Field tests with larvicides other than DDT for control of blackfly (Diptera: simuliidae) in New York.

EFFECTS OF AIR POLLUTION ON URBAN CLIMATES 635 between the ventilation of the streets and wind speed and wind direction. As can be seen in Fig. 11 at wind velocities below 2 m/s, ventilation was very poor, fresh air which entered the space between buildings from above did not reach the street level, and the carbon monoxide concentration in- creased considerably nearer the ground. It required a wind speed above 2 m/s (lower part of Fig. 11) for the vortex which formed within the street to reach street level but even then there was a great difference in the rate of ventilation between the windward side and the leeward side of the street. This effect produced a horizontal gradient of carbon monoxide across the street. Complete ventilation of the street and dispersion of the pollutants produced from low sources in the street required a wind velocity of 5 m/s or more. The accumulation of pollutants in streets also depends on the height of the buildings and the width of the street. Generally wind velocity is the most important factor in the dispersion of pollutants in cities. Low wind velocity leads to an accumulation of pollutants in the air as can be seen for CO in Fig. 12. New methods and techniques permit the use of tracers-in this case the carbon monoxide-to study the circulation system in cities and streets and the use of these techniques will certainly increase our understanding of small-scale circulation patterns. Conclusion In conclusion it may be said that the city which produces so many pollutants is itself an obstacle to the dispersion of these pollutants, and thus increases the dangers associated with the accumulation of the noxious components. Unfortunately, little informa- tion is available on the effects of urban climate on man. There seems to be general agreement that the increased concentration of pollutants in city air constitutes a hazard as far as respiratory diseases are concerned, and the results of the smog episodes in 1952 and 1962 in London, and Western and Central Europe, respectively, have been widely reported in the literature. The work by Lawther r on the effects of urban life on bronchitis and lung cancer deserves a special mention. While eye irritation is commonly attributed to the photo- chemical smog in Los Angeles, the air pollution in this city has so far not been reported to have shown any direct adverse effects on human health. Simultaneous investigations of air pollution and epidemiological studies are being conducted in many countries and cities all over the world and it must be hoped that one consequence of these studies will be that the level of air pollution can be gradually reduced despite the rapidly growing populations. r Lawther, P. J. (1966) Postgrad. Med., 24, 703. Field Tests with Larvicides other than DDT for Control of Blackfly (Diptera: Simuliidae) in New York * by HUGO JAMNBACK, New York State Museum and Science Service, Albany, N. Y., USA DDT is an unusually stable insecticide that, when applied to bodies of water, may accumulate to injurious levels in fish.a, b, c For this reason, and because of evidence of DDT-resistance in black- flies,d, e investigations of possible alternative insec- * Published by permission of the Assistant Commisioner, New York State Museum and Science Service. a Anderson, R. & Everhart, W. (1966) Trans. Amer. Fish. Soc., 95, 160-164. b Burdick, G. et al. (1964) Trans. Amer. Fish. Soc., 93, 127-136. c Burdick, G. et al. (1968) N. Y. Fish Game J., 15. d Jamnback, H. & West, A.-unpublished data. e Suzuki, T., Ito, Y. & Harada, S. (1963) Jap. J. exp. Med., 33, 41-46. ticides have been under way for the past few years. This paper deals with field tests of methoxychlor, Abate, Dursban, fenitrothion, and carbaryl,f all of which have shown some degree of effectiveness against larvae under laboratory conditions.s h, The larvicides were applied by aircraft as 15%- 20% insecticide in oil solution with 0.5 %-0.75% f The formulae of these insecticides are given in Kenaga, E. (1966) Bull. ent. Soc. Amer., 12, 161-217. g Jamnback, H. & Frempong-Boadu, J. (1966) Bull. Wld Hlth Org., 34, 405-421. h Travis, B. & Schuchman, S. (1968) J. econ. Ent., 61, 843-845. t Travis, B. & Wilton, D. (1965)fMosquito News, 25, 112-118. 