Abstract
One of the main visitors to Fabia bean crops (Vicia faba) in South America is the invasive bumblebee species Bombus terrestris. This is particularly true in Chile, where B. terrestris was first introduced in 1997 and is now common over much of the country. In this study, we evaluated the activity of the principal pollinators of V. faba over two cropping seasons by assessing their visitation rates while distinguishing between legitimate visits, likely to lead to pollination, and nectar robbery. We then determined the net contribution of insect visitation on pod and seed set. We recorded seven species of floral visitors. Most visits (legitimate visits and robbery) were from the honeybee (Apis mellifera), with B. terrestris being the next most common visitor. In the case of B. terrestris, 87.19% of visits were nectar robbery. On average, the same flower perforation was visited 23 times by B. terrestris during the flower's lifespan. In general, the frequency of legitimate visits varied with pollinator identity and year. For B. terrestris, each flower received an average of 0.95 legitimate visits during its entire lifespan. The time spent by B. terrestris visiting flowers for both nectar robbery or pollen collection decreased after the first day of flowering suggesting resource depletion. The number of pods, total seed number, and seed weight were lower where self rather than open pollination. This suggests that open pollination increased reproductive success. We conclude that B. terrestris was likely to contribute relatively little to pollination while at the same time depleting floral resources throughout the flowers’ lifespan.
Highlights
Vicia faba an important crop worldwide, with the main producers being China, Ethiopia and Egypt (FAO 2015)
Colletidae: Cadeguala occidentalis and Cadeguala albopilosa, and one Halictidae Corynura spp. (the latter was recorded by human rather than camera observations (Table 1))
The relative frequency of legitimate visits by B. ruderatus was low, 3.39% and 2.38% in years one and two, respectively, visiting 37.04% in 2018 and 45.95% in 2019 of the flowers observed by cameras
Summary
Vicia faba (broad bean, faba) an important crop worldwide, with the main producers being China, Ethiopia and Egypt (FAO 2015). The annual world production is estimated to be approximately 200,000 tonnes (Ansoleaga & Salinas 2010). The seeds of this crop are rich in proteins and the plant is adaptable to different environmental conditions (Crepon et al 2010). The dependency of V. faba on insect pollinators ranges from 4 to 84% (Aouar-sadil et al 2008; Bommarco et al 2012; Cunningham & Le Feuvre 2013; Bishop et al 2016; Bond & Poulsen 1983; Suso et al 2001), (Bartomeus et al 2014; Free 1966; Nayak et al 2015) reported yield increases from 40 to 185% when pollinated by insects. Pollinators promote self-pollination by stimulating the release of an exudate from the Consequences of Bombus terrestris on Vicia fabas pollination stigmas which promotes pollen germination (Bond & Poulsen 1983). Pollinators of V. faba will provide useful cross-pollination up until a threshold beyond which increased pollinator abundance results in no increase in yield (Suso et al 2001)
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