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Chemical Deception and Structural Adaptation in Microdon (Diptera, Syrphidae, Microdontinae), a Genus of Hoverflies
G Scarparo1,2, P d'Ettorre3, A Di Giulio4,5
1Department of Science, University Roma Tre, Viale G. Marconi 446, 00146, Rome, Italy.
Abstract:
Various organisms, especially arthropods, are able to live as parasites in ant nests and to prey upon ant broods without eliciting any aggressive behaviour in the hosts. Understanding how these intruders are able to break the ants' communication codes in their favour represents a challenging and intriguing evolutionary question. We studied the chemical strategies of three European hoverfly species, Microdon mutabilis (parasitic on Formica cunicularia), M. analis (parasitic on Lasius emarginatus) and M. devius (parasitic on L. distinguendus). The peculiar slug-like larvae of these three species live inside ant nests feeding upon their broods. Gas chromatography-mass spectrometry analyses show that: 1) these parasites mimic the host brood rather than the ant workers, although each differs distinctly in the extent of chemical mimicry; 2) isolation experiments indicate that after 14 days the responsible cuticular hydrocarbons (CHCs) are not passively acquired but synthesized by the fly larvae. Additionally, Microdon larvae show an array of protective structural features, such as a thick and multi-layered cuticle, retractable head, dome-shaped tergum and a flat and strongly adhesive "foot" (sternum). This combination of protective chemical and structural features represents a successful key innovation by Microdon species, and one that may facilitate host switching. The results of a preliminary adoption analysis confirm that Microdon larvae of at least some species can readily be accepted by different species of ants.
Insights
Hoverfly larvae successfully infiltrate ant nests by mimicking ant brood chemistry, not adult ants. These parasites synthesize their own chemical defenses, enabling survival among ants and potential host switching.
Area of Science:
- Evolutionary Biology
- Chemical Ecology
- Entomology
Background:
- Many organisms, particularly arthropods, parasitize ant nests and prey on ant broods without provoking aggression.
- Understanding how these intruders bypass ant communication and avoid host defense is a key evolutionary question.
Purpose of the Study:
- To investigate the chemical mimicry strategies of three European hoverfly species (Microdon spp.) parasitizing different ant hosts.
- To determine if cuticular hydrocarbons (CHCs) are acquired or synthesized by the parasitic larvae.
- To explore the role of structural adaptations in larval survival within ant nests.
Main Methods:
- Gas chromatography-mass spectrometry (GC-MS) analysis of hoverfly larvae and host ants.
- Isolation experiments to assess the origin of cuticular hydrocarbons (CHCs) over time.
- Observation of larval morphology and protective features.
- Preliminary adoption analysis to test interspecies acceptance.
Main Results:
- Hoverfly larvae mimic the chemical profile of host ant broods, not adult ants, with varying degrees of success.
- Cuticular hydrocarbons (CHCs) are actively synthesized by the fly larvae, not passively acquired, after 14 days.
- Larvae possess significant structural defenses: thick cuticle, retractable head, dome-shaped body, and adhesive 'foot'.
Conclusions:
- The combination of chemical mimicry and structural adaptations is a key innovation for Microdon larvae.
- These adaptations facilitate successful parasitism within ant colonies and may enable host-switching events.
- Microdon larvae demonstrate a high degree of acceptance by different ant species, highlighting their parasitic strategy.
