Efficacy of a fipronil bait in reducing the number of fleas (Oropsylla spp.) infesting wild black‐tailed prairie dogs

Bubonic plague (Yersinia pestis) is a deadly zoonosis with black‐tailed prairie dogs (Cynomys ludovicianus) as a reservoir host in the United States. Systemic insecticides are a promising means of controlling the vectors, Oropsylla spp. fleas, infesting these prairie dogs, subsequently disrupting the Y. pestis cycle. The objective of this study was to conduct a field trial evaluating the efficacy of a grain rodent bait containing fipronil (0.005%) against fleas infesting prairie dogs. The study was performed in Larimer County, CO, where bait was applied to a treatment area containing a dense prairie dog population, three times over a three‐week period. Prairie dogs were captured and combed for fleas during four study periods (pre‐, mid‐, 1^st post‐, and 2^nd post‐treatment). Results indicated the use of bait containing fipronil significantly reduced flea burden. The bait containing fipronil was determined to reduce the mean number of fleas per prairie dog >95% for a minimum of 52 days post‐initial treatment application and 31 days post‐final treatment application. These results suggest the potential for this form of treatment to reduce flea population density on prairie dogs, and subsequently plague transmission, among mammalian hosts across the United States and beyond.     

Field efficacy of rodent bait containing the systemic insecticide imidacloprid against the fleas of California ground squirrels

The efficacy of rodent bait containing the insecticide imidacloprid was evaluated for controlling fleas on the California ground squirrel, Spermophilus beecheyi. The bait was designed to deliver an oral dose of insecticide resulting in flea mortality when obtaining a blood meal. During the five‐week trial, performed at Vandenberg Air Force Base, Santa Barbara County, CA, a spot‐baiting technique was used to apply bait to ground squirrel burrows. Bait was applied six times throughout the trial. Results indicated that the use of a host‐targeted bait was effective in significantly reducing the flea burden on S. beecheyi. Efficacy at reducing flea abundance was near 100% at both day 15 and day 29 of the trial. Use of the bait also reduced the prevalence of flea‐infested S. beecheyi. Our results indicate that the use of rodent bait containing insecticide could provide an effective, economical method of controlling the fleas of S. beecheyi, the primary vectors of human plague in California.     

Method of insecticide delivery affects horizontal transfer of fipronil in the German cockroach (Dictyoptera: Blattellidae).

Horizontal transmission of insecticide occurs when foragers contact or ingest an insecticide, return to the aggregation or nest, and translocate the insecticide to the shelter and its vicinity. Relatively more sedentary members of the population then contact or eat the translocated insecticide and die. We evaluated three different methods of delivering fipronil to adult male German cockroaches, Blattella germanica (L.), for their potential to cause such secondary mortality in various developmental stages of the cockroach. Adult males topically treated with 5 ng of fipronil (approximately LD99) caused low mortality in untreated nymphs and no mortality in untreated adults within the same aggregation. Males exposed to residual fipronil on a glass surface translocated more insecticide, resulting in higher mortality of cockroaches they contacted, but only early instars were affected and no adult mortality was observed. Ingested fipronil bait, however, was most effectively translocated, and caused high mortality of untreated adults and nymphs. Ingestion of fipronil also caused greater secondary kill compared with a topical application of 25 ng, approximately the same amount recovered from the exterior of males that ingested 1 mg of 0.05% fipronil bait. Secondary mortality in the untreated population was significantly affected by the duration of contact between the treated and untreated cockroaches, the quantity and freshness of excretions from the treated insects, and the accessibility of the secretions to untreated cockroaches. The mechanisms that cause secondary kill may include ingestion of excreted fipronil residues, cannibalism of bait-fed cockroaches, as well as contact with fipronil-contaminated substrates.     

