Impact of Herbicides on Beneficial Insects of Blueberry - Cranberry

Impact of Herbicides on Beneficial Insects of Blueberry - Cranberry

Summary

Summary
We are investigating the effects of herbicides on the diversity and abundance of forage plants and beneficial Hymenoptera (bees and wasps) in blueberry fields in Maine and cranberry bogs in Massachusetts.

Objectives
* Determine the effects of herbicide use on flowering weeds (diversity and abundance) and Hymenoptera (diversity and abundance).

* Determine the extent that field border characteristics reduce the effects of herbicides on the diversity and abundance of Hymenoptera.

* Determine how the abundance and diversity of beneficial Hymenoptera influences crop productivity (fruit set, berry weight, and seeds per berry).

Abstract
The goal of this research is ultimately more sustainable production of lowbush blueberry and cranberry through more reliance on beneficial insects and less reliance on pesticides in these important and extensive agroecosystems in the Northeast. This in turn will contribute to a cleaner environment and safer, healthier food. Broadleaf herbicides kill plants that bees and wasps use for forage. Other herbicides control grasses, rushes, and sedges, which while not forage plants, may provide important microhabitats for beneficial bees and wasps.

Sixteen lowbush blueberry fields and ten cranberry bogs were sampled in 1998 for diversity and abundance of noncrop plants and Hymenoptera. In lowbush blueberry, 42 weed species were found; the number of flowering plant species present ranged from three to thirteen species per study site, including species in the adjacent forest. The most prevalent species were bunchberry, sheep laurel, raspberry, and bush honeysuckle. For cranberry, the number of species present ranged from 11 to 46 species per study site. The most prevalent weed species for cranberry were dodder, yellow loosetrife, dewberry, and cat’s ear.

Over 2,400 samples have been sorted into major categories of beneficial Hymenoptera, a subset of which have been sent to specialists out for identification so that the presence and abundance of individual species can be correlated with weed cover and yield findings.

A preliminary analysis investigating beneficial Hymenoptera abundance in blueberry for 1997 indicates that field size and percentage weed cover were related to the number of parasitoids that were recovered. In general, large fields had 41% more wasps than small fields, and the weedier fields had 27% more wasps than the less weedy fields.

An important new finding in 1998 is the presence of an excellent pollinator of cranberry, previously only known in New Jersey bogs — we have found the leafcutting bee Megachile addenda in Massachusetts cranberry bogs. In fact, it was the most abundant bee captured and was present in all bogs sampled in 1998, which suggests it has good potential as a supplemental pollinator in Massachusetts cranberry bogs.

Project Results
Hymenopteran abundance and diversity was again estimated in all fields and bogs using three sampling techniques: baited traps, flight interception traps; and malaise traps. In addition, nine 30 to 45 ft. towers of 2″ rigid conduit were erected at six sites and extended above the canopy of the forest. Each tower had intercept traps at various levels. Hymenoptera were collected throughout bloom on a weekly basis and then biweekly for six collection dates for each crop. Also, in four blueberry and three cranberry fields, sweep-net samples were taken as well as one-minute visual counts of bees in each of 15 one square meter vegetation plots during bloom. Additionally, 200 wooden nesting blocks for leaf cutting and mason bees (Megachilidae) were set up in the cranberry bogs; the bees will be reared out this February. In 1998 for cranberry, 11 nonparasitic bee genera were collected: Agopostemon, Andrena, Augochorella, Bombus, Ceratina, Colletes, Dialictus, Evylaeus, Lasioglossum, Megachile, and Osmia.

Cluster analysis was used to group cranberry bogs sampled in 1998 by floral and plant density per taxa. There were no groupings of floral or plant density that closely matched the cluster tree produced from an analysis of the number of bees by genus. At this time, it does not appear that the differences in bee communities and floral density between bogs are directly related. However, it should be noted that many of the bogs adjoined residential areas with ample floral resources. The analysis also revealed that clear regional differences existed between bee communities.

Among the categories of beneficial Hymenoptera, Dr. J. Cane has confirmed our identification of the leaf cutting bee Megachile addenda, which is an important new record for Massachusetts cranberry bogs. Cane found it to be an effective pollinator of cranberry in New Jersey bogs. In 1998, this species was the most frequently captured bee and was present in all bogs sampled, which suggests it has good potential as a supplemental pollinator in Massachusetts cranberry bogs.

There was no apparent relationship between the number of bees recovered in 1997 from blueberry fields and the variables of field size or weediness. By contrast, both field size and percentage weed cover were related to the number of parasitoids that were recovered. In general, large fields had 41% more wasps than small fields and the weedier fields had 27% more wasps than the less weedy fields.

A measure of herbicide-intensity for 1998 is being derived from our periodic visits to the study sites, grower spray records, and interviews with growers. It would be premature to draw major conclusions until the data are analyzed for the 1998 samplings.

To more fully understand the interactions that occur between the Hymenoptera of the blueberry field or cranberry bog and the adjacent forests, we extended our sampling transects into the adjacent forests at study sites. Once the samples are analyzed, we will be able to determine whether smaller fields with more forest edge reduce the effects of herbicides on beneficial bees and wasps.

To accurately assess how the abundance and diversity of beneficial Hymenoptera influenced crop productivity, the results from the Hymenoptera specialists need to be yet obtained. We are in the process of obtaining yield information for blueberry; it has been obtained for cranberry.

Reported December 1998. 1999 Northeast Region SARE/ACE Report.

Collaborators: