Relationship between three intensity levels of Toxocara canis larvae in the brain and effects on exploration, anxiety, learning and memory in the murine host

Outbred LACA mice were administered low (100 ova), medium (1000 ova), high (3000 ova) and trickle (4x250 ova) doses of Toxocara canis ova and the effect of infection was examined with respect to the number of larvae recovered from the brain and their behaviour. Recovery of larvae from the brain was generally low with the % recovery expressed in terms of the total dose administered being highest for the 3000 dose (6.1%) and 1000 dose (6%), followed by the 100 (4.4%) and trickle (3.5%) doses. The variation in larval recoveries was large between individual mice receiving similar doses. The level of infection in the brain was lower in mice receiving a multiple as opposed to an equivalent single dose of ova. Mice were then divided into three larval intensity groupings based upon the number of larvae recovered from their brain. The ranges for the groups were as follows: low intensity group, 0-15 larvae; moderate intensity group, 27-55 larvae; high intensity group, 66-557 larvae. Three behavioural tests were carried out on control and infected mice. Exploration and response to novelty was examined using a 'T' maze and learning was investigated by means of a water-finding task. Anxiety was measured using an elevated plus maze apparatus. Infected mice were less explorative and less responsive to novelty in the 'T' maze and this was particularly pronounced for the heavily infected mice. In the elevated plus maze, infected mice displayed reduced levels of anxiety to aversive and exposed areas of the maze, particularly in the case of the moderate and high intensity mice. There was evidence for impaired learning ability in the water task apparatus for moderate and high intensity mice. In general, the effects of infection on behaviour were more pronounced in the moderate and high intensity groups compared to the low intensity group.     

Prevalence and intensity of Angiostrongylus cantonensis in freshwater snails in relation to some ecological and biological factors

The purpose of the study was to record different intermediate hosts of A. cantonensis and to determine the infection prevalence and intensity of this parasite in freshwater snails in relation to some ecological and biological factors. The study was conducted at Al-Salam irrigation Canal and Al-Abtal village (north Sinai) for one year, from March 2004 to February 2005. Thirteen species of freshwater snails of nine families were examined for A. cantonensis infection. Six species were found infected with A. cantonensis larvae. These species were L. carinatus, C. bulimoides, C. cyclostomoides, B. alexandrina, L. natalensis and M. tuberculta. The infection prevalence of A. cantonensis in the examined snails ranged from 0.63 to 2.24%. L. carinatus snail had the highest prevalence, mean abundance and mean intensity of A. cantonensis infection. Positive correlations were found between both prevalence and mean abundance of A. cantonensis and host size in L. carinatus and M. tuberculata. Negative correlations were detected between salinity and prevalence, mean abundance and mean intensity of larvae of A. cantonensis. The results demonstrated seasonal and spatial variation in the prevalence, mean abundance and mean intensity of infection among examined snails. In this study, A. cantonensis larvae were found in a wide range of freshwater snails and M. tuberculata snail was recorded as a new intermediate host for the first time. In conclusion, further investigations in other areas and controlled laboratory experiments of infection approaches are required to evaluate the possible threat of this parasite on humans.     

Temporal occurrence of third-stage larvae of Elaeophora schneideri in Tabanus lineola hinellus on South Island, South Carolina

The occurrence of third-stage larvae of the arterial worm (Elaeophora schneideri) in populations of the horse fly, Tabanus lineola hinellus, was studied on South Island, Georgetown County, South Carolina. Over the period from mid-April to mid-October 1982, horse flies had a bimodal pattern of abundance with peak populations in June and September. During individual bimonthly horse fly collections, the prevalence of infection of T. l. hinellus ranged from 0 to 1.23%. Prevalence of infected horse flies was biphasic with peaks in mid-May (1.23%) and mid-August (1.22%), 2 to 4 wk prior to peaks in horse fly populations. The intensity of infection of T. l. hinellus increased as time progressed and was highest in late summer. This increase resulted in greater recovery of infective larvae during August-September (mean intensity = 25) than in May-June (mean intensity = 4). Both prevalence and intensity of infection of T. l. hinellus were low compared to primary intermediate hosts of E. schneideri in the western U.S.     

The effect of some biological and physical factors on infection of Biomphalaria glabrata with Angiostrongylus cantonensis.

