Resistance in Ticks And Insects of Veterinary Importance*

Resistance in Ticks And Insects of Veterinary Importance* R. 0. Drummond** U.S. Livestock Insects Laboratory U.S. Department of Agriculture Kerrville, Texas

According to Brown and Pal (1971), 104 species of arthropods associated with humans, domestic animals, their habitats, and their wastes had been documented by that time as resistant to acaricides or insecticides. The present report is limited to a review of the resistance in arthropods of importance to man's domestic animals, and concentrates on the changes since 1970 in the resistance of those arthropods listed in Table 1. The situation in respect to the housefly, Musca domestica L., and mosquitoes will be the subject of reviews by others. Previous to the review of Brown and Pal (1971), several other review articles had concentrated specifically on resistance (or control) of arthropods of veterinary importance. In the United States, Schoof (1959) reviewed resistance from 1946 to 1958, McDuffie (1960) discussed resistance in livestock pests, Harris et al. (1965) reviewed resistance, and Graham and Harris (1966) reported *This paper reports the results of research only. Mention of a pesticide in this paper does not constitute a recommendation for use by the USDA nor does it imply registration under FIFRA as amended. **The author wishes to recognize the contributions of Dr. R. H. Wharton, CSIRO, Australia, who reviewed this article and contributed to its timeliness.

303

TABLE 1 Arthropods

of Veterinary

Importance

Resistant to Acaricides

or Ins ecticides ' 3

b Year Species

Phaenicia

cuprina

Phaenicia

sericata

(Meigen)

indicated group

DDT

HCH-Dieldrin

Organophosphorus

—

1957

1966

—

1959

—

304

irritans

(L.)

—

1959

1962

calcitrans

(L.)

1948

1958

—

1957

—

—

—

1967

—

—

1967

—

1964

1964

1966

—

1957

—

—

1957

—

Haematobia Stomoxys

(Wiedemann)

resistant to

Linognathus

vituli

Linognathus

africanus

Linognathus

stenopsis

Haematopinus

(L.) Kellogg and Paine (Burmeister)

eurysternus

Bovicola

caprae

Bovicola

limbatus

(Nitzsch)

(Gurlt) (Gervais)

Boophilus

docoloratus

Boophilus

microplus

(Koch) (Canestrini)

Rhipicephalus

sanguineus

Rhipicephalus

evertsi

Rhipicephalus

appendiculatus

Dermacentor a

variabilis

(Latreille)

(Neumann) (Neumann)

(Say)

A f t e r Brown and Pal

(1971).

305

"^Date of first occurrence of resistance.

1956

1948

—

1954

1950

1964

—

1954

—

—

1960

—

—

1956

—

1959

1959

—

306

R. Ο. Drummond

recent developments in control. Internationally, Whitehead (1965), Wharton (1967), Roulston (1969), and Drummond (1970) reviewed resistance in ticks. Wharton and Roulston (1970) presented a comprehensive review of resistance in ticks, and recently, Harrison et al. (1973) reviewed resistance in ticks, Drummond et al. (1974) listed recent advances in tick control, and Wharton (1974, 1976) reviewed tick control with emphasis on Boophilus microplus (Canestrini), the southern cattle tick. In addition, the special problems associated with the con­ trol of ticks were an important part of the discussions, re­ commendations, and reports of the meetings of an FA0/0IE ad hoc Consultation on Control of Protozoal Tick-Borne Diseases of Cattle held in Nairobi, Kenya, Oct. 1972 (FAO, 1972) and an FAO Expert Consultation on Research on Tick-Borne Diseases and their Vectors held in Rome, Italy, May 1975 (FAO, 1 9 7 5 ) .

TICKS The most important problems of resistance in arthropods of veterinary importance are associated with ticks. Ticks that transmit diseases, paralyze animals, and are responsible for physical damage to livestock have been, of necessity, the objects of treatments with acaricides. Acaricides have been and can be used to control ticks; in fact, Boophilus spp. were eradicated from the United States with arsenic acid (arsenic a c i d ) . Thus it is a serious matter that several important species of ticks in other areas of the world have developed resistance to acaricides. BOOPHILUS

