DDT Emulsion Research Articles

Treatment of Trichomonas colpitis with DDT emulsion

According to Dr. Dani (Prague) and Associate Professor Kostich (Belgrade), trichomoniasis occurs in 39.5% of women, according to V.A. Sapozhnikova - in 48.7%, according to B.A.Teakharov - in 26.6% of men ...

DDT residues in crop and soil resulting from application to cowpea Vigna unguiculata (L.) walp. in the sub-humid tropics

DDT emulsion was applied by knapsack sprayer to cowpea Vigna unguiculata (L.) at a rate of 10kg a.i. ha −1 in each of two growing seasons per year for a four-year period in Ibadan, Nigeria. Partition of spray deposits between plant and soil was assessed at 1:3 respectively by methods involving crop cover estimation and dye recovery. DDT residues in soil and crop were determined by GLC analysis at the end of each growing season and showed disappearance of at least 60% of the applied pesticide. Field measurements were supplemented by studies on air entrainment and volatilisation rates from crop and soil. Accumulation of DDT in soil and its redistribution by ploughing were monitored. Residue levels reached a maximum of 1·7 μg g −1 total DDT after three spraying seasons and declined thereafter, despite repeated applications. In plots treated with a total of 70 kg a.i. ha −1 over the four years, the final residue in soil represented only 2–3% of the amount applied.

Nicotine sensitized DDT formulations.

Nicotine has been found an effective photosensitizer for DDT. At DDT: nicotine (1:5), DDT along with its formed degradation products DDD, DDE and DBP disappeared within 18 and 60 days under UV and sunlight respectively. Because of persistence, nicotine proved a superior photosensitizer to N, N'-diethylaniline. In DDT emulsifiable concen-trates it led to high alkalinity but no DDT degradation up to 60 days at 20_??_25°C. 0.1 and 0.5% DDT emulsions from these formulations showed no adverse effect on Daucus carrota, Vicia faba, Brassica oleracea var. botrytis, and Dahlia sp., but showed mild to severe phyto-toxicity against Pisum sativum and Cicer arietinum; caused by high concentration of nicotine. On Clerodendrum sp. in sunlight, these formulations showed over 20% faster DDT loss be-tween 3_??_15 days of application. DDT-nicotine mixtures showed no synergism against Tribolium castaneum Herbst.

Observations on the peri-domestic breeding behaviour and resting sites of Glossina tachinoides Westw. near Nsukka, East Central State, Nigeria.

In 1964–65, breeding sites of the tsetse fly G. tachinoides Westw. near Nsukka in south-eastern Nigeria were found in peri-domestic situations (particularly beneath stacked coco-yam tubers and at the base of fences of pig enclosures) and in adjacent farmland (particularly beneath banana and coco-yam plants, under Lantana camara, at the base of farmland fences and around derelict farm buildings). Between them, these sites provide moisture conditions suitable for year-round breeding of G. tachinoides and are not exposed to unsuitably high temperatures (>90°F) for long periods. The night-time resting sites of G. tachinoides in three villages five miles east of Nsukka were sought between May and November 1966 using ordinary torchlight. The most popular resting-sites were dried fronds of oil and coconut palms used for fencing pig enclosures, but a few flies also rested on man-made objects in the villages and on vegetation nearby. Most flies were resting less than two feet above ground level. Day-time observations confirmed the night-time findings. G. tachinoides could probably be controlled, if not eradicated, in the Nsukka area by two applications, a fortnight apart, of DDT emulsion concentrate to pig enclosure fences and pig styes up to a height of 2–3 ft during March–May when the fly population is most concentrated around confined pigs.

White-Pine Weevil Control in Plantations with Heptachlor Granules

Experiments showed that 5% granular heptachlor applied within a 2-foot radius of tree bases by portable power duster was highly effective in controlling Pissodes strobi (Peck) in plantations of eastern white pine, Pinus strobus L. Applications provided adequate control of the overwintering adults for at least 5 years. The timing of treatments had little effect on the control obtained. The greatest weeviling reduction, averaging 95%, occurred in the 2nd year after treatment. A measure of control was obtained also in plantings where only the weeviled tree and those immediately adjacent received treatment. In nearby areas where tree leaders were treated with a DDT emulsion, initial adult mortality was higher, but repopulation soon occurred. Efforts directed at controlling hibernating adult weevils in the duff at the tree base will overcome the numerous problems existing in current leader treatment methods.