2327D 636 NOTES Triton X-161 added as a surfactant to facilitate initial penetration of the insecticide into the water. One or more swaths were applied at right angles across the test streams, the insecticide being emitted through 3 D-4 nozzles at 40 lbf/in2 (2.8 kgf/cm2) at the rate of 1 US gallon per flight mile (3.1 1 per flight km) from the aircraft flying just above the trees at 90 miles/h (145 km/h). Methoxychlor In early tests, 20% methoxychlor applied at the rate of 1 US gallon per flight mile was as effective as DDT in reducing blackfly larval populations." Since then, 10% and 15% solutions have been tested. The results are given below. In 1966, 9 streams were treated with 10% metho- xychlor in oil solution by flying a single swath across each. It was applied at the rate of 1 gallon per flight mile as described above. In 8 of the 9 streams blackfly larvae were eliminated, or nearly eliminated, for 1/4 mile (0.4 km), but in 6 out of 9 the control was poor as judged by the criterion of elimination or near elimination for 1/2 mile (0.8 km) below the swath (Table 1). TABLE 1 RESULTS IN 1966 OF AERIAL SPRAYING FOR BLACKFLY LARVAL CONTROL WITH 10% METHOXYCHLOR IN OIL SOLUTION WITH 0.75 % TRITON X-161 Average number of Stream tested Date blackfly larvae per unittested Before 48 hours after treatmentl treatmenta Mountain Creek 6 May 150 0 for 1/2 mile Murmur Creek 7 May 20 0 for 1/4 mile 10 at 1/2 mile North Vly Outlet 20 May 50 0 for 1/4 mile 1 at 1/2 mile Sand Lake Outlet 20 May 10 1 for 1/4 mile 6 at 1/2 mile Mill Pond Outlet 20 May 100 0 for 1/4 mile 90at 1/2mile Sheriffs Lake Outlet 20 May 5 0 for 1/4 mile 2 at 1/2 mile Massaweple Pond 24 May 500 100 at 1/4 mile Outlet 500 at 1/2 mile Trout Creek 24 May 50 0 for 1/4 mile 20 at 1/2 mile 50 at I mile Crystal Creek 27 May 5 0 for 1/2 mile a 1 mile 1.6 km approx. TABLE 2 RESULTS IN 1968 OF AERIAL SPRAYING FOR BLACKFLY LARVAL CONTROL WITH 15 % METHOXYCHLOR IN OIL SOLUTION WITH 0.5% TRITON X-161 a Average no. of larvae per plastic tag b Stream tested Before treatment: 24 hours 96 72 24 after hours hours hours treatment Mil Outlet, Arietta - 20 25 0 Beaver Meadow Brook, Indian Lake 26 30 - 0 Forks Brook, Indian Lake 17 9 12 0 Beaver Brook, Indian Lake 14 12 11 0 Big Brook (Pt. 1) Indian Lake 20 22 9 0 Big Brook (Pt. 2) Indian Lake 45 37 39 0 Center Brook, Indian Lake 5 8 9 0 Johnny Mack Brook, Indian Lake 9 10 5 0 East Inlet Brook, Long Lake 8 5 5 0 South Pond Outlet, Long Lake 6 10 12 0 Shaw Brook, Long Lake 12 10 13 0 Big Brook, Long Lake 6 8 4 0 a Plastic tag evaluation method. b Each count was an average of 3 tags. The effectiveness of the 15% methoxychlor solu- tion was evaluated differently. An area of approxi- mately 700 m2 (1813 kM2) was treated with this formulation applied at the rate of 1 gallon per flight mile in parallel swaths 1/4 mile apart as has been described previously.1 Bright orange, plastic indic- ator tags were placed in 12 widely separated streams in the control area 5 days before treatment, and migrating blackfly larvae soon attached themselves to the tags. Counts of the numbers of larvae on the tags were made 4, 3 and 1 day before treatment and 1 day after treatment, 3 tags in each stream were averaged for the counts given in Table 2. An average of 14.5 larvae per tag were present before treatment but 1 day after treatment all the larvae on the tags had disappeared, indicating excellent con- trol. This method of assessing the effectiveness of treatment has the advantages of speed and objectiv- ity. It is similar, in principle, to the " Canadian J Jamnback, H. & Collins, D. (1955) Bull. N.Y. State Mus., 350. BLACKFLY CONTROL IN NEW YORK WITH LARVICIDES OTHER THAN DDT 637 cones " used by Wolfe & Peterson k and