Several biological and physical factors which may influence infection of Biomphalaria glabrata snails with the first stage larvae of Angiostrongylus cantonensis were studied. These factors were: the size of snails, the number of first stage larvae to which snails were exposed, the age of larvae, individual exposure compared with mass exposure of snails, the length of exposure period and the effect of temperature and light. The results showed that young snails, 2 mm in diameter, became infected with significantly smaller numbers of third stage larvae than larger snails (4, 8, 12 and 16 mm). No significant differences in the intensity of infection were evident between the larger size groups. The number of third stage larvae recovered from snails was directly related to the number of first stage larvae to which the snails were exposed. The mean percentage recovery per snail was more or less constant regardless of the infective dose. First stage larvae showed a slight reduction in their survival rate within 7 and 4 days, at 24 degrees C and 26 degrees C respectively, after which a sharp decrease in their survival rate occurred. However, the infectivity of larvae was progressively reduced from the second day at these two temperatures. The mean intensity of infection in snails was independent of whether the infection was by mass or individual exposure. The average number of first stage larvae entering a snail was greatest during the first half hour of exposure, this decreased considerably during the second half hour, and thereafter the number of larvae which entered a snail was low. It was concluded that 26 degrees C was the optimal temperature for infection and that the presence or absence of light had no effect on the infection.     

Constraints on parasite fecundity and transmission in an insect-STD system

Parasites that are sexually transmitted (causing sexually transmitted diseases, or STDs) can have important effects on host population dynamics, but we know almost nothing for such parasites about constraints on fecundity and transmission. In this study, we have examined the effect of two potentially important constraints in one of the few empirically well-studied animal-STD systems, the ladybird, Adalia bipunctata , and its sexually transmitted mite, Coccipolipus hippodamiae . Using a factorial design, we manipulated: (i) within-host competition, by varying infection intensity; and (ii) host condition, by introducing dietary stress. Infection with C . hippodamiae significantly reduced ladybird survival whether or not diet was restricted, and restricting diet led to reduced survival regardless of infection status. Increased infection intensity and reduced host condition (dietary stress) both independently constrained per capita rates of parasite egg production and the development of infective larvae. Furthermore, when host condition was compromised, significantly fewer larvae were transmitted per adult mite during copulation. The effect of infection intensity on per mite transmission was more complex: there was no significant effect when hosts were fed normally, but when the ladybirds were nutritionally stressed higher infection intensity was associated with a slight increase in the numbers that were transmitted (despite the fact that mite fecundity was reduced under these conditions). These results indicate that host condition and within-host competition may both play an important role in shaping the epidemiology of the A . bipunctata – C . hippodamiae system, by influencing the parasite's basic reproductive ratio (R₀) and the rate of epidemic spread. Our data also extend general insights into STD ecology, by highlighting the importance of constraints on disease dynamics that are likely to be widespread.     

Whole-body analysis of a viral infection: vascular endothelium is a primary target of infectious hematopoietic necrosis virus in zebrafish larvae

The progression of viral infections is notoriously difficult to follow in whole organisms. The small, transparent zebrafish larva constitutes a valuable system to study how pathogens spread. We describe here the course of infection of zebrafish early larvae with a heat-adapted variant of the Infectious Hematopoietic Necrosis Virus (IHNV), a rhabdovirus that represents an important threat to the salmonid culture industry. When incubated at 24 °C, a permissive temperature for virus replication, larvae infected by intravenous injection died within three to four days. Macroscopic signs of infection followed a highly predictable course, with a slowdown then arrest of blood flow despite continuing heartbeat, followed by a loss of reactivity to touch and ultimately by death. Using whole-mount in situ hybridization, patterns of infection were imaged in whole larvae. The first infected cells were detectable as early as 6 hours post infection, and a steady increase in infected cell number and staining intensity occurred with time. Venous endothelium appeared as a primary target of infection, as could be confirmed in fli1:GFP transgenic larvae by live imaging and immunohistochemistry. Disruption of the first vessels took place before arrest of blood circulation, and hemorrhages could be observed in various places. Our data suggest that infection spread from the damaged vessels to underlying tissue. By shifting infected fish to a temperature of 28 °C that is non-permissive for viral propagation, it was possible to establish when virus-generated damage became irreversible. This stage was reached many hours before any detectable induction of the host response. Zebrafish larvae infected with IHNV constitute a vertebrate model of an hemorrhagic viral disease. This tractable system will allow the in vivo dissection of host-virus interactions at the whole organism scale, a feature unrivalled by other vertebrate models.     

