Dynamics of soluble sugars and secondary metabolites in fruit of Juglans australis attacked by Anastrepha fraterculus and Ceratitis capitata (Diptera: Tephritidae)

Abstract

The development and fitness of phytophagous insects are tightly linked to the nutritional quality of their host plants and many studies have examined the influence of primary and secondary metabolites of plants and their effects on the development of insects. Herbivore tactics to modify plant metabolic pathways to lower host toxicity need to be better understood as they are critical to a better understanding of herbivore–host plant relationships. To contribute to this end, in this study we analyzed temporal patterns of glucose, sucrose, fructose, and total soluble sugar contents, as well as tannins, phenols, and flavonoids in the mesocarp of fruit of native walnut (Juglans australis), uninfested and infested by Anastrepha fraterculus and Ceratitis capitata (sometimes simultaneously in a single fruit). Both fly species are polyphagous tephritids whose larvae feed on a wide variety of hosts. We observed a high correlation between infestation and adult emergence of these two insects which was positive in the case of sugar content and negative in the case of toxic secondary metabolites in fruit. At particular ripening stages, infested fruit contained higher levels of sugars and lower levels of phenols and tannins than non-infested fruit. We discuss the possibility that A. fraterculus and C. capitata, each with different egg-laying strategies, may modify metabolical pathways in the fruit for their own benefit through larval activity with the help of bacteria in their gut. Alternatively, the patterns observed may be simple side effects of larval feeding and associated growth of opportunistic microorganisms.