International Program to Monitor Cat Flea Populations for Susceptibility to Imidacloprid.

An international team of scientists and veterinarians was assembled in 1999 to develop a monitoring program to determine the susceptibility of cat fleas, Ctenocephalides felis felis (Bouché) (Siphonaptera: Pulicidae), to imidacloprid. Cat flea eggs were collected, shipped to laboratories, and tested for their susceptibility to imidacloprid. Over 3,000 C. felis populations were collected from 2002 to 2017 from 10 different countries. Of these, 66.3% were collected from cats and 33.7% from dogs. C. f. felis populations (n = 2,200) were bioassayed by exposing cat flea eggs and the emerging larvae to a Diagnostic Dose (DD) of 3 ppm imidacloprid in larval rearing medium. Flea eggs hatched and developed in the untreated controls in 1,837 of the isolates (83.5%) bioassayed. Flea isolates (n = 61) that had ≥5% survival at the DD of 3 ppm were retested with a second DD of 3 ppm. None of them had ≥5% survival to the second dose of 3 ppm. Of the 1,837 valid C. felis isolates tested, there has been no evidence of a decreased susceptibility to imidacloprid over the past 17 yr. The methods outlined in this article should provide an acceptable protocol for testing many of the new active ingredients that have been registered for cat flea control.

Pesticide compatibility with natural enemies for pest management in greenhouse gerbera daisies.

Pesticides commonly used in commercial greenhouse management were evaluated for compatibility with two biological control agents: a leafminer parasitoid (Diglyphus isaea [Walker]), and a predatory mite (Neoseiulus californicus [McGregor]). These natural enemies were exposed to miticides, fungicides, and insecticides targeting leafminers, thrips, and whiteflies, according to label directions in laboratory vial assays, after which mortality at 12, 24, and 48 h was recorded. Greater mortality of predatory mites than leafminer parasitoids was observed overall, illustrating that fewer pesticides were compatible with predatory mites compared with the parasitoid. However, some commonly used pesticides were found to cause high mortality to both the leafminer parasitoid and predatory mites. Twospotted spider mite (Tetranychus urticae Koch) infestations often disrupt leafminer (Liriomyza trifolii [Burgess]) biocontrol programs. Therefore, potentially compatible miticides (bifenazate, hexythiazox, spiromesifen, acequinocyl, etoxazole, and clofentezine) identified in laboratory trials were also evaluated in a greenhouse study and found to be compatible with leafminer biocontrol.

Gonotrophic development and survival in field populations of Musca domestica (Diptera: Muscidae) at dairies in California, Minnesota, and Georgia, and the relationship of fly age to relative abundance of (Z)-9-tricosene (muscalure).

Adult female Musca domestica L. were collected in 2004 and 2005 from dairies in California, Minnesota, and Georgia. Relative abundance of (Z)-9-tricosene (muscalure) among the dominant eight hydrocarbons was determined. Fly heads then were removed to quantify pterin levels and estimate fly age, abdomens were dissected to score gonotrophic development and parity (follicular relics), and spermathecae were examined for sperm. Daily survival was assessed using two estimates of time required to become gravid: laboratory-based degree-day (DD) estimates and estimates based on pterin values in field-collected flies matched to their stages of gonotrophic development. Among newly emerged females (oocyte stage 1) with detectable muscalure, it comprised < approximately 1.5% of cuticular hydrocarbons. In muscalure-positive flies, muscalure comprised a higher proportion of cuticular hydrocarbons in older flies from California and Minnesota (6-9% when gravid) versus flies from Georgia (<2% when gravid). Females mated in early-intermediate stages of egg development. Life expectancy, using laboratory-derived estimates of time needed to become gravid, ranged from 3.6 to 10.6 d. Using equivalent pterin-based time estimates, life expectancy ranged from 4.0 to 19.5 d. Mean DD ages (12 degrees C threshold) of gravid flies varied widely (53-95 DD) and were congruent with laboratory-based estimates (52-57 DD) in only 7 of 12 farm-year combinations. Thus, house flies under natural conditions often required more time to develop eggs than laboratory models would predict, extending daily survival estimates based on gonotrophic age by 11-74%.

Characterization of age and cuticular hydrocarbon variation in mating pairs of house fly, Musca domestica, collected in the field.