Control of the Banana Scab Moth by Injection of DDT Emulsion into the Fruit Spathe

(1968). Control of the Banana Scab Moth by Injection of DDT Emulsion into the Fruit Spathe. Pest Articles & News Summaries. Section A. Insect Control: Vol. 14, No. 4, pp. 523-525.

殺虫剤の土壌施用に関する研究 : 第3報 浸透性有機リン剤のバレイショのオオニジュウヤホシテントウ防除効果

The band application of 5 % Di-Syston granules at 6kg per 10a in the seed furrow at planting time revealed excellent control of the large 28-spotted lady beetle, Epilachna vigintioctomaculata MOTSCHULSKY, throughout all of the stages of potato growth. This effect was considered to be owing to the death of the greater part of both larvae and adults of the species, within one or two days after the benining of feeding by the systemic toxicants absorbed through the root. The present method was about same or greater in effectiveness to the usual pest control method with two sprayings of 0.05% MEP or DDT emulsions and others in the period from the stage of flower-bud formation to the flowering time. The application of the granules in fertilizer bands beneath the seed pieces of potato had more or less poor effects on the control of pest compared with the above method. Di-Syston granules was more effective than PSP-204 granules in the tested dosages. About 6kg per 10a seemed to be the suitable dosage for controlling major insect pests including the large 28-spotted lady beetle and for the good yields of potato tubers. No detrimental insecticidal residues on the harvested potato tubers was recognized in the practical application of dosages below 6 or 10kg of Di-Syston or PSP-204 granules.

Aircraft applications of insecticides in East Africa. XV.--Very-low-volume treatment of a seed-bean crop with DDT in oil solution.

Experiments are described on the aerial application of very low volumes (0·5 gal./acre) of oil solutions of DDT to control two pests, Heliothis armigera (Hb.) (bollworm) and Acanthomia horrida (Germ.) (brown bug), of the seed-bean crop in northern Tanzania. The method was compared with an improved variant of the standard commercial method of aerial control, in which DDT emulsion is applied at 1·85 gal./acre. This improved variant was also compared with a standard commercial treatment. Very-low-volume (solution) treatments were made with rotary atomisers, normal volume (emulsion) treatments with boom-and-nozzle equipment. The results were assessed, by measuring the amount of DDT deposited on filter papers and on the leaves of the crop and by estimating pest mortality from counts made immediately before and 48 hours after spraying.A direct comparison of very-low- and normal-volume treatments under identical conditions was not possible, but it was established that under similar conditions the proportion of DDT emitted that was deposited at crop level (percentage recovery) was much the same for the two methods, varying between 41 and 62 per cent, according to conditions. The lower leaves of a fairly young crop of an open variety received about 60 per cent, of the deposit on the upper leaves, but in a mature crop of a tall dense variety this percentage fell to 35.Standard commercial practice, with the aircraft flying very close to the crop, gave a recovery of about 55 per cent, in moderately good conditions but with a variation in deposit density across the swath of over 7:1. An identical application from 10 ft. above crop, as in our method gave in rather better conditions a recovery of 62 per cent., with the deposit-density variation reduced to 2:1. This performance was much the same as that achieved by the type of emulsion application used in the other experiments described.In similar conditions, both very-low and normal-volume treatments gave very similar mortalities of Heliothis. Acanthomia was present in only one experiment and was less readily controlled; it required deposits at crop level of about 0·4 lb./acre to give satisfactory mortality, whereas in the same experiment 0·25 lb./acre gave 96 per cent, mortality in a relatively young Heliothis population containing only 10 per cent, of sixth-instar larvae.Older Heliothis larvae required higher dosages, 0·4 lb./acre at crop level killing only 53 per cent, of a population containing 62 per cent, of sixth-instar larvae. It was shown that there is a regular decrease in the kill inflicted by a given dosage on the successively later instars (from 92 per cent, of the third to 66 per cent, of the sixth) with a recorded deposit of 0·63 lb. DDT per acre.Except in the first experiment, mortalities were much below those claimed for commercial treatments, even at lower rates of DDT per acre. The reasons for this are discussed, together with the advantages to be expected from a change to the very-low-volume technique with solutions.

