Efeito do galhador na alocação de nutrientes em folhas de Solanum lycocarpum

Abstract

Gall makers are an example of herbivores that use host plants to guarantee their own development. Based on the premise that plants with higher nutrient content are preferred in the gall induction process, since these nutrients are drained for their formation and insect development, we verified if plants with galls presented lower concentrations of nutrients in leaves than plants without the galls formation. In addition, the galls size plays an important role in the amount of offspring produced in the plants. In this way, we also evaluated the relationship between galls developmental characteristics, such as diameter, galls number in each plant and nitrogen concentration with the number of insects that emerged and died of them to determine possible relationships between the galls and their host plant. To test these hypotheses, we performed a gall induction experiment in a greenhouse during two years and followed the development of the germinated plants until the final process of galls development. Our results showed that the galls presence in Solanum lycocarpum alters the allocation of macro and micronutrients within the plant, which are redirected to the inductive insects development. In general, the galls number developed in S. lycocarpum individuals positively affected the emerged and died number of insects and galls size. The galls size had a positive relationship only with the emerged number of insects from them. We also observed the existence of a negative relationship between leaves nitrogen concentration of the host plant and number of emerged insects from the galls, that is, redirection of this nutrient from the host plant leaves to the development of the insects inside the galls and survival chance. Our results are consistent with the hypothesis that gall makers drain some nutrients for their benefit and gall formation, as well as the galls number and size are related to the number of insects formed in them, and consequently their chance of survival. There is a natural mortality rate of these insects of approximately two individuals per gall, and nineteen would be the ideal size of offspring left by the female.