Nancy C. Hinkle

Development of a Larval Bioassay for Susceptibility of Cat Fleas (Siphonaptera: Pulicidae) to Imidacloprid

Abstract Strategies for controlling cat fleas, Ctenocephalides felis felis (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.

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.

Ekbom Syndrome: The Challenge of "Invisible Bug" Infestations

Ekbom Syndrome is synonymous with delusory parasitosis, a belief that ones body is infested by invisible bugs. Persons suffering from this syndrome often claim to feel dermal sensations and to visualize the bugs, although no one else can see them. Ekbom Syndrome is a delusional condition; it is intractable and cannot be corrected by argument or evidence. Ekbom Syndrome sufferers exhibit a range of predictable behaviors in their attempts to eliminate their infestations, including seeking identifications and treatment from physicians and entomologists. Frequently they also experience comorbid psychological conditions. Because this is a delusional affliction, successful treatment typically requires neuroleptic medications, necessitating intervention by medical professionals.

Efficacy and Longevity of Nitenpyram Against Adult Cat Fleas (Siphonaptera: Pulicidae)

Abstract 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.

Monitoring Northern Fowl Mites (Acari: Macronyssidae) in Caged Laying Hens: Feasibility of an Egg-Based Sampling System

Abstract 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 ≈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 them 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 ≈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 (r 2 = 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.

Forum: Hematophagous Strategies of the Cat Flea (Siphonaptera: Pulicidae)

Hematophagy of the cat flea, Ctenocephalides felis felis (Bouche), was investigated. Blood feeding in the adult stages nearly doubled the weight of mixed-sex fleas. However, within 12 h, the gained weight was lost. Protein mass tripled after feeding, but starvation caused a reduction in protein with the percentage protein remaining constant (5%). Both in vivo and in vitro rearing of cat fleas was successful in allowing flea survival, feeding, fecal production, and reproduction. In vivo rearing, infesting cats with 50 fleas per week, resulted in a mean of 332 fleas per cat. Because 68% were female, male survival times on the host were shorter than those of females. Female fleas produced 1 egg per h, and combined sexes averaged 0.77 mg of feces per day. Average blood ingestion for defecation was 6.97 @ml of blood. In vitro rearing resulted in lower egg production (12%), feces production (50%), and ingestion of blood for defecation. Two types of flea feces were found--spherules and coils. Within 24 h of first feeding, almost all feces were spherules <0.07 mm in diameter. After 10 days of feeding, 60-70% of the feces were coils. These adult feces are the natural larval diet of cat flea larvae.

Ekbom Syndrome: A Delusional Condition of "Bugs in the Skin"

Entomologists estimate that more than 100,000 Americans suffer from “invisible bug” infestations, a condition known clinically as Ekbom syndrome (ES), although the psychiatric literature dubs the condition “rare.” This illustrates the reluctance of ES patients to seek mental health care, as they are convinced that their problem is bugs. In addition to suffering from the delusion that bugs are attacking their bodies, ES patients also experience visual and tactile hallucinations that they see and feel the bugs. ES patients exhibit a consistent complex of attributes and behaviors that can adversely affect their lives.

Resistance in Constant Exposure Livestock Insect Control Systems: A Partial Review with Some Original Findings on Cyromazine Resistance in House Flies

Insecticide resistance development in three continuous exposure livestock insect control systems is discussed. These include residual pyrethroid sprays and cyromazine feed-through for house flies, and insecticide cattle ear tags for horn flies. All three of these systems selected for resistance problems in the field within two years. Other discontinuous use patterns of these same chemicals have been used on the same insects in the field and selected for much lower or no resistance. The conclusion is that these systems waste the resource of insect susceptibility, especially with mobile insects with short generation time such as the flies discussed here.

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 ηg 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.

Determining a Diagnostic Dose for Imidacloprid Susceptibility Testing of Field-Collected Isolates of Cat Fleas (Siphonaptera: Pulicidae)

Abstract The susceptibility of four laboratory strains of cat fleas, Ctenocephalides felis (Bouché), 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.