Roof rats and other rodents are a common pest in agriculture, causing extensive amounts of damage and losses. Poultry farms provide an abundance of resources that attract rodents but our ability to control them in these locations is limited. Bait stations can become sources of nesting or go unused if the target species only travels in aerial locations. Any uncontrolled rats will quickly overpopulate agricultural buildings due to their high reproductive rates. We tested alternative baiting devices at a large poultry farm to develop a station that was easily utilized in aerial locations and well accepted by roof rats. We deployed ContraPest®, a contraceptive liquid bait, in the devices and tracked consumption monthly. We monitored the rat populations for 16 months with remote cameras to measure changes in activity before and during ContraPest baiting using a general index approach. Linear regression showed a significant relationship between ContraPest consumption and the general index. As rats continuously consumed ContraPest from the new baiting devices, activity steadily declined. Within one year of using ContraPest, rat activity reduced by 94%, showing a significant difference from starting activity levels. These results demonstrate the impact an antifertility agent can have on rat populations when used successfully within an integrated pest management program.

Traditional rodent management tools, such as traps and lethal rodenticides, are acute measures to reduce commensal rodent populations. Given the growing concerns regarding effectiveness, environmental safety, and animal welfare related to these tools, it has become imperative to find new methods. Fertility control is an emerging potential alternative to these tools as a safe, humane and effective method of long-term population management. SenesTech, Inc. has developed a liquid fertility management bait that causes follicle depletion in the ovaries of female Sprague Dawley rats and compromises sperm production in male Sprague Dawley rats in laboratory settings. These studies have shown significant decreases in litter sizes following bait consumption, but acceptance of this bait by wild rodents needed to be confirmed. Bait acceptance was tested within refuse rooms of the New York City subway system. Bait was provided ad libitum for 90 days. Uptake was evaluated by examining, via fluorescence microscopy, the presence of the bait marker rhodamine B, which manifests as fluorescent bands in whiskers. Presence of these bands indicated that 51% of the captured population had consumed the bait, and of these, 58% had taken the bait more than once. These results demonstrate that wild rats will consume a liquid fertility management bait, even in the presence of highly palatable and abundant food within the refuse rooms. This study establishes the successful acceptance of a bait by wild rats. Further investigation is needed to evaluate the effectiveness of this product for the management of urban Norway rat populations.

A non-toxic liquid fertility control bait for rats has recently become commercially available (ContraPest® from SenesTech, Inc.). This product contains two chemicals, both of which impair spermatogenesis in male and reduce ovulations in female rats. We tested the efficacy of this bait in wild-caught adult black rats from the island of Hawai’i in a short-term laboratory trial. A control group (n = 25) was offered placebo bait and the treatment group (n = 25) was offered fertility control bait, both ad libitum, during a 15-day introduction period and during the first of four breeding rounds, for a total of 58 days of exposure. After treatment, all rats were provided placebo bait for the remainder of the study and randomly paired with mates from within their treatment groups for two additional breeding cycles. Treatment and control groups comprised 10 breeding pairs each, with random re-pairings between breeding rounds. The treatment group produced no litters during the first and second breeding rounds, while 70% of the control females produced litters. In the third breeding round, 70 days after stopping treatment, the treatment group produced three litters (six pups) compared to seven litters (24 pups) in the control group. During a fourth and final breeding round, control rats were crossed with treated rats, producing six litters (27 pups) from treated dams and nine litters (40 pups) from control dams, indicating no apparent infertility effect 99 days after cessation of treatment. This study demonstrates that the reproduction rate of wild-caught black rats can be chemically suppressed if provided ad libitum access to the fertility control bait under laboratory conditions.

Norway rats cause extensive crop loss, infrastructure damage, and are vectors for zoonotic diseases. Due to growing efficacy, environmental, and animal welfare concerns related to traditional pest management tools, it is important to find new methods for controlling commensal rodents. Fertility control is emerging as a safe, humane, and effective method of long-term pest population management. SenesTech Inc. has developed an oral, liquid fertility management bait with two active ingredients: 4-vinylcyclohexene diepoxide (VCD) and triptolide. Previously, a 95% reduction in pups was observed through three breeding rounds when wild-caught Norway rats were caged in pairs and offered this bait for 50 days. Following these results, wild-caught Norway rats (n=6 males; n=15 females per group) were placed in open arenas, offered bait (in the presence of rat chow and water) ad libitum for 56 days, and allowed to breed for four rounds. Animals were bred within their treatment paired groups (control or treatment) for the first three rounds and then treatment cross-bred during the fourth round. Through three breeding rounds, 255 pups were born to control breeding pairs, compared to 12 pups born to treated breeding pairs. In the final round, 93 pups were born to control females paired with treated males and 80 pups were born to treated females paired with control males. A significant reduction in epididymis weight, and in testis weight and volume, was observed in treated males, while ovarian weight was reduced in treated females. These results indicate that fertility was dramatically reduced in wild caught Norway rats after consuming fertility management bait. Rats voluntarily consumed the treatment bait, and this free selection is essential for future field trials where the ability of the bait to reduce wild rat populations will be assessed in agricultural and urban settings.

Lethal rodenticides and other lethal tools of managing commensal rodent populations long-term are not sustainable due to population rebounds and increasing resistance to rodenticides. The use of integrated pest management (IPM) programs are more prevalent due to consumer desire to decrease rodenticide use and utilize environmentally friendly, humane methods. IPM plans often require multiple tools to control an infestation, such as physical, biological and chemical measures. Here, we propose that rodent population management would benefit from a new tool aimed at targeting the biological source of overabundance: reproduction. SenesTech, Inc. (Flagstaff, AZ USA) has developed ContraPest®, a liquid bait that limits the reproductive capacity of both male and female wild Norway and Roof rats. The two active ingredients, 4-vinylcyclohexene diepoxide (VCD) and triptolide, deplete all stages of follicles in the female and disrupt spermatogenesis in the male. Laboratory and field studies reveal that ContraPest® is palatable and repeatedly consumed by rats even when provided with ad libitum food and water. Studies involving laboratory and wild caught rats have demonstrated a 93 - 100% reduction in litter sizes of rats treated with ContraPest® compared to control rats. ContraPest® was tested on free ranging rat populations in agricultural and urban settings. Rat populations on protein production farms decreased by an average of 46% following 100 days of treatment with ContraPest®. In a complex urban environment, where property boundaries limit access to populations and foraging areas, ContraPest® reduced the seasonal population peak by 67% after 133 days of baiting. These studies, combined with all of our field studies and population reduction models, demonstrate that ContraPest® is a highly effective rodent contraceptive bait in a variety of environments. We strongly believe that adding/implementing fertility management via ContraPest® to an IPM program would enhance long-term rodent population control in rural, urban, and agricultural environments.