Pollination efficiency of bumblebee, honeybee, and hawkmoth in kabocha squash, Cucurbita maxima, production in Kagoshima, Japan

Abstract

Kabocha squash, Cucurbita maxima Duchesne, in delayed-start culture is one of the major cultivation systems in southwestern Japan. Honeybee introduction or hand-pollination has been practiced in this crop system, but the species composition, abundance, and pollination efficiency of major pollinators remain unclear. In the current study, we investigated which insect(s) accomplish pollination of kabocha squash. Among the total visitations to female flowers, honeybees, mostly Apis mellifera L. (Hymenoptera: Apidae), dominated at 94.4% and 85.3% at the experimental field in 2019 and 2020, respectively, followed by the bumblebee Bombus diversus diversus Smith (Hymenoptera: Apidae) and the hummingbird hawkmoth Macroglossum pyrrhosticta Butler (Lepidoptera: Sphingidae). The number of pollen grains on the body surface of B. diversus diversus individuals was significantly greater than that on honeybees, such that a single visit by B. diversus diversus deposited 5–6 times more pollen grains on a stigma than a honeybee visit, meaning that the bumblebee is a more efficient pollinator at the individual level. However, visitations by numerous honeybees compensated for their lower individual efficiency and resulted in fruit set. In addition, we report for the first time that a lepidopteran can pollinate squash: our data indicate that pollen grains deposited by several visits of M. pyrrhosticta were likely to exceed the estimated minimum number of pollen grains required for fruit set. Our survey at the experimental field and at three private farms revealed that far more pollen than is required for fruit set was deposited on the stigmas by wild pollinators and wintering honeybees. These findings indicate that kabocha squash production in delayed-start culture in this region is practicable without pollination enhancement effort, such as honeybee introduction or hand-pollination.

Diurnal and geographic variations of pollinator importance for Cucurbita maxima Duchesne

“…This result supported our preliminary survey of C. maxima conducted in the same sites and season from 2017 to 2018 (Ikemoto unpublished data and Ikemoto et al, 2021). Although the previous study carried out at the same site of Kagoshima in autumn 2019 and 2020 (Kamo et al, 2022) reported B. d. diversus visiting C. maxima, we did not find any individuals in this study. Such an inconsistent result between the two studies could simply be because the experimental periods in our study were earlier than the appearance season of the workers (Kinota et al, 2013).…”

“…pollinate, or at least visit the flowers (Ali et al., 2014; Hoehn et al., 2008; Pfister et al., 2017). On the other hand, in Japan, elucidation of pollinator importance of each insect for squashes is scarce, except for a few studies conducted in northern (Hokkaido) and southern (Kagoshima in Kyushu) areas (Abe & Kumano, 2017; Kamo et al., 2022). In other words, we still lack information for Honshu, the main island of Japan.…”

Geranium sylvaticum increases pollination probability by sexually dimorphic flowers

“…In a previous study on Cucurbita maxima , bumblebees carried considerably more pollen on their bodies than honeybees (Kamo et al, 2022). Due to their pollen transport capacity and behavior within the flower, bumblebees also effectively deposited more pollen than honeybees or other floral visitors (Kamo et al, 2022). Honeybee, Apis mellifera , is a non‐native farmed insect in Finland.…”

“…Insect morphology imposes selective pressure on flowers to match the reproductive displays of the sexes. In a previous study on Cucurbita maxima, bumblebees carried considerably more pollen on their bodies than honeybees (Kamo et al, 2022). Due to their pollen transport capacity and behavior within the flower, bumblebees also effectively deposited more pollen than honeybees or other floral visitors (Kamo et al, 2022).…”

Multiyear study of pollinator efficiency and importance of a wide array of pollinators in a field-cultivated strawberry plot

“…However, flower visits by wild pollinators may fluctuate over time [ 17 ], and there may be multiple important pollinators whose relative importance may change over the years. Although several studies have investigated the relative importance of multiple pollinators over time [ 6 , 18 , 19 ], few have investigated their fluctuations over multiple years [ 6 , 20 , 21 ]. Moreover, no studies have estimated the proportional importance of each major flower visitor to the total pollination service of the field crops.…”