Exotic plants growing in crop field margins provide little support to mango crop flower visitors

Abstract

Introduced plant species integrate into native trophic networks, often disrupting flower-visitation patterns. Although non-native invasive plants frequently occur in disturbed natural vegetation bordering crop fields, their impact on crop pollination has not been studied. We investigated whether an invasive plant (Lantana camara) influences flower visitation to mango (Mangifera indica), a pollinator-dependent crop, and whether the invasive supports mango pollinators when mango is not flowering. We surveyed insect flower-visitation in mango orchards bordering natural vegetation and within adjacent natural vegetation, with and without L. camara present, before, during and after mango flowering. We used these data to calculate the indirect effect of L. camara on mango through shared flower visitors before, during and after mango flowering, and the effects of the invasive on crop productivity. Lantana camara had a positive effect on mango flower visitation at low to medium mango flower density, but not at high mango flower densities. Although L. camara and mango shared flower visitor species, the frequency with which these flower visitor species visited the crop and the invasive differed markedly before, during and after mango flowering. Furthermore, the potential indirect effect of L. camara on mango via shared visitors was greatest when mango was flowering, but significantly lower before and after mango flowering, suggesting that the invasive is unimportant in the diet of mango flower visitors when the crop is not flowering. Contrary to findings in previous studies using native species in mango fields, there was a trend (not significant) for lower mango fruit production in fields with L. camara. This suggests that Lantana does not contribute to an increase in successful pollination of mango. Although our focal alien invasive plant species facilitated flower visitation of crops, it had no effect on mango production, and provided little support to mango flower visitor species that live longer than the crop's flowering period. Given that L. camara is detrimental to grazing and was not associated with increased mango production, the removal of this invasive is advisable.