The Vertebrate Pest Control Research Advisory Committee, through a cooperative agreement with the California Department of Food and Agriculture (CDFA), funded laboratory studies at the National Wildlife Research Center (NWRC). The objective of the studies was to obtain efficacy data for controlling house mice (Mus musculus) and deer mice (Peromyscus maniculatus) that would provide partial fulfillment of the requirements established by the Environmental Protection Agency (EPA) for the re-registration of the CDFA’s 0.01% chlorophacinone and 0.01% diphacinone grain bait labels. Swiss-Webster mice and deer mice from an on site breeding colony were placed on 15- day, two-choice feeding and efficacy trials. The control treatment groups received two dishes each containing the Office of Pesticide Programs (OPP) designated standard rat and mouse challenge diet. The treated groups received one dish of the standard OPP rat and mouse challenge diet and a second dish of the treated grain baits: 0.01% chlorophacinone (two groups of 20 animals, Groups II and III ), or 0.01% diphacinone (two groups of 20 animals, Groups II and III ) grain bait. Results from the treated groups of the four tests are reported. House mice on 0.01% chlorophacinone: female mortality was 100% in Group II and 90% in Group III. Total dietary consumption of treated bait was 23.0% of the total bait consumption. House mice on 0.01% diphacinone: female mortality was 90% in Group II and 100% in Group III. Total dietary consumption of treated bait was 18.2% of the total bait consumption. Deer mice on 0.01% chlorophacinone: female mortality in Groups II and III was 100%. Total dietary consumption of treated bait was 63.1% of the total bait consumption. Deer mice on 0.01% diphacinone: female mortality in Groups II and III was 100%. Total dietary consumption of treated bait was 66.3% of the total bait consumption. In conclusion, the female house mice ate less than the male house mice with the same mortality rate (between 90% and 100%); while the female Peromyscus ate more than the male Peromyscus, they had the same mortality rate (100%). The anticoagulant grain bait test mortality results for both house mice and deer mice met the suggested performance standard for the EPA Pesticide Assessment Guidelines.

A two-choice, taste preference study was conducted using 18 northern pocket gophers to evaluate pelleted sorghum, granulated sorghum, and wax block baits containing either 0.01 to 0.05% quinine or 0.10 to 5.0% sucrose. Bait consumption was significantly higher across treatments (P ≤ .001) for granulated sorghum, followed by pelleted sorghum, and wax blocks. Gophers also showed a high frequency of moving the granulated bait in their cheek pouches to be deposited at alternate locations within their cages. Although increasing sucrose concentration did not produce significantly (P ≥ .10) enhanced consumption for any of the baits, a trend toward increasing preference with increased concentration was noted for the wax block bait. During quinine tests, bait consumption was again significantly highest (P ≤ .01) for granulated sorghum followed by pelleted sorghum and wax block. Quinine treatment also failed to significantly (P ≥ .10) alter bait consumption across the tested concentrations. However, there was a minor trend toward decreasing preference with increasing concentrations in the wax block group. Data indicated that pelleted bait had the advantage of producing more consistent consumption levels without the animals carrying bait in their cheek pouches for caching and subsequent spillage. Although the wax block baits were most influenced by the taste treatments, consumption levels were extremely low. In comparison with most wild rodent species, northern pocket gophers were found to be insensitive or indifferent to both taste stimuli over a wide concentration range.

Trapping is an integral tool in research and control of damage caused by pocket gophers (Thomomys spp.). We evaluated three types of traps (Macabee®, Cinch, Blackhole® Rodent) in a California field trial by comparing the number of captures to activity at the sets (capture efficiency) and separately, the duration of time from first to last capture (time efficiency). On each of six study plots established on irrigated agriculture fields, 60 trap stations were established at locations of gopher mounds. One trap type was used per station and traplines were run continuously for about four days. We captured a total of 256 gophers. Overall, the Cinch trap had the highest capture efficiency (41.7%), followed by the Macabee® trap (27.7%) and the Blackhole® trap (18.3%). The Cinch trap had a significantly greater (P=0.003) capture efficiency than either of the other two trap types, which did not differ (P>0.05). From a time efficiency standpoint, the Cinch trap also ranked first (0.046), the Macabee® trap second at 0.036 and the Blackhole® trap last (0.032), though the differences were not significant (P=0.693). We conclude that the Cinch trap was the most efficient of the three trap types for capturing gophers in this study. Its chief drawback is that the large baseplate makes it more time-consuming to set. The Blackhole® Rodent trap was the least efficient for capturing gophers, and very time-consuming to set and check. Furthermore, the floor of the trap (solid plastic) may have induced trap shyness, even when covered by soil. The Macabee® ranked intermediate in both capture efficiency and time efficiency. Due to its small size and ease to set and check, it will probably remain a popular alternative for capturing pocket gophers. An integrated pest management approach is recommended for the most effective control of pocket gophers.

Baker Performance Chemical Incorporated entered into a cooperative agreement with the National Wildlife Research Center to evaluate acrolein as a fumigant for controlling northern pocket gophers (Thomomys talpoides). In October 1996, a 44.5 ha (110 acre) irrigated alfalfa hay field was selected as the study site in Franklin County, Washington. Eight treatment units (TUs), six fumigated, and two control, were established on the study site. On the six fumigated TUs, 58.9% of the sample plots were inactive, whereas, all sample plots (100%) on the two control TUs were active. The 58.9% mean reduction in pocket gopher activity on the six fumigated TUs was below the minimum efficacy standard of 70% established by the Environmental Protection Agency (EPA 1982). Possible reasons for the pocket gophers surviving the acrolein treatment are discussed.

Valley pocket gophers (Thomomys bottae) cause considerable damage each year to a variety of crops. In the fall of 1997, efficacy data were collected after the hand placement of anticoagulant grain baits into underground burrows of Valley pocket gophers in northern California. Twenty-four Treatment Units (TUs) were divided into one of four treatment groups: 1) 0.01% diphacinone; 2) 0.005% diphacinone; 3) 0.01% chlorophacinone; and 4) 0.005% chlorophacinone grain baits. Each treatment group contained five treated TUs and one control TU. Active burrow systems were hand baited with the respective baits. Efficacy was determined through use of the open-hole index and radio telemetry. Neither the 0.005% or 0.01% chlorophacinone or diphacinone grain baits met the Environmental Protection Agency’s 70% standard for verifying efficacy of rodenticides. Potential reasons for the low efficacy of less than 10% for the four treatment groups are discussed.