Dietary self-selection in Anastrepha obliqua wild females (Diptera, Tephritidae)

C. Cresoni-Pereira & F. S. Zucoloto

Dept. of Biology, FFCLRP, USP, Av. Bandeirantes, 3900, Ribeirão Preto, SP, Brazil, 14040-901

It has been shown that some insect species are able to select, among different food, a ratio which provides a suitable balance of nutrients. This behavior is called self-selection, and its two basic rules are non-casualty and its current benefit to insect. Anastrepha obliqua, a fruitfly species, needs to feed on an optimum quantity of protein when adult to produce eggs; therefore it would be advantageous if these insects could select optimum levels of carbohydrates and proteins. The object of present study was to verify whether A. obliqua females are self-selective and whether there is a variation in this behavior during the all life. Recently emerged wild females were separated at random in 6 groups with 6 repetitions each (10 females/repetition). Diets containing these sucrose: brewer yeast ratio were offered to groups from 1 to 5: 5.0g:6.5g (?1:1), 11.0g:6.5g (?2:1), 19.5:6.5 (3:1), 27.0g:6.5g (?4:1) e 35.0g:6.5g (?5:1), respectively. To group 6 sucrose (11.0g) and yeast (6.5g) were offered in separated diets, in order to verify if females would select the same nutrients ratio that provided the best performance in the first 5 groups. Analysed parameters were ingestion, longevity and egg production. Ingestion was greater in groups 1 and 2 than in other groups, including the group 6, which ingested statistically less from the 2 diets than all other groups. Ingestion of sucrose and yeast by this group during the reproductive phase , (1 st to 60 th day after emergence) was 0.69?0.10 and 0.33?0.06 mg/female/day, respectively, indicating that females are self-selective, because this ratio is ?2:1, coinciding with the sucrose: yeast ratios that provided the best performances in groups 1 to 5: ?1:1 and ?2:1. The other ratios were efficient to longevity, but no eggs were produced. The sucrose and yeast ingestion, after reproductive phase, was 0.42?0.16 and 0.02?0.02 mg/female/day, respectively. There is not an yeast preferential ingestion here because the nutritional target is no longer the reproduction. This fact proves the self-selection ability of A. obliqua females and shows the role of insect's nutritional status and development stage on behavioral variations with regard to food choices.  Index terms: fruitfly, nutrition, protein, carbohydrates"

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