, and Geometridae) suggest equivocal results: countershading was more likely to be found in larger species in Saturniidae but not in the other families. The field predation experiment assuming avian predators did not support size-dependent predation in countershaded prey. Collectively, we found only weak evidence that body size is associated with countershading in caterpillars. Our results suggest that body size is not a universal factor that has shaped the interspecific variation in countershading observed in caterpillars.     

Effects of environmental humidity on the survival and development of pine caterpillars, Dendrolimus tabulaeformis (Lepidoptera: Lasiocampidae)

The pine caterpillar, Dendrolimus tabulaeformis is one of the most important pests on Pinus tabulaeformis and other pine species in North China. In the present study, effects of relative humidity (RH) on the development and survival of pine caterpillars and soil moisture (SM) on their diapausing larvae were investigated. Low RH (20%) deferred the development of eggs and larvae, reduced egg hatching and larval surviving compared to 40%, 60% and 80% RH. Both low (20%) and high (100%) RH reduced egg hatching, but only 20% RH deferred the development of larvae, prolonged developmental duration and reduced the body mass and body length of larvae. The SM influenced the survival of diapausing larvae significantly. The dry treatment significantly reduced the supercooling points (SCPs), whereas increased the mortality and reduced body mass from 56.9 to 36.5 mg and body water content from 78% to 63% after 2 weeks' exposure. Therefore, higher RH is more favorable for the development of early instars and survival of diapausing larvae of the pine caterpillars.     

Larvae of Maculinea rebeli, a large-blue butterfly and their Myrmica host ants: patterns of caterpillar growth and survival

Maculinea rebeli caterpillars spend their final instar as specific parasites of colonies of the ant Myrmica schencki . This paper describes 14 experiments in which 604 caterpillars were reared with six species of Myrmica . About 40% of caterpillars died during an initial period of integration: survival was significantly greater among the larger caterpillars, in M. schencki nests, and in nests that had ant-brood present. The growth of the survivors was extremely variable. After three weeks they had gained 2–18 times their initial body weight and appeared to belong to two distinct types: fast and slow developers. Only 11% of caterpillars died during the next 37 days of growth, before a fall in temperature to below c. 14 C caused them to overwinter. By then, the caterpillars weighed from 5–90 mg (mean 22 mg).
Caterpillars of all weights lost 33% of their mass during winter, and 8% died, before rising temperatures caused growth to resume in spring. Ofthe 363 that survived winter, 44% died during a period of spring growth and 12% pupated after about seven weeks. The latter came mainly from the largest caterpillars before winter and pupal size (mean weight 81 mg) was also related to prewinter caterpillar size. The remaining 44% of post-winter caterpillars continued to grow slowly and then entered another quiescent phase and were still alive after one year in the nest. A small number of these pupated in the second year, an average of 404 days after adoption.
It is calculated that an average-sized Myrmica schencki colony of 350 workers can produce 4–5 adult butterflies; this laboratory result agrees well with field observations. The results are discussed in the light of a previous behavioural study.     

Quantitative analysis of dipeptidyl peptidase inhibitor P32/98 and its main metabolite in rat, dog, mouse, monkey, human plasma and human urine using liquid chromatography-tandem mass spectrometry: application to pharmacokinetic evaluation

A sensitive, specific and robust assay was developed for the simultaneous determination of the oral antidiabetic drug candidate P32/98 and its main metabolite P57/99 in different biological fluids using LC-MS/MS in the atmospheric pressure chemical ionization (APCI) positive mode. Both analytes were isolated from the biological matrices by solid phase extraction using a strong cation exchanger. This assay was successfully cross-validated for rat, dog, mouse, monkey, human plasma and human urine. The pre-study validation results, as well as the in-study quality control (QC) data obtained, demonstrate the feasibility of the assay for pharmacokinetic evaluation of the compounds in different species and confirm the robustness of the assay for routine use.     

Evolution and losses of spines in slug caterpillars (Lepidoptera: Limacodidae)

Larvae of the cosmopolitan family Limacodidae, commonly known as “slug” caterpillars, are well known because of the widespread occurrence of spines with urticating properties, a morpho‐chemical adaptive trait that has been demonstrated to protect the larvae from natural enemies. However, while most species are armed with rows of spines (“nettle” caterpillars), slug caterpillars are morphologically diverse with some species lacking spines and thus are nonstinging. It has been demonstrated that the evolution of spines in slug caterpillars may have a single origin and that this trait is possibly derived from nonstinging slug caterpillars, but these conclusions were based on limited sampling of mainly New World taxa; thus, the evolution of spines and other traits within the family remains unresolved. Here, we analyze morphological variation in slug caterpillars within an evolutionary framework to determine character evolution of spines with samples from Asia, Australia, North America, and South America. The phylogeny of the Limacodidae was reconstructed based on a multigene dataset comprising five molecular markers (5.6 Kbp: COI, 28S, 18S, EF‐1α, and wingless) representing 45 species from 40 genera and eight outgroups. Based on this phylogeny, we infer that limacodids evolved from a common ancestor in which the larval type possessed spines, and then slug caterpillars without spines evolved independently multiple times in different continents. While larvae with spines are well adapted to avoiding generalist predators, our results imply that larvae without spines may be suited to different ecological niches. Systematic relationships of our dataset indicate six major lineages, several of which have not previously been identified.     

Studies on Entomopathogenic Fungi Isolated from Dead Pine Caterpillars, Dendrolimus spectabilis

ABSTRACT ABSTRACT Entomopathogenic fungi isolated from pine caterpillars, as biological control agents were evaluated against the 5th instar larvae of silkworms, bombyx mori . The body weights of silkworm larvae were reduced by entomopathogenic fungi. Virulence of the spores isolated from the insects was more stronger than that of the spores isolated from media. LD₅₀ value of the pathogen was 6,464x10³ spores/ml. Entomopathogenic fungi, Beauveria , isolated from dead pine caterpillars was possible agents for use in microbiological control.     

