Insecticide Drift Research Articles

Sweep netting samples, but not sticky trap samples, indicate beneficial arthropod abundance is negatively associated with landscape wide insecticide use

Abstract Insecticide use and landscape context are major drivers for the abundance of beneficial arthropods, such as predators, parasitoids and pollinators. However, the relative importance of local and landscape‐wide insecticide use is not well understood, and it is unclear to what extent impacts of insecticides on beneficial arthropod populations are moderated by landscape composition. We collected and analysed data on beneficial arthropod abundance and local and landscape‐wide insecticide use across 38 Dutch landscapes. We used regression to study the associations between beneficial arthropod abundance (response), insecticide use and landscape factors. Insects were sampled by sweep netting and yellow sticky traps in field margins (‘sampling sites’) in the summer of 2017 and 2018. We paired organic and conventional sites in the same landscape setting. We used three indicators of insecticide use: management (organic vs. conventional), Treatment Frequency Index of insecticides applied in the field adjacent to the sampling site, and the estimated landscape‐wide average quantity of insecticides applied per ha within a 1 km radius around the sampling site. Abundances of beneficial arthropods in field margins, assessed by sweep netting, were negatively associated with the estimated quantity insecticide applied in the surrounding landscape, while arthropod sampling by sticky traps did not show this relationship. Pollinator abundance was negatively associated with conventional management and with the frequency of insecticide applications in the adjacent field, while predator and parasitoid abundance did not show significant associations with local insecticide use indicators. Negative impacts of insecticide use were not moderated in more diverse landscapes with higher proportions of semi‐natural habitats. Policy implications. Insecticide impacts on arthropod populations extend beyond the fields in which they are used. Awareness of the potential landscape‐wide effects of pesticides, either through drift of pesticides or insect movement, may encourage land managers to adopt practices to reduce insecticide drift and the frequency of insecticide applications, thereby reducing the impacts of landscape‐wide exposure on arthropods that provide services to agriculture. Risk assessments of insecticides and pesticide use regulations need to account for potential spill‐over effects and consider landscape‐scale consequences associated with the source–sink dynamics of arthropods.

Biological control of Halymorpha halys (Stål) (Hemiptera: Pentatomidae) in apple orchards versus corn fields and their adjacent woody habitats: High versus low pesticide-input agroecosystems

Halymorpha halys is an invasive pest in the USA that inflicts damage to specialty crops, and conventional growers have increased use of broad-spectrum insecticides to manage this pest. The impacts of pest management programs on natural enemies of H. halys were examined in high vs. low intensity insecticide input agroecosystems in western North Carolina (USA). Apple orchards and corn fields, with their adjacent wooded habitats, served as the high and low-input environments, respectively. Sentinel egg masses and yellow sticky cards were deployed in these agroecosystems to compare predation and parasitism on H. halys eggs, and presence, abundance, and richness of natural enemies. A total of approximately 85% of all sentinel eggs deployed in apple orchards in both 2018 and 2019 produced a healthy stink bug nymph, higher than all other habitats. A total of 26.6% and 32.9% of eggs deployed in wooded habitats bordering corn exhibited mortality due to natural enemy attack in 2018 and 2019, respectively. Comparatively, eggs deployed in apple borders had 10.0% and 17.8% of total eggs killed by natural enemies, in 2018 and 2019, respectively. Corn agroecosystems generally had greater predation and parasitism of sentinel eggs, and greater richness and abundance of predators detected on yellow sticky cards compared to apple agroecosystems. Wooded habitats bordering crops serve as population reservoirs for H. halys, allowing for egg laying and dispersal into crops. If these areas are protected as refuge areas free from insecticide drift, such as from apple orchards, they can also harbor thriving natural enemy populations that could reduce populations of H. halys. Wooded areas free from harsh broad-spectrum insecticides are an important component for successful conservation and augmentative biological control in neighboring crops.

