Journal of the American Mosquito Control Association, lO(l):7-9, 1994

SURVIVAL, FECUNDITY, AND EGG FERTILITY OF C ULI CO I D E S VARII PE N N I S (DIPTERA: ) FED ON CALVES INOCULATED WITH IVERMECTIN'

F. R. HOLBROOK

Arthropod-borneAnimal DiseasesResearch Laboratory, United States Department of Agriculture, Agricultural Research Service, P. O. Box 3965, UniversityStation, Laramie, Wy 82A71-3965

ABSTRACT. Female Culicoidesvariipennis were fed at l-18 days postinoculation on calves treated with a commercial injectable formulation of ivermectin at the recommendedrate of 2OOpg/kg of body weight. There were no significant differencesbetween treated and untreated in the survival rate of the at 24 h and 48 h postinoculation and the number of eggsproduced per living female. There was a significantly greater mean hatch rate ofeggs from flies fed on the untreated animals (65.80/o)than those fed on the treated animals (52.8o/o).The recommendeduse rate of ivermectin does not appear to provide significant mortality for female C. variipennis,nor affect eggdeposition or hatch rate sufficiently to reduce vector populations.

INTRODUCTION MATERIALS AND METHODS variipennis (Coq.) is the principal Four mixed-breedbeefcalves from the current vector of bluetongue viruses (Price and Hardy year's crop that were 6 months of age at the 1954)and epizootic hemorrhagicdisease viruses beginning of the tests were utilized. They were (Joneset al. 1977)of ruminants in North Amer- housed indoors in separate rooms for several ica. Culicoides variipennis has been shown also weeks prior to testing to decreasepossible con- to be a competentvector of exotic African horse- tact with biting insectsand to facilitate handling. sicknessviruses (Boorman et al. 1975) and of The sameindividual calveswere usedas control indigenous Onchocerca cemicalis Railliet and and treatment animals (2 each) in 2 tests con- Henry (Jonesand Collins l98l). Control rec- ducted at intervals of 93 days, more than 3 times ommendations for C. variipennis have empha- the period when invermectin is detectable in sized livestock production practices, water and blood plasma in (Fink and Porras 1989). wastemanagement, and the useoflarvicides and The invermectin used was a commercially adulticides(Jones et al. l98l; Holbrook 1985, available aqueousformulation containing lo/ow /v 1988;Mullens and Rodriguez1990). ivermectin (Ivomec, Merck and Co., Inc., Rah- Ivermectin, a macrocyclic lactone glycoside way, NJ 07065). It was inoculated subcutane- isolated from the soil microorganism, Strepto- ously into the neck of a calf at a single dosageof mycesavermililrs (Chen et al. 1989),has dem- 20Ope/ke of body weight. onstrated a broad spectrum of activity against The C. variipennisadult femalesused for these parasitic infections in vertebrates (Campbell tests were from a colony maintained continu- 1989), and has been evaluated against a variety ously at the -borne Diseases of hematophagousinsects. The recommended ResearchLaboratory since 1957, and originated dose of 200 pglkg of body weight, to be admin- from a collection in Sonora, TX, USA (Jones istered subcutaneouslyin the shoulder, was se- 1960). In pesticide trials, individuals from this lected after numerous dose-titration trials (Benz colony have produced results similar to those et al. 1989). In studies with cattle in Australia, from wild populations (Holbrook 1982). Two a single subcutaneousinoculation of ivermectin hundred and fifty pupae of the same age were at2OOpg/kgofbody weight in 4 cattle gavemean placed in emergencecages and held in an incu- mortalities at 48 h postfeedingof >990/ofor l0 bator at 26 + l"C with a l3L: I lD photoperiod. days and >40olofor l8 days to Culicoidesbrev- The adults usedwere thosethat emergedon days i/arsrsKieffer (Standfastet al. 1984).The follow- 3 to 4. The flies were held until day 5 with water ing studies were conducted to assessthe effects provided in a vial with a dental cotton wick. of a single dose of ivermectin at 2OOpg/kg of These2448-h-old flies were anesthetizedfor l5 body weight in calves against C. variipennis. sec with CO, gas and transferred to 4 feeding cages,0.24-1iter ice cream containers covered with a tightly stretched nylon stocking. A cage was rThis paper reports the results of research only. placed against a shaven area on an animal and Mention of a commercial or proprietary product does held with an elasticbandage for a feedingperiod not constitute a recommendation or an endorsement of 30 min. After feeding, the cageswere placed of this product by the U.S. Department of Agriculture. on a chill table and all fully engorgedfemales Joup.r.ler or rrrr Aurrucm Mosquno CoNrnol Assocnnor.r Vor. 10, No. I