MICROPLUS

The widest spectrum of resistance to acaricides has been demonstrated by Boophilus microplus: it has been documented in Australia, Asia, Africa, South America, and other areas. However, the greatest diversity of resistance is found in Australia, and it is there that the major research activity with Β. microplus is found. The first resistance to acaricides in Β. microplus in Australia (and in most other areas where resistance has occurred) was found in 1937 for arsenicals. By 1950, Β. microplus was resistant to chlorinated cyclodiene compounds, in 1954 to DDT, and finally in 1964 to organophosphorus and carbamate acaricides. At least eight distinct strains of Β. microplus in Aus­ tralia now show unique and overlapping resistance to a vari­ ety of organophosphate and carbamate acaricides. The Mt. Alford and Gracemere strains, found in 1970 (O Sullivan and 1

Resistance in Ticks

307

Green, 1 9 7 1 ) , have resistance similar to that of the Biarra and Ridgelands strains, respectively, but have increased re­ sistance to chlorpyrifos [0,0-diethyl 0-(3,5,6-trichloro-2p y r i d y D p h o s p h o r o t h i o a t e ] and diazinon [0,0-diethyl 0- (2-isopropyl-6-methyl-4-pyrimidinyl) phosphorothioate] (Roulston, 1971). The Bajool, Tully, and Ingham strains, found in 1972 and 1973 (Roulston and Nolan, 1 9 7 5 ) , have different resis­ tance spectra. Thus, the resistance problem with B . microplus in Australia continues to become more complex. As resistance has become a problem, acaricidal control of organophosphorus- and carbamate-resistant ticks in Australia has been accomplished by increasing the concentration of the chemical in dips, by decreasing the interval between dippings, by changing to similar types of acaricides for which resis­ tance is not highly developed, or by using new classes of acaricides. For example, an acaricide such as chlordimeform [iV -(4-chloro-o-tolyl)-i^,iV-dimethylformamidine] used alone or in combination with organophosphorus acaricides has given satisfactory control of resistant strains (Roulston et a l . , 1971) though vat management, especially pH stabilization, must be handled carefully with chlordimeform (Kearnan, 1 9 7 1 ) . Other recently introduced acaricides that are used for the control of resistant ticks include a cyclic amidine. Bay Vb6896, "clenpyrin" [N-(l-butyl-2-pyrrolidenylidene)-3,4-dichloroben-zenamine] (Enders et a l . , 1 9 7 3 ) , that causes slackening of the muscles of ticks (Andrews and Stendel, 1 9 7 5 ) ; a thiourea, Ciba-Geigy CGA-13444, "chloromethiuron" [N*- (4-chloro-2-methylphenyl)-N,2V-dimethylurea] ; and a triazapentadiene, amitraz (Ν ,Ν' - [ (methylimino)dimethylidyne]Jbis [2,4-xylidine]) (Palmer et a l . , 1971; Wharton, 1 9 7 6 ) . Also, Schuntner et al. (1974) found that piperonyl butoxide (a-[2(2-butoxyethoxy)ethoxy]-4,5-(methylenedioxy)-2-propyltoluene) used in combination with carbaryl (1-naphthyl methylcarbamate) restored the effectiveness of carbaryl against the carbarylresistant Biarra strain of B. microplus. 1

Plainly new chemicals with different modes of action must be found if resistant ticks are to be controlled, but it is just as plain that the ticks will develop resistance to these compounds if they are used in the same manner as the acari­ cides to which the ticks are now resistant. Therefore, every effort must be made to prevent or delay selection for resistance to any new acaricides. However, such an effort requires information about how resistant ticks survive acari­ cides. Thus, in recent years workers in Australia investiga­ ted the inheritance and mechanism of resistance in Β. microplus. In an excellent review of the genetics of resistance. Stone (1972) listed five factors that may singly or in combi­ nation allow arthropods to become resistant: (1) reduced