Comparison of the drift potential of two application methods for the control of oak processionary moths with biocidal products in an oak avenue

The control of oak processionary moths (OPM; Thaumetopoea processionea) with biocidal products has become more important to protect humans from its urticating hairs. Two important application methods are cannon sprayers and helicopters. However, drift of insecticides to non-target areas might occur during the treatment resulting in potential risks for non-target organisms. Until now, information about the direct drift resulting from the applications are missing because equipment for the application of biocidal products is not tested or regulated within Europe. The aim of this work is to measure the direct drift in up to 100 m distance resulting from the application of biocidal products using a cannon sprayer and helicopter in an oak avenue. Furthermore, two different nozzles were tested for the helicopter application. The results show high drift potential with decreasing concentrations in relation to the distance to the treated area. Considering the 50th percentile of the results, the cannon sprayer produced generally more drift than the helicopter. Considering the 90th percentile at near distance, the helicopter equipped with ID-120-05 POM nozzles showed a significantly lower drift than both other tested techniques, the helicopter equipped with the Airmix 110 05 nozzles and the cannon sprayer. Hundred m away from the treated area, both nozzles installed at the helicopter showed a lower drift than the cannon sprayer. For the first time, this study shows the drift potential of applications of biocidal products and shows the possibilities to reduce drift into non-target areas by choosing appropriate equipment. This leads to a reduction of risks for non-target organisms in the vicinity of treated avenues.

Insecticide drift and its effect on Kampimodromus aberrans (Oudemans) in an Italian vineyard-hedgerow system

When a pesticide is applied in a vineyard, the fraction can drift away from the target and affect the abundance of beneficial arthropods in adjacent crops or hedgerows. A field experiment was conducted in north-eastern Italy using an air-assisted sprayer in order to evaluate the spatial distribution of etofenprox drift in a vineyard-hedgerow system and its effect on the predatory mite Kampimodromus aberrans. Three scenarios of decreasing potential drift were compared, all in still wind conditions. In the worst case of free expansion of drift, 12% of the applied rate drifted for 6–7 m with minor effect on K. aberrans abundance, according to the dose–response assay results; the presence of a hedgerow reduced the drift by about 80%. The hedgerow was also effective when good agronomic practices were followed, and the effect of drift on K. aberrans was not significant, its abundance being mainly linked to the patchiness of the natural population. Because of lateral drift, i.e. not in the direction of air-flow from sprayer, spray was detected at very low concentration in the contiguous untreated vineyard. This had no effect on K. aberrans but had the capacity to contaminate organic crops and provide a risk to surface water and bystanders. This suggests that an environmental regulatory scheme taking hedgerows into account should be supported and implemented on a catchment or regional scale.

Does insecticide drift adversely affect grasshoppers (Orthoptera: Saltatoria) in field margins? A case study combining laboratory acute toxicity testing with field monitoring data

The current terrestrial risk assessment of insecticides regarding nontarget arthropods considers exclusively beneficial organisms, whereas herbivorous insects, such as grasshoppers, are ignored. However, grasshoppers living in field margins or meadows adjacent to crops may potentially be exposed to insecticides due to contact with or ingestion of contaminated food. Therefore, the present study assessed effects of five active ingredients of insecticides (dimethoate, pirimicarb, imidacloprid, lambda-cyhalothrin, and deltamethrin) on the survival of Chorthippus sp. grasshopper nymphs by considering two routes of exposure (contact and oral). The experiments were accompanied by monitoring field margins that neighbored cereals, vineyards, and orchards. Grasslands were used as reference sites. The laboratory toxicity tests revealed a sensitivity of grasshoppers with regard to the insecticides tested in the present study similar to that of the standard test species used in arthropod risk assessments. In the field monitoring program, increasing grasshopper densities were detected with increasing field margin width next to cereals and vineyards, but densities remained low over the whole range of field margins from 0.5 to 20 m next to orchards. Grasshopper densities equivalent to those of grassland sites were only observed in field margins exceeding 9 m in width, except for field margins next to orchards. These results may indicate that current insecticide risk assessments are insufficiently protective for grasshoppers in field margins.