Evaluation of the palatability and toxicity of candidate baits and toxicants for mongooses (<Emphasis Type="Italic">Herpestes auropunctatus</Emphasis>)

The small Indian mongoose (Herpestes auropunctatus) is an invasive pest species responsible for damage to native avian, reptile, and amphibian species on Hawaii, Croatia, Mauritius, and several Caribbean Islands, among other regions. Mongoose control has been pursued through a variety of means, with varying success. One toxicant, diphacinone, has been shown to be effective in mongooses and is co-labeled in a rodenticide bait for mongoose control in Hawaii; however, preliminary observations indicate low performance as a mongoose toxicant due likely to poor consumption. We evaluated the efficacy and palatability of 10 commercial rodenticide baits, technical diphacinone powder, and two alternative acute toxicants against mongooses in laboratory feeding trials. We observed poor acceptance and subsequent low overall mortality, of the hard grain-based pellets or block formulations typical of most of the commercial rodenticide baits. The exception was Tomcat® bait blocks containing 0.1% bromethalin, an acute neurotoxin, which achieved up to 100% mortality. Mortality among all other commercial rodenticide formulations ranged from 10 to 50%. Three-day feedings of 0.005% technical diphacinone formulated in fresh minced chicken achieved 100% mortality. One-day feedings of para-aminopropiophenone (PAPP), a chemical that reduces the oxygen-carrying capacity of the blood, achieved 100% mortality at concentrations of 0.10 to 0.15%. Bait acceptance of two sodium nitrite formulations (similar toxic mode of action as PAPP) was relatively poor, and mortality averaged 20%. In general, commercially produced rodenticide baits were not preferred by mongooses and had lower mortality rates compared to freshly prepared meat bait formulations. More palatable baits had higher consumption and achieved higher mortality rates. The diphacinone bait registered for rat and mongoose control in Hawaii achieved 20% mortality and was less effective than some of the other commercial or candidate fresh bait products evaluated in this study.     

Comparative efficacy on dogs of a single topical treatment with fipronil/(S)-methoprene or weekly physiological hygiene shampoos against Ctenocephalides felis in a simulated flea-infested environment

Flea infestations of pets continue to persist due to the lack of knowledge of flea biology and ecology. It is not unusual that pet owners believe regular hygiene, such as shampooing their dogs can replace regular insecticidal treatment. The objective of this study was to compare in a flea simulated environment, modelling exposure similar to that found in a home, that the use of regular physiological shampoo does not control fleas adequately when compared to a long acting topical formulation. Three groups of six dogs were formed: one untreated control group, one group treated monthly with the topical formulation of fipronil/(S)-methoprene, and a third group treated weekly with a hygiene shampoo. All dogs were infested with adult unfed Ctenocephalides felis fleas (200±5) on Days -28 and -21. Each animal's sleeping box was fitted with a plastic cup mounted to the inside roof of the box. The sleeping bench of each animal was covered with a carpet to accommodate flea development. The dogs were maintained in their kennels throughout the study. In order to maintain the environmental flea challenge, C. felis pupae (100±5) were placed in the plastic cup in each animal's sleeping box on Days -14, -7, 0, 7, 14, 21, 28, 35 and 42. The dogs were combed and fleas counted weekly on Days -1, 3, 10, 17, 24, 31, 38, 45, and 51. The fleas were placed immediately back on the dogs. On Day 60, fleas were counted and removed. Flea infestations in the untreated control group at each count averaged between 46.2 and 74.2 fleas throughout the study. The average number of fleas infesting dogs was significantly different (p<0.05) between the untreated and the two treatment groups and between the two treatment groups at all counts throughout the two months study (Days 3, 10, 17, 24, 31, 38, 45, 51 and 60). The efficacy was never below 99.1% in the fipronil/(S)-methoprene group, and efficacy in the shampoo group was never above 79.2%. Weekly shampooing in treatment group 3 was intentionally delayed after Day 42, to evaluate wether missing a weekly bath would affect the flea population. The Day 48 data indicate that forgetting or delaying a single weekly shampooing resulted in a clear increase in flea numbers and a significant decrease in efficacy from 68.2% to 34.8%. The fipronil(S)/methoprene treatment allowed a continuous control as demonstrated by the high efficacy against fleas, and also the number of flea-free dogs on seven of the nine weekly assessments, in spite of what was essentially a continuous flea challenge model.     