Changes in transmission of Baylisascaris procyonis to intermediate hosts as a function of spatial scale

Physical changes in landscapes alter the abundance and distribution of species. Higher-order effects can occur when changes in ecological processes result in altered interspecific interactions and subsequent changes in a species' abundance or persistence. Baylisascaris procyonis , a roundworm parasite of raccoons ( Procyon lotor ), is pathogenic to numerous small vertebrates that serve as intermediate hosts, including white-footed mice ( Peromyscus leucopus ). Raccoons have responded positively to agriculturally induced changes in landscapes, with potential consequences for intermediate hosts of B . procyonis . We examined white-footed mice from a homogeneous, predominantly forested landscape in south-central Indiana and a heterogeneous, predominantly agricultural landscape in northwestern Indiana for presence of larval B . procyonis . We compared prevalence of infection, intensity of infection, and average number of larvae per mouse between the landscapes, and among forest patches within the highly fragmented agricultural landscape. Prevalence, intensity of infection, and average number of larvae were significantly higher in the highly fragmented landscape. Within the agricultural landscape, regression models predicted probability of infection, intensity of infection, and average number of larvae per mouse per patch as functions of forest patch area and isolation. We conclude that positive responses of raccoons to agriculturally induced fragmentation of forests have resulted in increased encounter rates between white-footed mice and infective stages of B . procyonis between and within landscapes, resulting in increased transmission of the parasite to intermediate hosts.     

Movement of Pomphorhynchus bulbocolli larvae from the hemocoel to the peripheral circulation of Gammarus pseudolimnaeus

Acanthors and early acanthellae of Pomphorhynchus bulbocolli were observed in the peripheral circulation of experimentally infected laboratory-reared Gammarus pseudolimnaeus. This has not previously been reported for larval P. bulbocolli during development in the intermediate host. The timing of larval movement from hemocoel to vessels and sinuses was related to intensity of infection. In an experimental group with a low mean intensity of infection, the movement of larval P. bulbocolli into the peripheral circulation occurred later (9 days postfeeding) than in a group with a high mean intensity of infection (2 days postfeeding). Larvae were observed in the peripheral circulation for a longer period of time in amphipods from the group with the high mean intensity of infection. Dead and slightly melanized acanthors and early acanthellae were present in the hemocoel at the time living larvae moved into the peripheral circulation. Only 1 incidence of a hemocytic response to the larvae was observed in the first 20 days postfeeding.     

Spatio-temporal dynamics of the parasitic nematode Anguillicola crassus in Flanders, Belgium

Despite Egusa's earlier warning of the damage that the parasitic nematode Anguillicola crassus could inflict on the European eel Anguilla anguilla, its introduction in Europe was a fact in the early 1980s. Based on an elaborate dataset on Anguillicola crassus infection of 11 river catchments, this paper presents the results of a detailed study on the dispersal of the parasite in Flanders, Belgium, and the host-parasite relationship. In addition, data from 1986 and 1997 are used for comparative purposes, providing a perspective on the temporal infection pattern over 15 yr. The presence of A. crassus in Flanders was first discovered in 1985; 2 yr later a survey revealed a prevalence of 34.1% and a mean infection intensity of 5.5, based on adult nematodes only, and 10 yr later the parasite was present at all 11 sites sampled. Prevalence had increased to 62.5 % but the mean infection intensity had decreased to 3.9 adults per infected eel. Finally, in the year 2000, a third study revealed that A. crassus was present in 139 of 140 investigated sites; a further increase in prevalence to 68.7% and a decrease in mean infection intensity to 3.4 adults per infected eel was observed. When all larval stages were taken into account, mean prevalence amounted to 88.1% and mean intensity to 5.5 adults. The high infection level in Flanders is thought to be the result of restocking with glass eel and yellow eel, both of which are susceptible to A. crassus. The general infection parameters were similar in all 11 river catchments. It is possible that in Flanders both prevalence and mean infection intensity are stabilizing due to density-dependent regulation of the parasite infrapopulation. Fibrotic swimbladder walls were observed, mainly in large eels, and 20% of the total number of nematodes consisted of encapsulated larvae in the surveys of 1997 and 2000; 8 cases of swimbladder regeneration were observed.     

