In most phytophagous insects, larvae are less mobile than adults and the success of their development depends on the quality of the plant chosen by the adult. According to the “mother knows best hypothesis”, adult preferences are expected to be correlated to performances of larvae, maximizing fitness with adults choosing plants were larvae have optimal development. However, a correlation between adult preference and larval performance is not always found in empirical studies. In a meta-analysis gathering 140 studies including species from different ecological and phylogenetic contexts, Gripenberg et al. (2010) showed that correlations between these two traits differed between specialist and generalist species. Thus, the aim of our study was to test empirically whether the relationship between female preference and larval performance was identical for specialist and generalist species from a same community.
We studied six species of fruit flies (Diptera: Tephritidae) occurring in La Réunion including four generalist (C. catoirii, C. capitata, C. quilicii and B. zonata) and two specialist species (D. demmerezi and Z. cucurbitae). We measured in laboratory the females fecundity and the larval survival on 29 host plants present in La Réunion belonging to 15 families and evaluated the relationship between the preference and the performance.
As expected, specialist species laid eggs on less host plants, mostly belonging to the Cucurbitaceae family, than generalists which laid eggs on all host plants. This study brings empirical evidence that the preference-performance relationship differed according to the degree of specialization with a strong correlation for specialists and no relationship for generalists.
Being selective is useful to specialists that are more adapted to survive on their host plants compared to generalists. However, choosing the best plant on which to oviposit has a cost in term of time and energy especially for generalists that are facing many variable stimuli from different plants which may explain their non-selectivity. Generalist species of the Tephritidae family are known to be able to survive on many plants having a high nutritive value. Generalist females may have no benefit to undergo costs that implies the selection of host plants. These costs involve specific life history traits such as a weak fecundity driving the choice of the female for the best hosts or a long lifetime necessary to look for the most nutritive hosts. In the future, it would be interesting to determine which mechanisms underlie the host selection by specialists.