Control of flea populations in a simulated home environment model using lufenuron, imidacloprid or fipronil

Control strategies were evaluated over a 6-month period in a home simulation model comprising a series of similar carpeted pens, housing matched groups of six cats, in which the life-cycle of the flea Ctenocephalides felis felis Bouche (Siphonaptera: Pulicidae) had been established. Additional adult fleas were placed on the cats at intervals to mimic acquisition of extraneous fleas from outside the home. Treatment strategies included a single subcutaneous deposition of injectable lufenuron supported by initial treatments with a short-acting insecticidal spray, or monthly topical applications of imidacloprid or fipronil. An untreated control group indicated that conditions were suitable for flea replication and development. Controls had to be combed on 18 occasions to remove excessive flea burdens and two developed allergic reactions. Lufenuron cats were combed once and required two insecticidal treatments in the first month to achieve control. Even so, small flea burdens were constantly present thereafter. Imidacloprid and fipronil treatments appeared to give virtually complete control throughout. Single fleas were found on imidacloprid cats on two occasions, whereas none were recovered from fipronil cats at any time after the first treatment. Tracer cats were used to monitor re-infestation rates at the end of the trial period. Small numbers of host-seeking fleas were demonstrated in all treatment pens, indicating that total eradication had not been accomplished. It is concluded that the home environment simulation model incorporating tracer animals could provide a powerful tool for studying flea population dynamics under controlled conditions but improved techniques are needed for quantifying other off-host life-cycle stages.     

Phyllotreta cruciferae and Phyllotreta striolata responses to insecticidal seed treatments with different modes of action

The strategy used most commonly in western North America to protect seedlings of canola (Brassica rapa L. and Brassica napus L.) from attack by adults of the flea beetles Phyllotreta cruciferae (Goeze) and Phyllotreta striolata (Fabricius) (Coleoptera: Chrysomelidae) involves planting seed coated with insecticide for systemic activity. Previous research determined that the two beetle species responded differently to the most commonly used neonicotinoid seed dressings. However, other insecticides that exploit different modes of action have commercial potential for managing infestations of these pests, but no information exists on their efficacies for these flea beetle species. Studies were conducted to compare effects of the neonicotinoid compounds, thiamethoxam and imidacloprid, to spinosyn and fipronil as systemic seed treatments for reducing feeding damage to canola seedlings and increasing mortality of P. cruciferae and P. striolata. Phyllotreta cruciferae experienced greater mortality and caused less feeding damage than P. striolata to seedlings treated with the neonicotinoid compounds. Mortality increased and feeding damage decreased significantly when beetles fed upon seedlings treated with fipronil, indicating its potential usefulness for control of these pests. However, spinosyn seed treatment was relatively ineffective against either beetle species. Higher rates of P. striolata mortality with fipronil than thiamethoxam suggest that fipronil may provide improved flea beetle control over hundreds of thousands of hectares in western North America where flea beetle populations are dominated by P. striolata, and control with thiamethoxam has been suboptimal.     

Systemic efficacy of nodulisporic acid against fleas on dogs

Nodulisporic acid A (NSA) is a novel natural product from a new structural class that was shown previously to have insecticidal activity against blowfly larvae. To determine if there was useful systemic efficacy against fleas (Ctenocephalides felis). NSA was evaluated in an artificial membrane flea feeding device and in dogs. In the artificial membrane flea feeding device, adult C. felis were allowed to feed on bovine blood containing various concentrations of NSA through a Parafilm membrane. NSA killed the fleas with a 50% lethal concentration of 0.68 microg/ml and was approximately 10-fold more potent than the systemic insecticide ivermectin. In the initial probe dog test, a single beagle was challenged with 100 C. felis before oral dosing with 15 mg/kg of NSA. Flea counts conducted at 72 hr postdosing showed an 88% reduction relative to control. Re-challenge of the same dog at 5 days postdosing showed 50% reduction of fleas at day 7, demonstrating some residual flea activity. In a confirmatory study, 8 dogs were challenged with 100 fleas just before oral dosing with 15 mg/kg of NSA (4 dogs) or vehicle (4 dogs). There was 99% reduction of fleas at 48 hr postdosing in the NSA-treated dogs relative to control. Additional challenges with 100 fleas were performed on these 8 dogs at 48-hr intervals to determine the duration of efficacy, and there was 97, 51, and 0% reduction of fleas relative to control on days 4, 6, and 8, respectively. No adverse effects were observed in the dogs in these studies. These data show that NSA has potent oral activity in the dog for the control of fleas, while lacking overt mammalian toxicity.     

