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ARS Home » Midwest Area » Madison, Wisconsin » Vegetable Crops Research » Research » Research Project #427525

Research Project: The Reliability of Trapping Methods in Identifying Wild Pollinators of Crops

Location: Vegetable Crops Research

Project Number: 5090-21000-068-02-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Sep 14, 2014
End Date: Sep 13, 2019

The objective of this study is to determine the reliability of trapping methods commonly used in crop pollination studies to identify the wild insects that contribute to the pollination of crops. This study will also provide information on the wild pollinators of specific crops and their potential role in pollination and yield, starting with alfalfa. This study will help distinguish between true insect pollinators, which move pollen from flower to flower and pollinates the flowers, from insect visitors, insects which mainly steal pollen and/or nectar from the flowers and do little pollination. Trapping may also collect insects that are in the area but do not pollinate or visit the crop's flowers. This study will compare the abundance and presence of insect pollinators caught using the bee traps to the diversity of pollinators and visitors observed from direct pollinator observations of the crop. Estimating the reliability of trapping methods in identifying true pollinators of specific crops is extremely important given the current widespread use of these trapping techniques in the study of the role and impact of wild pollinators on crop pollination. Identifying the wild pollinators of specific crops and their contribution to crop yield is also very important as it helps determine how much farmers need to rely on managed pollinators for their crop, at least in specific regions.

The trapping method most commonly used in the study of crop pollination is the bee cup trap. These bee cups are plastic cups painted different colors, typically fluorescent blue, yellow, or white, and are filled with a 20% propylene glycol solution and a few drops of unscented dish soap. The bee traps are typically hung from stakes and elevated to the level of the flowering crop or placed on the ground. We will place a number of these bee traps in alfalfa seed production fields. The contents of the traps will be emptied every week for three weeks during peak alfalfa flowering. After each collection period, new propylene glycol solution will be added to each cup. At collection, all bees and other insects will be stored in 70% ethanol until they can be dried, pinned and identified to the species level as feasible. Each week, during which traps will be set up, we will also perform direct pollinator observations of alfalfa flowers. We will select groups of alfalfa racemes (flower clusters) and record in 10 minute intervals all insects visiting the alfalfa racemes in the patch. We will record the number of flowers visited by each pollinator on a raceme and the number of racemes visited. We will note whether an insect is foraging for nectar or pollen and whether it is carrying pollen in pollen sacs and/or on its body. We will catch a few insects of each type that visited the flowers for future identification at the species level. We will do these pollinator observations at different periods throughout the day and each day of the week where traps are set up for a total of 8 hours of direct pollinator observations per week. The group of racemes observed within a field will change over time. We will compare the presence and abundance of specific bees using the bee trap method and the direct pollinator observations and determine whether a bee pollinated the flowers, stole nectar or pollen or was simply passing through the field. These data will help determine the reliability of the bee cup traps in identifying true pollinators of a crop, starting with alfalfa. The abundance of the insects identified as true pollinators will be used to estimate their potential contribution to crop yield.