Table l. Survival, fecundity, and fertility in fully engorged Culicoides variipennis females fed on untreated calves and calves treated with ivermectin at 200 pglkg of body weight. Test I Test 2 No. No. o/osurvival o/osurvival fe- Eggs/female fe- Eggs/female Dav Treatment 24h 48 h males (o/ohatch) 24h 48h males (Vohatch) Control 95.2 88.9 s6 55.9(70.8) 65.5 46.6 27 63.1(6e.5) Ivermectin 90.7 66.3 57 58.0(64.3) 90.1 74.3 75 4O.3(4r.7) 4 Control 98.7 97.4 225 47.9(88.5) 98.6 95.8 68 34.0(54.6) 5l Ivermectin 96.1 90.3 186 90.4(48.2\ 100 100 32 34.8 (49.7) 8 Control 81.8 61.3 84 83.2(63.1) 100 98.8 79 36.5(54.3) Ivermectin 92.9 82.6 r28 77.6(50.4\ r00 100 53 r7.e(56.9) ll Control 96.9 93.3 l8l 84.3(7r.2) 94.8 87.5 84 50.4(54.9) Ivermectin 98.0 96.4 I 89 t27.7 (64.8) 100 100 50 22.2(43.9) l5 Control 95.7 89.0 t46 95.2(77.4) 98.5 97.7 r27 l8.l (59.5) Ivermectin 94.9 89.9 160 78.4(50.8) 96.5 89.6 r29 37.O(42.1) l8 Control 92.4 77.9 l 13 85.2(79.4) 96.0 88.0 22 4.9 (46.7) Ivermectin 96.6 92.7 216 94.4(89.9) 96.6 89.8 53 19.3(30.6) I Test l, day 5; Test 2, day 4. and l0-15 males were put in holding cagescov- 42.45;df : 1,22;P < 0.0001).There was a sig- eredwith fine mesh organdy.Flies were supplied nificantly greaterhatch rate of eggsfrom females a vial of 100/osugar water and held in an incu- fed on the untreated animals (i : 65.80/o)than bator at 26 + l"C with a l3L:l lD photoperiod. from those on the treated animals (r : 52.8o/o) A plastic container with a moist cotton pad cov- (F: 5.34;df : 1,22;P < 0.05). ered with a disk of filter paper was provided for oviposition. Mortality counts of females were DISCUSSION made at 24 and 48 h postfeeding(days 6 and 7). Eggswere laid on moist filter paper disks and The samedoserate of 200 pg/kgofbody weight collectedon days 8, 9, and 10. The "egging" that produced 99o/omortality for l0 days in C. paperswere placedin Petri dishesover moisture brevitarsisin Australia (Standfastet al. 1984)did for 5 days, when counts were made of total not produce significant mortality in C. variipen- hatched and unhatched eggs. nls femalesin the tests reported here. This dose Data on survival, eggproduction, and egghatch of 200 pg/kg of body weight produces a peak rate were analyzedby analysesofvariance and blood concentration of 44 ng/ml (Fink and Por- Scheffe'stest using SYSTAT software (Wilkin- ras 1989).The LCro for C. variipennli (Holbrook son 1989). and Mullens 1994) is 350 nglml of blood, and the initial dosewould have to be increasedto ca. 1,600pg,/kg of body weight to producethis blood RESULTS level. Dose rates of 6,0OOpg/kg (30 times the The data on survival, eggsper living female, recommendeduse level) have beenadministered and egghatch for the 2 tests are shown in Table to cattle without noticeable ill effects (Pulliam l. There were no significant differencesin sur- and Preston1989). vival rates of females at either 24 h or 48 h The nonsignificanteffects ofthe 200 pglkg dos- postfeedingbetween the untreated animals and age on total egg production and eggsper living the treated animals in either test. However, there female found here are not surprising, as similar were significant differencesbetween mean sur- resultswere reported in testsin which the highest vival rates of female C. variipennis between 24 blood level of invermectin (1,000 nglml) (Hol- h (x : 94.5o/o)and 48 h (7.: 87.2o/o) postfeeding brook and Mullens 1994) was ca. 23 times the in both tests(F: 