Effectiveness of Native Bees as Pollinators

Posted May 7th, 2010 at 11:57 am.

Rosemary Malfi

Mentor: Dr. Neal Williams

Pollination is an ecological service essential to the fertilization of many agricultural crops. These crops require a pollinator in order to reproduce, and for many crops, this pollinator is a bee. Bees are particularly adept at pollination, and in the case of many crops, the presence of bees is essential to their success. Among these crops are watermelon (Citrullus lanatus) and cherry tomatoes (Lycopersicon esculentum), which feature as the target crops in our study. In order to ensure a higher yield, many farmers manage honeybees (Apis mellifera), investing time and money into their care, with the expectation that these colonies will effectively pollinate the farm’s crops. Unfortunately, the honeybee populations, both domesticated and feral, have declined by 50-70% since 1946 (USDA 1980; data from 1980-2001, E. Mussen, personal communication). In light of this drastic drop in honeybee colonies, focus has been shifted to the ability of native pollinators to fertilize crops.

Native bees have gone largely unrecognized as effective pollinators of agricultural crops, but the value of their services is being evaluated now that the number of honeybee colonies is suffering. In our study we are going to determine the effectiveness of native pollinators. We will do this by measuring the pollen deposition per visit to a crop per species using the bridal bag technique, in which a flower is kept from pollinators by a bag, and unveiled for one visitation, at which time the flower will be taken to the lab for observation under a microscope to determine the amount of pollen deposited by that individual bee. This will be multiplied by the rate of visitation per bee genus (to a crop flower), data which will be obtained by observation, to yield the amount of pollen deposited by a type of bee per visit per crop flower. In conjunction with determining the respective efficacies of these native pollinators, it is also our imperative to understand how these bee species are differentially sensitive to landscape changes. Using GIS (Geographical Information System) to map the landscape surrounding the 20 farm sites included in our study (located in Montgomery County and Bucks County) and the rate of visitation to a crop per species, we will determine the abundance of a species in relation to the surrounding habitat. If a particular species of native bee, which is especially effective at pollinating certain crops, is, for example, present in more abundance when X amount of riparian exists within a 2 km buffer of a farm site, it would then be beneficial to replicate farms to maintain a similar surrounding landscape.

1. Kremen, C., Williams, N.M., Bugg, R.L., Fay, J.P. & Thorp, R.W. (2004). The area requirements of an ecosystem service: crop pollination by native bee communities in California. Ecology Letters, 7, 1109-1119

Filed under: 2005,Malfi, Rosemary,Williams, Dr. Neal by Ann Dixon

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