Vol. 22 (September 2020) Insect Environment
Symbiosis in urban jungle: An association between Lycaenidae caterpillars and ants
Swathi H A Department of Studies in Genetics and Genomics, University of Mysore, Mysore-Karnataka, India Corresponding author: [email protected]
In nature organisms protect themselves from predators using adaptations such as aposematism, mimicry, crypsis and masquerade. The Lycaenidae family of butterflies commonly known as blues represents nearly 40% of all known butterfly species. Lycaenid caterpillars maintain myrmecophilous associations with ants by secreting limited amounts of sugars, amino acids or by chemically mimicking the ant odour. In turn, ants harvest these secretions and do not attack the caterpillars. Therefore, these phytophagous insects defend themselves from natural enemies by associating with ants and provide nutritional rewards in return (Oliver & Stein, 2011).
Lycaenid caterpillars associate with different species, genera or sub-families of ants. The larvae feed on plant tissue and tender leaves (Pierce et al., 2002). These caterpillars have specialized adaptations such as appeasement pheromones and nectar glands (Atsatt, 1981). Tactile organs help in sensing tail pheromones of ants which directs the ant aggregation towards the caterpillars. Pore cupola organ is an epidermal gland that secretes appeasement pheromones which helps to reduce aggressive behaviour in ants. Dorsal nectar organ (DNO) is a larval organ that has a nectar gland which secretes carbohydrate rich substances for the ants to feed on as the reward. These secretions alter neurotransmitters in the brain of the ants resulting in low locomotor activity and increase in ant aggression towards predators and parasitoids (Basu & Kunte, 2020).
Protection of Lycaenid caterpillar by ants: Ant aggregation around the caterpillar provides them with the necessary protection from predators and parasitoids and therefore the caterpillars can easily feed on the terminal foliage of the plants which are young and nutrient rich. Consumption of more nutritious food throughout the day can permit shorter development time. This type of protection can encourage behavioural crypsis (the ability of an animal to avoid detection by other animals) among Lycaenidae (Baylis & Pierce, 1993).
A rare Lycaenid caterpillar Tarucus nara (Common name: Striped Pierrot) was observed foraging on Ziziphus mauritiana associated with Camponotus compressus
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(Carpenter ant) (Fig 1a) in a scrub habitat at Mysore, Karnataka. Tarucus nara larvae feed on the top epidermal and dermal layer of the leaves (Fig 1a). Another example of caterpillar associated with two different species of ants was observed in Chilades lajus (Lime Blue) feeding on citrus sp., it was found to be associated with Tapinoma melanocephalum (Ghost ant) and Camponotus sp. (Fig 2a and Fig 2b) in an urban habitat at Bangalore, Karnataka.
These observations show that a mutualistic relationship exists between ants and Lycaenidae caterpillars, and some species of Lycaenids exhibit mutualism with multiple species of ants. Different species of ants were observed on the respective host plants of the caterpillars. It is speculated that there might be species specific preference for the host plant by the ants. Further studies with different species of Lycaenid caterpillars, their association with different species of ants and the ant - host plant relationship can provide more insights on this mutualistic behavior.
References:
Atsatt, P. (1981). Lycaenid Butterflies and Ants: Selection for Enemy-Free Space. The American Naturalist, 118(5), 638-654. doi: 10.1086/283859
Basu, D., & Kunte, K. (2020). Tools of the trade: MicroCT reveals native structure and functional morphology of organs that drive caterpillar–ant interactions. Scientific Reports, 10(1). doi: 10.1038/s41598-020-67486-5
Baylis M, Pierce NE. (1993). The effects of ant mutualism on the foraging and diet of lycaenid caterpillars. In: Caterpillars: Ecological and Evolutionary Constraints on Foraging. New York: Chapman and Hall; pp. 404-421.
Oliver, J., & Stein, L. (2011). Evolution of influence: signaling in a lycaenid-ant interaction. Evolutionary Ecology, 25(6), 1205-1216. doi: 10.1007/s10682-011-9478-6
Pierce, N., Braby, M., Heath, A., Lohman, D., Mathew, J., Rand, D., & Travassos, M. (2002). The Ecology and Evolution of Ant Association in the Lycaenidae (Lepidoptera). Annual Review of Entomology, 47(1), 733-771. doi: 10.1146/annurev.ento. 47.091201.145257
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Fig 1a: Tarucus nara caterpillar association with Camponotus compressus. Fig 1b: Tarucus nara adult.
Fig 2a: Chilades lajus caterpillar association with Tapinoma melanocephalum. Fig 2b: Chilades lajus association with Camponotus sp. Fig 2c: Chilades lajus adult.
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