Effects of Some Spray Adjuvants on DDT Emulsifiable Concentrate

A laboratory study was made on the effects of some metallic salts and cationic surface-active agents on the deposition of DDT emulsifiable concentrate sprays. An anionic surface-active agent, Atlox 3300® (isopropyl amine dodecyl benzene sulfonate), was used as the emulsifier for the DDT spray. The adjuvants were injected into the spray stream at various concentrations during the spraying operation. Beeswax- and collodion-coated glass vials were used as the standard surfaces for spraying. The total amount of spray deposit was determined by weight and the quantity of DDT by chemical analysis. The effectiveness of the metallic salts in increasing spray deposits was in the following order: FeCl3·6H2O>Pb (NO3)2>CaCl2·2H2O>ZnCl2>MgCl2·6H2O. The effectiveness of cationic surface-active agents was in the following order: Armac 18D® (acetic acid salts of fatty amine) >Armac C® (acetic acid salts of fatty amine)>Hyamine 2389® (methyl dodecyl benzyl trimethyl ammonium chloride) > CTAB (cetyl trimethyl ammonium bormide) >Emcol E-607® N-(laurol colaminoformylmethyl) pyridinium chloride> Arguad 12-50® (alkyl quaternary ammonium chloride) > Ethomeen C/15® (ethoxylated tertiary amine). The change in dynamic surface tension was related to spray deposit, i.e., the adjuvants which increased the dynamic surface tension also increased the amounts of spray deposit. A converse relation was also demonstracted. When water and xylene were emulsified with the anionic surface-active agent, an oil-in-water type of emulsion was formed. With the exception of Ethomeen C/15, the addition of adjuvants produced an inverted type of water-in-oil emulsion. In the case of the cationic surface-active agents, further addition reverted the water-in-oil to an oil-in-water type of emulsion. The adjuvants reacted with the DDT emulsion spray to form a precipitate and the adhesive quality of this precipitate appeared to influence the quantity of the spray deposit. The nature of the sprayed surface also influenced the quantity of the deposit, the amount being lower on a collodion than on a beeswax surface.

The toxicity of insecticides to larvae of the codling moth, Cydia pomonella (L.). II. Maintenance of a toxic deposit in the field.

The persistence, as assessed by biological and chemical methods, of field deposits on apples from two spray programmes, each of DDT, carbaryl or azinphos-methyl, was compared throughout eight weeks following the first application in an orchard in south-eastern England. Newly emerged larvae of the codling moth, Cydia pomonella (L.), were used to assess, in the laboratory, the biological activity of the deposits. The spray programmes studied were (1) two applications of conventional concentrations (i.e., 0·1 per cent, for DDT and for carbaryl, 0·04 per cent, for azinphos-methyl) three weeks apart and (2) three applications of half these concentrations at two-weekly intervals. DDT wettable powder, carbaryl and azinphos-methyl were compared in 1961, DDT emulsion, DDT wettable powder and carbaryl in 1963. Results of biological and chemical assessment of the deposits are presented graphically. Over-all, the performance of the three-application programmes was as satisfactory as that of the two-application programmes, although a smaller amount of chemical was used. The serious reduction in deposit caused by heavy rain shortly after the first application of DDT wettable powder and of carbaryl in 1961 is noted. In the absence of heavy rain, carbaryl was biologically the most persistent, but the best performances of the other chemicals were almost as good as that of carbaryl.LD50 values of fresh deposits obtained by field spraying were shown to be similar to those obtained by laboratory dipping.Comparison of the toxicity of fresh and weathered field deposits of similar magnitude indicated that the biologically available proportion of a DDT deposit from either formulation decreases as a result of weathering. This phenomenon was not found to occur with carbaryl and either not at all or to a much lesser extent with azinphos-methyl.The deposits obtained in the comparison of the spray programmes were separated into their fresh and aged components, so that differences in the contribution to the final deposit provided by each application could be seen. With the very persistent DDT emulsion, only about half of the six-week deposits was composed of chemical from the final application, but, with the much less persistent carbaryl and azinphos methyl, the six-week deposits were almost entirely derived from the final application. By substitution in an equation to obtain the rates of decay of the deposits from the three-application programmes of all chemicals, it is shown that deposits from the second and third applications were, in all cases, more persistent than those from the first. Possible reasons for this difference are discussed.The significance, in terms of field control, of the results for the larvicidal activity of the deposits from the different spray programmes is indicated. It is concluded that data on the LD90 of insecticidal deposits on apples, together with measurement of their persistence in the field, can be used to assess the probable field performance of codling-moth insecticides and to determine the most efficient means of employing them, although the deposit level that ensures 90 per cent, larval mortality in the field is higher than the LD90 determined in the laboratory.