308

R. Ο. Drummond

penetration or uptake of the chemical, (2) increased storage or excretion of unchanged chemical, (3) reduced conversion of the chemical to the active toxicant, (4) increased detoxication of the toxicant, and (5) reduced sensitivity of the b i o ­ chemical system to the toxicant. Mechanism (4) has now been demonstrated in the Mackay strain, mechanism (5) in the Ridgelands and Biarra strains, and a combination of mechanisms (4) and (5) in the Gracemere and Biarra strains (Schnitzerling et al., 1 9 7 4 ) . The studies of the biochemistry of resistance in Β. microplus have proceeded along several lines. Schnitzerling et al. (1974) characterized the resistance spectra of the Mt. Alford, Gracemere, and Silkwood strains and found that the pattern of the Silkwood strain was similar to that of the Mackay strain; however, that strain had changed its mechanism of resistance from that originally described by Roulston et al. (1969). Studies of the enzymatic activity of the cytochrome system (Shanahan and O'Hagan, 1 9 7 3 ) , cholinergic systems (Schuntner and Smallman, 1 9 7 2 ) , and of forms of acetylcholinesterases (Nolan et al., 1972; Nolan and Schnitzerling, 1975) in Β. microplus hopefully will give greater understanding of the resistance mechanisms in ticks. A considerable amount of research effort has also been devoted to the study of formamidine c o m p o u n d s — t h e i r recogni­ tion as acaricides (Roulston et al., 1 9 7 1 ) ; their laboratory evaluation (Knowles and Roulston, 1 9 7 3 ) ; their effect on hy­ peractivity of larvae (Atkinson and Knowles, 1974) and on de­ tachment of adults (Stone et al., 1 9 7 4 ) ; their metabolism (Schuntner, 1 9 7 1 ) ; their effect on monoamine oxidase in ticks (Atkinson et al., 1 9 7 4 ) ; and their activity in relation to antagonism by piperonyl butoxide (Knowles and Roulston, 1972; Knowles and Schuntner, 1 9 7 4 ) . Brown and Pal (1971) and Wharton and Roulston (1970) re­ ported resistant strains of Β. microplus in many areas of the world. Since these reports, few documentations of resistance of Β. microplus have been received. Nunez et al. (1972) re­ ported that, of 20 strains tested, only one strain called "K," from Corrientes, Argentina, was resistant to coumaphos (0,0diethyl 0-(3-chloro-4-methyl-2-oxo-2H-l-benzopyran-7-yl) phosphorothioate] and ethion [0,0,0',0 -tetraethyl S,S'methylene-Jbis(phosphorodithioate)]. Grillo-Torrado and Gutierrez (1970), also in Corrientes, Argentina, found a "G" strain re­ sistant to coumaphos and dioxathion [5,5"-p-dioxane-2,3-diyl 0,0,0',0'-tetraethyl-Jbis (phosphorodithioate) ] ; and later, Grillo-Torrado et al. (1972) found that strain "22" was re­ sistant to coumaphos; ICI 29661, "pyrimithate" (0-[2-(dimethylamino)-6-methyl-4-pyrimidinyl] 0,0-diethyl phosphorothioate); and compound 4072 [2-chloro-l-(2,4-dichlorophenyl) vinyl diethyl p h o s p h a t e ] . Amaral et al. (1974) found that 1

Resistance in Ticks

309

strains "D" from Rio Grande do Sul and "M" from Minas Gerais, Brazil were resistant to coumaphos, dioxathion, and ethion but that a new acaricide, American Cyanamid AC-84633, "nimidane" (4-chloro-iV-1, 3-dithietan-2-ylidene-2-methylbenzena m i n e ) , controlled these strains. With the continued use of carbamate and organophosphorous acaricides, more strains of resistant B. microplus will be discovered. These strains should be carefully catalogued and their resistance spectra carefully defined. OTHER

SPECIES

In addition to the instances documented by Brown and Pal (1971) in other species of ticks was the resistance of B. decoloratus (Koch, Berlin strain) to certain organophosphates and carbamates recorded in 1966 in South Africa (Shaw et a l . , 1967). The strain is still limited in distribution, and new strains have not appeared (Whitehead, 1 9 7 5 ) . Nayar and Isa (1973) reported that Rhipicephalus evertsi Neumann in Tanzania was resistant to toxaphene (chlorinated camphene containing 67%-69% chlorine) and to lindane (1,2,3,4,5,6-hexachlorocyclohexane, gamma isomer of not less than 99% purity) and that Amblyomma variegatum (F.) was resistant to toxaphene. JonesDavies (1974), in a survey of 65 strains of ticks in Rhodesia, found strains of Boophilus decoloratus resistant to arsenic, toxaphene, and both arsenic and toxaphene; strains of Rhipi cephalus appendiculatus Neumann and R. evertsi resistant to toxaphene; and strains of Hyalomma rufipes Koch resistant to arsenic and both arsenic and toxaphene. Kitaka et al. (1970), in Uganda, found strains of Boophilus decoloratus (on exotic cattle from K e n y a ) , Rhipicephalus evertsi, and R. appendiculatus resistant to toxaphene. Whitehead (1973) reported indications of resistance to chlorinated hydrocarbons in Amblyomma hebraeum Koch in Sqaziland. Wharton (1976) reported that resistance to organophosphorus acaricides had developed in B. decoloratus, R. appendiculatus, R. evertsi, and A. hebraeum in South Africa. ACARICIDE

