- Author: Dong-Hwan Choe
- Author: Kathleen Campbell
- Author: Michael K Rust
- Posted by: Elaine Lander
Many parks, recreational areas, and outdoor venues in California are home to yellowjacket wasps (Vespula spp.). Yellowjackets are commonly attracted to human food items, creating a serious nuisance and a potential stinging threat. If found, nests (usually underground) can be effectively treated with targeted insecticide applications (e.g., dusts containing pyrethroids). However, baiting could be a feasible alternative method to suppress yellowjackets over a wide area, especially if nests cannot be located. Currently, only one active ingredient (esfenvalerate) is registered for use within bait in California to control yellowjackets, and its efficacy is marginal because it is repellent and fast-acting. Effective active ingredients and optimal bait formulations have yet to be identified.
Foraging wasps seek out protein-rich foods for developing larvae in the nest. These foragers have strong preferences for some meats, and in the past, meats impregnated with insecticides have been used as baits. However, meat loses its attractiveness after less than a day, requiring the use of fresh meat, which has been a major hurdle in developing a commercial ”ready-to-use” bait product.
To overcome this challenge, a team of researchers from the University of California conducted experimental trials using non-meat materials as matrices for yellowjacket baits. Due to their high absorbency of water and water-soluble compounds as well as biological inertness, hydrogels were considered as possible candidates for this use. As a first step in this investigation, we observed whether foraging western yellowjacket wasps (V. pensylvanica) would accept polyacrylamide hydrogel crystals that were hydrated with chicken juice containing a toxicant.
Field Trials
The study was conducted at two different sites in southern California. Site A was a private country club (~15 acres) with supporting recreational infrastructure (e.g., picnic tables, barbecue facilities, children's playgrounds, etc.). The site was surrounded by mixed conifer and oak forest. Site B was a multiple-use regional park (~161 acres) surrounded by undeveloped wilderness areas composed primarily of riparian and coastal sage scrub. Yellowjacket foraging activity was monitored using traps containing a chemical lure, heptyl butyrate.
In 2014 and 2016, sites were baited with hydrogel bait with 0.025% (wt/wt) fipronil*. Ten yellowjackets per trap per day was used as an action threshold for baiting. To prevent consumption by non-target organisms, the bait was provided at “bait stations” within three small plastic cups placed inside a cage.
Wasps were readily attracted to the bait, manipulated the bait with their mandibles, and flew away with small pieces of the bait (Figure 1). After 24 hours, the approximate amount of bait removed from in each cup in grams (g) was estimated.
Results
The behavioral observations at the bait stations and the amount of bait taken clearly indicated that polyacrylamide hydrogel was an excellent matrix for yellowjacket baiting. The meat-like physical texture and chemical inertness of the hydrogel may explain its acceptance by foraging yellowjackets. With its ability to absorb large amounts of liquids and to resist evaporation, hydrogel bait might also remain palatable for longer periods of time compared with meat-based bait.
The use of hydrogel for bait formulation may enable manufacturers to develop a commercial ready-to-use bait product for yellowjacket control. Hydrogel baits could be pre-packaged in bait containers, though dehydrated formulations would need to be hydrated with a prescribed amount of water before use. We observed that very few non-target insects were attracted to these baits; Argentine ants and velvety tree ants were occasionally seen foraging at the bait stations. Ants were excluded by using commonly available pyrethroid-impregnated “ant guards” designed for hummingbird feeders. This study used the liquid contents from canned chicken meat as an attractant / feeding stimulant. We are currently working on replacing this “chicken juice” with a mixture of synthetic and natural attractants and feeding stimulants which would be better suited for commercialization.
*Use of fipronil in combination with chicken meat (or juice) is strictly experimental and is not registered for yellowjacket control in California. Such use by licensed professionals would currently be considered illegal.
[Originally published in the Winter 2020 issue of the Green Bulletin.]
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- Author: Belinda J. Messenger-Sikes
- Author: Karey Windbiel-Rojas
New label changes will alter how fipronil is applied by pest management professionals (PMPs) in urban environments, particularly between November and February, during California's typical rainy season.
Concerns over continued detections in urban watersheds of fipronil, a broad-spectrum insecticide commonly used against ants and other pests, led to the California Department of Pesticide Regulation (DPR) asking certain pesticide manufacturers to modify the labels of liquid formulations of fipronil to reduce negative impacts of this pesticide on the environment. These use restrictions apply to surface applications along foundation perimeters of structures.
