The Antimetabolite IMIDAZOLE AS A PESTICIDE

ROY J. PENCE

Irnidazole, an antimetabolite of histamine and nicotinic acid, has been found to be a safe and effective pesticide and is now undergoing field tests. Developed at U.C., Los Angeles, the new material has been patented and given the trade name “lrnutex.” Imidazole, when synergized with boric acid, may be employed at low levels to proof fabric satisfactorily against attack. When synergized with 2-Aminopyridine, along with several newer synergists, and combined with base oil, imidazole is capable of controlling a number of and related species. Effectiveness is significantly increased by adding two surfact- ants to base oil. A hydrophilic surfactant increases the physiological activity of imidazole without improving the physical properties of the oil carrier, while per- chloroethylene directly increases solubility. The particularly exciting quality about the material is its low mammalian toxicity.

HE METABOLIC EFFECTS of antime- haps a single atom has been omitted, exist largely upon a diet of com- Ttabolites within the systems of fab- or added where it does not belong. With bined with essential contaminants, and ric-feeding insects have been studied for such a chemical structure the deceptive because the identity of these requirements the last six years. Some of these com- resemblance to a vitamin may cause it to has been learned through dietetic studies, pounds, when formulated in suitable lipid- smell or even taste like a vitamin to a it was reasoned that specific antimetabo- soluble carriers, have recently been found fabric-feeding insect, but it will never lites might be employed to antagonize, to perform as effective contact pesticides serve the same purpose. Once taken into metabolically, the dietary needs of all in addition to their already proven meta- the system of the insect, the antimetab- fabric-feeding insects. bolic values. One of the most promising olite becomes an inhibitor antagonistic 22 proven effective of the antimetabolites is imidazole (gly- to the growth regulator it resembles. The oxaline or 1,3-diazole), which has an antimetabolite does not fit into the diges- A total of 114 growth-factor analogs extremely low mammalian toxicity. tive processes, and physiological compli- have now been tested with 57 demon- Antimetabolites closely resemble a cations develop and interrupt normal me- strating varying degrees of metabolic vitamin or other growth substance in tabolism. When low-level antimetabolites significance. Of this number, 22 have chemical structure but, by design, are are applied to test fabrics, early instar proved to be of sufficient value to “proof” slightly altered in their manufacture. Per- larvae driven by hunger to eat increasing wool satisfactorily against fabric insect amounts of the pseudo-vitamins soon die attack. Imidazole, one of the most of either a vitamin deficiency or related promising, has been currently selected for commercial development based on its CALIFORNIA AGRICULTURE forms of hastened starvation while allow- Progress Reports of Agricultural Research ing minimum losses in fiber weight. effectivenes, economy, and negligible priblished monthly by the University of Cali! mammalian toxicity. The acute oral toxic- fornia Division of Agricultural Sciences. Field tests ity (LDSO mg/kg) of pure imidazole Williaiii W. Paul ...... Manager Agricultural Publications Imidazole has been tested in the field for laboratory has been estab- Jerry Lester...... Editor California Agriculture by a few accredited control opera- lished at between 1,000 and 1,500 mg/ tors, who are reporting a sufficient knock- kg with recent results revealing imida- Articles published herein may be republished or reprinted provided no advertisement for a down of insects and related zole satisfactorily to have passed acute commercial product is implied or imprinted. Please credit: University of California to comply with standard “clean-out” re- inhalation toxicity tests specified for Division of Agricultural Sciences. California Agriculture will be sent free upon quirements within infested dwellings “Hazardous Substances” by the U. S. request addressed to: Editor, California selected for these tests. The chemical was Food and Drug Administration. Agriculture 207 University Hall 2200 Uni- versity Avenue. Berkeley, Califoinia 94720. also found to be odorless and nonirritat- Imidazole is the nucleus of histamine To simplify the information in California Agriculture it is sometimes necessary to use ing to the eyes or respiratory system. and serves as a pharmaceutical intermedi- trade names of producta or equipment. No Preliminary results, from both laboratory ate for the manufacture of certain anti- endorsement of named products is intended nor is criticism implied of similar producta and field, indicate that imidazole should histamines. It is sold commercially as an which are not mentioned. prove a valuable tool for many phases of antimetabolite for histamine. Current 141 pest control. experiments with imidazole, plus a few Inasmuch as fabric-feeding insects other antihistamines that have compara-