later Canadian workers, and the polyethylene tape strips described by Williams & Obeng.1 The bright orange tags used in New York cost about 3 US cents each and are sturdy enough to be re-usable.m, n They are of standard dimensions, 7 in by 3/4 in (180 mm by 22 mm), brightly coloured for visibility, and flat so that they can easily be carried in a pocket. They can be used in small streams where there in not enough water for cones and in very swift streams where the plastic cone is distorted by water pressure. In addition to being highly effective, methoxychlor is safer than DDT. Studies of the effects and persistence of methoxychlor as compared to DDT indicate " . . . DDT to have a greater and more permanent effect on food organisms. The behaviour of methoxychlor is completely different from that of DDT, and it appears... (from the point of view of conservationists)... much more satisfactory as a larvicide "'.c For these reasons, methoxychlor is the only larvicide recommended for blackfly control in New York State, USA. However, the search for more effective and less costly larvicides is continuing. Of special interest are the phosphates and carba- mates that differ from DDT in basic structure, thus reducing the chance of cross-resistance. Abate Abate emulsion is effective when dripped into streams at concentrations as low as 0.05 ppm/ 30 min.0 Application of 18%-20% Abate in oil solution from aircraft at the rate of 1 gallon per flight mile greatly reduced blackfly larval popula- tions. However, small numbers of larvae in many sites in the tested streams survived even though the over-all percentage reduction was high. Abate emulsifiable concentrates were less effective than solutions when applied at the same rate and in the same way.P k Wolfe, L. & Peterson, D. (1958) Canad. J. Zool., 36, 863-867. 1 Williams, T. & Obeng, L. (1963) Ann. trop. Med. Parasit., 56, 359-361. m Plastic labels, orange, catalogue number 10-54, Economy Label Sales Company, Box 350, Daytona Beach, Florida, USA. n The mention of specific companies or of certain manufacturers' products does not imply that they are endorsed or recommended in preference to others of a similar nature which are not mentioned. o Swabey, Y., Schenk, C. & Parker, G. (1967) Mosquito News, 27, 149-155. P Jamnback, H. & Means, R. (1968) Proc. New Jersey Mosq. Exterm. Ass., 55. Our data on Abate are in agreement with those of Quellenec,q who found that it was less effective than DDT and that small numbers of apparently normal larvae were present after an otherwise " effective " treatment with Abate. Dursban A 15%-Dursban in oil solution was tested in April 1968 using the aerial application equipment already described. In 2 tests, crossing streams with a single swath at right angles applied at the rate of 1 gallon per flight mile there was a considerable, but far from complete, reduction in larval populations (Table 3). The dosage was then doubled by flying 2 swaths across the same section of a stream, equivalent to 2 US gallons per flight mile (5.2 1/flight km). Larval populations were greatly reduced but small numbers of larvae survived as was the case with Abate. In the formulation tested, Dursban was less effective than methoxychlor when applied at the same rate under field conditions. Travis & Schuchman h found Dursban to be at least 10 times as effective in killing blackfly larvae as Abate, methoxychlor, or ronnel (= Korlan) in the laboratory. In contrast, they noted that only methoxychlor was effective as a detaching agent. This distinction between mortality and detachment under laboratory conditions may not apply under field conditions because larvae that detach in streams are carried to still pools where they may die directly as a result of insecticide poisoning, or indirectly from anoxia. Fenitrothion A 15 %-fenitrothion in oil solution was simulta- neously tested with Dursban in April 1968, using the same aircraft and method of application. Fenitrothion was less effective than Dursban in 2 tests when applied in one swath crossing