House flies, Musca domestica L., were collected in copula over two summers from six dairies located in three climatically distinct regions in the U.S.A. southern California, Minnesota and Georgia. Ages of males and females from a total of 511 mating pairs were estimated using pterin analysis. Cuticular hydrocarbon profiles and gonotrophic ages of females also were evaluated. Mean age of mating males ranged from 54 to 102 degree-days (DD) (4-10 days based on field air temperatures), depending on the farm. Very young males (< 10-20 DD) and old males (> 200 DD) were rare in mating pairs. Mean female age at mating ranged from 20 to 46 DD (2.5-4 days). All mating females had eggs in the early stages of vitellogenesis and 99.2% were nulliparous. However, some older and parous females were collected, demonstrating that re-mating can occur in the field. Head width measurements of mating pairs suggested that assortative mating by size did not occur. The cuticular hydrocarbon profiles of females were determined, with emphasis on (Z)-9-tricosene (muscalure). Overall, only 55% of mating females had detectable amounts (> 4 etag per fly) of (Z)-9-tricosene. Of the females that had detectable (Z)-9-tricosene, variation in amount per female was high in all fly populations, and thus was not statistically related to the size or age of the mating female. The proportion of mating females with detectable levels of (Z)-9-tricosene varied by geographic region. Seventy-one, 63, and 27% of females from southern California, Minnesota and Georgia had detectable amounts of (Z)-9-tricosene. Principal components analysis of the eight most abundant hydrocarbons from mating females, by state, revealed state-level distinctiveness of hydrocarbons in house fly populations, which may reflect genetic variation associated with environmental stresses in those geographical zones.

Transmission of Salmonella to broilers by contaminated larval and adult lesser mealworms, Alphitobius diaperinus (Coleoptera: Tenebrionidae).

The ability of the lesser mealworm, Alphitobius diaperinus (Panzer), commonly known as the darkling beetle, to transmit marker Salmonella Typhimurium to day-of-hatch broiler chicks was evaluated, as well as the spread to nonchallenged pen mates. In trial 1, day-of-hatch chicks were orally gavaged with 4 larval or 4 adult beetles that had been exposed to marker Salmonella-inoculated feed for 72 h. In addition, chicks were gavaged with the marker Salmonella in saline solution. These chicks were then placed into pens to serve as challenged broilers. In trial 2, all pens received 2 challenged chicks that were gavaged with larvae or beetles that had been exposed to marker Salmonella-inoculated feed for 24 h and then removed from the inoculated feed for a period of 7 d. At 3 wk of age, cecal samples from the marker Salmonella-challenged broilers and from 5 pen mates in trial 1, or 10 pen mates in trial 2, were evaluated for the presence of the marker Salmonella in their ceca, and at 6 wk of age, all remaining pen mates were sampled. To monitor the presence of the marker Salmonella within pens, stepped-on drag swab litter samples were taken weekly. For the Salmonella-saline pens, 29 to 33% of the broilers that had been challenged and 10 to 55% of the pen mates were positive at 3 wk of age, and only 2 to 6% had positive ceca at 6 wk. For the pens challenged with adult beetles, 0 to 57% of the challenged broilers and 20 to 40% of the pen mates had positive ceca at 3 wk, and 4 to 7% were positive at 6 wk. The pens challenged with larvae had the greatest percentage of marker Salmonella-positive broilers; 25 to 33% of the challenged broilers and 45 to 58% of pen mates were positive at 3 wk, and 11 to 27% were positive at 6 wk. These results demonstrated that ingestion of larval or adult beetles contaminated with a marker Salmonella could be a significant vector for transmission to broilers.

Determining a diagnostic dose for imidacloprid susceptibility testing of field-collected isolates of cat fleas (Siphonaptera: Pulicidae).

The susceptibility of four laboratory strains of cat fleas, Ctenocephalides felis (Bouche), to imidacloprid was determined by three different laboratories, by using a standardized bioassay protocol. The probit lines generated by the different laboratories were very similar, with LC50 values ranging from 0.32 to 0.81 ppm. Based on these data, a diagnostic dose (DD) of 3 ppm imidacloprid in larval rearing media was provisionally identified for detecting shifts in tolerance, possibly as a consequence of incipient imidacloprid resistance. None of the larvae from the susceptible laboratory strains survived the DD. Eighteen field-collected isolates were evaluated for their susceptibility to imidacloprid and to validate a DD of 3 ppm. Probit lines from 18 field-collected isolates were very similar, with LC50 values ranging from 0.14 to 1.52 ppm. When exposed to the DD, between 3 and 10% of the exposed larvae emerged as adults from only three of the 18 isolates. All other field isolates gave 100% mortality at the DD. Under the criteria established (>5% survivorship at 3 ppm), two isolates would be established on mammalian hosts and more extensive tests conducted to exclude or confirm the presence of resistance. The DD of 3 ppm is robust enough to eliminate most of the susceptible isolates collected until today, yet low enough to identify possible isolates for further testing.

