Outcome of Conserving and restoring pollination services in organic farms of Yolo and Solano Counties, Northern California

We surveyed the native pollinators visiting strawberries, tomatoes, squash, eggplant, watermelon and muskmelon on several or more organic farms for each crop. Twenty-six or more species6 of native bees in 19 genera were found to visit these crops (see Appendix 1). While some crops were visited by only a few species, others were visited by most of them. Interestingly, there seemed to be little specialization by bees on particular crops. A few species visited all of the crops (e.g. Halictus tripartitus). A few crop species (watermelon, strawberry) received visits from most of the 19 genera of crop-visiting bees. Thus a complex of native bees in this region appears to be well-adapted to the agro-ecosystem and readily visits a variety of agricultural crops.

We studied pollination services in five crops: tomato, eggplant, strawberry, muskmelon and watermelon. The percentage of visits from native bees, out of all visits by bees (e.g. native plus introduced honey bees), varies from crop to crop, and from farm to farm within crops (Table 1). Since native bees often make up a large proportion of the flower visitors to these crops, they are thus potentially important pollinators. In addition, they may provide "insurance" in the event that honey bee populations decline due to disease or management problems. 

Although bees may visit crop flowers frequently, visitation alone does not ensure pollination. For this reason, we carried out several different studies to assess how effective different bee species are as pollinators. We restricted these studies to watermelon, a plant that has separate male and female flowers, large, sticky pollen, and requires animal vectors for pollination.