Trichinella spiralis in the black bear (Ursus americanus) of Pennsylvania: distribution, prevalence and intensity of infection

Samples of tongue or diaphragm from 2,056 black bears harvested in Pennsylvania during the 1981-1983 hunting seasons were examined for larvae of Trichinella spiralis by peptic digestion. Sixteen males and 21 females were infected. The overall prevalence of infection was 1.8%. Infected animals were distributed widely throughout the range of the bear in Pennsylvania. In samples from infected bears, the geometric mean density of muscle larvae was 7.8 per g of tissue (LPG). There were neither sex- nor age-related differences in prevalence or intensity of infection. Virtually all bears harvested in Pennsylvania are consumed as food, which often is shared widely among hunters, their friends and relatives. Furthermore, high densities of larvae occurred in some bears (i.e., 300, 348, 465, 512, 555, and 912 LPG). Thus, a basis for potential, single-source outbreaks of severe human trichinosis exists.     

Vertical transmission of Nosema fumiferanae (Microsporidia: Nosematidae) and consequences for distribution, post-diapause emergence and dispersal of second-instar larvae of the spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae)

We examined vertical transmission of Nosema fumiferanae in the eastern spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae), and how it affects overwintering distribution and survival and spring emergence and dispersal of second-instar larvae in outbreak populations. Females containing 5.0 x 10(5) spores or more consistently produced 100% infected progeny. Transmission efficiency was still 50% at burdens as low as 0.2 x 10(5) spores per moth. Infection intensity in offspring increased with maternal spore load but became highly variable above 25 x 10(5) spores per female. Nosema multiplied in second instars for at least 1 month after they entered dormancy, regardless of temperature (2 degrees C versus 21 degrees C). Infection did not affect the distribution of overwintering larvae in a white spruce canopy. Dormancy survival between late-summer and the following spring was lower in families from infected females and was negatively correlated with larval infection intensity. Infection delayed larval emergence from hibernacula in the spring and resulted in delayed dispersal of emerged larvae, at least when parasite prevalence and infection intensities were high. Infected larvae were less successful in establishing feeding sites after dispersal. Our results underscore the potential of Nosema infection to negatively affect processes early in the budworm life cycle.     

Histopathological appearances in primary and secondary infections with Strongyloides ratti in mice

Dawkins H. J. S., Muir G. M. & Grove D. I. 1981. Histopathological appearances in primary and secondary infections with Strongyloides ratti in mice. International Journal for Parasitology11: 97–103. The histological appearances of the skin, lungs and small intestines of mice with primary and secondary infections with S. ratti are described. When the skins of mice with a primary infection were examined, larvae were seen scattered throughout the dermis. An inflammatory reaction of neutrophils and eosinophils was first noted around larvae 12 h after infection. By 48 h, mononuclear cells were prominent. The intensity of the inflammatory reaction gradually increased to a maximum on the fifth day and the larvae were destroyed. Very few larvae were seen in the lungs; those observed were located in the alveolar spaces and were not surrounded by an inflammatory infiltrate. Worms in the small intestines were found mostly in the crypts of Leiberkuhn, and were probably located within the epithelial layer; there was no significant villous atrophy or cellular infiltration. Marked differences were found in the tissues of mice with secondary infections. In the skin, oedema and neutrophils and eosinophils were seen around worms as early as 2 h after infection. By 24 h after infection, there was a mixed inflammatory infiltrate and worms were undergoing disintegration. Larvae in the lungs were surrounded by polymorphonuclear and mononuclear cells 48 h and 72 h after infection and the engulfed larvae were undergoing lysis. Only a few worms were seen in the intestines of mice with a secondary infection; the histological appearances were similar to that found in animals with primary infections. It is suggested that the rapid development of an oedematous reaction in the skins of immune mice may facilitate the entry of larvae into the bloodstream and that inflammatory cells destroy many larvae in the lungs of immune mice.     

Anisakis simplex larvae: infection status in marine fish and cephalopods purchased from the Cooperative Fish Market in Busan, Korea