Acaricide resistance in northern fowl mite (Ornithonyssus sylviarum) populations on caged layer operations in Southern California.

Southern California caged layer operations were visited over 3 yr. Northern fowl mites from 26 field populations were tested for acaricide resistance using a capillary pipette and glass dish bioassay. One was a susceptible field population with no pesticide exposure for over 30 yr (reference site for resistance ratio calculation). Technical and commercial formulations of malathion, carbaryl (Sevin), permethrin, and a commercial formulation of tetrachlorvinphos/dichlorvos (Ravap) were tested. Malathion did not have high activity for mites relative to other materials, but resistance to both technical and commercial formulations was low (< 5x). Resistance to other materials was moderate to extreme. Frequency of carbaryl resistance (> 10x) was higher with the commercial (88%) than the technical material (41%); 19% of the populations had resistance > 100x to commercial carbaryl. Frequency of Ravap resistance (> 10x) was 68%; 8% of populations had resistance > 100x. Frequency of permethrin resistance (> 10x) was 72% for the technical material and 88% for the commercial formulation. Extreme permethrin resistance (> 1,000x) was observed in 56 and 50% of mite populations assayed using the technical and commercial formulations, respectively. Among sites, resistance to permethrin was uncorrelated with resistance to other chemicals, suggesting a different resistance mechanism. Resistance to carbaryl and Ravap was highly correlated [r = 0.76 at the LC50 level (concentrations estimated to be lethal to 50% of the test population) and r = 0.99 at the LC95 level], suggesting a common resistance mechanism. Producers currently depend completely on pesticides to control mite infestations. Mite resistance to registered materials emphasizes the need for integrated control measures.

Efficacy and longevity of nitenpyram against adult cat fleas (Siphonaptera: Pulicidae).

Nitenpyram (Capstar) is a fast acting, orally administered flea treatment that is absorbed into the blood of the host animal and is readily available for uptake by feeding fleas. We examined the efficacy of a single dose of nitenpyram against adult cat fleas, Ctenocephalides felis (Bouché), over several days. We recorded adult flea mortality and flea egg production on treated and untreated cats. Nitenpyram provided 100% kill of all fleas on the host at the time of treatment and for up to 24 h after treatment. Between 24 and 48 h after treatment, there was a 98.6% reduction in adult flea numbers. From 48 to 72 h, there was a 5% reduction in adult fleas. There was a 97% reduction and 95.2% reduction in the number of flea eggs collected from treated versus untreated animals during the first 48 h and from 48 to 72 h, respectively. In addition, we quantified three distinct behavioral responses of infested adult cats treated with nitenpyram to determine the extent of any immediate, overt behavioral responses in treated animals. A significant increase in scratching, biting, licking, and twitching occurred for 5 h. The biting and licking continued for 7 h after treatment. Administration of nitenpyram provides an effective mechanism to eliminate adult fleas from hosts for up to 48 h after treatment.

Development of a larval bioassay for susceptibility of cat fleas (Siphonaptera: Pulicidae) to imidacloprid.

Strategies for controlling cat fleas, Ctenocephalidesfelisfelis (Bouché), have undergone dramatic changes in the past 5 yr. With the advent of on-animal treatments with residual activity the potential for the development of insecticide resistance increases. A larval bioassay was developed to determine the baseline susceptibility of field-collected strains of cat fleas to imidacloprid. All four laboratory strains tested showed a similar level of susceptibility to imidacloprid. Advantages of this bioassay are that smaller numbers of fleas are required because flea eggs are collected for the test. Insect growth regulators and other novel insecticides can also be evaluated. Using a discriminating dose, the detection of reduced susceptibility in field strains can be determined with as few as 40 eggs.

Monitoring northern fowl mites (Acari: Macronyssidae) in caged laying hens: feasibility of an egg-based sampling system.