CALIFORNIA AGRICULTURE, JANUARY, 1965 13 was in accordance with modified C.S.- Photomicrograph of a wool fiber containing M.A. standards of evaluation, and in- a few mandibular scars caused by the linear cluded a log of body weight losses. In feeding of a young . This this study, 25 larvae per test (No. 20 constitutes the degree of feeding damage to mesh size) were used rather than the wool impregnated with an antimetabolite. 10 larvae customarily employed for these Enough treated wool is ingested to disrupt the studies. Also included in the tables is a insect’s metabolism but not enough to damage record of the body-weight losses of 25 the fobric from which the fiber was withdrawn. larvae confined to empty C.S.M.A. cells devoid of any food supply. As carpet are basically scavengers, cast of the larvae were removed daily from species of carpet beetles, Attagenus all cells in order to rule out the factor piceus (Olivier) , flavipes Le- of sustenance obtained from this readily conte, and A. verbasci (L.). It has also available by-product source of nutrient been learned that boric acid will syner- supply. All tests were compared with the gize imidazole. Boric acid alone applied body-weight gains of standard controls. at 1% to wool fabric has little effect on these insects. Yet fabric saturated High performance with or dipped into a solution of as little Imidazole’s high degree of perform- as 0.25% of imidazole and 1% boric ance in the systems of fabric-feeding acid will satisfy the minimum excrement- insects led to experiments with this com- weight-yield tolerances established under pound on other species of insects, espe- C.S.M.A. standards. cially those also existing on a unidiet, such as cereals, and comparable dried Treated wool food products. Owing to imidazole’s low When imidazole was added to wool mammalian toxicity, it was considered fabric as a proofing agent and tested sufficiently safe to be incorporated into under C.S.M.A. standards, its metabolic foodstuffs on an experimental basis. effects were logged by recording the daily Imidazole in a 1% aqueous solution was body weight losses and mortality of the sprayed over spread cereals, allowed to insects, as well as the final weight of their dry, and then exposed to insect attack total excrement, in contrast to lesser of the saw-toothed grain beetle, Oryzae- losses of control insects when subjected philus surinamensis (L.) , the drugstore to complete starvation. Also consistent beetle, Stegobium paniceum (L.), the with standards, was the significant lack confused flour beetle, Tribolium confu- of fiber weight loss following the required sum Jacquelin du Val, the yellow meal- 14 days of insect exposure. It should be worm, Tenebrw molitor L., and the understood that confined carpet beetle Indian-meal moth, Plodia interpunctella larvae must sample minute quantities of (Hubner) . Appreciable mortality of the imidazole-treated fibers in order to sat- feeding insects, along with minimal feed- isfy the need for food. Although fiber ing damage, was observed in contrast to losses cannot be observed by the unaided that of the untreated controls. However, eye, they are sufficient to indicate that the tests were conducted on an empirical enough was ingested to denote symptoms basis with no statistical data attempted ble metabolic effects on fabric-feeding of a metabolic effect-which subse- as of this writing. The value of imidazole insects, indicated that histamine performs quently dulled the appetite and discour- as a mosquito larvacide is promising. In a more important biological function aged feeding. This was further evidenced three separate tests it has been shown within the systems of a number of species by the limited amount of pelleted excre- that imidazole at 1 ppm resulted in 100% of insects than hitherto suspected. - ment¶ which, upon microscopic examina- control of the larvae of Culex pipiens ther and more detailed investigations in tion, revealed symptoms of catabolic fasciatus Say, and 88% control with 0.5 this area are required. Sufbcient experi- wastes, as was observed by its negative ppm. According to the U. S. Fish and mental evidence has now been accumu- response to the excitations of ultraviolet Wildlife Service, the LD,, (lethal dosage lated to demonstrate the reversal of the illumination at 3,650 Angstrom units. causing 50% deaths) of imidazole to “toxic” symptoms of imidazole by hista- Fecal pellets excreted following normal small rainbow trout is approximately 12 mine and histamine derivatives. food intake fluoresce brightly. ppm compared with other In testing the effects of imidazole on The following data illustrate the effects which are toxic in the range of 0.003 to fabric-feeding insects, it has been shown of imidazole on test insects with the re- 0.015 ppm. Additional work in this area that 1% of actual imidazole, when ap- versal effects of histamine and three of continues. plied to wool fabric, will satisfactorily its derivatives: Table 1 offers data on the The significant metabolic values of pass all C.S.M.A. (Chemical Specialties effects of imidazole once it is within the imidazole led to the supposition that the Manufacturers Association) standards of system of the larvae of two species of compound might perform equally effec- evaluation for control of clothes moths, carpet beetles, Attagenus piceus and An- tively if it could be administered directly Tineoh bisselliella (Hummel) , and three threnus fiavipes. The method of testing into the insect’s system. The success of