The toxicity of insecticides to larvae of the codling moth, Cydia pomonella (L.). I. Intrinsic toxicity and persistence.

The deposits found on apples at various times after application of 11 insecticides were determined by chemical analysis of samples from an orchard in south-eastern England sprayed in 1959 and 1960. The results, from samples taken simultaneously, of studies of the effectiveness of these and other chemicals for control of the codling moth, Cydia pomonella (L.), have already been reported.The period in which 50 per cent, of an initial deposit disappeared in the field (half-life) was calculated from the chemical data and used as a measure of persistence. For comparisons of intrinsic toxicity, the levels of fresh deposits causing 50 per cent, mortality of newly emerged codling-moth larvae (LD50) were determined in the laboratory by chemical and biological tests on apples dipped in a range of concentrations of commercial formulations. The LD50's, in μg./cm.2, were less than 0·025 for carbophenothion, parathion and diazinon, between 0·025 and 0·05 for azinphos-methyl and -ethyl, between 0·05 and 0·10 for malathion, DDT and carbaryl, between 0·1 and 0·5 for DDD and dimethoate, between 0·5 and 1·5 for lead arsenate and above 1·5 for phenkapton.Chemicals with an LD50 exceeding about 0·1 μg./cm.2 were considered not worth further investigation as codling-moth larvicides. The LD90's of the remainder were found and were taken as the minimum deposits that would have an adequate effect from the standpoint of control (minimum effective levels). From the half-life values, the periods for which the deposits found in the orchard in 1960 should have remained above the minimum effective levels were calculated; these were 24 days for DDT emulsion, 22 for DDT wettable powder, 15 for carbophenothion, 14 for carbaryl, 12 for azinphos-ethyl, 11 for parathion, 7 for malathion and 6 for diazinon. They were in good agreement with the results of the biological tests except in the case of DDT emulsion, the effectiveness of which was unexpectedly short-lived.

Adjuvants in Sprays for Insect Control on Sweet Corn

Everglades sweet corn must be sprayed at regular intervals to control the corn stem weevil (Hyperodes humilis (Gyllenhal)), budworms, and earworms. From eggs embedded in the leaf sheaths or hypocotyl of the young corn plant, corn stem weevil grubs hatch to mine through the stem. Beginning within a day of seedling emergence, about six sprays must be applied twice weekly or every four days to control this pest. The fall armyworm Spodoptera frugiperdca (J. E. Smith), and the corn earworm, Heliothis zea (Boddie), feed within the whorls of the growing plants as budworms and also upon the ears as earworms. Budworm control sprays must be applied once or twice weekly between cessation of corn stem weevil sprays and initiation of earworm control sprays. From the day after the first silks appear until shortly before harvest, earworm control sprays must be applied daily or every other day depending upon population density and weather conditions. DDT emulsions are more effective than DDT wettable powder sprays for sweet corn insect control (Harris 1961, 1961a). However, emulsions frequently damage plants, especially at the high concentrations needed for corn stem weevil control when the plants are young and tender. DDT wettable powder sprays are less likely to damage plants or be incompatible with the fungicide wettable powders that are frequently added to the spray. Therefore, it is desirable that the efficacy of DDT wettable powder sprays be made more nearly equal to that of emulsions by the use of adjuvants or by some other measure. Triton X-100 (a wetting agent made by Rohm and Haas Company) was evaluated as an adjuvant in DDT wettable powder sprays. Under heavy population pressures, even the most effective! of recommended practices may not adequately control sweet corn insects. At one time, 2.5 gallons of white mineral oil was recommended as an additive to 1 gallon of 25% DDT emulsifiable concentrate in 50 gallons of emulsion per acre (Anonymous 1956) to control earworms in Florida. The DDT emulsifiable concentrate was supposed to supply enough emulsifier to emulsify the mineral oil. Frequently poor yields and off-color husks resulted. The recommended amount of white mineral oil was first reduced to 1.75 gallons (Brogdon and Marvel 1959) but later completely withdrawn from recommendations (Brogdon, Marvel, and Mullins 1963). A miscible spray oil2 was substituted for the white mineral oil and evaluated at several dosages to seek a level less likely to affect sweet corn yield or quality adversely and yet increase the efficacy of DDT emulsion against earworms. The miscible spray oil was also evaluated at a single dosage in toxaphene and DDT emulsions for budworm control.