Managing plague on prairie dog colonies: insecticides as ectoparasiticides

Human health practitioners and wildlife biologists use insecticides to manage plague by suppressing fleas (Siphonaptera), but insecticides can also kill other ectoparasites. We investigated effects of deltamethrin and fipronil on ectoparasites from black‐tailed prairie dogs (Cynomys ludovicianus, BTPDs). In late July, 2018, we treated three sites with 0.05% deltamethrin dust and 5 sites with host‐fed 0.005% fipronil grain. Three non‐treated sites functioned as experimental baselines. We collected ectoparasites before treatments (June‐July, 2018) and after treatments (August‐October, 2018, June‐July, 2019). Both deltamethrin and fipronil suppressed fleas for at least 12 months. Deltamethrin had no detectable effect on mites (Arachnida). Fipronil suppressed mites for at least 12 months. Lice (Phthiraptera) were scarce on non‐treated sites throughout the study, complicating interpretation. Concentrating on eight sites where all three ectoparasites where found in June‐July, 2018 (before treatments), flea intensity was greatest on BTPDs carrying many lice and mites. These three ectoparasites co‐occurred at high numbers, which might facilitate plague transmission in some cases. Lethal effects of insecticides on ectoparasite communities are potentially advantageous in the context of plague management.     

Advances in the control of Ctenocephalides felis (cat flea) on cats and dogs

Cat fleas are the most important ectoparasite of cats and dogs worldwide. During the past ten years, topical and oral applications of insecticides such as fipronil, imidacloprid, lufenuron and, most recently, selamectin have revolutionized cat-flea control. Recent studies show that these therapies eliminate the need to treat indoor and outdoor environments, and their use markedly reduces the severity and prevalence of flea allergic dermatitis. Surveys have yet to reveal the development of insecticide resistance to these chemical compounds. Extending the longevity of these effective host-targeted therapies should be a major goal of the veterinary community.     

Laboratory and field evaluation of flocoumafen for rodent control

A new anticoagulant rodenticide, flocoumafen, at a concentration of 0·005% in the bait in 24 h no-choice and 48 h choice laboratory feeding tests was found to cause 100% mortality of the Indian bush rat Golunda ellioti, the Indian gerbil Tatera indica and the soft-furred field rat Rattus meltada. In field trials in sugar cane and wheat, where these species and the Indian mole rat Bandicota bengalensis and Mus spp. were present, about 65% rodent control was obtained with a single treatment with 0·005% flucoumafen bait at the rate of 1 kg/ha. The performance of a single treatment with flocoumafen was comparable with that of 2·4% zinc phosphide, a conventional acute rodenticide. Unlike zinc phosphide, however, two treatments with a 10-day interval with flocoumafen resulted in significantly higher rodent control compared with the single treatment, indicating the superiority of flocoumafen over zinc phosphide in repeat baiting treatments.     

Suppression of female melon fly,Zeugodacus cucurbitae,with cue‐lure and fipronil bait stations through horizontal insecticide transfer

Melon fly, Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae), is an important quarantine tephritid fruit fly with resident populations established in Hawai'i, USA. In the male‐annihilation approach, male flies are targeted using dispensers with cue‐lure (C‐L) and insecticides, typically organophosphates. The efficacy of the male annihilation approach is thought to be limited to individual male flies, contacting the lure and the pesticide, after which they die. Alternative classes of insecticides, such as fipronil, have been investigated for use in male‐annihilation. We hypothesized that ingestion of fipronil by male flies could lead to horizontal transfer and mortality in female flies. Horizontal insecticide transfer extends pesticide control beyond the individual contacting the toxicant through indirect contact via food sharing or other mechanisms. We tested the possibility for horizontal transfer of fipronil from male to female Z. cucurbitae through field and laboratory studies. Two repeated field trials were conducted to compare the numbers of female flies collected in fields treated with Amulet C‐L (0.34% fipronil active ingredient) bait stations, sanitation, and spot treatments of GF‐120 Fruit Fly Bait to numbers collected in fields where sanitation and spot‐treatments were used without Amulet C‐L. In fields with Amulet C‐L bait stations in conjunction with sanitation and weekly protein bait spot treatments of GF‐120 Fruit Fly Bait, female captures were significantly lower than those in field plots treated with weekly protein bait spot treatments and sanitation. In subsequent laboratory studies, all females died within 6 h after direct exposure to male flies that had access to Amulet C‐L for 1–4 min. The possibility that male regurgitant could be a mechanism for horizontal transfer and subsequent female mortality was determined by collecting regurgitated droplets from fipronil‐fed male flies and feeding them to males and females. Both male and female flies exposed to regurgitant from fipronil‐fed male flies or droplets containing fipronil had higher mortality than the male and female flies that were exposed to regurgitant or droplets with only the C‐L compound or sugar solution. Thus, female flies do experience mortality from exposure to regurgitant from males that have fed on fipronil laced solutions. This provides evidence of at least one mechanism of horizontal transfer of insecticide in tephritid fruit flies. These findings are discussed in the context of Z. cucurbitae integrated pest management programs in Hawai'i.     

