Fight together or escape? an insect affair!

Fungi specialised to attack insects (in the photo from the blog Hyphal Happenings) are commonly present in the environment so that they have driven many aspects of the insect evolution, affecting behavioural, chemical and immune systems.

In a recent paper published in PLoS One, Christine Turnbull and colleagues compared the activity of cuticular antifungal compounds in thrips species (Insecta: Thysanoptera) representing a gradient of increasing group size and sociality: solitary, communal, social and eusocial, against the entomopathogen Cordyceps bassiana. Solitary and communal species showed little or no activity. In contrast, the social and eusocial species killed this fungus, suggesting that the evolution of sociality has been accompanied by sharp increases in the effectiveness of antifungal compounds. This paper suggests a new insight into the evolution of thrips sociality since traits enabling nascent colonies to defend themselves against microbial pathogens should be considered essential for social evolution. Are fungal entomopathogens an integral part in the evolution of insect sociality in general?

ResearchBlogging.orgInterestingly, a very different response has been reported by Hatano and colleague in aphids where entomopathogenic fungi stimulate transgenerational wing induction in the pea aphid Acyrthosiphon pisum (Hemiptera: Aphididae)  allowing aphids to leave patches containing entomopathogenic fungi. Indeed, pea aphids infected with pathogens and maintained in groups on broad bean plants produced a higher proportion of winged morphs than uninfected control aphids.

Wing induction in aphids has been also related to the presence of predators and parasitoids, but unlike predators and parasitoids the effect of  entomopathogenic fungi is independent of physical contact with other aphids, suggesting that physiological cues induce wing formation in infected aphids. Indeed, when maintained in isolation, aphids infected with fungi pathogens also produced higher proportions of winged offspring than control aphids.

As a whole, specialised fungal entomopathogens intensified the degree of sociality and group size in some insects enabling primitive nascent colonies to combat microbial pathogens whereas the same selective agent prompted aphids (that are generally not social insects) to induce wings also in isolated aphids in order to quickly escape infected patches.

Therefore, if you see fungi pathogens fight them with our family or escape them!

References

Turnbull C, Wilson PD, Hoggard S, Gillings M, Palmer C, Smith S, Beattie D, Hussey S, Stow A, Beattie A (2012). Primordial enemies: fungal pathogens in thrips societies. PloS one, 7 (11) PMID: 23185420
Hatano E, Baverstock J, Kunert G, Pel, J, Weisser W. (2012). Entomopathogenic fungi stimulate transgenerational wing induction in pea aphids, Acyrthosiphon pisum (Hemiptera: Aphididae) Ecological Entomology, 37 (1), 75-82 DOI: 10.1111/j.1365-2311.2011.01336.x

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