INFERENCES ON COMPETITIVE INTERACTIONS FROM DISTRIBUTION PATTERNS OF COEXISTING ANASTREPHA FRATERCULUS AND CERATITIS CAPITATA POPULATIONS.

DEVESCOVI, FRANCISCO; SEGURA, DIEGO F ; LIENDO, MARÍA C ; BACHMANN, GUILLERMO ; VERA, MARÍA T ; MILLA, FABIÁN H ; BOUVET, JUAN P; CLADERA, JORGE L

Congreso; VIII International Symposium on Fruit Flies of Economic Importance; 2010

Background: Anastrepha fraterculus (native to South America) and Ceratitis capitata (exotic species in this region) have shared host fruit species in Argentina for more than one century. Little is known about the mechanisms that allow the coexistence of these tephritids. Previous works suggested that avoidance of infested fruit would act as a stabilizing force minimizing the negative effects of interspecific competition. We tested here the hypothesis that these species exploit available resources avoiding larval competition by analyzing the spatial distribution of infestation, particularly co-occurrence patterns. Methods: A. fraterculus and C. capitata infestation patterns were evaluated from pupae obtained from Psidium guajava. Fruit were collected in Northeast region of Argentina (Concordia) and were processed individually. Frequencies of fruit infested by one, both or none species were compared with two theoretical distributions, expected under a random oviposition hypothesis and under an avoidance (of already infested fruits) hypothesis. As an alternative method we use null models (Ecosim 7.0). Each method was tested at three spatial scales, for each sampling date. Results: Both methods showed that infestation patterns varied according to the spatial scale. At the largest scale there was a tendency towards co-infestation, while at a reduced scale (particularly at the tree scale), the pattern revealed either a random oviposition behavior or avoidance of infested fruit. At this scale, a tendency towards avoiding infested fruit occurred only when fruit infestation levels were moderate. Conclusions: Our study suggests that competition avoidance behavior could be density-dependent. This mechanism could, at least partially, permit the coexistence of A. fraterculus and C. capitata. Other factors, such as environments and host species associated with agro-ecosystems could also be playing a role in structuring population densities.