Effectiveness of Insecticides Against the Corn Earworm in Sorghum Heads1

Of 12 chemicals tested against the corn earworm, Heliothis zea (Boddie), in sorghum heads, carbaryl, DDT, mevinphos, Telodrin® (1,3,4,5,6,7,8,8-octachloro-1,3,3a,4,7, 7a-hexahydro-4,7-methanoisobenzofuran), and naled gave the best control. The addition of pyrethrum to DDT emulsion spray did not increase the effectiveness of this insecticide. When comparable dosages and gallonages of the same insecticides were applied, control was usually better against the smaller larvae. A residue test with carbaryl showed residues well within the accepted tolerance on grain and forage.

Residual Effectiveness of DDT Emulsion Sprays with and without Horticultural Oil Against the Smaller European Elm Bark Beetle1

Prior to World War II, Dutch elm disease control in Eastern United States was based entirely on sanitation. Funds and manpower were available through such government programs as WPA. Bromley (1948) reported sprays containing lead arsenate effective against elm bark beetles. Whitten (1945) reported that DDT controlled the smaller European elm bark beetle, Scolytus multistriatus (Marsham). Plumb (1950) and Matthysse et al. (1954) reported effective control of elm bark beetles and Dutch elm disease by dormant mist-blown applications of concentrated DDT-xylene emulsions. Following World War II, DDT became available and its use increased.

Insects Destructive to Bitterbrush Flowers and Seeds in Southwestern Idaho1

Studies were conducted to identify and evaluate the insects associated with flowers and seeds of bitterbrush. A 1.5 % lindane emulsion spray was applied to reduce insect infestation on bitterbrush shrubs but proved to be phytotoxic. A 2% DDT emulsion spray was substituted but also caused some injury. Six hundred flowers were selected for weekly observation on 10 sprayed shrubs and the same number on 10 unsprayed shrubs. Normal-appearing seeds resulted from 21 to 25 % of the flower buds on sprayed and unsprayed shrubs, respectively. Production of fewer normal seeds on sprayed shrubs indicates that the phytotoxic effect of DDT added to or exceeded the effects of insects. Causes of damage to flowers and seeds were determined by weekly examinations and dissections until June 26, when seed drop began. During the bud and flower stages, a thrips, Frankliniella occidentalis (Pergande), caused most identifiable damage. After seeds had formed and were still attached to the shrubs, a gall midge, possibly Phytophaga sp., led other insects in amount of seed destroyed, followed by the gelechiid, Filalima sp. near sperryi Clarke. Additional, less conspicuous damage possibly may result from punctures made by sucking insects, among which the pentatomid bug, Chlorochroa sayi Stal, was identified as a common seed feeder.

Toxicity of Insecticides to Cryptophlebia illepida (Lepidoptera: Eucosmidae), a Pest of the Macadamia Nut1

The toxicity of emulsions of aldrin, chlordane, DDT, dieldrin, heptachlor, lindane, and malathion to larvae of Cryptophlebia illepida (Butler), a potentially serious pest of the macadamia nut ( Macadamia ternifolia F. Muell.), was determined. The most toxic insecticides as contact poisons against the first- and third-instar larvae were malathion, DDT, and lindane. Chlordane and heptachlor were practically non-toxic at the highest concentration tested (20 mg/ml). Only malathion and lindane showed significant toxicity to the fifth-instar larvae. Lindane, DDT, and malathion were also the most toxic of the insecticides applied as contact-stomach poisons. As was previously found in the contact toxicity study, only lindane and malathion exhibited measurable toxicity to the fifth-instar larvae. The vapors of malathion, aldrin, lindane, and heptachlor at 20°C, were toxic to first- and third-instar larvae. However, only the vapor of malathion was toxic to fifth-instar larvae. DDT and dieldrin did not show any vapor toxicity. Chlordane, despite its relatively high vapor pressure, showed little fumigant action. It appeared that malathion was significantly more toxic against the three larval stages as a contact insecticide than it was as a contact-stomach poison. DDT was the only chlorinated hydrocarbon insecticide that appeared to be more toxic as a contact poison than as a contact-stomach poison. The other chlorinated hydrocarbon insecticides were more toxic as contact stomach poisons than as contact poisons.