TESTING

Since information concerning resistance in ticks outside Australia is fragmentary and not standardized, the Food and Agriculture Organization (1972, 1975) proposed a Global Acaricide Resistance Monitoring Program. In this program, tests for resistance would be conducted at cooperating laboratories with a standard Acaricide Resistance Test Kit. Samples of resistant ticks would be sent to a World Acaricide Resistance Reference Center where the strains would be maintained and additional baseline data on resistance and susceptibility

310

R. Ο. Drummond

obtained. In addition, this World Center would store and analyze resistance data and disseminate information on re­ sistance. Such a program would be indispensable in document­ ing resistance and allowing for the effective use of acari­ cides for the control of ticks. The World Health Organization (1970) presented a tentative method of determining the resistance or susceptibility of adult ticks to acaricides. Unfed adult ticks would be treated topically (a microdrop on the dorsum) with acaricides in methyl ethyl ketone. Privora et al. (1970) reported on re­ sults with the WHO testing kit and the WHO standard method by using them with Dermacentor marginatus (Sulzer). However, with the WHO method or any other method that involves unengorged ticks, the exact age of the ticks must be known. As ticks age, they become increasingly susceptible to acaricides (Mount et al., 1970; Darrow and Whetstone, 1972; Rupes et al., 1972a, 1972b) so unless the specific age of the stage is known it is difficult to exactly determine whether increased or decreased mortality is a result of the absence or presence of physiological vigor or a result of resistance or suscepti­ bility to acaricides. FAO (1971) proposed a method in which unfed tick larvae are confined in an envelope or "packet" of paper impregnated with acaricide dissolved in olive oil. It was this technique that was presented (FAO, 1975) as the base for the standard test in the Acaricide Resistance Test Kit of the Global Acari­ cide Resistance Monitoring Program. Several other techniques have recently been used to test acaricides for the control of ticks. Shaw (1966) described an immersion test, the "Shaw" test, in which larvae were placed in filter paper and dipped into emulsions of acari­ cides. This technique has been extensively used to determine resistance in ticks. Fiedler (1968) described the "tea bag" technique in which ticks are confined in packets of heatsealable rice paper, and the packets are dipped in acaricides. This technique was used by Gladney et al. (1972) to evaluate a number of acaricides for the control of the brown dog tick, Rhipicephalus sanguineus Latreille. Drummond and coworkers, in a series of tests, evaluated water-based emulsions, suspensions, and solutions of acari­ cides as dips for the inhibition of oviposition and hatch of eggs from treated female Dermacentor albipictus (Packard), the winter tick (Drummond et al., 1971a); Anocentor nitens (Neumann), the tropical horse tick (Drummond et al., 1 9 7 1 b ) ; Boophilus microplus and Β. annulatus (Say), the cattle tick (Drummond et al. , 1 9 7 3 ) ; and Amblyomma americanum ( L . ) , the lone star tick (Drummond and Whetstone, 1 9 7 3 ) . In all of these tests the rankings of concentrations that produced 50% inhibition of estimated reproduction for each of the acari-

