RE: Pumpkins Squash and gourds
I have published a paper on movement of the neonicotinoids imidacloprid and thiamethoxam into nectar and pollen of squash. It is in PLoS ONE, an open access journal, so you can get it easily:
Stoner KA, Eitzer BD (2012) Movement of soil-applied imidacloprid and thiamethoxam into nectar and pollen of squash (Cucurbita pepo). PLoS ONE 7(6): e39114. doi:10.1371/journal.pone.0039114
Another paper, with more chemicals and methods of application:
Dively GP, Kamel A (2012) Insecticide residues in pollen and nectar of a cucurbit crop and their potential exposure to pollinators. J Agric Food Chem. 60: 4449-4456.
If the plants are still flowering, you might want to collect nectar and pollen for later analysis. It is really easy to do with cucurbits – they put out so much nectar and pollen that you can bag male flowers ready to open the night before and collect nectar the next morning with a pipette, and pollen by scraping the synadrium (fused anther cone). For my analytical chemistry collaborator, I need to get 1 g or more of nectar or pollen to get a good analysis.
In my study, we applied the neonics once to the soil through either a spray in the seed hole or through drip, early in the season. Galen Dively applied it through drip later in the season and got higher residue concentrations.
There are many opportunities for squash bees to be exposed to neonics on a cucurbit crop – through pollen and nectar, but also in soil, since they are soil nesting bees often making nests in or around the crop field, and the neonics are often applied to the soil. I am doing some work on this on pumpkin and winter squash farms in CT, but there is much work to do. In Florida, where the pest pressure is probably higher, and therefore the neonics are likely to be used in higher concentrations, you may be more likely to find effects.
Our station plants a pumpkin squash and gourd patch for display and for student involvement each year. We have had very little yield this year. Our vegetable crops person did not order bees for pollination this year as we usually have excellent pollination. We normally see lots of squash bees. Since I have been told I have checked the field several times for pollinators. There are no squash bees. In trying to figure out what has happened I have determined neonicotinoids were applied through the drip. Our weather pattern has been very unusual this year. I can take samples but do not see a protocol easy enough to follow for archiving them and probably will not do so. I cannot prove anything conclusively. I feel compelled to comment on our situation. Having looked at recent literature reporting concentrations of these insecticides in pollen and nectar of cucurbits and looking at the general absence of other insects I am concerned. On pumpkin, squash and gourd planted sequentially oligolectic pollinators will have a much higher dose over time than a generalist. This really does need to be studied with some depth. They will be visiting these plants all season as bloom progresses and it will be their only source of food. Dosage will be much increased. I believe the strategy of using neonicotinoids prophylactically through the drip to avoid application of other insecticides at flowering in order to help pollinators is at best questionable. I pass this observation along for what it is worth. It will be interesting to look for squash bees next year.
T. Charles Riddle
University of Florida