The infection status of marine fish and cephalopods with Anisakis simplex third stage larva (L3) was studied over a period of 1 year. A total of 2,537 specimens, which consisted of 40 species of fish and 3 species of cephalopods, were purchased from the Cooperative Fish Market in Busan, Korea, from August 2006 to July 2007. They were examined for A. simplex L3 from the whole body cavity, viscera, and muscles. A. simplex L3 were confirmed by light microscopy. The overall infection rate reached 34.3%, and average 17.1 larvae were parasitized per infected fish. Fish that recorded the highest infection rate was Lophiomus setigerus (100%), followed by Liparis tessellates (90%), Pleurogrammus azonus (90%), and Scomber japonicus (88.7%). The intensity of infection was the highest in Gadus macrocephalus (117.7 larvae per fish), followed by S. japonicus (103.9 larvae) and L. setigerus (54.2 larvae). Although abundance of A. simplex L3 was not seasonal in most of the fish species, 10 of the 16 selected species showed the highest abundance in February and April. A positive correlation between the intensity of L3 infection and the fish length was obvious in S. japonicus and G. macrocephalus. It was likely that A. simplex L3 are more frequently infected during the spring season in some species of fish. Our study revealed that eating raw or undercooked fish or cephalopods could still be a source of human infection with A. simplex L3 in Korea.     

Changes in worm burden, haematological and serological response in rats after single and multiple Angiostrongylus cantonensis infections.

Thirteen groups of rats were first sensitized with single or double doses of 5--30 third-stage larvae of Angiostrongylus cantonensis, followed by a challenge infection with 100 larvae at various periods after the primary infection. Seven other groups of rats receiving only the sensitizing infection served as the controls. In all the sensitized rats, a significantly (p less than 0.05) smaller mean number of adult worms was found established in the challenge infection as compared to the control. The frequency of the sensitizing dose and timing of the challenge infection appeared to influence the intensity of the host's response. There was no conclusive evidence to indicate that the immune response could retard the growth, development, or sex ratios of the worms established in subsequent infections. A positive haemagglutinating antibody response was first observed in some rats as early as four weeks post-infection with 100 larvae when the worms began migrating from the brain to the lungs. The antibody response and eosinophilia were most pronounced during the oviposition of the female worms and hatching of first-stage-larvae. Changes in white blood cell, lymphocyte, and neutrophil counts were also followed in some groups.     

Eicosanoid biosynthesis inhibitors influence mortality of Pieris brassicae larvae co-injected with fungal conidia

Influence of fungal species (conidia spores) on mortality of Pieris brassicae larvae differed when injected into the larvae. The effects of B. bassiana (ARSEF-1151) were expressed in a conidial dose-dependent manner on mortality of the larvae. An increased and faster mortality of the larvae followed B. bassiana (ARSEF-1151) infection when the spores were co-injected with the eicosanoid biosynthesis inhibitors (dexamethasone, naproxen, phenidone, esculetin). These compounds express different modes of action. These lethal effects were reversed when dexamethasone was injected with eicosanoid precursor arachidonic acid (20:4n-6). Nodulation is the predominant cellular reaction to bacterial and fungal injection in insects. Injection of each of five fungal species showed that nodulation intensity varies according to infecting fungal species. These findings support the idea that virulent effects of entomopathogenic, fungal species can be increased when P. brassicae immune systems are suppressed.     

Effects of age and splenectomy on heavy infection of Angiostrongylus cantonensis in rats

This study was designed to determine the effects of age and the role of spleen in rats with heavy Angiostrongylus cantonensis infection. Young rats (8 weeks) infected with 100 larvae were found to have significantly higher worm recovery rate (75.0±6.6%) than the adult (6 months) (55.7±1.5%) and the aging ones (13 months) (57.6±4.0%). Moreover, the recovery rate in adult rats with 400 larvae (33.6±10.67%) was significantly lower than those with 100 larvae (55.7±1.53%) or 200 larvae (53.3±5.4%). The splenectomized young rats with 100 larvae had a significantly higher recovery rate (84.3±2.5%) than the intact (75.0±6.6%) or sham splenectomized ones (74.4±3.8%). Although titers of antibody against A. cantonensis increased with time, those against young adults were significantly higher before week 4 whereas those against adult worms become significantly higher since week 4. Titers in the splenectomized rats were also found to be significantly lower than those in the intact ones. These finding indicate that young rats are more susceptible to A. cantonensis. Crowding effect may occur in rats with heavy infections. The effects of splenectomy on the host are independent of the intensity of infection.     