Resistance in Ticks

311

cides were correlated with high significance between the spe­ cies. Most recently, several strains of B. micropuls from Mexico and south Texas were tested by the same technique and found equally susceptible to nine commonly used acaricides (Drummond et a l . , 1 9 7 6 ) . Kigaye and Matthysse (1973) reported that exposing R. sanguineus larvae to the inside surface of disposable Pasteur pipettes treated with insecticides in acetone was a highly satisfactory technique for testing acaricides. Matthysse et al. (1975) used this same technique to determine the toxicity of several acaricides to larval R. sanguineus, to protonymphs or adult females of Ornithonyssus sylviarum (Canestrini and F a n z a g o ) , the northern fowl mite, and to adult female Chorioptes bovis (Hering), the chorioptic mange mite. The diversity of these techniques for testing acaricides points out the need for a standardized testing technique. It is also important that the interrelationships between the data obtained with the different techniques be defined in a series of tests in which the resistance or susceptibility of several species or strains of ticks is determined by the different techniques at a single laboratory. The assessment of acaricidal activity of tick detachment agents was investigated with B. microplus larvae in the lar­ val packet test (Knowles et al. , 1973) and against adult Β. microplus by Stone and Knowles (1973) and by Gladney et al. (1974) for A. americanum, R. sanguineus, and Dermacentor andersoni Stiles, the Rocky Mountain wood tick.

INSECTS The impact of resistance on the practical control of arthropods of veterinary importance, other than ticks, has been of little consequence. In all cases except that of Phaenicia (-Lucilia) cuprina (Wiedemann), the sheep blowfly, in Australia, resistance has not been widespread and has been overcome by a slight shift in insecticides. SHEEP

BLOWFLY

The sheep blowfly developed widespread resistance to dieldrin (1,2, 3,4,10,10-hexachloro-6, 7-epoxy-l,4,4a,5,6,7,8, 8a-octahydro-l, 4-en<5o-exo-5,8-dimethanonaphthalene, 85% mini­ mum) in 1957, to diazinon [0,0-diethyl 0-(2-isopropy1-6methyl-4-pyrimidinyl) phosphorothioate] in 1965, and to car­ bamates in 1967 (Harrison, 1969; Shanahan and Roxburgh, 1974a). Shanahan and Roxburgh (1974b) have recorded the colonization of a strain, called "CG," of P, cuprina that has a resistance factor of 112X (double the previously

312

R. Ο. Drummond

recorded ceiling of resistance) to diazinon. Although sheep blowfly larvae can still be controlled in the field, there is a continuing program to monitor resistance, find new in­ secticides, and develop alternative methods of control (Shanahan and Roxburgh, 1 9 7 4 c , d ) . OTHER

INSECTS

The resistance of the horn fly, Haematobia irritans ( L . ) , in Louisiana in 1962 to ronnel [0,0-dimethyl 0- (2,4,5-trichlorophenyl) phosphorothioate] (Burns and Wilson, 1963) w a s substantiated by Harris et al. (1966), who collected flies from the same location, exposed them to ronnel for 18 of 28 generations, and selected a strain that had a resistance factor of 50X. No new resistance has been reported in Stomoxys calcitrans (L.), the stable fly. Harris et al. (1972) tested strains of stable flies from Japan, Thailand, New Zealand, South Africa, and the United States (Kerrville, Texas) and detected differ­ ences in susceptibility to toxaphene, DDT [1,1,1-trichloro2,2-bis (p-chloropheny1)ethane], lindane, malathion (diethyl mercaptosuccinate 5-ester with 0,0-dimethyl phosphorodithioa t e ) , and ronnel, but they concluded that none was highly re­ sistant to the insecticides. (Exposure of the strains to insecticide before collection was unknown.) Resistance of the face fly, Musca autumnalis De Geer, in the United States was not detected in recent tests (Robinson et al., 1 9 7 6 ) . Baker (1969) reported that a strain of sucking lice, Linognathus africanus Kellogg and Paine, on Angora goats in South Africa that was resistant to rotenone (1,2,12,12a-tetrahydro-2-isopropenyl-8,9-dimethoxy[l]benzopyrano[3,4-Jb]furo[2, 3-h][l]benzopyran-6(6a#)-one) and possibly to chlorinated hydrocarbons in 1963 was also, in 1966, resistant to the or­ ganophosphorus compounds dioxathion and dichlofenthion [0-{2, 4-di chlo ropheny 1) 0, 0-diethyl phosphorothioate] . Treeby (1966a, 1966b) found that a strain of Bovicola (Damalinia) ovis (Schrank), the sheep biting louse, infesting sheep in England w a s resistant to lindane but susceptible to carbophenothion (S-[[ (p-chloropheny1)thio]methyl] 0,0-diethyl phosphorodithioate). Rosa et al. (1969) found that a strain of Psoroptes ovis (Hering) from Buenos Aires Argentina was not adequately controlled with two dips of lindane and that diazinon dips were effective. However, later, Rosa and Lukovich (1970) reported that resistant strains could not be established. Although resistance of Boophilus microplus, Boophilus decoloratus, and a few other species of ticks, and of Phaenicia cuprina is of concern to certain livestock producers.