Description, seasonal morphological variation, and molecular identification of Paraxanthus barbiger megalopae obtained from the natural environment

Larval identification represents a powerful tool for detailed studies on recruitment and population dynamics in marine invertebrates. However, intra-specific morphological variation can become a serious limitation for the correct identification at species level. High morphological variation can be expected in species with continuous breeding periods because larvae are exposed to seasonal fluctuations in physical and biological factors during their development in the plankton. We describe, for the first time, the megalopae of Paraxanthus barbiger, one of the most common and abundant brachyuran crabs along the coast of Chile. To validate larvae identification, the 16S rRNA gene was sequenced from both megalopae and adults, and was compared with sequences of three sympatric species. In addition, size, body shape, and appendage setation pattern variations were analyzed with a year-round sampling scheme. The results demonstrated high seasonal phenotypic plasticity in size. Despite these differences, certain conservative characteristics exist which can be very useful for identification at species level.     

Buoyancy studies and microscopy of skin and subdermal extracellular matrix of the antarctic snailfish,Paraliparis devriesi

The Antarctic snailfish Paraliparis devriesi (Liparididae) occupies an epibenthic habitat at a depth of 500–650 m in the subzero waters of McMurdo Sound, Antarctica. Although lacking a swim bladder, this species is neutrally buoyant through the combined effects of reduced skeletal ossification and expansion of a watery gelatinous subdermal extracellular matrix (SECM). The SECM serves as a low density buoyancy agent. It comprises a mean of 33.8% of the body weight, the largest known proportion of any adult fish. The SECM is loose connective tissue dominated by ground substance consisting of glycosaminoglycans, especially hyaluronic acid, and immobilized water. Although the SECM is 97% water, elevated levels of NaCl provide an osmotic strength greater than that of other body fluids. Only small amounts of antifreeze compounds have been identified in P. devriesi; therefore, freezing avoidance may result from the combined effects of antifreezes and the elevated osmolality of body fluids. The skin overlying the SECM is thin (85–200 μm) and loose, and unlike most other fishes, the epidermis is several times thicker than the dermis. The midepidermis, has a distinctive layer of vacuolated club cells of unknown function. Light and electron microscopy indicate that the skin is unspecialized for protection against entry of ice. © 1994 Wiley-Liss, Inc.     

Comparing the physiological effects and function of larval feeding in closely‐related endoparasitoids (Braconidae: Microgastrinae)

Abstract The larvae of most endoparasitoid wasps consume virtually all host tissues before pupation. However, in some clades, the parasitoid larvae primarily consume haemolymph and fat body and emerge through the side of the host, which remains alive and active for up to several days. The evolutionary significance of this host‐usage strategy has attracted attention in recent years. Recent empirical studies suggest that the surviving larva guards the parasitoid broods against natural enemies such as predators and hyperparasitoids. Known as the ‘usurpation hypothesis’, the surviving larvae bite, regurgitate fluids from the gut, and thrash the head capsule when disturbed. In the present study, the ‘usurpation hypothesis’ is tested in the association involving Manduca sexta, its parasitoid Cotesia congregata, and a secondary hyperparasitoid Lysibia nana. Percentage parasitoid survival is higher and hyperparasitism lower when cocoons of C. congregata are attached to the dorsum of M. sexta caterpillars. Fat body contents in several associations involving solitary and gregarious parasitoids feeding on haemolymph and fat body are also compared. The amount of fat body retained in parasitized caterpillars varies considerably from one association to another. In M. sexta and Pieris brassicae, considerable amounts of fat body remain after parasitoid emergence whereas, in Cotesia kariyai and Cotesia rufricus, virtually all of the fat body is consumed by the parsasitoid larvae. The length of post‐egression survival of parasitized caterpillars differs considerably in several tested associations. In Pseudeletia separata, most larvae die within a few hours of parasitoid emergence whereas, in M. sexta, parasitized larvae live up to 2 weeks after parasitoid emergence. Larvae in other associations parasitized by gregarious and solitary endoparasitoids live for intermediate periods. The results are discussed in relation to the adaptive significance of different feeding strategies of immature parasitoids and of the costs and benefits of retaining the parasitized caterpillar in close proximity with the parasitoid cocoons.     

Can plants mediate the humoral immunity and biochemical metabolism of entomopathogen‐infected caterpillars?

Plant‐insect herbivore‐entomopathogen interactions are one of the hot topics in biological control and humoral immunity, and biochemical metabolism are important responses of herbivores to pathogen infection. Entomopathogens are key biocontrol agents of caterpillars, but how plants affect the responses of caterpillars to these organisms is not well understood. We studied hormonal immunity (lysozyme and phenoloxidase activities) and biochemical metabolism (total protein and lipid contents) of Beauveria bassiana‐infected beet armyworm (Spodoptera exigua) larvae that feed on five different host plants (soya bean, Chinese cabbage, edible amaranth, water convolvulus and pepper). Results indicated that plant species differentially affected lysozyme and phenoloxidase activity and lipid content, but had no effect on protein content of pathogen‐infected caterpillars. Both lysozyme and phenoloxidase activities were generally higher in entomopathogen‐infected larvae that feed on edible amaranth or water convolvulus compared with the other three plants from days 1 to 5 after treatment. Plant species did not affect in regular changes during the 5 days in the lipid content of infected or non‐infected caterpillars. Our study reveals that plants fail to affect the biochemical metabolism but plants can mediate the humoral immunity of caterpillars to defend against pathogens. This study provides insight into plant‐mediated effects on the response of herbivores to pathogens.