Comparative efficacy on dogs of a single topical treatment with the pioneer fipronil/(S)-methoprene and an oral treatment with spinosad against Ctenocephalides felis

In the study reported here, the pioneer fipronil/(S)-methoprene topical product (FRONTLINE^® PLUS, Merial Limited, Duluth, GA) was compared to the oral spinosad product (COMFORTIS^® Elanco, Greenfield, IN) for efficacy against adult fleas and preventing egg production. The product presentations, doses and labelling were the one applicable in the USA. Using a standard protocol, 200 cat fleas of mixed sex were applied to dogs on Days 1, 7, 14, 21, 28, 35, and 42. Dogs were combed to remove fleas 24 hours post-infestation, the fleas were counted, collected, and then reapplied to each dog following completion of their respective count. At 48 hours post-infestation, comb counts were performed and fleas were removed. No fleas were collected from any dog in the fipronil/(S)-methoprene group at any 24 or 48 hours post-infestation assessment throughout the six weeks study, yielding a preventive efficacy of 100%. For the spinosad treatment, efficacy was 100% at 24 hours and 48 hours through Day 16, and thereafter declined. The results observed in the spinosad-treated dogs were highly variable between animals. At the 24 and 48 hours counts following the Day 21 infestation, only five of eight spinosad-treated dogs (62.5%) were flea-free. Following the Day 28 infestation, spinosad efficacy fell to 85% and 89%, for the 24 hours and 48 hours counts, and only two dogs (25%) were flea free, compared to 100% flea-free dogs in the fipronil/(S)-methoprene group. No fleas were collected from the fipronil/(S)- methoprene treated dogs throughout the entire study, therefore, no eggs were collected at any time from any dog in the group. However, in the spinosad group adult fleas were found on dogs starting on Day 21 and by Day 30, 42 eggs were collected from one dog that had 107 adult fleas counted at 48 hours. At Day 37 and Day 49, more than 100 eggs were collected from each dog in the spinosad-treated and control groups.     

Compatibility of entomopathogenic nematodes with fipronil

The survival and infectivity of infective juveniles (IJs) of three species of entomopathogenic nematodes, Steinernema carpocapsae Weiser, S. arenarium (Artyukhovsky) (Rhabditida: Steinernematidae) and Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae), were determined after exposure to different concentrations (250, 500, 1000 and 2000 ppm) of fipronil, an insecticide acting on the GABA receptors to block the chloride channel. Heterorhabditis bacteriophora was very tolerant to all concentrations of fipronil, with the highest mortality of 17% being observed at 2000 ppm of fipronil after 72 h exposure. Steinernema carpocapsae showed a similar response, with the highest mortality of 11.25% of IJs being observed after 72 h exposure to 2000 ppm of fipronil. Steinernema arenarium was, however, more sensitive to fipronil, and at 2000 ppm mortality rates of 94.6% and 100% were observed after 24 and 72 h, respectively. Fipronil had negligible effects on the infectivity of the three nematode species tested. The IJs which survive exposure to all concentrations of fipronil tested can infect and reproduce in Galleria larvae. The moderate effects on entomopathogenic nematodes of a lower fipronil concentration (250 ppm) and the field rates (12-60 ppm) of fipronil used as insecticide, suggest that direct mixing of entomopathogenic nematodes and fipronil at field rates is a viable integrated pest management option.     

