Red wood ants stalked by a Trojan horse

Highlighting upcoming research from Thomas Parmentier entitled ‘Host following of an ant associate during nest relocation’, to be published shortly in Insectes Sociaux

Even more fascinating than ants, is the extremely diverse group of arthropods that live strictly in their nests. Gradually, we learn that these creatures, commonly  referred to as myrmecophiles or ‘ant loving’, possess an array of chemical, morphological and behavioural adaptations to by-pass ant aggression and to make a living in the hostile nest environment (Kronauer and Pierce 2011). Many myrmecophiles are parasites that feast on a lavish banquet of brood and other resources found in the nest (Parmentier et al. 2016a).

What is rather unknown so far, is how myrmecophiles move in the landscape and target new nests. It can be expected that myrmecophiles are prompted to colonize new nests, when nest conditions start to deteriorate or when competition with other myrmecophiles becomes too strong. During my current postdoc project, I study the spatial dynamics of myrmecophiles associated with European red wood ants. These ants are famous for their large mound nests and aggression, yet their nests harbour a rich community of myrmecophiles (Parmentier et al. 2014).

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Last spring, I visited a study site in the north of Belgium and to find out whether the wood ant colonies (Formica polyctena) made it through the winter and whether new nests were founded. Then, I observed that one colony was moving to a new nest site a couple of metres away. As I have been curious for a long time how myrmecophiles would respond to the desertion of their home, I carefully inspected the horde of moving workers. To my surprise, I saw that a group of larvae of the beetle Clytra quadripunctata (Chrysomelidae) were crawling among the moving colony towards the new nest site. A bit later, some larvae were also dragged by the workers to the new nest. Luckily, these days, smartphones are equipped with rather decent cameras, so I was able to record this rare event. There are some old and anecdotal notes which suggest that some myrmecophiles are also able to track their host during relocations to a new permanent nest site, but this has not been recorded so far.

The biology of Clytra quadripunctata is rather peculiar. The adults are adorable beetles that feed on plants near the nest. After mating, the female drops her eggs. The larvae enter the nest and remain there probably for 2 years (Donisthorpe 1902). Lab tests demonstrated that the larvae are brood predators and scavengers. They preferentially reside in the heated brood chambers in the centre of the nest (Parmentier et al. 2016b). The larvae of this beetle are protected by a pear-shaped case in which they can retract. After pupation, the adults sneak out of the ant nest.

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My observations suggest that the beetle larvae adaptively respond to rare nest-moving events. Interestingly, they can find the new nest site on their own or be carried by workers unaware of the danger that is hiding in the case. Nonetheless, a significant fraction of the larvae did not find the new nest and remained in the abandoned nest. Wood ants are thought to move occasionally when microclimatic conditions become suboptimal. However, they may also be triggered to relocate to a new nest site in order to reduce parasite load. This could end up in an evolutionary arms race where the host will move more frequently and more distantly, whereas the parasite will develop more advanced strategies to follow or locate its host. This is a tempting hypothesis that deserves further research.

This observation has galvanized me to unravel some more secrets of myrmecophile dispersal the coming years. More information on the progress of my research on myrmecophiles can be found at:

https://www.researchgate.net/profile/Thomas_Parmentier

 

Donisthorpe HSJK (1902) II. The Life History of Clythra quadripunctata, L. Trans R Entomol Soc London 50:11–24.

Kronauer DJC, Pierce NE (2011) Myrmecophiles. Curr Biol 21:208–209.

Parmentier T, Dekoninck W, Wenseleers T (2014) A highly diverse microcosm in a hostile world: a review on the associates of red wood ants (Formica rufa group). Insectes Soc 61:229–237.

Parmentier T, Bouillon S, Dekoninck W, Wenseleers T (2016a) Trophic interactions in an ant nest microcosm: a combined experimental and stable isotope (δ13C/δ15N) approach. Oikos 125:1182–1192

Parmentier T, Dekoninck W, Wenseleers T (2016b) Do well-integrated species of an inquiline community have a lower brood predation tendency? A test using red wood ant myrmecophiles. BMC Evol Biol 16:12.

 

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