Effects of Nosema bombi and Captan on lab-reared colonies of Bombus vosnesenskii (Hymenoptera: Apidae)

Bumblebees (Bombus sp.) provide important pollination services to numerous commercial fruit and vegetable crops.  Fungicides used in these crop systems may be applied during bloom when workers are out foraging.  Exposed workers can then introduce fungicide residues into the nest environment through nectar and pollen collected from treated flowers.  Laboratory studies investigating the sub-lethal effects caused by fungicide exposure commonly use Bombus impatiens, the Eastern bumblebee or Bombus terrestris, the Buff-tailed bumblebee as model organisms.  Few studies have used bumblebee species native to the Western United States with even fewer investigating possible sub-lethal interactions of fungicide exposure and internal gut pathogens.  In this study we investigated the effects of Captan 50, a commercial fungicide and Nosema bombi, an obligate internal bumblebee parasite along with their interaction on the health and productivity of exposed microcolonies.  Microcolonies were established from full-sized Bombus vonsnesenskii hives that were raised from wild-caught queens reared in a laboratory setting.  Mean times for first, 50%, 100% mortality of original worker population along with time to larval deposition was determined for each treatment.  Mean number of total larvae produced during the experiment was also determined for each treatment.  The results of this study can be used to show how fungicides interact with bumblebee pathogens and the effect of their presence on hive development translating to pollination services.  Understanding the interactions between pesticides and insect pathogens will help to determine how crop management practices influence pollinator health.