The toxicity to adult mosquitos and the residual properties of some N-acyl-N-methylcarbamates.

454 NOTES The Toxicity to Adult Mosquitos and the Residual Properties of some N-Acyl-N-methylcarbamates by A. B. HADAWAY and F. BARLOW, Tropical Pesticides Research Unit, Porton Down, Wiltshire, England Members of a new group of compounds, the N-acylN-methylcarbamates, have been evaluated forresidual action against adult mosquitos, as part of the World Health Organization's collaborative scheme. These compounds were supplied by Boots Pure Drug Co. Ltd, Nottingham, England; those that were solid were purified by recrystallization from petroleum ether. Toxicity by topical application Solutions of each compound in di-isobutyl ketone applied from a microburette to the dorsal surface of the thorax of 1-2-day-old female Anopheles were stephensi and Aedes aegypti mosquitos. Two batches of 20 mosquitos were treated at each of four doses and were stored at 250C and 70% r.h. for 24 hours before mortality counts were made. Median lethal doses determined from probit kill/log dosage regression lines, together with those of the parent non-acylated compounds, are given in Table 1. Most of the compounds were highly toxic to both species and, with the exception of OMS-979, all were more toxic to Anopheles stephensi than to Aedes aegypti. In general, acylation resulted in a loss of intrinsic toxicity to mosquitos. TABLE I TOXICITY OF COMPOUNDS BY TOPICAL APPLICATION Median lethal dose (ng per female) to Insecticide OMS No. - 832 162 828 831 830 978 31 829 973 30 975 135 982 93 976 174 974 47 979 29 - a The 1865c M.p. (°C) 3-ethylphenyl N-methylcarbamate 3-ethylphenyl N-acetyl-N-methylcarbamate 3-isopropylphenyl N-methylcarbamate 3-isopropylphenyl N-acetyl-N-methylcarbamatea 3-isopropylphenyl N-propionyl-N-methylcarbamatea 3-isopropylphenyl N-butyryl-N-methylcarbamatea 3-isopropylphenyl N-isobutyryl-N-methylcarbamatea 3-tert-butylphenyl N-methylcarbamate 3-tert-butylphenyl N-acetyl-N-methylcarbamate 3-tert-butylphenyl N-propionyl-N-methylcarbamate 3-sec-butylphenyl N-methylcarbamate 3-sec-butylphenyl N-acetyl-N-methylcarbamatea 3-methyl-4-methylthiophenyl N-methylcarbamate 3-methyl-4-methylthiophenyl N-acetyl-N-methylcarbamate 3,5-dimethyl-4-methylthiophenyl N-methylcarbamate 3,5-dimethyl-4-methylthiophenyl N-acetyl-N-methylcarbamate 3,4-dimethyl-6-chlorophenyl N-methylcarbamate 3,4-dimethyl-6-chlorophenyl N-acetyl-N-methylcarbamate 3,5-dimethyl-4-dimethylaminophenyl N-methylcarbamate 3,5-dimethyl-4-dimethylaminophenyl N-propionyl-N-methylcarbamate 1-naphthyl N-methylcarbamate 1-naphthyl N-acetyl-N-methylcarbamate 1-naphthyl N-butyryl-N-methylcarbamate samples of these compounds were Anopheles stephensi Chemical name 74 liquid 13 13 74-75 1.9 liquid 7 liquid liquid liquid 7 7 14 143-144 2.4 4.7 10 liquid liquid 60-61 liquid 73 56-57 121-123 40-41 131-132 53-54 88-88.5 liquid 2.0 38 2.5 4.9 2.5 4.0 4.1 13 9 40 141-142 4.6 101-103 60-61 5.3 13 technical grades containing varying proportions of impurities. Aedes aegypti 26 27 3.5 17 17 10 22 5.6 11 14 3.8 75 4.8 8.1 4.8 7.8 9.5 17 12 22 19 19 98 TOXICITY TO MOYQUITOS AND PERSISTENCE OF N-ACYL-N-METHYLCARBAMATES 455 TABLE 2 INITIAL AND RESIDUAL CONTACT TOXICITY TO A. STEPHENSI ON PLYWOOD PANELS AT DOSAGE OF 1 g/m2 Compound (OMS No.) 162 828 831 830 978 31 829 973 30 975 135 982 982 93 976 174 974 47 979 a Initial contact toxicity: Mean %_kill Residual toxicity (No. of weeks with _______ after contact time of > Forulaionkill 70 % after time of mi 330 min mi mn ~5 mm mm1 contact 15 mm 1 hour) 2min_ 12mm Formulation a 50 % w.p. 25 % w.p. 25 % w.p. 25 % w.p. 25 %^w.p. 50 % w.p. 25 % w.p. 25 % w.p. 25 % w.p. 25 %jw.p. <10g7crystals <10 25 % 50 % 25 % 75 % 25 % 25 % 25 % 100 100 100 100 100 12 100 100 100 100 65 100 15 66 4 0 100 50 44 crystals w.p. 16-20 2-4 4-8 12-16 2-4 >32 4-8 8-12 12-16 4-8 12 100 95 >32 w.p. w.p. 4 95 43 100 94 w.p. w.p. 4 83 34 100 100 12 >32 8-12 w.p. w.p. 4 41 50 98 100 23 16-20 16-20 >32 28-32 w.p.