Invasive ant (Anoplolepis gracilipes) disrupts pollination in pumpkin
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Yellow crazy ant (Anoplolepis gracilipes (F. Smith); “YCA”) is known for its aggressive predatory ability and ability to exert exploitation competition on both native and other invasive ants via floral nectar. We argue that YCA invasion can exert both interference and exploitation competition on legitimate pollinators. In pumpkin fields (Cucurbita maxima L.) of south India, YCA infested the flowers, particularly the pistillate flowers, for nectar foraging. Pumpkin is a honey bee-mediated cross-pollinated monoecious plant that produces disproportionately very few pistillate flowers. We hypothesize that YCA presence in the flowers can affect the visitation rate and foraging time of honey bees in the flowers, the fruit set in pumpkins, and can exert predatory pressure on the honey bees if the bees linger in ant-colonized flowers. Both YCA and honey bees preferred to forage on the limited pistillate flowers in the plants. After colonizing the flowers, YCA did not retreat for hours, even upon disturbance by competitors, such as honey bees. Both the visitation frequency and the foraging time of honey bees were drastically reduced in ant-colonized flowers, and none of the ant-colonized flowers developed into fruits, suggesting that the YCA exert both an ecological and evolutionary pressure on pumpkin. The ants preyed upon about 17% of the honey bees that lingered in ant-colonized flowers, and the time the bees spent foraging predicted the fate of the bees. Exploitation competition exerted by the YCA on pumpkin may have far-reaching consequences for the pollination and productivity of this cash crop.
KeywordsInvasive species Competition Mutualism Pollination Pollination crisis Honey bee Crop production
We thank the two anonymous reviewers and the subject editor for their constructive comments on the previous versions of the manuscript. We also thank Judith Bronstein for the comments on the original version of the manuscript. We thank Sangeetha Varma for sampling ants in the study sites using pitfall traps in the 2016–2017 cultivation period. PAS would like to thank the committee for the Conservation, Research, and Exploration of National Geographic Society and Kerala State Economic and Planning Affairs for the grants that supported this research. PAS also thanks University Grants Commission (New Delhi) for awarding the Raman Fellowship for Post-Doctoral Studies at the University of Arizona. We thank all the farmers who cooperated in our research and bore the loss incurred due to our research. We thank Kayla Sale for proof reading the revised manuscripts.
VCS studied the effect of yellow crazy ant on honey bee visits; TVJ studied the effect of yellow crazy ant on fruit set in pumpkin; MVN, KSR, and PPM took the census of staminate and pistillate flowers in eighteen pumpkin fields; PAS studied the predation pressure of yellow crazy ant on honey bees, analyzed the data, and wrote the manuscript.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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