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Summer Research Fellowship Programme of India's Science Academies

Interruption and exploitation competition exerted by floral ants on foraging behaviour of pollinators in pumpkin, Cucurbita maxima

Sajad Hussain Mir

Division of Entomology, Sher-e-Kashmir University of Agricultural Sciences and Technology of Kashmir, India 193201

Palatty Allesh Sinu

Department of Animal Science, Central University of Kerala, Kasaragod 671316

Abstract

Pumpkin is an important vegetable crop in India; it has been cultivated in about 72,000 ha area, and about 15.82 lac metric tonnes of pumpkin are produced annually. Pumpkin is a honey bee-mediated cross-pollinated monoecious plant that produces, somewhat disproportionately, very few pistillate flowers. The flowers are short-lived (just hours), blooming at dawn and closing well before noon. Pumpkin plants set fruit only if pollinated by honeybees, and fruit quality is enhanced by intensive pollinator activity. Male flowers produce nectar and pollen, while female flowers offer higher quantities of nectar but no pollen. There are several factors predicting the pollination or fruit set in pumpkin. Among them, ant colonization is a major biotic threat. The presence of invasive ants in pumpkin flowers has negative effects such as pollinator harassment or flower avoidance by pollinators. In addition to direct interactions like predation, indirect interactions among floral visitors (e.g., exploitative competition) can also discourage visitation by pollinators and negatively impact plant reproduction. Floral visitation by ants can result in damage to floral structures, reduced pollen viability, harassment of other floral visitors, and avoidance by floral visitors in response to ant abundance and species exploitation or alteration of floral resources. Intrusion by native and invasive ants can exert both interference and exploitation competition on legitimate pollinators in pumpkin fields (Cucurbita maxima L.). The presence of native and invasive ants in staminate and pistillate 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. 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 native and invasive ants exert both an ecological and evolutionary pressure on pumpkin. Honey bees, the key pollinators spent less time in flowers when occupied by the native and invasive ants. The duration of visits by honey bees, the most common floral visitor, declined with both increasing abundance and increasing ant floral visitation.

Keywords: Pumpkin; Floral ants; Pollinators; Pollination crisis.

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