14 CALIFORNIA AGRICULTURE, JANUARY, 1965 EFFECTS OF IMIDAZOLE-TREATED TEST FABRIC AT 0.5% AQUEOUS, AND STARVATION, ON THE BODY WEIGHT OF TWO SPECIES OF CARPET BEETLE LARVAE’ Weight (mg.) Weight change (mg.) Category Imidarole- Starved Check Imidazole- Starved Check treated (check) (untreated) treated (check) (unkeated) Ab BE A 8 A 8 A 8 A B A 8 Original weight 41.6 27.6 42.0 27.7 41.6 28.0 ...... Weight after 3 days 39.7 24.1 40.8 23.8 42.1 25.3 - 1.9 - 3.5 -1.2 - 3.9 + 0.5 - 2.7 Weight after 5 days 38.5 19.4 40.3 21.1 43.0 24.0 - 3.1 - 8.2 -1.7 - 6.6 + 1.4 - 4.0 Weight after 7 days 35.9 17.9 38.3 18.9 u.7 25.5 - 5.7 - 9.7 4.7 - 8.8 + 3.1 - 2.5 Weight after 10 days 34.1 16.9 38.1 17.5 48.8 41.5 - 7.5 -10.7 -3.9 -10.2 + 7.2 $13.5 Weight after 14 days 28.6 15.2 37.1 16.4 51.0 49.6 -13.0 -12.4 4.9 -11.3 + 9.4 +21.6 Weight after 18 days 25.5 12.3 35.5 14.1 51.1 52.6 -16.1 -15.3 4.5 -13.6 +10.5 +24.6 Total excrement weight yield (mg.) 2.2 1.3 1.7 2.2 58.8 69.0 Mortality (%) 12 32 0 4 0 4 Change from original weight (%) -38.7d -55.4” -15.5 49.1d +25.2 -I-87.9”