Pour-On Treatments of DDT or Toxaphene for Horn Fly Control1

Cattle naturally infested with horn flies, Haematobia irritans (L.), were treated by the pour-on technique with 100 ml. of aqueous emulsions of DDT or toxaphene. Treatments with either material at 12 g . per animal provided effective control in excess of 3 weeks. Treatments with either material at 6 g. per animal provided effective control for a period of 1 to 2 weeks. No practical differences in effectiveness were noted between DDT and toxaphene. No evidence of insecticide resistance was noted.

The effect of DDT on Myzus persicae (SULZ.) and Brevicoryne brassicae (L.) (Aphididae) in relation to the spread of cauliflower mosaic and cabbage black ring spot viruses

Previous work in Britain has shown that insecticides, even systemic ones, fail to protect brassica plants in the seed-bed from virus diseases transmitted by aphids, and an explanation was sought through experiments carried out at Rothamsted. Observations on the effect on apterae and alates of Myzus persicae (Sulz.) of contact with leaves detached from cauliflower plants previously treated with a 0·2 per cent. DDT emulsion spray showed that exposure for up to 30 min. was insufficient to kill the majority of those tested, although many were temporarily incapacitated; alatae of Brevicoryne brassicae (L.) were even less affected.In cage experiments using infected and healthy cauliflower seedlings, apterae of M. persicae were able to transmit cauliflower mosaic virus (ClMV) and cabbage black ring spot virus (CBRSV) from infected to healthy seedlings when no spray was used, but failed to do so when the infected plants were sprayed with DDT; when alates were used in similar tests using only CBRSV, only low rates of transmission were obtained. In similar experiments using turnip seedlings and ClMV, transmission by apterae of M. persicae was high on untreated plants when the infector plant was itself untreated, but distinctly lower when it was sprayed with DDT; alates of M. persicae were found to transmit ClMV from a DDT-treated infector to untreated plants but not to a treated plant. Virus spread was thus reduced but not prevented by the use of DDT sprays. It is considered that these results lend support to the hypothesis that increase of virus within a seed-bed is preponderantly the result of the arrival, in succession, of many individual viruliferous alates from outside.

European Elm Scale Control Investigations1

Foliage applications of Sevin® (1-naphthyl N -methylcarbamate), Diazinon® (O,O-diethyl O-(2-isopropyl-4-methyl-6-pyrimidinyl) phosphorothioate), Guthion® (O,O-dimethyl S -(4-oxo-1,2,3-benzotriazin-3-(4 H )-ylmethyl) phosphorodithioate), and several mixtures of DDT and malathion emulsions, gave excellent control of European elm scale ( Gossyparia spuria (Modeer)) when applied between July 1 to July 14. Sprays applied during June or in late July and August failed to give satisfactory control. Sprays containing dieldrin and endrin gave no control. Control was obtained with systemics injected into trunks of elms when crawlers were emerging from under old female scales, but not when the injections were made 2 weeks prior to crawler emergence. Soil treatments, either soil saturation or applications of granules, produced very erratic results. Although superior dormant oils when applied at dosages from 3% to 5% with a hydraulic sprayer gave good immediate kill, control was only temporary because European elm scale populations soon reached injurious levels again.

Control of a Corn Stem Weevil (Hyperodes humilis), and Fall Armyworm with DDT and Parathion in South Florida1

During the season of 1959–60 at Belle Glade, Florida, DDT and parathion emulsion sprays were tested to determine the number of applications required to control the corn stem weevil ( Hyperodes humilis (Gyllenhal)) and the fall armyworm ( Laphygma frugiperda (J. E. Smith)) on young sweet corn. Populations of these insects were decreased significantly and yields of U. S. Fancy and total marketable ears were increased significantly by six applications of DDT or of parathion when applied on the day of seedling emergence and at 4-day intervals thereafter. An application of DDT at planting time preceding the post-emergence DDT sprays resulted in slightly greater infestations by the stem weevil and significantly lower yields. Postemergence DDT treatments resulted in significantly greater stands than in the untreated cheek in a test in which the corn stem weevil was the major pest.