Insecticide drift deposition on noncrop plant surfaces and its impact on two beneficial nontarget arthropods, aphidius colemani viereck (hymenoptera, braconidae) and coccinella septempunctata L. (coleoptera, coccinellidae)

Drift of the pyrethroid insecticide lambda-cyhalothrin into field margins bordering wheat and its effect on nontarget arthropods was investigated under field conditions. Insecticide deposition on leaf surfaces of broad beans exposed within field margins at 1-, 2-, and 3-m distance from the field edge and directly within the crop was quantified using a fluorescent tracer. The toxicity of leaf deposits to the aphid parasitoid Aphidius colemani Viereck (Hymenoptera: Braconidae) and to larvae of the ladybird Coccinella septempunctata L. (Coleoptera: Coccinellidae) was estimated. Mean corrected mortalities of A. colemani were < 50% (1 m) and < 30% (2 and 3 m), and mortalities of C. septempunctata larvae were < or = 80% (1 m), < or = 67% (2 m), and < or = 52% (3 m) 12 and 24 h postexposure to drift deposits. High positive correlation coefficients proved the relationship between leaf deposits and mortalities of test organisms. The connection of drift deposit measurement and exposure bioassay provides a promising approach to determining effects of insecticide drift on nontarget arthropods. However, due to the patchiness of drift deposition on noncrop plant surfaces, risks to nontarget arthropods at defined distances from the sprayed crop are not highly predictable.

EARLY SEASON CONTROL OF SAN JOSE SCALE AND CATFACING INSECTS ON PEACH, 2003

The trial was conducted at the Missouri State Fruit Experiment Station in Mountain Grove, MO. The trial block consisted of 13-yr-old, 9-ft-tall 'Red Haven' and 'Encore' trees with 20 20 ft spacing in a 2.2-acre section of a 3.8-acre block. Treatments and an unsprayed check were arranged in a CRB design consisting of two to four replicates. There was a minimum of a one tree buffer between treatments to minimize the effects of insecticide drift. Insecticides were applied to single trees dilute to run-off with a high-pressure handgun sprayer (200 psi) on 30 Apr, 20 May, or both dates. Insecticides were applied on 23 Apr to most of the treatment trees, but because of rain (> 2 inch) shortly after the applications were made, treatments were reapplied on 30 Apr. The first application (30 Apr) corresponded with shuck split and early emergence of first generation adult SJS (33 DD51 after first adult trap catch = 17 Apr). The second application (20 May) corresponded with early emergence of first generation SJS crawlers (17 Apr +402 DD51). Insecticide treatments included Phaser 50 WP, Esteem 35 WP, Pounce 3.2 EC (2 fl oz/100 gal), Provado 1.6F, Assail 70 WP, Diazinon 50W, and Sunspray UltraFine Spray Oil. Danitol 2.4 EC was substituted for the second application (20 May) of Sunspray UltraFine Spray Oil because insufficient quantities of spray oil were available for both applications. A total of 60 peaches per treatment were evaluated for insect damage on 17– 20 Jun (17 Apr +736–815 DD51), at the end of the SJS first generation. In addition to determining presence or absence of SJS damage on peaches, a 0 to 11 quantitative scoring system where 0 = 0, 1 = 0–3, 2 = 3–6, 3 = 6–12, 4 = 12–25, 5 = 25–50, 6 = 50–75, 7=75–87, 8=87–94, 9=94–97, 10=97–100 and 11 = 100 'b surface area infected/damaged was used to estimate the percentage of the fruit surface area damaged by SJS. Peach damage means were separated using a Fisher's Protected LSD Test (P £ 0.05).

