Immunity in a Social Insect

Journal of Insect Physiology, 2011

Behavioral Ecology and Sociobiology, 2007

The bene®t of sociality in relation to disease susceptibility was studied in the dampwood termite Zootermopsis angusticollis. Although contact with high concentrations of fungal conidia is lethal, the survivorship of nymphs exposed to spore suspensions ranging from 6´10 6 to 2´10 8 spores/ml of the fungus Metarhizium anisopliae increased with group size. The survivorship (measured as LT 50 ) of isolated individuals ranged from 3.0 to 4.8 days, but infected nymphs living in groups of 10 and 25 individuals survived signi®cantly longer (5.6±8.3 and 5.6±9.1 days, respectively). In most cases, there were no signi®cant dierences in the survival distributions of the 10-and 25-termite groups. When nymphs were infected with concentrations of 7´10 1 ± 7´10 4 spores/ml and allowed to interact with healthy nestmates, fungal infections were not contracted by the unexposed termites. Moreover, infected termites bene-®tted from social contact with unexposed nestmates: their survival rates were signi®cantly higher than those of infected termites living with similarly infected nestmates. Allogrooming, which increased in frequency during and after exposure to conidia, appeared to remove potentially infectious spores from the cuticle, thus increasing termite survivorship. These results suggest that allogrooming plays a crucial role in the control of disease and its death hazard in termites. The infectionreducing advantage of group living may have been sig-ni®cant in the evolution of social behavior in the Isoptera.

Proceedings of the …, 2002

The extraordinary diversity and ecological success of the social insects has been attributed to their ability to cope with the rich and often infectious microbial community inhabiting their nests and feeding sites. Mechanisms of disease control used by eusocial ...

Biology letters, 2009

African Journal of Microbiology Research, 2012

Coptotermes formosanus Shiraki with entomopathogenic fungi (Metarhizium anisopliae, strain 2049 and strain 406; Beauveria bassiana, strain 3005 and 200436) and bacteria (Bacillus thuringiensis, Escherichia coli, Ralstonia solanacearum and Staphylococcus aureus), were checked by inhibition zone assay against B. thuringiensis, E. coli, R. solanacearum and S. aureus bacteria. Among all the successful inducers, two peaks at different times were observed, suggesting that there might be different antimicrobial peptides. Furthermore, the results showed that entomopathogenic fungi greatly induced the antimicrobial response of the homogenates as compared to bacteria. The pattern of antimicrobial response varied with the time of treatment, and with the strain of micro-organism. For the time course, after 4 to 8 h of infection, the homogenates started showing antimicrobial activity. Homogenates infected with M. anisopliae strain (2049) showed the highest activity against B. thuringiensis after 18 h post inoculation. While, B. bassiana strain (3005) showed the highest activity against B. thuringiensis after 12 h postinoculation. The antibacterial activity was only observed from the homogenates prepared between 4-80 h post-inoculation. Furthermore, for the different microbial strain, a Gram-negative bacterium, E. coli was found to be highly resistant, showing no growth inhibition. While, both the studied Gram-positive bacteria found to be susceptible to the homogenates, resulting very high antibacterial activity. Among all the microbes, R. solanacearum and S. aureus were found to be poor inducer of immune system in the studied insect. The results provide the first evidence of the induction of antimicrobial response in C. formosanus workers. The current findings open new avenues for further exploration of molecular mechanism of immune response in termites.

Proceedings of the Royal Society of London B, 2006

Recent research has shown that low genetic variation in individuals can increase susceptibility to infection and group living may exacerbate pathogen transmission. In the eusocial diploid termites, cycles of outbreeding and inbreeding characterizing basal species can reduce genetic variation within nestmates during the life of a colony, but the relationship of genetic heterogeneity to disease resistance is poorly understood. Here we show that, one generation of inbreeding differentially affects the survivorship of isolated and grouped termites (Zootermopsis angusticollis) depending on the nature of immune challenge and treatment. Inbred and outbred isolated and grouped termites inoculated with a bacterial pathogen, exposed to a low dose of fungal pathogen or challenged with an implanted nylon monofilament had similar levels of immune defence. However, inbred grouped termites exposed to a relatively high concentration of fungal conidia had significantly greater mortality than outbred grouped termites. Inbred termites also had significantly higher cuticular microbial loads, presumably due to less effective grooming by nestmates. Genetic analyses showed that inbreeding significantly reduced heterozygosity and allelic diversity. Decreased heterozygosity thus appeared to increase disease susceptibility by affecting social behaviour or some other group-level process influencing infection control rather than affecting individual immune physiology.

