Lycaenid-tending ants can contribute to fitness gain of the infested host plants by providing nutrients

Abstract

Ground-nesting ant species are known to promote plant growth by soil nutrient enhancement. Camponotus compressus ants regularly visit the extrafloral nectary-bearing, lycaenid-infested cowpea, Vigna unguiculata plants and construct a shelter for the lycaenid caterpillars at the plant base. The present study shows that ants may influence the overall fitness of the infested cowpea plants by providing nutrients via soil and foliar pathways. Total carbon, nitrogen and phosphorous content of ant constructed shelter (ACS) soil of the lycaenid-harbouring plants were assessed, microbes from the ACS soil were isolated and their plant growth promotion ability was evaluated. Nitrate content of the ant faecal matter was estimated and overall plant fitness was assessed in terms of its growth and yield. The results revealed higher content of total C, N and P in the debris and chamber soil of ACS as compared to the control soil from the base of ant-excluded plants. The microbes isolated from the ACS and ant nest soil were found to possess plant growth promotion abilities. Ant faecal matter was found to contain substantial amount of nitrate. The ant-included, lycaenid-infested plants as well as those lacking the caterpillars demonstrated significantly higher number of pods, number of seeds per pod, root length, shoot length, plant height, number of leaves, plant fresh and dry weight as compared to the control plants. Lycaenid caterpillar tending ant species with a high propensity for visiting plants thus have the potential to increase plant fitness by increasing nutrient availability via multiple pathways.