Impact of insecticide drift on aphids and their parasitoids: residual toxicity, persistence and recolonisation

The effects of the insecticide Lannate ® 20 L on target and non-target organisms were studied in sprayed and drift areas of kohlrabi ( Brassica oleracea). The study comprised eight field plots (each 12.5 m×6 m), providing four replicates of a water control and the application with Lannate ® 20 L at 0.45 kg/ha. Each plot comprised a 4 m wide sprayed area and a 2 m wide “drift” area, left unsprayed. The parasitoid Aphidius colemani (Hymenoptera; Braconidae) and its host aphid Myzus persicae (Hemiptera; Aphididae) served as indicator organisms. The residual toxicity of Lannate ® 20 L to A. colemani and M. persicae was quantified in an exposure experiment. Plants were taken from the field at different time intervals following the insecticide treatment to expose test organisms to plant surfaces in the laboratory. Mortality rates of A. colemani were 94% on plants removed on the day of the application from the treated area and 79 and 69% on plants 0.6 and 2 m downwind from the treated area. No toxic effects on parasitoids were observed 4 days after treatment (a.t.). M. persicae were less susceptible to Lannate ® 20 L residues compared to A. colemani. M. persicae mortality was 46% on plants collected from the sprayed area on the day of the application and 5 and 8% on plants collected from the drift area. In addition, densities of aphids and aphid mummies in the treated and drift areas of field plots were assessed from 1 day pre-treatment to 14 days post-insecticide application. Spraying significantly decreased aphid densities, but the population built up again. Compared to the control, no effect was detected on aphid population densities in the drift area of field plots. Densities of mummies in the insecticide treated area of plots were lower compared to densities in the control from 1 day post-application. There was no effect on mummy densities in the drift area. Recolonisation of field plots following the insecticide treatment was estimated by the release of A. colemani. Since A. colemani is not indigenous in northern Germany it was possible to determine their dispersal into the crop by mummy collections. Recovery of A. colemani mummies was low.

Assessing insecticide drift during and after center-pivot chemigation to corn using glass plates and gauze pads.

Insecticide application to corn through center-pivot irrigation systems (chemigation) is a common practice. According to Kohl et al. (1987), drift during and subsequent to chemigation may be a potential problem. Published data are available on pesticide drift from conventional applications (Bode et al. 1976; Byass and Lake 1977; Draper et al. 1981; Draper and Street 1981; Nordby and Skuterud 1975; Smith et al. 1982; Threadgill and Smith 1975; Ware et al. 1969, 1969, 1970; Yates et al. 1974). However, paucity of data exist regarding insecticide drift from chemigation (Byers et al. 1993). This study was undertaken to: a) measure drift using gauze pads and glass plates during and subsequent to chemigation of chlorpyrifos, permethrin, and carbaryl to corn; and b) estimate potential human exposure from drifted insecticides.

Ecological effects of experimental insecticide applications on invertebrates in sahelian temporary ponds

AbstractThe ecological impact offour insecticides used to control desert locustswas investigated during experimental field trials in natural temporary ponds in a cultivated savannah area of Senegal, West Africa. The insecticide formulations, dose rates, and application techniques were similar to those used in operational desert locust control. Average initial concentrations of fenitrothion, diflubenzuron, deltamethrin, and bendiocarb in pond water were 80, 10.4, 0.45, and 24.0 μg/L, respectively. Diflubenzuron and deltamethrin virtually disappeared in 24 h. Pseudo–first‐order half‐lives were 34 h for fenitrothion and 17 d for bendiocarb. Fenitrothion and deltamethrin significantly reduced population densities of backswimmers of the genus Anisops (Hemiptera, No‐tonectidae) and in addition caused an extensive kill of other species of insects. Both insecticide applications were also followed by reductions of zooplankton densities, especially Cladocera, and deltamethrin eradicated populations of fairy shrimp (Streptoce‐phalus spp.: Branchiopoda, Anostraca). Diflubenzuron only affected crustaceans, i.e., cladocerans and fairy shrimp. The least harmful insecticide in the study was bendiocarb, which only reduced the density of cladocerans. Recovery proceeded at fixed rates, which were different for each taxon. Anisops spp. recovered from the treatments in 1 to 4 weeks, most likely through aerial migration. Cladocerans returned to normal densities in 3 to 6 weeks. Streptocephalus spp., however, whose resting eggs presumably need desiccation during the dry season to be able to hatch, did not reappear until the next rainy season, one year later. It is concluded that contamination of temporary ponds in the Sahel by insecticide drift from desert locust control operations with any of the four insecticides should be avoided.

