Project Details

ProjectID: 749
Agency Project ID: Mini-grant
Region: North Central
State: OH
PI: Williams, Roger
Funding Amount: 9,872
Year: 2009
Project Duration: 12 months
Institution/Organization Funded: Ohio State University
Funding Agency/Program: USDA/NIFA/Regional IPM Centers: Center Internal Grants
Project Status: Completed

Abstract/Summary/Justification: Recent studies of Hymenopteran pollinators have revealed that many important species are either severely threatened or in steep population decline. Many factors are thought to contribute to this decline, although much research has been focused on imidacloprid, a neonicitinoid insecticide. The squash bee, Peponapis pruinosa, is arguably the most important native pollinator of cultivated squash and pumpkin, yet the effects of imidacloprid on this species
are unknown. This proposal aims to test the effects of imidacloprid on the squash bee through laboratory and field studies. The results from this study will help determine if imidacloprid has a negative effect on the squash bee and, if so, the implications for pollination efficiency. As the squash and pumpkin industry is a multi-million dollar industry, and 2 of the top 5 pumpkin
producing states are in the North Central Region, the proposed research will benefit pumpkin production across North America.

Objectives and Goals: 1) Assay lethal and sub lethal effects of the pesticide imidacloprid on P. pruinosa - Foraging adults of both sexes will be collected in cucurbit fields at OSU’s Waterman Farm and OARDC, Wooster. Treatments will consist of imidacloprid added to a 50% sugar water solution in concentrations equivalent to recommended field rates. Recommended rates of Admire (imidacloprid) are 0.24 to 0.38 lb. ai/acre with a seasonal limit of 0.50 lb. ai/acre. In an
effort to conserve the number of bees required to evaluate a range of treatment rates we initially will test the low rate of 0.12 lb. ai/acre and the high seasonal rate of 0.50 lb. ai/acre along with an untreated control. If either of these rates shows a significant treatment effect, we will then test additional rates to determine a treatment threshold. Our untreated control will consist of a 50% sugar water solution. Each treatment will be replicated 15 times with each replicate consisting of an individual bee placed in a ventilated clear plastic cylindrical holding container (20 x 7.5 cm) along with a cotton dental wick saturated with the candidate solution. Observations of bee activity and mobility will be conducted at ½, 1, 2, 4, 8, and 24 hrs post treatment. Each
observation will last 10 minutes and total time of active movement will be recorded. Average time of active movement will be compared among control and treated bees. Mortality will also be recorded. Significant differences in activity and percent mortality among treatments will be determined through ANOVA.
2) Determine P. pruinosa abundance relevant to other pollinators within imidacloprid treated and untreated commercial pumpkin fields - We will evaluate the relative abundance of P. pruinosa to other Hymenopterous pollinators at 4 commercial pumpkin plantings in central Ohio and 4 commercial plantings in
northeastern Ohio. Within each area, we will sample 2 imidacloprid treated fields and 2 untreated fields. Plantings will range in size from 1 to 5 acres. Study sites will be visited weekly to determine when foraging bees first appear. Weekly visits will be conducted throughout the season until bee activity becomes minimal or halts altogether. The density of active nests will be recorded weekly throughout the nesting season in each of 5 randomly located plots measuring 1 m x 1 m and transecting the field. Flagging will be placed at the corners of each plot to assist in relocating the plots for subsequent readings. The number of nest sites will be recorded weekly throughout the season allowing us to compare the frequency of nesting within an equal area of
treated and untreated plots. At the same time flower visitations by the squash bee and other Hymenopterous pollinators in treated and untreated fields will be recorded on a weekly basis. To accomplish this we will observe 20 randomly chosen flowers at 5 locations across the field and record the number and type of bees within each flower. Flower gender will also be recorded. This data will allow us to calculate the percent of flower visitation attributable to the various bee types. Bee observations will be conducted in the early morning because females are most active early in the morning and the cucurbit flowers close by mid day. Significant differences in nest densities, and flower visits for treated and untreated plantings will be determined using repeated measures ANOVA, including patch size as a potential factor.

Measurement of Results: Imidacloprid has a negative effect on the squash bee. We initially started with the high rate of 0.50 lb ai/acres, however this resulted in complete mortality after 24 hr. Next we tested the 0.12 lb ai/acre rate, which also resulted in complete mortality within 24 hr. We then halved the rate to 0.06 lb ai/acre, in which again resulted in complete mortality of the bees by 24 hr. It then seemed that we needed to try and determine at what minimal rate mortality dropped off, therefore we halved the rate two more times, 0.03 lbs ai/acre and 0.015 lbs ai/acre. These rates still resulted in high mortality, but not complete. In this study we did not reach a minimal rate which had no affect on the squash bee.

In the field, the bee data is scattered. Some farms, such as Ramseyer and Miller have very low numbers of foraging squash bees. This we expect is not because of imidacloprid exposure, but possibly other contributing factors including field rotation and heavy tillage. The population did not follow an expected trend, in which the numbers would increase as the season carried on. Some fields increased population, while others, like Moreland, have fluctuated significantly. Nesting density has not been monitored closely, because of the lack of nests at the present time. This data is still being collected and will continue until the season ends.

Outputs and Deliverables: no data
Outcomes: Overall, imidacloprid has a negative effect on P. pruinosa. It is still not clear as to what other factors may contribute to low population densities in some commercial fields, however, some ideas in mind are: over-rotation of crops, deep soil turnover affecting nesting sites, and other pesticide influence. Some future research opportunities may look at attraction differences in pumpkin cultivars to mature bees; artificial manipulation of squash bee populations and field management; regional and generational differences in DNA, as well as if there are other aspects which may contribute to the decline of P. pruinosa populations. Another future prospect is to analyze the effects of pesticides on the brood females and the possible contamination of pollen transferred from parent to offspring in the reproduction cycle. Many factors are still available for research, and new information is expected to benefit the pumpkin industry and our knowledge of the effects of insecticides on pollinators.

Impacts: no data
Target Pest(s): no data
Target Commodities/Sites: Native Cucurbit Pollinator;Peponapis pruinosa;squash;pumpkin

Target Areas of Emphasis: native pollinators

Control Measures: Imidacloprid

Keywords: Native cucurbit pollinator;Peponapis pruinosa;Imidacloprid;Hymenoptera;Population decline

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