Two nationwide changes to labels of liquid fipronil products were approved by the U.S Environmental Protection Agency (EPA) in April 2017, with the goal of keeping this active ingredient out of watersheds. These new restrictions are:
- Do not allow application to enter or runoff into storm drains, drainage ditches, gutters, or surface waters.
- Do not apply directly to sewers or drains, or to any area like a gutter where drainage to sewers, storm drains, water bodies, or aquatic habitats can occur, except as directed by this label.
Pre- or post-construction subsurface termite treatments and bait formulations are exempt from the new limitations.
California-specific label changes
In addition to these nationwide label amendments, there are some California-specific label changes. These came about through discussions among DPR, the Pest Control Operators of California (PCOC), the registrants of Termidor SC and Taurus SC, and the University of California, Riverside. The California-specific amended label was accepted by DPR in November 2017.
In California, surface applications of liquid fipronil products along foundation perimeters of structures will be further restricted as noted in Figure 2 and Table 1.
Research
UC Riverside considered these application restrictions in an applied research project and concluded that there were no significant effects on pest control efficacy for Argentine ants and that the runoff potential was low. During field efficacy trials conducted by PCOC using these new restrictions, there were no noticeable changes in callbacks observed.
Can I use products with the old label?
Containers with the revised label have been available in California since December 2017. According to California law, registrants can continue selling product with the old label until October 2019, which is 18 months after the US EPA's acceptance of the new label. Enforcement of product labels is based on the actual product label in hand. If an applicator legally obtained a product with the old label, then they can continue to use it under those label directions.
The new label restrictions for structural perimeter applications of liquid formulations are hoped to reduce the amount of fipronil detected in urban surface water systems.
[From the Spring issue of the UC IPM Green Bulletin]
Argentine ants can be a damaging ant pest species in both agricultural and urban environments in California. Outdoors, they disrupt biological control by tending honeydew-producing pests and protecting them from natural enemies. Argentine ants are also common invaders of urban residential settings, making them the nuisance ant species most often treated by pest management professionals (PMPs).
Application restrictions
In an effort to reduce pesticide runoff, in 2012 the California Department of Pesticide Regulation (DPR) issued restrictions for pyrethroid use on hardscapes by licensed professionals. In addition, the U.S. Environmental Protection Agency approved new label amendments in April 2017 for fipronil products that will significantly change the way PMPs can apply fipronil in outdoor settings for Argentine ant control. While it is not yet known how these new changes will reduce off-site pesticide contamination, it is a good time to start investigating effective alternatives for ant control.
Improving baiting
Baiting with sugar-based liquid baits has been shown to be an effective control method for Argentine ants but requires bait stations to store and dispense the bait. Bait stations can be expensive and labor-intensive to maintain. To overcome these challenges, a group of researchers at UC Riverside—Drs. Jia-Wei Tay, Mark Hoddle, Ashok Mulchandani, and Dong-Hwan Choe—developed a natural hydrogel matrix to deliver liquid ant baits (Figure 1). The use of hydrogels may allow practitioners to apply liquid bait directly to the surface of the ground where ants forage without the need for a bait station.
What is hydrogel and how does it work?
Beads of alginate hydrogel, derived from seaweed, were mass-produced using a modified shower head nozzle (view the 11-minute video at youtu.be/NVMql2xClBk or the 36-second video below). The hydrogel beads were conditioned for 24 hours in a liquid bait (25% sucrose solution with a small amount of the insecticide thiamethoxam). This amount of thiamethoxam is significantly less than the percentage found in current commercial ant bait products. The highly absorbent hydrogel acts as a controlled-release formulation that keeps the liquid bait available and palatable for an extended period. The team determined the hydrogel's properties such as water uptake and water loss characteristics, pesticide intake, and the acceptance by foraging Argentine ants. In small-scale laboratory tests, the hydrogel bait provided excellent control against all stages (e.g., workers, brood, and queens) of the Argentine ant colony within 14 days.
Field results and future uses
To determine the efficacy of the alginate hydrogel bait in urban areas, it was field-tested around residential homes in the summer of 2016 (Figure 2). Argentine ant activity levels were estimated by consumption of a sucrose solution put out in monitoring vials over a 24-hour period. Based on the monitoring data, hydrogel bait containing 0.0001% of thiamethoxam provided a 79% reduction in ant activity eight weeks after treatment.
In 2017, the team coordinated field trials to evaluate the effectiveness of alginate hydrogel baits in controlling Argentine ant populations in commercial citrus groves. While this bait delivery system is currently only experimental, the research team hopes to find a pesticide manufacturer interested in commercializing this patent-pending technology to provide a highly-efficient, low-impact outdoor baiting option for Argentine ants and other sugar-seeking pest ant species.
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