Resistance in Ticks

313

the resistance of other arthropods of veterinary importance does not receive the same attention because it is not of the same magnitude. Yet this resistance is an alarming fact and the outlook for developing new acaricides and insecticides for the control of highly resistant strains of ticks and in­ sects is not very bright, though the synthetic pyrethroids (Elliott et a l . , 1974) presently seem highly effective for the control of a variety of arthropods, especially flies, affecting livestock. However, house flies, which are resis­ tant to so many insecticides, have recently been shown to be capable of becoming resistant to insect growth regulators (Cerf and Georghiou, 1974a) and to an inhibitor of chitin synthesis (Cerf and Georghiou, 1 9 7 4 b ) . Chemicals may well remain our first weapon against arthropods of veterinary importance, but it is obviously im­ perative that other methods of control, such as host resis­ tance, parasites, predators and pathogens, induced sterility, genetic mechanisms, environment alteration, and other tech­ niques, either alone or in concert, be investigated for use in local or widespread pest management programs for the con­ trol of ticks and insects of veterinary importance.

REFERENCES Amaral, Ν. Κ., Monmany, L. F. S., and Carvalho, L. A. F. (1974). Acaricide AC84,633: first trials for control of Boophilus microplus. J. Econ. Entomol. 67, 387-389. Andrews, P., and Stendel, W. (1975). Mechanism of action of clenpyrin on the cattle tick. Pestic. Sci. 6, 129-143. Atkinson, P. W., and Knowles, C. 0. (1974). Induction of hyperactivity in larvae of the cattle tick, Boophilus microplus, by formamidines and related compounds. Pestic. Biochem. Physiol. 4, 417-424. Atkinson, P. W., Binnington, K. C., and Roulston, W. J. (1974). High monoamine oxidase activity in the tick, Boophilus microplus, and inhibition by chlordimeform and related pesticides. J. Aust. Entomol. Soc. 13, 207-210. Baker, J. A. F. (1969). Resistance to certain organophos­ phorus compounds by Linognathus africanus on Angora goats in South Africa. J. S. Afr. Vet. Med. Assoc. 40, 411414. Brown, A. W. Α., and Pal, R. (1971). Insecticide Resistance in Arthropods. WHO Monogr. Ser. 38. Burns, E . G., and Wilson, Β. H. (1963). Field resistance of horn flies to the organic_phosphate insecticide ronnel. J. Econ. Entomol. 56, 718. Cerf, D . C , and Georghiou, G. P. (1974a). Cross-resistance to juvenile hormone analogues in insecticide-resistant

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strains of Musca domestica L. Pestic. Sci. 5, 759-767, Cerf, D . C , and Georghiou, G. P. (1974b). Cross-resistance to an inhibitor of chitin synthesis, TH6040, in insecticide-resistant strains of the housefly. J. Agric. Food Chem. 22, 1145-1146. Darrow, D . I., and Whetstone, Τ. M. (1972). Age and suscepti­ bility of nymphal lone star ticks to selected ixodicides. J. Econ. Entomol. 65, 156-158. Drummond, R. 0. (1970). Current worldwide research on control of ticks involved in animal diseases. Misc. Publ. Entomol. Soc. Am. 6, 367-372. Drummond, R. 0., and Whetstone, Τ. M. (1973). Lone star tick: Laboratory tests of acaricides. J. Econ. Entomol. 66, 1274-1276. Drummond, R. 0., Gladney, W. J., Whetstone, Τ. Μ., and Ernst, S. E. (1971a). Laboratory testing of insecticides for control of the winter tick. J. Econ. Entomol. 64, 686-688. Drummond, R. 0., Gladney, W. J., Whetstone, Τ. Μ., and Ernst, S. E. (1971b). Testing of insecticides against the tropical horse tick in the laboratory. J. Econ. Entomol. 64, 1164-1166. Drummond, R. 0., Ernst, S. E., Trevino, J. L., Gladney, W. J., and Graham, 0. H. (1973). Boophilus microplus and B. annulatusi Laboratory tests of insecticides. J. Econ. Entomol. 66, 130-133. Drummond, R. 0., Gladney, W. J., and Graham, Ο. H. (1974). Recent advances in the use of ixodicides to control ticks affecting livestock. Bull. Off. Int. Epizoot. 81, 47-63. Drummond, R. 0., Ernst, S. Ε., Trevino, J. L., Gladney, W. J., and Graham, Ο. H. (1976). Tests of acaricides for con­ trol of Boophilus annulatus and Β. microplus. J. Econ. Entomol. 69, 37-40. Elliott, Μ., Farnham, A. W., Janes, N. F., Needham, P. Η., and Pulman, D. A. (1974). Synthetic insecticide with a new order of activity. Nature (London) 248, 710-711. Enders, Ε., Stendel, W., and Wollweber, H. (1973). New com­ pounds active against resistant cattle ticks (Boophilus spp.): Relationship between structure and activity with­ in the group of cyclic amidines. Pestic. Sci. 4, 823838. Food and Agriculture Organization (1971). Recommended methods for the detection and measurement of resistance of agricultural pests to pesticides. Tentative method for larvae of cattle ticks, Boophilus spp.-FAO Method No. 7. FAO Plant Prot. Bull. 19, 15-18. Food and Agriculture Organization (1972). Report of FA0/0IE ad hoc Consultation on Control of Protozoal Tick-borne