Northern fowl mites were monitored on a caged-layer operation in southern California for 22 mo. Three experienced observers underestimated actual numbers of mites in the vent region approximately 80% of the time. Errors were higher for heavy infestations. Observer estimates were highly correlated with each other (r > 0.89, P < 0.01) and with mite numbers estimated by vent feather removal (r > 0.82, P < 0.01). Mites on hens varied between houses and over time. Molting consistently reduced mite numbers, but did not eliminate then in a flock. Long-term monitoring of individual sentinel hens demonstrated that some hens would support high numbers of mites for several months or more. Use of a new sequential hen sampling plan required approximately 1 min per hen, if mite numbers were estimated. At this site, treatment decisions often could be reached in < 20 min per house. Mite scores (index of estimated mites per hen) were well correlated with percentage of hens infested in both test houses. In a chronically infested house, prevalence of mites on eggs averaged 8.5%, with a range of 0-55%. Applications of tetrachlorvinphos-dichlorvos by the producer appeared to be based on mites on > about 20% of eggs. The chemical was marginal for controlling mites on hens (25% reduction in percentage of hens infested), but effectively reduced mites on eggs (95% fewer mites on eggs at 1 wk and 90% at 2 wk). When data were grouped by mite index score on hens, there was a strong relationship (r2 = 0.83, P < 0.01) between mite prevalence on eggs and the scores of the hens which laid them. Sampling 100 eggs evenly spaced in a house required < 7 min, and adult mites were easily seen. Sampling mites on eggs appears to be useful to localize at least high-level infestations, and egg-based sampling for mites merits further investigation.

Review of insecticide resistance in cat fleas (Siphonaptera: Pulicidae).

Insecticide resistance often is blamed for failures of insecticides to control cat fleas, Ctenocephalides felis (Bouché). Yet the genetics and adaptive advantage of resistance traits remain unexamined. Lethal doses of insecticides that kill 50% of the population fluctuate 7-fold within a cat flea strain. Many reports of flea resistance may be attributable to variable mortality from effects of solvents, substrates, humidities, temperatures, colonization, and ages of fleas. Resistance ratios (ratios of lethal doses of a resistant to a susceptible strain) are < 690-fold in fleas; lower than many other arthropods. This, plus strain variability, hinders resistance detection. Relationships between resistance levels, control failures, and health threats are unclear. Insensitive acetylcholinesterase, knockdown recovery, glutathione transferase conjugation, and mixed function oxidase/cytochrome P450 are demonstrated resistance mechanisms in cat fleas. Ecological genetics of resistance in cat fleas probably involves flea transfer among hosts, host movements, refugia, founder effects, and mortality from abiotic factors. Understanding cat flea resistance requires population monitoring before, during, and after insecticide treatments using conventional and rapid molecular bioassays. Sustained insecticide release devices such as flea collars and long-lived insecticide residues for premises possibly contribute to the development of resistance. New systemic and topical insecticides, especially when given prophylactically, may act similarly. Eliminating insecticides prevents insecticide resistance but necessitates application of biorational tactics incorporating mechanical, environmental, and cultural controls. Using high temperatures, low humidities, host grooming and such tactics as decreasing doses, increasing action thresholds, rotating insecticides, and leaving spatial and temporal refugia may suppress cat flea resistance.

Host grooming efficiency for regulation of cat flea (Siphonaptera: Pulicidae) populations.

Grooming efficiency was studied by infesting domestic short-hair cats, Felis catus L., with known numbers of cat fleas, Ctenocephalides felis felis Bouché, then collecting the cat feces and extracting the fleas to determine how many had been groomed off, varying the infestation level. Some hosts were found to be significantly more efficient at grooming fleas than others, with the best groomer removing 17.6% of its flea burden daily, compared with only 4.1% removed by the poorest groomer. Cats were more efficient at grooming fleas at infestations of < 50 fleas and > 150 fleas. Mean on-host flea longevity was 7.8 d.

Residual effectiveness of insect growth regulators applied to carpet for control of cat flea (Siphonaptera: Pulicidae) larvae.

Three insect growth regulators, fenoxycarb, methoprene, and pyriproxyfen, formulated as total release aerosols, were tested for their residual effectiveness on carpet in bioassays with cat flea, Ctenocephalides felis (Bouché), larvae. All treatments except methoprene produced significant mortality for the 7-mo duration of the test. In general, fenoxycarb and the higher rates of pyriproxyfen reduced adult flea emergence by > 80%.

Larvicidal effects of boric acid and disodium octaborate tetrahydrate to cat fleas (Siphonaptera: Pulicidae).

