The house mouse is probably the most widespread invasive mammalian species, being ubiquitous worldwide. In commensal situations, they are known mainly for property damage, for consumption and contamination of stored foods, as a noise/sanitation/odor nuisance, and as a vector of some diseases. In some field settings, they also cause considerable damage to field crops and to natural resources, such as when introduced to islands. We rely heavily upon sanitation, rodent-proofing, capture devices, and rodenticides to control populations and reduce damage. However, a number of situations exist whereby these traditional methods are not adequate or appropriate: crop damage during “mouse plagues” in Australia, livestock feed consumption and contamination and disease hazards in poultry and animal facilities in the U.S., and natural resource damage on small islands. In this review, challenges and some potential solutions to house mouse management are presented, including genetic resistance to anticoagulants, the effectiveness of baits given abundant food resources, the re-invasion problem and need for perimeter strategies, efforts with fertility control, and the need for effective multi-capture trap devices. In difficult situations, an IPM strategy that incorporates a combination of methods closely integrated with land uses and management practices is necessary.

Commensal rats cause significant damage to human food supplies and property around the world. They also cause severe ecosystem disruption, and even species endangerment, when introduced to islands. Effective attractants could help manage rat populations by increasing the probability of getting rats to detection stations, traps, and bait stations. Bait stations may contain a rodenticide, a fertility control agent, a disease vaccine, or an ecto-parasite control chemical. Effective rat attractants have not been made commercially available, although a few candidates have been identified over the years. We investigated 18 commerciallyavailable materials for their attractiveness to groups of wild Norway rats in a pen study. The most promising candidate attractants, based on the number of station visits, were almond, ginger, and lemon extracts. However, a subsequent, brief field trial at a livestock feedlot with a resident Norway rat population did not result in greater rat capture numbers with any of the 3 attractants over traps only containing water. It appears that additional testing of these and other materials will be necessary before an effective attractant can be discovered and made available for Norway rat population management.

The majority of rabies cases reported to the Centers for Disease Control each year occur in wildlife including skunks, raccoons, bats, foxes, and coyotes. Currently, oral rabies vaccination campaigns are employed to immunize coyotes, foxes, and raccoons. Though skunks are vectors of 6 rabies strains, there is currently no effective oral vaccine or delivery system for skunks. More information is needed to determine if baits currently used are sufficiently attractive to skunks, or if the baits are difficult for skunks to handle and consume. We observed bait manipulation by skunks in penned feeding trials to determine the bait type most conducive to ingestion and delivery of a mock vaccine to skunks. Smaller baits were easier for skunks to manipulate and consume, and vaccine containers coated with bait facilitated sachet puncture and increased the potential for vaccine delivery. Our information will be useful in the development of baits and vaccine containers for large-scale rabies vaccination campaigns that target skunks.

Aerial delivery of rabies vaccine-laden bait is effective and efficient for large-scale vaccination of wildlife. Oral rabies vaccine (ORV) contained in a sachet (or blister pack) inside baits that serve as the mode of delivery currently are used for orally immunizing foxes, raccoons, and coyotes. The technique remains in the vaccine-development stage for oral immunization of skunks. Since skunks are a major vector of the rabies virus, concurrent development of a bait that is sufficiently attractive to skunks would facilitate an immediate mode of delivery once a vaccine is developed. We ran a palatability experiment with different shapes and flavors of baits to assess uptake by captive skunks. The flavors most preferred were fish and chicken. We also evaluated the fate of the sachet (punctured or not) inside baits, which would assist in assessing the delivery of a vaccine dose. On average, cylindrical-shaped baits had a higher percentage of punctured sachets than did rectangular-shaped baits, and baits with their matrix directly coated onto the sachet had a higher percentage of punctured sachets than did those baits in which the sachet was “held.” We also used sulfadimethoxine, a short-term quantifiable biomarker, as a mock vaccine inside sachets in an attempt to quantify the amount of liquid ingested by skunks after consuming baits of different shape and size. While this information could have been useful for assessing the amount of vaccine delivered via sachet puncture, it could not be determined due to an aversive tasting biomarker. For effective ORV bait uptake by skunks, modifications to current baits should include a smaller size and a meat flavor matrix that is directly coated onto the sachet.

Nutria were introduced from South America to the United States in the 1930s for fur farms and, due to releases and escapees, are currently established in 15 states. Nutria are important to the Louisiana fur industry, but they also cause extensive damage to coastal marsh ecosystems when populations are high. Louisiana uses an incentive program for hunters and trappers during trapping season (winter), which helps to control the fast-growing nutria populations. While this approach is effective, additional management tools are needed to control nutria year-round and over large areas. Other tools for nutria control include toxicants, baits and lures, and multiple-capture traps. In this study, we evaluated nutria responses to olfactory cues in a Y-maze that potentially could be used as lures in traps or bait stations. Three olfactory cues were selected more frequently than others: Nutria #1 (apple-based commercial lure), nutria gland secretion, and female nutria fur extract. We also evaluated attention by nutria to two species of fertilized and non-fertilized marsh plants that potentially could be used as lures in multiple-capture traps on coastal marsh. Nutria did not show a strong preference for either plant species, but they gave significantly more attention to fertilized plants than non-fertilized plants or soil treatments. Results with nutria urine were equivocal. The materials identified in this study show potential for the development of additional tools to manage nutria populations and their impacts on coastal marsh ecosystems.

Nutria are large semi-aquatic, herbivorous rodents native to South America, but were brought to the United States in the early 1900s for the fur farming industry. At high densities, nutria damage marsh vegetation. To more effectively manage nutria, we identified effective attractants and designed a multiple capture trap (MCT). Four lures (nutria urine, nutria fur extract, synthetic anal gland secretion, and a commercially available apple-based lure) were examined under field conditions, using leg-hold traps. A total of 285 nutria were captured during a 10-day trial with 1,000 trap-nights. All lures tested increased trapping success from 42% to 120% over untreated traps, with nutria fur extract being the most effective. Additionally, the lures did not attract nontarget animals. Next, we tested the MCT: 6 were baited with foods (carrots, corn, and sweet potatoes), and another 6 used trays of fertilized marsh plants as the lure. During the 10-day trial, with 122 trap-nights, 10 nutria were caught in the food-baited traps and 12 in the marsh plant-baited traps. As many as 3 nutria were captured overnight in one trap. On two occasions, individual nutria escaped the traps when approached by a person. No non-target animals were captured, however, it was suspected that swamp rabbits were entering the MCTs to feed and then were able to go back out the “one-way door”.