Conservation Biocontrol Results

On this page, you will find a summary and detail for recent research projects by Principal Investigator, Dr. Vera Krischik, and her research staff on beneficial insect and pollinator conservation including biocontrol, land management best practices, and pesticide effects on pollinators and beneficial insects.

Effects of chronic insecticide exposure on bumble bees

Declines in bee populations around the world have been attributed to various factors, one of which is pesticide use. The purpose of this project was to examine the toxicity of several insecticides to bumble bees (Bombus impatiens). We found that chlorantraniliprole (4 ppm), an insecticide commonly used for Japanese beetle control, was less toxic to bees than the neonicotinoid clothianidin (0.02 ppm). Allso, clothianidin resulted in a decrease in brood production and movement. 

Published:  Scholer, J. and V. Krischik. 2014. Chronic exposure of imidacloprid and clothianidin reduce queen survival, foraging, and nectar storing in colonies of Bombus impatiens. PLoS ONE 9(3): e91573. doi:10.1371/journal.pone.0091573

Summary:  Papers on sublethal effects of neonicotinoid insecticides on native bee behavior, compiled by Krischik Lab, 2020.

Effects of acute insecticide exposure on butterflies

The purpose of this study was to examine the lethal effects of four insecticides on monarch butterflies (Danaus plexippus) and painted lady butterflies (Vanessa cardui). Acute exposure bioassays were carried out to determine LC50 values for monarch and painted lady larvae exposed to bifenthrin (pyrethroid), chlorantraniliprole (ryanoid), clothianidin (neonicotinoid), and imidacloprid (neonicotinoid), and painted lady adults exposed to clothianidin. We found that chlorantraniliprole was the most toxic insecticide for both species; for monarch larvae, the LC50 for chlorantraniliprole was 5-20x lower than that of the other insecticides, while for painted lady larvae it was 20-9000x lower. Additionally, although painted lady larvae were more sensitive than monarchs to chlorantraniliprole, monarch larvae were substantially more sensitive to the other three insecticides. 

Effects of chronic insecticide exposure on butterflies

Chronic exposure bioassays were carried out to evaluate sublethal effects of clothianidin (neonicotinoid) on monarch (Danaus plexippus) and painted lady (Vanessa cardui) butterflies. Butterfly larvae were fed treated (0-40 ppb) foliage from third instar to pupation. We found that 40 ppb clothianidin significantly reduced the number of larvae that pupate for both monarchs and painted ladies. In addition, 40 ppb clothianidin resulted in greater mean days to pupation for monarch larvae, while there was no significant effect for painted lady larvae. 

Pesticide residues in wildflowers near crops

Pesticide drift from agricultural applications can be a source of harmful pesticide exposure for pollinators. In this project, we sampled wildflowers on the margins of potato, soybean, and corn fields. For wildflower samples collected on habitat near potato fields in MN, we found that 100% of 36 samples had at least one pesticide and as many as 15 different pesticides.

Beneficial insect habitat (beetle banks and stem nesting bees)

Beneficial insect nesting and overwintering habitats (beetle banks and stem nesting bee huts) were installed at three sites in Washington County. The purpose of this project was to investigate the effect of beetle banks and native bee stem huts on insect abundance and species richness. During a citizen science field day Nov. 4th 2019, overwintering insects were counted at 36 beetle banks and 36 stem nesting bee huts. Beetle banks had an average of 131 insects per sample, compared to 1 insect per sample in control plots including both adult and larvae. The most abundant beetle bank insects were millipedes, spiders, staphylinid, dermestid and sowbugs. 95% of the stem nesting bee huts were occupied (details to come).

A field day was held on Nov 2, 2019 at St.Croix Regional Park, Washington Co Parks, with Dan Mc Swain Natural Resources coordinator. near Stillwater, MN. Around 30 people attended the Field Day and learned about beetle banks and stem nesting bees.research that determined that beetle banks in the field are a way to conserve good insects. Research showed that  hanging stem nesting attracts and accrues stem nesters and around 75% of the stems were occupied in one year.

Research: In 2019 Beetle bumps, which are overwintering ground areas for bees and beneficial insects, and hanging bee nests, were installed at 3 sites: 2 in Stillwater, MN at St Croix Bluffs Park with the help of Dan MacSwain, Natural Resources Coordinator and Washington County Parks; and 1 site in Hastings, MN at Laurie Schneider, Pollinator Friendly Alliance. The first insect count in Feb 2019 revealed that the BEB contained more beneficial insects than on the bare ground. Beetle bumps need to be added to restorations, parks, backyards and gardens to provide habitat for good bugs and bees.

Outreach:  St. Croix Regional Parks is a model for other park systems to integrate beetle bumps and hanging nest in their habitat restoration and wild areas.  Counts clearly demonstrate beneficial insects used the beetle bumps for overwintering and nesting thus increasing populations of good bugs and predatory insects to naturally control unwanted insects and increase biodiversity. The beetle bump project was visually engaging for 10,000’s of park visitors who were curious and learned about them. Washington County Parks integrated the beetle bumps and bee huts into their public educational and naturalist programs. In March, 2020, a fact sheet and talk will be presented at the Best Practices for Pollinators Summit in Minneapolis, Minnesota for 400 state, county, local and private industry land managers.

Partnerships:  Washington County Park System serves 40,000 visitors each year. Their park and naturalist educators are now including beetle bumps in their public education programming. Xerces Society is promoting beetle bumps as a tool for rural and urban spaces. This research will support their outreach efforts with farmers, rural, and urban people. Pollinator Friendly Alliance, Washington Conservation District and Board of Soil & Water Resources is including beetle bump suggestions in information tailored for Minnesota’s Lawns to Legumes incentive program to convert turf to biodiverse pollinator habitat. 

Pesticide residues in ornamentals

Imidacloprid (neonicotinoid) is an insecticide commonly used in ornamental plants. The purpose of this study was to measure imidacloprid residue levels in ornamentals based on the label application rate, which is often higher than the rate for agricultural applications. We found that imidacloprid residue levels in ornamentals were significantly higher than neonicotinoid residues near agricultural fields.

Published:  Krischik, V., M. Rogers, G. Gupta, and A. Varshney. 2015.Soil-applied imidacloprid is translocated to ornamental flowers and reduces survival of adult Coleomegilla maculata, Harmonia axyridis, and Hippodamia convergens ladybeetles, and larval Danaus plexippus and Vanessa cardui. PLoS ONE, March 26

Effects of neonicotinoids on birds

The goal of this study was to determine imidacloprid residue levels in leaves and seeds of green ash trees (Fraxinus pennsylvanica) following a soil drench, and to compare residue levels to lethal and sublethal doses for birds reported in literature. The imidacloprid levels detected in green ash (mean 35 ppb) were not high enough to pose lethal or sub-lethal risks to birds.


These 2017-2020 conservation biocontrol research and outreach programs were made possible through a grant from the Legislative-Citizen Commission on Minnesota Resources (LCCMR) which makes funding recommendations to the Minnesota Legislature for special environment and natural resource projects on behalf of the citizens of Minnesota.