Can the exotic pathogen Nosema ceranae affect the amount of Cucurbita maxima pollen grains transported by the native bee Eucera fervens?

Abstract

Eucera and Xenoglosa are the two most frequent squash pollinators, and they both rely solely upon plants of the genus Cucurbita for pollen intake to feed their offspring. The present study reports the first case of Eucera fervens individuals infected with Nosema ceranae spores and assesses the possible impact of this microsporidian on the squash pollen transportation carried by this South American native bee. From the total 963 bees visiting pumpkin flowers, the most frequent bee species was E. fervens (89.8%). A total of 90 bees were sampled for pollen count and Nosema detection. Bees were carrying an average of 62 pollen grains (7–426) and an average of 19 Cucurbita pollen grains (1–93). Nosema was present in 98% of the samples (71/72), while its mean intensity was 1.65 × 106 spores (1.5 × 105–6.78 × 106). A positive correlation between the total pollen grains and the number of pumpkin pollen grains transported by E. fervens was observed. The Cucurbita maxima pollen transported by E. fervens was not explained by N. ceranae spores loads. Nevertheless, a positive correlation between the total pollen grains transported by E. fervens and the N. ceranae intensity was observed suggesting and effect of the microsporidian on bee behavior.