Parasites and size-assortative schooling in three-spined sticklebacks

Recent field studies carried out in lacustrine environments have suggested that fish schools may be assorted with respect to parasite infections, but the generality and strength of parasite-assortative schooling in fish is unclear. In this study, data are presented on the body size and externally visible macroparasite load of 366 individual three-spined sticklebacks Gasterosteus aculeatus L. (Gasterosteidae, Teleostei) from six naturally formed schools captured in the Gullmarsfjord on the west coast of Sweden. Length–frequency analysis suggested that two separate year classes (presumed 0+ and 1+) were represented in the sample. Individual schools were assorted by body size, and contained largely fish of a single year class. The number of fish in the school was negatively related to median body size of members. Probability of infection increased significantly with fish length for two parasites ( Cryptocotyle lingua (Trematoda) and Glugea anomala (Microsporidia)), and marginally for a third (chalimus larvae of Caligus sp. (Copepoda)). After correcting for body-size effects, the proportion of school members infected with C. lingua and G. anomala did not differ significantly from a model of random assortment by infection status. However, two of the six schools were found to have significantly more, or significantly fewer, members infected with Caligus sp. chalimus larvae than predicted by the random model. Significant inter-school differences in the intensity of C. lingua infection were also detected, but these resulted from the combined effects of size-assortment and a strong correlation between body size and infection intensity. The results of this study provide only limited support for the existence of active parasite-assortative schooling in marine sticklebacks, and are discussed in relation to recent studies of parasite assortment amongst host fish in other ecosystems.     

Morphological and molecular diagnosis of anisakid nematode larvae from cutlassfish (Trichiurus lepturus) off the coast of Rio de Janeiro, Brazil

Anisakid nematode larvae from Trichiurus lepturus off coast of Rio de Janeiro were studied using light, laser confocal and scanning electron microscopy, in addition to a molecular approach. Mitochondrial cytochrome c-oxidase subunit 2 (mtDNA cox-2), partial 28S (LSU) and internal transcribed spacers (ITS-1, 5.8S, ITS-2) of ribosomal DNA were amplified using the polymerase chain reaction and sequenced to evaluate the phylogenetic relationships between the nematode taxa. The morphological and genetic profiles confirmed that, of the 1,030 larvae collected from the 64 fish examined, 398 were analysed, of which 361 were Hysterothylacium sp. and 37 were Anisakis typica. Larvae of Hysterothylacium sp. were not identified to the species level due to the absence of similar sequences for adult parasites; however, the ITS sequence clustered in the phylogenetic tree with sequences of H. deardorffoverstreetorum, whereas an mtDNA cox-2 and LSU concatenated phylogenetic analysis demonstrated the presence of two clades, both of them under the same name as the larval H. deardorffoverstreetorum. Data on the occurrence of parasites during the winter and summer months were compared using the t-test. The greatest prevalence and intensity of infection were recorded for larval Hysterothylacium, with a prevalence of 51.56% and an intensity of up to 55 parasites per fish. The larval Anisakis exhibit a higher abundance and intensity of infection in the winter months, and those of Hysterothylacium during the summer. However, the t-test indicated no significant differences between the abundance and intensity of infection recorded during the months of collection for either of these larval nematodes. All sequences generated in this study were deposited in GenBank.     

Dietary plant phenolic improves survival of bacterial infection in Manduca sexta caterpillars

Plant phenolics are generally thought to play significant roles in plant defense against herbivores and pathogens. Many plant taxa, including Solanaceae, are rich in phenolic compounds and some insect herbivores have been shown to acquire phenolics from their hosts to use them as protection against their natural enemies. Here, we demonstrate that larvae of an insect specialist on Solanaceae, the tobacco hornworm, Manduca sexta L. (Lepidoptera: Sphingidae), acquire the plant phenolic chlorogenic acid (CA), and other caffeic acid derivatives as they feed on one of their hosts, Nicotiana attenuata L. (Solanaceae), and on artificial diet supplemented with CA. We test the hypothesis that larvae fed on CA‐supplemented diet would have better resistance against bacterial infection than larvae fed on a standard CA‐free diet by injecting bacteria into the hemocoel of fourth instars. Larvae fed CA‐supplemented diet show significantly higher survival of infection with Enterococcus faecalis (Andrewes & Horder) Schleifer & Kilpper‐Bälz, but not of infection with the more virulent Pseudomonas aeruginosa (Schroeter) Migula. Larvae fed on CA‐supplemented diet possess a constitutively higher number of circulating hemocytes than larvae fed on the standard diet, but we found no other evidence of increased immune system activity, nor were larvae fed on CA‐supplemented diet better able to suppress bacterial proliferation early in the infection. Thus, our data suggest an additional defensive function of CA to the direct toxic inhibition of pathogen proliferation in the gut.