Myrmica ants

Not all caterpillars achieve this comfortable lifestyle. Enjoying the ants hospitality depends on being taken home by the right kind of ants. The caterpillars have no control over this crucial matter, because the first Myrmica ant to notice a caterpillar takes it off to its own nest. Although each Myrmica species can distinguish its own larvae from those of related species, all local Myrmica ants accept the caterpillars as their own. How this comes about is unclear. Like other insect larvae living openly in ant nests, the caterpillars presumably carry the odor of ant larvae. Perhaps they smell enough... 

Akino T., Knapp J. J., Thomas J. A. and Elmes G. W. (1999) Chemical mimicry and host specificity in the butterfly Maculinea rebeli, a social parasite of Myrmica ant colonies. Proc. R. Soc. London Ser. B, 266, 1419-1426. 

Elmes, G. W., Akino, T Thomas, J. A., Clarke, R.T. and Knapp, J. J. (2002). Interspecific differences in cuticular hydrocarbon profiles of Myrmica ants are sufficiently consistent to explain host specificity by Maculinea (large blue) butterflies. 

Cammaerts, M. C., Evershed, R. P. and Morgan, E. D. (1981) Comparative study of the Dufour gland secretions of workers of four species of Myrmica ants. J. Insect Physiol., 27, 59-65. 

Such sesquiterpene homologues seem plentiful, particularly in ants. The three farnesene homologues from the Dufour glands of Myrmica ants are an example (Figure 6.24). Their purpose there is unknown. In the Dufour gland of the ant Manica rubida nine isomers and homologues of farnesene were found. Their function is again unknown. 

Figure 6.24 Homologues of farnesene found in Myrmica ants, containing one, two or three homomevalonate units replacing mevalonate...

An example from ants is the acceptance of the caterpillar of the parasitic butterfly Maculinea rebeli by its host Myrmica schencki [132]. The caterpillar chemically mimics ant larvae and, in its final instar, drops from its food plant and waits for a foraging ant worker to bring it to the brood chambers of the host colony [133]. 

To date, only two other sets of inquilines have been directly examined for their ability to biosynthesize suites of cuticular hydrocarbons that mimic that of their hosts. Larvae of the syrphid fly Microdon albicomatus are obligate predators of the ant Myrmica incompleta, and have qualitatively identical hydrocarbons as host pupae (but different relative abundances). As with the beetles above, [l-14C]acetate was directly incorporated into the fly cuticular hydrocarbons in the same proportions as the various classes of hydrocarbons present (Howard et al., 1990). The other study was by Akino et al. (1999) and involved the larvae... 

Howard R. W., Stanley-Samuelson D. W. and Akre R. D. (1990) Biosynthesis and chemical mimicry of cuticular hydrocarbons from the obligate predator, Microdon albicomatus Novak (Diptera Syrphidae) and its ant prey, Myrmica incompleta Provancher (Hymenoptera Formicidae). J. Kansas Entomol. Soc. 63, 437 443. 

Lenoir, A., Malosse, C. and Yamaoka, R. (1997). Chemical mimicry between parasitic ants of the genus Formicoxenus and their host Myrmica (Hymenoptera, Formicidae). Biochem. Syst. Ecol., 25, 379-389. 

The function of alkaloids in 30 species of ladybirds has been discussed. The presence of alkaloids is shown to be related to the existence of aposematic colour and not to their carnivorous or phytophagous nature. Alkaloids constitute an effective defence against predators, e.g. ants, Myrmica rubra, and quails, Coturnix coturnix. 

Myrmica rubra show that salicylaldehyde is a more potent deterrent that salicin (63) or its aglycone saligenin (83), The eggs of some of the beetles that feed on members of the Salicaceae contain salicin. Salicylaldehyde is detected in neonate larvae, suggesting that salicin is quickly converted to the aldehyde (Pasteels et al., 1986 Rowell-Rahier and Pasteels, 1986). This shift to members of the willow family appears to have occurred at least three times independently. The species that shifted are able to exploit a food source, yet are well protected. The larvae are provided with an additional method of defense the adults are able to sequester sufficient salicin in the eggs to make them potentially lethal to ants and to provide protection for the neonate larvae (Pasteels et al., 1986, 1988, 1989 Rowell-Rahier and Pasteels, 1986). 

Age effects may influence an individual s reaction to a chemical stimulus. Thus, in Myrmica rubra ants (see Section 11.5.3) callow individuals respond only to Dufour s gland secretions whereas older ants are attracted by both mandibular and Dufours gland pheromone (Cammaerts, 1974). Additionally, sensory adaptation or habituation can influence response level to a stimulus (Waage, 1979 Weseloh, 1980). 

---