Host preference of the bean weevil Zabrotes subfasciatus

Abstract

It is largely known that the range of an insect diet is mostly determined by oviposition behavior, mainly in species with endophytic larvae such as Zabrotes subfasciatus. However, the proximate factors determining host choice and the subsequent steps leading to the expansion or reduction of the host number and occasional host shifts are largely unknown. We analyzed various factors determining host preference of Z. subfasciatus through the evaluation of: (i) oviposition preference of a wild population of Z. subfasciatus on the usual host (bean) and unusual hosts (lentil, chickpea and soy), and the performance of the offspring; (ii) artificial selection for increasing preference for hosts initially less frequently chosen; (iii) comparison of oviposition behavior between two different populations (reared for ~30 generations in beans or chickpeas, respectively); (iv) oviposition timing on usual and unusual hosts; and (v) identification of preference hierarchies. We found that when using unusual hosts, there is no correlation between performance and preference and that the preference hierarchy changes only slightly when the population passes through several generations on the less frequently accepted host. We also found a positive response to artificial selection for increasing oviposition on the less preferred host; however, when the host-choice experiment involved two varieties of the usual host, the response was faster than when the choice involved usual and unusual hosts. Finally, beetles reared on an unusual host (chickpea) for 26 generations showed similar good fitness on both usual and unusual hosts, indicating that the use of a new host does not necessarily result in the loss of performance on the original host. Nevertheless, this population showed lower fitness on the usual host than that of the original population, suggesting an underlying partial trade-off phenomenon which may contribute to a broadening of diet of this insect species.

Intraspecific competition in Zabrotes subfasciatus: Physiological and behavioral adaptations to different amounts of host

“…This finding indicates that the egg distribution pattern is a flexible trait that changes according to the environment and reflects the intensity of the phenotypic plasticity shown by Z. subfasciatus . The oviposition behavior responds differently from artificial selection when compared to the host preference, in which genetic changes (positive response to selection) are easily observed (Teixeira & Zucoloto, 2003, Teixeira et al , 2008). Thus, the broadening of the bean weevil's diet or even the change of the host preference hierarchy are traits which are more subjected to selection than the egg distribution pattern, which remains constant after dozens of generations.…”

“…We suggest that due to the abundance of its usual host, that is, the common bean ( P. vulgaris ), and also due to the stored products characteristics (seasonal variations in availability), over time it is more common for a population of Z. subfasciatus to find extreme changes in the amount of resources than the inclusion of a new host in its diet. The consequence is that the inclusion of a new host is more gradual and slower (Teixeira et al , 2008) than the adaptation to a new situation of host amount and competition conditions.…”

“…This procedure was repeated for 41 generations. The parameters used to measure each generation's fitness were: fecundity (average number of eggs, m); survival (% of adult emergence, V); and life cycle duration (average longevity in days, T), all combined in the following equation λ = Ln (m.V)/T (see Teixeira et al, 2008).…”

“…Adaptation to environmental alterations, such as an increased competition for food, depends on the development of a series of physiological and/or behavioral changes (Wassermann & Futuyma, 1981; Zucoloto, 1993; Gould, 2002; Teixeira & Zucoloto, 2003). These changes may be due to phenotypic plasticity, that is, the property of a given genotype to produce different phenotypes in response to distinct environmental conditions (Stearns, 1992; Pigliucci, 2002; West‐Eberhard, 2003; Teixeira et al , 2008, 2009). A genotype is non‐plastic if it shows the same phenotype in all environments (Pigliucci, 2001).…”

Females of the weevil Zabrotes subfasciatus manipulate the size and number of eggs according to the host seed availability

“…The capital‐breeding weevil Zabrotes subfasciatus , in which larval resources are the sole source for the future egg maturation, uses Phaseolus vulgaris seeds as its main host (Teixeira & Zucoloto, 2003; Teixeira et al , 2008). Despite not feeding as adults, females of this insect species are able to lay eggs only after finding host seeds, which starts the process of vitellogenesis (Pimbert & Pierre, 1983).…”