5.35;df : 1,46;P < 0.05). estimated blood level in the tests reported here' There were no significant differences in the The decreasein mean egghatch rate from the numbers of eggsproduced by those females fed femalesfed on the treated animals in the current on the untreated animals or on the treated ani- trials was similar to those reported at a 5 times mals. There were significantly more eggs pro- higher concentrationof 200 nglml ofblood (Hol- duced per female in Test I than in Test 2 (F : brook and Mullens 1994). Those results were Mencr 1994 Cuttcoons yARrrpENNIs NlD Iwrvrqrrx obtained in vitro using defibrinated blood fed to C. Campbell (ed.). Ivermectin and abamectin. the in a membrane feeding system. There Springer-Verlag,New York. may be increased biological availability and en- Chen.S. T., O. D. Hensensand M. D. Schulrnan. 1989. pp. (ed.). hanced efficacy of ivermectin with an in vivo Biosynthesis, 55-72. /z: W. C. Campbell Ivermectin and abamectin. Springer-Verlag, New treatment. produced per York. The difference in number ofeggs Fink, D. W. and A. G. Porras. 1989. Pharmacoki- female betweenTest I and Test 2 may be linked netics of ivermectin in animals and humans, pp. to increasingsensitivity ofthe calvesto the bites I l3-130. In: W. C. Campbell (ed.). Ivermectin and of C. variipennls females. Akey et al. (1989) abamectin.Springer-Verlag, New York. showed that sequential feeding on a naive calf Holbrook, F. R. 1982. Evaluations of three insecti- by cagedC. variipennis eventually produced lo- cides againstcolonized and field-collectedlarvae of calized edema,accompanied by a sigrrificantin- Culicoides variipennis (Diptera; Ceratopogonidae).J. creasein the percentageof femaleswith a partial Econ.Entomol. 75:7 36-737. blood meal and a higher than normal percentage Holbrook, F. R. 1985. Researchon the control of bluetongue in livestock by vector suppression,pp. plasma. were observed at of No local reactions 617-620. In: T. L. Barber and M. M. Jochim (eds.). the site of feeding during Test 1. On day 7 of Bluetongue and related orbiviruses. Alan R. Liss, Test 2, serum was observedransuding from the Inc.. New York. skin ofone control calfat the site where the cage Holbrook, F. R. 1988. Bluetonguein the United States: had been fastened,and similar transudateswere status,transmission, and control through vector sup- noted from all 4 calvesby day I l. Even prior to pression.Bull. Soc.Vector Ecol. l3:350-353. the time that these transudatesbecame notice- Holbrook, F. R. and B. A. Mullens. 1994. Effectsof able,an increasedplasma percentage in the blood ivermectin on mortality, fecundity, and eggfertility (Coq.) (Diptera: meal could have affectedegg production. in Culicoides variipennis Cerato- pogonidae).J. Am. Mosq. Control Assoc.l0:70-73. Jones,R. H. 1960. Mass-productionmethods for the ACKNOWLEDGMENTS colonization of Culicoides variipennis sonorensis. J. Econ.Entomol. 53:.73l-735. I thank S. K. Agun and D. Metcalf for assis- Jones,R. H. and R. C. Collins. 1981. Culicoidesvar- tance in conducting these experiments, G. R. iipennis and Onchocerca cervicalis as a model for Richardson (IJSDA-ARS) for statistical consul- human onchocerciasis,pp. 1012-1013.1n.'W. Slu- tation, and C. N. McKinnon (USDA-ARS) for sarski(ed.). Review ofadvancesin parasitology.Pol- statistical analyses.I also thank C. C. L. Chase ish Scientific Publishers,Warsaw. 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