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Diseases of Cattle (Nairobi, Kenya, Oct. 1 9 7 2 ) . AGA:FAO/ OIE/TD/72, 27 pp. Food and Agriculture Organization (1975). Report of FAO Ex­ pert Consultation on Research on Tick-borne Diseases and 1975/2, Their Vectors (Rome, Italy, May 1 9 7 5 ) . AGA: 17 p p . Fiedler, 0. G. H. (1968). A new biological method for evalu­ ating the efficacy of acaricides against ticks. J. S. Afr. Vet. Med. Assoc. 39, 84-87. Gladney, W. J. , Dawkins, C. C , and Drummond, R. 0. (1972). In­ secticides tested for control of nymphal brown dog ticks by the "tea-bag" technique. J. Econ. Entomol. 65, 174-176. Gladney, W. J., Ernst, S. Ε . , and Drummond, R. 0. (1974). Chlordimeform: A detachment-stimulating chemical for three-host ticks. J. Med. Entomol. 11, 569-572. Graham, 0. Η., and Harris, R. L. (1966). Recent developments in the control of some arthropods of public health and veterinary importance. Bull. Entomol. Soc. Amer. 12, 319-325. Grillo-Torrado, J. Μ., and Guttierrez, R. 0. (1970). Fosfororesistencia de una cepa argentina de garrapata Boophilus microplus - su medicion. .Rev. Med. Vet. (Buenos Aires) 51, 113-125. Grillo-Torrado, J. Μ., Gutierrez, R. 0., and Arriete, A. P. (1972). El "factor de resistencia" en larvas de la garrapata Boophilus microplus (Can.) Lah. a los compuestos organo-fosforados. Su significacion en la eficacia de los garrapaticidos. Rev. Invest. Agropecu. Ser. 4, 9, 25-35. Harris, R. L., Graham, 0. Η., and McDuffie, W. C. (1965). Resistance of livestock insects to insecticides in the United States. Agric. Vet. Chem. Agric. Eng. 6, 78-81. Harris, R. L., Frazar, E . D . , and Graham, Ο. H. (1966). Re­ sistance to ronnel in a strain of horn flies. J. Econ. Entomol. 59, 387-390. Harris, R. L., Graham, 0. Η., and Frazar, E. D . (1972). Susceptibility of five strains of stable flies to certain insecticides. J. Econ. Entomol. 65, 915-916. Harrison, I. R. (1969). Development of organophosphorus re­ sistance in the Australian sheep blow fly, Lucilia cuprina (Wied). Soc. Chem. Ind. Monogr. 33, 215-223. Harrison, I. R., Palmer, Β. Η., and Wilmshurst, E . C. (1973). Chemical control of cattle tick-resistance problems. Pestic. Sci. 4, 531-542. Jones-Davies, W. J. (1974). Recent advances in tick control. Rhod. Sci. News 8, 71-73. Kearnan, J. F. (1971). Additive to control resistant ticks. Advisory Leaflet Queensland Agric. J. 716.

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