Naturwissenschaften, 1999

Dampwood termites, Zootermopsis angusticollis, show an alarm response after detecting the presence of spores of the pathogenic fungus Metarhizium anisopliae. Termites in direct contact with a high concentration of spores (10 7 spores/ml) show a striking vibratory display which appears to convey information about the presence of pathogens to nearby unexposed nestmates through substrate vibration. Nestmates not directly in contact with spores that perceive the vibrational signal increase significantly their distance from the spore-exposed vibrating termites, apparently to escape from the source of infection. The fleeing response is not induced by the presence of the spores alone or by pheromones, and requires the perception of the vibrations propagated through the substrate. This "pathogen alarm behavior" appears to be a previously unrecognized communication mechanism that allows termites to reduce disease risks within the nest.

Journal of Insect Science, 2010

Termites live in nests that can differ in microbial load and thus vary in degree of disease risk. It was hypothesized that termite investment in immune response would differ in species living in nest environments that vary in the richness and abundance of microbes. Using the drywood termite, Incisitermes schwarzi Banks (Isoptera: Kalotermitidae), as a model for species having low nest and cuticular microbial loads, the susceptibility of individuals and groups to conidia of the entomopathogenic fungus, Metarhizium anisopliae Sorokin (Hypocreales: Clavicipitaceae), was examined. The survivorship of I. schwarzi was compared to that of the dampwood termite, Zootermopsis angusticollis Hagen (Termopsidae), a species with comparatively high microbial loads. The results indicated that I. schwarzi derives similar benefits from group living as Z. angusticollis: isolated termites had 5.5 times the hazard ratio of death relative to termites nesting in groups of 25 while termites in groups of 10 did not differ significantly from the groups of 25. The results also indicated, after controlling for the influence of group size and conidia exposure on survivorship, that Z. angusticollis was significantly more susceptible to fungal infection than I. schwarzi, the former having 1.6 times the hazard ratio of death relative to drywood termites. Thus, disease susceptibility and individual investment in immunocompetence may not be dependent on interspecific variation in microbial pressures. The data validate prior studies indicating that sociality has benefits in infection control and suggest that social mechanisms of disease resistance, rather than individual physiological and immunological adaptations, may have been the principle target of selection related to variation in infection risk from microbes in the nest environment of different termite species.

Behavioral Ecology and Sociobiology, 1998

The bene®t of sociality in relation to disease susceptibility was studied in the dampwood termite Zootermopsis angusticollis. Although contact with high concentrations of fungal conidia is lethal, the survivorship of nymphs exposed to spore suspensions ranging from 6 ´10 6 to 2 ´10 8 spores/ml of the fungus Metarhizium anisopliae increased with group size. The survivorship (measured as LT 50 ) of isolated individuals ranged from 3.0 to 4.8 days, but infected nymphs living in groups of 10 and 25 individuals survived signi®cantly longer (5.6±8.3 and 5.6±9.1 days, respectively). In most cases, there were no signi®cant dierences in the survival distributions of the 10-and 25-termite groups. When nymphs were infected with concentrations of 7 ´10 1 ± 7 ´10 4 spores/ml and allowed to interact with healthy nestmates, fungal infections were not contracted by the unexposed termites. Moreover, infected termites bene-®tted from social contact with unexposed nestmates: their survival rates were signi®cantly higher than those of infected termites living with similarly infected nestmates. Allogrooming, which increased in frequency during and after exposure to conidia, appeared to remove potentially infectious spores from the cuticle, thus increasing termite survivorship. These results suggest that allogrooming plays a crucial role in the control of disease and its death hazard in termites. The infectionreducing advantage of group living may have been sig-ni®cant in the evolution of social behavior in the Isoptera.

Insectes Sociaux, 2006

Pathogens have likely infl uenced life-history evolution in social insects because their nesting ecology and sociality can exacerbate the risk of disease transmission and place demands on the immune system that ultimately can impact colony survival and growth. The costs of the maintenance and induction of immune function may be particularly signifi cant in termites, which have a nitrogen-poor diet. We examined the effect of fungal exposure on survival and reproduction during colony foundation in the dampwood termite Zootermopsis angusticollis by experimentally pairing male and female primary reproductives and exposing them to single ('acute') and multiple ('serial') dosages of conidia of the fungus Metarhizium anisopliae and recording their survival and fi tness over a 560 day period. The number of eggs laid 70 days post-pairing was signifi cantly reduced relative to controls in the serial-exposure but not the acute-exposure treatment. Reproduction thus appeared to be more resilient to a single pathogen exposure than to serial challenge to the immune system. The impact of fungal exposure was transient: all surviving colonies had similar reproductive output after 300 days post-pairing. Our results suggest that disease can have signifi cant survival and fi tness costs during the critical phase of colony foundation but that infection at this time may not necessarily impact long-term colony growth.