Pattern of Host Use by Two Competing Fruit Fly (Diptera: Tephritidae) species

F. DEVESCOVI; D.F. SEGURA; M.C. LIENDO; G. BACHMANN; M.T. VERA; S. BRENGI; F.H. MILLA; J.P. BOUVET; J.L. CLADERA

Mazatlán, México

Congreso; 7th Meeting of the Working Group on Fruit Flies from the Western Hemisphere; 2008

Sharing limiting resources has got a negative effect on individuals. This can lead to the development of mechanisms that allow them to escape competition. The use of host marking pheromones is an example of these mechanisms, and previous studies in our laboratory showed that such mechanism works intraspecifically and also interespecifically between Ceratitis capitata (Cc) and Anastrepha fraterculus (Af). We analyze here infestation patterns in guava in 5 sampling sites of Argentina, aiming at determine the relative abundance of these species and whether they tend to avoid interspecific competition in the field following what was found in laboratory conditions. Fortnightly samplings were made during the whole fruiting season. Fruits were kept individually and the number of pupae of each species was recorded. A relative abundance index was calculated using the number of recovered pupae (RAI = Cc/(Cc+Af)). We found that Af predominated over Cc in almost every tree, although the relative importance of Cc increased along the season. Strong variation in RAI within sites showed there is a strong local effect on host utilization, indicating differences with previous reports. RAI patterns were opposite to those expected according to the degree of environmental disturb. Several cases of fruit simultaneously infested by both species were found along the season. This shows that competition avoidance mechanisms described in laboratory did not prevent interespecific competition. Observed frequencies of co-infested fruit were compared with the expected values under three models of host use (random oviposition and two models that consider different avoidance rates). The random oviposition model was generally the best model, fitting the data in almost every tree. The other two models fitted the co-infestation pattern in only 50-70% of the cases, with some trees fitting better than others. Possible causes of this variation are discussed.