Attractiveness of bait matrices and matrix/toxicant combinations to the citrus pests Iridomyrmex purpureus (F.Smith) and Iridomyrmex rufoniger gp sp. (Hym., Formicidae)

Abstract: Six bait matrices were tested for palatability to the ants Iridomyrmex purpureus and I. rufoniger gp sp., which are important pests of citrus in south‐eastern Australia. Granulated citrus pulp and rice bran impregnated with brown sugar were not accepted by either species, but ground dry dog food and ground insects (with or without added sugar) were highly attractive to both ant species. The ground dog food was impregnated with various toxicants at concentrations of up to 1% (w/w) and tested for palatability to both ant species. Technical grade pyriproxyfen, fipronil, and fenoxycarb were incorporated using organic solvents, whereas formulated fenoxycarb (Insegar^®) was incorporated as an aqueous suspension prior to drying and granulation. Relative to the blank samples (carrier solvents only), bait acceptance by I. purpureus was not significantly reduced (P > 0.05) by any of the treatments except 1% technical fenoxycarb. Bait acceptance by I. rufoniger gp sp. was significantly suppressed by 0.2% fipronil, but not by higher concentrations. When water was used as the carrier solvent the blank sample was significantly (P < 0.05) less attractive to I. purpureus than the untreated control, suggesting that wetting of dog food‐based baits in field situations may irreversibly reduce their attractiveness. Laboratory colonies were used in choice and no‐choice tests to assess the efficacy of dog food baits containing fipronil (0.05–0.2% w/w). The corrected mortality for I. purpureus ranged from 88 to 100% and from 90 to 97% in the no‐choice and choice tests, respectively. In no‐choice tests I. rufoniger gp sp. corrected mortality varied from 52 to 60%, but in choice tests the corrected mortality did not exceed 26%. Ground dog food containing fipronil (0.05–0.2% w/w) has the potential to provide effective control of I. purpureus in citrus orchards, but alternative toxicants or lower fipronil concentrations may be required for control of I. rufoniger gp sp.     

Toxicity of fipronil to German and American cockroaches

Topical and oral toxicity of fipronil, compared to chlorpyrifos, was determined for the German cockroach, Blattella germanica (L.), and American cockroach, Periplaneta americana (L.). Fipronil and Combat bait matrices were evaluated for their attractancies to both species. In the topical toxicity tests, LD50's of fipronil, at 72 h after topical application, were 0.03 and 0.02 µg/g for adult B. germanica and P. americana, respectively. Fipronil was significantly more toxic than topically applied chlorpyrifos (LD50's were 0.06 and 0.16 µg/g for B. germanica and P. americana, respectively). The oral toxicity of fipronil and chlorpyrifos in Petri dish experiments, against both species, was affected by stage (for B. germanica), diet concentration, and feeding assay. Fipronil caused higher mortality of B. germanica than chlorpyrifos in two feeding assays (continuous and abbreviated). Both compounds were equally toxic to adult males of P. americana at all rates. Fipronil caused higher nymphal mortality than chlorpyrifos 48–72 h after exposure in both feeding assays. In large population chamber tests, fipronil bait was more effective and faster in killing P. americana than Raid and Combat. LT50's were 0.8, 2.4, and 7.6 d for fipronil, Raid (a.i. = chlorpyrifos), and Combat (a.i. = hydramethylnon) baits, respectively. Mortality reached 96.5, 93.4, and 84.6%, respectively, at the end of the 14 d test. In the bait attractancy tests, both strains of B. germanica were attracted similarly to fipronil and Combat bait matrices. P. americana were attracted more to fipronil than to Combat bait matrix or to other alternative foods.     

Distribution and insecticide resistance of the plague flea Xenopsylla cheopis in Maharashtra State, India

Distributions are reported for commensal rat fleas, predominantly Xenopsylla cheopis (Rothschild), in the State of Maharashtra, India, including the city of Bombay, during 1965-80. The X.cheopis flea index was high in most parts of Maharashtra, but low in Bombay. Rattus rattus Linnaeus is the principal host of X.cheopis, but the host range includes Bandicota bengalensis Gray, Golunda ellioti Gray, Mus musculus Linnaeus, Rattus blandfordi Thomas, R. norvegicus Berkenhout, Suncus caerulaeus Lerr, S. murinus Linnaeus and Tatera indica Hardwicke. X.cheopis was found to have high degrees of resistance to DDT, malathion and fenthion, tolerance to gamma HCH (= gamma BCH) but susceptibility to dieldrin. This insecticide resistance situation may contribute to the high flea indices prevailing in the state, with consequent risks of plague outbreaks. Two other species of rat flea, X.astia Rothschild and X.brasiliensis (Baker) were found to be less common than previously recorded. Their apparent replacement by X.cheopis is tentatively attributed, at least partly, to the selective advantage of insecticide resistance in the latter species.     