Borate products varied in efficacy against larval cat fleas, Ctenocephalides felis felis Bouché, with some effective at rates of 23 micrograms/cm2 when larvae were exposed to the compounds in sand. Powdered boric acid, granular boric acid, and disodium octaborate tetrahydrate (Polybor) at rates of 200 micrograms/cm2 produced < or = 90% mortality of larvae exposed in carpet for 96 h. LC50 values of larvae exposed in treated carpets for 96 h were 23 micrograms/cm2 for powdered boric acid, 40 micrograms/cm2 for granular boric acid, and 47 micrograms/cm2 for polybor.

Egg production, larval development, and adult longevity of cat fleas (Siphonaptera: Pulicidae) exposed to ultrasound.

Adult cat fleas, Ctenocephalides felis felis (Bouché), on cats (Felis catus) were exposed to emissions from an ultrasonic flea collar worn by the cat. No significant differences were found in total numbers of eggs produced per day (mean = 524 control, 614 treatment), in length of larval development time (mean = 7.7 d control, 7.7 d treatment), or in total daily pupal production (mean = 485 control, 445 treatment) between the treatment and the control groups. Tests off the host were conducted to determine whether ultrasonic exposure caused mortality in adult fleas; no significant differences were found in daily mortality between the treated and control fleas during 1 wk of exposure.

Effect of temperature on toxicity of three pyrethroids to horn flies.

Predictive models describing best-fit regression equations for per cent mortality of horn flies as a function of temperature were determined for each of three pyrethroid insecticides (fenvalerate, flucythrinate and permethrin) over the temperature range 20-35 degrees C. Susceptible horn flies, Haematobia irritans (L.), were exposed to c. an LC70 dose of each pyrethroid using a residue-on-glass method. This technique used confined exposure in chambers with temperatures of 20, 25, 30 and 35 degrees C. Within this range, mortality was greatest at 25 degrees C with all three insecticides. Estimated temperature-mortality equations for each pyrethroid revealed different responses of horn flies to each of these insecticides. Horn flies exposed to flucythrinate demonstrated a linear mortality response that varied inversely with temperature. The response to permethrin was described by a quadratic equation, while the response to fenvalerate was best fitted by a cubic equation.

Method for determining settling rates of Bacillus thuringiensis serotype H-14 formulations.

A water-column apparatus is described in which settling rates of Bacillus thuringiensis serotype H-14 [B.t. (H-14)] formulations can be indirectly quantified using mortality of mosquito larvae at restricted depths as an index of B.t. (H-14) activity. To illustrate the type of data provided by this method, commercial B.t. (H-14) products (Bactimos, Teknar, Vectobac) and experimental formulations were compared at the manufacturers' recommended rates for mosquito control. All evaluations utilized laboratory-reared, 4th-instar Aedes aegypti larvae. The procedure can be used to provide an index of suspension properties of different B.t. (H-14) formulations and to measure dispersion rates of granular formulations resting at the bottom of a water column. Standardization of the method provides a convenient and practical means of generating comparative data on the effectiveness of B.t. (H-14) and other mosquito larvicides against specific target species.

Role of insects in the transmission of bovine leukosis virus: potential for transmission by stable flies, horn flies, and tabanids.

The ability of stable flies (Stomoxys calcitrans), horn flies (Haematobia irritans), and tabanids (Diptera: Tabanidae) to transmit bovine leukosis virus (BLV) was investigated. Stable flies and horn flies were fed on blood collected from an infected cow, and the flies' mouthparts were immediately removed, placed in RPMI-1640 medium, ground, and inoculated into sheep and calves. Infection of sheep occurred with mouthparts from as few as 25 stable flies or 25 horn flies. However, sheep were not infected when removal of stable fly mouthparts was delayed greater than or equal to 1 hour after blood feeding. Infection of calves occurred after inoculation of mouthparts removed immediately after feeding from as few as 50 stable flies or 100 horn flies. Infected blood, applied by capillary action to the mouthparts (labella) of 15 deer flies (Chrysops sp) and a single horse fly (Tabanus atratus) caused infection in each of 2 sheep. Infection did not occur in 2 calves inoculated daily for 5 days with mouthparts from 50 horn flies collected after feeding on a BLV-infected steer. Four calves receiving bites from 75 stable flies interrupted from feeding on a BLV-positive cow also were not infected. Seronegative cattle held for 1 to 4 months in a screened enclosure with positive cattle in the presence of biting flies were not infected with BLV. The feeding behavior of each insect is discussed to assess their potential as vectors of BLV.