a stream at right angles at the rate of 1 gallon per flight mile (Table 3). Later, in May 1968, the same formulation was applied in 3 swaths flown over the same section of stream, equivalent to 3 US gallons per flight mile (9.1 1 per flight km). Blackfly larvae were eliminated by this treatment for at least 1 mile downstream Q Quellenec, G. (1967) Testing the effectiveness of an Abate solution against African blackfly larvae in the River Yanaon, Upper Volta (unpublished working document WHO/VBC/67.35; WHO/ONCHO/67.59). A limited number of copies of this document is available to persons officially or professionally interested on request to Distribution and Sales, World Health Organization, 1211 Geneva, Switzerland. 638 NOTES TABLE 3 RESULTS IN 1968 OF AERIAL SPRAYING FOR BLACKFLY LARVAL CONTROL WITH 15 % DURSBAN AND 15 % FENITROTHION IN OIL SOLUTION WITH 0.5 % TRITON X-161 Rate Average no. of blackfly larvae per unit Strearn tested Date tested of application(US gallons/ Before 48 hours after flight mile)a treatment treatment b Dursban c Sammy's Creek 6 April 1 60 5 for 75 yards 20 beyond 75 yards Murmur Creek 6 April 1 300 10 for 1/2 mile Oswagatchie River 6 April 2 500 1 for 1/2 mile Fenitrothion Black Creek 6 April 1 40 10 for 1/2 mile Ruprick Rd Creek 6 April 1 500 20 for 1/2 mile Crystal Creek 15 May 3 150 0 for 1 mile a I US gallon/flight mile = 3.1 I/flight km. b 1 yard = 0.9 m approx.; I mile = 1.6 km approx. c Dow No. M3345. from the swath within 24 hours of treatment, however, several dead crayfish were seen at this time. Live fingerling and larger trout were observed and no dead or abnormal ones, but there was no system- atic investigation of the effects of fenitrothion applied at this dosage. Carbaryl Carbaryl dissolves poorly in oils and was tested in wettable powder suspensions (Sevin Instant Wettable Powder). In this form it was clearly less effective than methoxychlor, giving poor control at 3 times the rate of application needed with metho- xychlor and good control at 7 times the rate.* Since then, we have tested a 20% carbaryl dispers- ible oil formulation (Sevin Oil Dispersion) with 0.5% Triton X-100 added. This formulation was applied by aircraft at the rate of 1 gallon of oil suspension per flight mile to Silvermine Creek on 24 May 1966. Pretreatment counts of 150 blackfly larvae per unit were not reduced 24 or 48 hours after treatment. Quellenec et al.r using a drip can to treat streams, also reported that higher concentrations of carbaryl than DDT were required to produce an equivalent effect. However, they also noted that " when used in larger concentrations [it] can cross stretches of very still water and remain effective over considerable distances without harming fish fauna ". While carbaryl is less effective than DDT or methoxychlor, it is potentially useful because of its solubility in water (40 ppm at 30°C). This is a considerably greater solubility than that of the other larvicides tested. If sufficiently stable in aqueous solution, it may remain effective for longer distances in water than non-soluble formulations would. However, it should be noted that at high concentra- tions, carbaryl may be toxic to other stream fauna. Burdick et al.8 reported that Sevin in oil suspension applied by aircraft at 1.25 lb technical per acre (1.4 kg/ha) in 2 streams caused reductions of 49% and 97%, respectively, in the weight of in- vertebrate fish food. They concluded that " Sevin should not be used where the spray can fall on flowing streams if fish production is to be main- tained ". r Quellenec, G. et al. (1967) Tests of the effectiveness of a Sevin-based insecticide powder against African blackfly larvae in the River Yanaon, Upper Volta (unpubished working document WHO/VBC/67.34; WHO/ONCHO/67.58). A limited number of copies of this document is available to persons officially or professionally interested on request to Distribution and Sales, World Health Organization, 1211 Geneva, Switzerland. 8 Burdick, G., Dean, H. & Harris, E. (1960) N.Y. Fish Game J., 7, 14-25.