a A arouo of 25 larvae (No. 20-mesh size1 was weiehed and olaced on imidazolbtreated test fabric confined to standard 2“ X 2“ cells. b A & Afiagenus piceus. . C 8 = Anthrenus flavipes. d lnciudes weight of dead insects. such entry would be dependent upon a Although the beneficial effect of a hydro- thrips, including Cuban Laura1 thrips, suitable liquid hydrocarbon carrier hav- philic surfactant on oil has not been fully and whiteflies. With very little phyto- ing high lipid-soluble characteristics, and explained in a physical and/or chemical toxicity being observed at this early stage, whether the compound could be applied basis, it has been demonstrated in a considerable investigation lies ahead to as a contact spray. A few of the standard physiological sense. Hydrophilic surfact- understand fully the effectiveness of imi- base oil carriers used by pest control ants will not “wet” oil or recognizably dazole when specifically formulated for operators (deodorized kerosenes) were improve upon its penetrating capabilities. plant insects with careful consideration tested to determine their solubility values. Yet, once the lipid layer of an insect given to plant tolerances. Imidazole is not oil-soluble and requires cuticle has been penetrated by the sur- a mutual solvent, such as oleic acid or factant-treated oil, there is biological Residual effects isopropyl alcohol, before it can be com- indication that the surfactant present will Imidazole lacks a longlasting residual pletely dissolved in an oil carrier. instantly combine with the first encoun- effect because it tends to evaporate into tered aqueous content of the cuticle and the atmosphere. It is therefore necessary Contact effect then carry the active toxicant in all direc- that it be deposited in sufficient quantity Imidazole at 1.5% in base oil was tions into and throughout the insect body. to prolong its activity. The following in- tested and found to have a definite Imidazole, 1.5%, synergized with formation has been obtained from resid- contact effect on a number of species of 0.5% 2-Aminopyridine and combined ual data accumulated as of this writing. insects and related arthropods. In order with base oil, has been tested both with Test procedure was to dissolve imidazole to quicken its knockdown time and im- and without surfactants. Tests were con- in acetone, allowing 2.5 ml. of the liquid prove effectiveness, a number of syner- ducted on adults of the German cock- to flow freely over glass surfaces, which gists were tried. Three revealed definite roach. The technique for this testing was are then set aside to dry. The actual activity, although detracting somewhat to apply a single free drop of each formu- imidazole quickly became plated over the from the safety of imidazole alone. These lation from the tip of a No. 30 hypo- surfaces in long crystals, at which time synergists are formaldehyde, phenol, and dermic needle onto the folded wing cov- it was subjected to longevity studies to 2-Aminopyridine, the latter having some ers of each cockroach at a point between determine the lethal effects of the deposits contact value of its own. Recently it has the meso- and metathorax. The drop on immature cockroaches that were been learned that pyrethrins at 0.10% would then eventually work its way forced to crawl over the treated surfaces. of actual, or as little as 0.03% when through the wings and into the thorax The tests indicated that 1% imidazole synergized with 0.15% of piperonyl proper. Thirty cockroaches, 15 of each was active for 6 days; 2% imidazole, butoxide, will, when added to imidazole, sex, were treated per test, with time active for 9 days; 3% imidazole, active improve knockdown, while maintaining recorded for knockdown. for 14 days; and 4% imidazole was ac- a low mammalian toxicity fgr the total tive for 17 to 24 days. formulation. New and more effective Effectiveness The tendency of imidazole to lose its synergists, classified under patent con- To date, imidazole when properly identity in the atmosphere is noted only tinuations, are currently being employed formulated has been found effective on when it is deposited onto hard surfaces. to improve imidazole performance. an experimental basis against a long list Once it has been integrated with wool of insects and related arthropods, includ- fibers, its effectiveness is long-lasting. Base oil ing silverfish, cockroaches, termites, Bioassays of three-month-old imidazole- Base oil is known to readily penetrate carabid beetles, bedbugs, fleas, flies, mos- treated test fabric indicate that imidazole the lipid of an insect cuticle but lacks the quitoes, ticks, spiders, and phytophagous may remain active in wool for 11 months high degree of solubility expected of it mites. Included also are all fabric-feeding or longer. Detailed studies of the longev- under these circumstances. Two adju- and many stored-products insects. Syner- ity of imidazole in wool are currently vants will contribute toward the efficacy gized imidazole at 0.75% aqueous with underway. of any designed for use in oil. 0.5% agricultural spray oil added has The first of these is a hydrophilic sur- killed many of the common plant insects Roy J. Pence is Specialist, Department factant which, when added to oil, notice- including aphids, cicadas, mealybugs, of Entomology, University of California, ably improved its total effectiveness. scale insects (both soft and armored), Los Angeles.

CALIFORNIA AGRICULTURE, JANUARY, 1965 15