Benefits, Costs and Constraints of Anti-Parasitic Grooming in Adult and Juvenile Rodents

Grooming behaviour plays various roles in the health care, reproduction, and social life of an individual vertebrate. However, the reasons for the variability in time spent grooming amongst species, populations and individuals are not fully understood. We tested the hypothesis that the main role of grooming is ectoparasite removal and thus that time spent grooming by an animal reflects the costs of parasite infestation offset against the costs of grooming. The test was conducted on a rodent, Meriones crassus, that is parasitised by a flea, Xenopsylla conformis. We monitored behaviour of juvenile and adult rodents before and after flea infestation and quantified the probability of mortality of fleas with respect to the time spent grooming in adults compared with juvenile rodents. We predicted that: (1) increased costs of flea infestation (e.g. in parasitised as opposed to flea‐free rodents and in juveniles as opposed to adults) increases time spent grooming and (2) mortality probability per flea increases with increasing time spent grooming and is higher for fleas on juveniles than for fleas on adult rodents. We were interested to discover at the expense of which activity grooming is increased. Our findings established that the major role of grooming is in flea removal, as exposure to fleas evoked grooming activity in all rodents and grooming activity explained 57–70% of the variation in flea mortality. Furthermore, we showed that the rise in grooming activity was at the expense of resting. However, we found only partial support for the predicted increase in grooming time with increasing costs of flea infestation. Flea infestation did indeed increase the time spent grooming by rodents. Nevertheless, juvenile rodents who incur higher costs of flea infestation spent less time grooming than adults and sustained similar flea densities, suggesting that these hosts are constrained by some other factors, such as feeding time.     

长爪沙鼠体蚤和巢蚤数量研究

1982～1996年对内蒙古自治区鄂托克前旗长爪沙鼠Meriones unguiculatus体蚤和巢蚤的数量进行了调查和分析,得到如下结果。获体蚤15种,同型客蚤指名亚种Xenopsylla conformis conformls (50.8%) 和秃病蚤蒙冀亚种Nosopsyllus laveiceps kuzenkovi (40.6%)为优势种。获巢蚤15种,秃病蚤蒙冀亚种(74.3%)为优势种;盔状新蚤Neopsylla galea (11.9%)和叶状切唇蚤突高亚种Coptopsyllus lamelliferardua (8.1%)为常见种。年巢蚤指数的均值是年体蚤指数的6.92倍。体蚤指数与巢蚤指数不相关(P>0,05),体染蚤率与巢染蚤率不相关(P>0.05)。不同年份 的体蚤和巢蚤多样性比较稳定。连续两年春季或秋季秃病蚤巢蚤指数大于10只后,可能流行动物鼠疫。     

Secondary transmission of toxic baits in German cockroach (Dictyoptera: Blattellidae)

The death rates of three toxic gel baits (fipronil bait, 0.05%; hydramethylnon, bait 2.15%; and abamectin B1 bait, 0.05%) were estimated in Blattella germanica (L.). After ingestion, all three baits killed similar proportions of cockroaches, but they died more rapidly after ingestion of fipronil bait than after ingestion of abamectin B1 bait or of hydramethylnon bait. Laboratory experiments evaluated the impact of secondary transmission of fipronil bait and hydramethylnon bait. Mortality rates caused by secondary transmission were higher for fipronil bait than for hydramethylnon bait. Under controlled laboratory conditions, secondary transmission occurred mainly through direct contact with, or ingestion of, traces of baits dispersed in the environment by contaminated cockroaches. These traces were either deposited by "trampling" in the environment or on dead contaminated cockroaches. Social interactions and cannibalism played a minor role in secondary transmission of these two baits.