Our results suggest that the lower size variation in bilateral flowers might have evolved under selection favoring the control of pollinator behavior on flowers to enhance the accurate placement of pollen on the body of the pollinator, independent of pollinator type. Because of the limited research on this issue, future work should be conducted in various types of plant-pollinator communities worldwide to further clarify the issue.

Oriental persimmon, Diospyros kaki Thunb. (Ericales: Ebenaceae), is a generally diclinous tree. Because the representative cultivar, 'Fuyu', sets nearly exclusively female flowers and has low parthenocarpic ability, it requires pollen from other cultivars for pollination. Here, we identified the most important pollinator of D. kaki in hilly orchards surrounded by secondary forest in Hiroshima, southwestern Japan. To estimate the contribution of each flower visitor to pollination, we used an index of potential pollen transport, namely the rate of visitation per female flower multiplied by the estimated number of pollen grains on the body surface. Among nine functional groups, the value of this index was greatest for bumblebees followed by small bees, whereas that for honeybees was low because of the relatively few Diospyros pollen grains on the body surface. Bombus ardens ardens Smith (Hymenoptera: Apidae) was the predominant bumblebee species in terms of both monitored frequency of visits by insects and number collected for identification. We also counted the fruit set and seed number of 'Fuyu' fruit in various pollination treatments using exclusion mesh to assess the effectiveness of insects of different sizes. Bombus ardens ardens was the most important pollinator and small bees were the second most important.Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

During the last few decades, pine wilt disease has spread to cool-climate regions in Japan and, more recently, the potential risk of it spreading into the European midwest has also become a concern. In a coastal pine stand (84.7 ha) in Akita, near the northern limit of pine wilt disease in Japan, we investigated seasonal variations in the incidence of damage caused by the disease to trees and oviposition by the disease's insect vector, Monochamus alternatus, during a two-year period. Foliage discoloration occurred throughout each year, and its seasonal variation showed a bimodal pattern in Pinus thunbergii (a higher peak in May-June and a smaller peak in October) and a clear peak in June in P. densiflora, which differed from the patterns in seasonal variation seen for warm-climate regions. Oviposition scars by M. alternatus were found in 40-45% of the trees damaged each year. The percentage of trees that had oviposition scars was higher in P. thunbergii than in P. densiflora. This appeared to reflect the difference in seasonal discoloration pattern between the two species.

No 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.