= wettable powder. Contact toxicity Plywood panels were sprayed with aqueous suspensions of wettable powder formulations at a dosage of 1 g active ingredient per m2, and were stored and tested at 25°C and 50 %-55 % r.h. Batches of 2-3-day-old blood-fed female A. stephensi were exposed on the treated panels for known times and then stored at 25°C and 70 % r.h. for 24 hours before mortality counts were made. The number of weeks for which mortalities exceeded 70% after an exposure of one hour was adopted as the measure of residual contact toxicity (Table 2). Initially, the contact toxicity of deposits was generally high and where comparisons were possible the acylated compounds were found to be better contact insecticides than the parent compounds, despite their lower intrinsic toxicity. This is probably related to the fact that many of the acylated compounds are liquid and completely miscible with non-polar solvents, whereas those that are solid possess physical properties favouring penetration through the insect cuticle.a However, deposits of a Hadaway, A. B.&Barlow, F.(1966) Bull.ent. Res.,56,569. OMS-982, both from a wettable powder formulation and from pure suspensions of crystals of size < l10u, showed unexpectedly low contact toxicity. The residual contact toxicity of the N-acyl-Nmethylcarbamates was, however, less than that of the corresponding N-methylcarbamates. The most persistent of the acylated compounds were OMS982, OMS-976, OMS-979 and OMS-830, which were effective for >32, 28-32, 16-20 and 12-16 weeks, respectively. To some degree, a higher contact toxicity will compensate for increased volatility. Thus, OMS-979 has about the same persistence (as measured by bioassay) as OMS-47, even though it is twice as volatile. It is, however, a better contact insecticide and so can withstand a greater loss of deposit while still giving the required 70% kill after an exposure of one hour. Three of these compounds-OMS-830, OMS-976 and OMS-982-were tested on dried mudbricks made from Babati and Magugu soils. The bricks were sprayed with aqueous suspensions of wettable powders at a dosage of 2 g active ingredient per m2, and stored and tested at 25°C and 80 % r.h. Deposits of all three compounds on Babati bricks 456 NOTES TABLE 3 PERCENTAGE LOSS PER DAY OF CARBAMATE INSECTICIDES FROM DEPOSITS ON GLASS-PAPER AT A DOSAGE OF I g/m2 a Pretge loss per day for compound where RI H acetyl propionyl butyryl gob 34b 021b 3.2 40 27 3-sec-butylphenyl 8 40 b 3-methyl-4-methylthiophenyl 0.4 3-isopropylphenyl 3-fert-butylphenyl 3,5-dimethyl-4-methylthiophenyl 3,4-dimethyl-6-chlorophenyl 3,4-dimethyl-6-dimethylaminophenyl 1-naphthyl 16 0.18 0.87 45t1 1.1 3.7 14 2.6 0.16 isobutyryl 41.7 0.70 0.75 Insecticides have formula R'1O-CO-N(R2)CH3. b The samples of these compounds contained varying proportions of impurities. The principal impurities are likely to be the corresponding 4-isomers, and these would not interfere with the method of a (...truncated)