Canyon Drift and Dispersion of Bacillus thuringiensis and Its Effects on Select Nontarget Lepidopterans in Utah

A study was conducted to determine the effects of Bacillus thuringiensis Berliner var. kurstaki drift on 2 lepidopteran species, Incisalia fotis Strecker and Callophrys sheridanii W. H. Edwards, and to test the efficacy of exclusion plots for mitigation on Neominois ridingsii W. H. Edwards. Incisalia fotis and C. sheridanii experienced significant mortality from drift when fed host plants placed up to 3,000 m from the down-canyon edge of the application site. Drift concentrations and mortality were greatest near the boundary of the application site, although they sometimes varied in an inconsistent manner. The 1993 bioassay data correlate with the observed reduction in adult I. fotis populations following B. thuringiensis applications during previous years. An exclusion plot established for N. ridingsii failed to provide protection. All 3 species are concluded to be sensitive to B. thuringiensis and mitigative procedures are warranted during gypsy moth ( Lymantria dispar L.) eradication or suppression projects when the projects encompass large tracts of their respective ranges. Because of the lethal dosages of insecticide drift observed on larval host plants, it is concluded that mitigation procedures such as establishment of exclusion plots may not provide protection for B. thuringiensis -sensitive nontarget species when steep mountainous terrain is involved. Under these conditions other approaches may be warranted.

Pyrethroid Insecticides at Standard and Reduced Rates for Management of Sunflower Beetle Larvae, 1996

Abstract A grower-established sunflower field (planted on 25 May with a seeding rate of 23,300 per acre) was found to have sufficient SB larvae (5 per plant) to conduct our insecticide evaluations. This site in north-central South Dakota (Ipswich) was used to evaluate 3 pyrethroid insecticides at standard and reduced rates for management of SB larvae. Plots were 25 ft long by 8 rows (36 inch spacing) wide and the study was arranged in a RCBD with 4 replications. Treatment plots were buffered by 2 untreated rows to prevent cross-contamination between plots due to insecticide drift. Pre-application evaluations used whole-plant counts which were carried out on 20 plants per plot. Treatments were applied to plots on 2 Jul at V-8 stage of sunflower physiological development. Applications were made using a CO2-propelled backpack sprayer system equipped with a 6.7 ft long, 4-nozzle (TeeJet 8001 flat fan; spaced 20 inches apart) boom. The system was calibrated to deliver a spray volume of 15 gpa while traveling at 3 mph. Efficacy was evaluated at 7 and 24 DAT using the same counting technique and number of plants sampled as pre-application sampling. Data were analyzed with SAS’s General Linear Models procedure and means were compared using DMRT.

Ground-Applied Insecticide Rescue Treatments in Whorl-Stage Corn to Control First Generation European Corn Borer Larvae, 1995

Abstract An irrigated corn field near Delmont, SD, was chosen to evaluate granular and liquid insecticide treatments for management of first-generation ECB, larvae. Preapplication counts indicated that the site had a severe larval infestation (shotholing damage was observed in &amp;gt;90% of surveyed plants). Stadial composition of the population was 18, 39, 32, and 11 % 1st-, 2nd-, 3rd-, and 4th-instar larvae, respectively. Two untreated control plots were used to compare 6 granular insecticide formulations and 9 liquid treatments for efficacy in preventing larval tunneling damage. The study was arranged in a RCBD with 4 replications. Individual treatment plots were single, 30.5-m rows spaced 76 cm apart. All treatment rows were buffered on either side by an untreated row to minimize the likelihood of cross-contamination between plots due to insecticide drift. Treatments were applied on 6 Jul at whorl (approximately 1 wk prior to tasseling) stage of development. Granules were directed into plant whorls using a pneumatic applicator powered by a 3.5 hp engine mounted on a Highboy. Noble metering units attached to a modified chain-driven apparatus regulated the amount of granules released into the applicator. Liquid treatments were applied to whorls using a single-nozzle (TeeJet 8003 flat fan) CO2-propelled sprayer system mounted on the Highboy. Approximately 5 wk following insecticide applications (15 Aug), 20 corn plants were randomly chosen from each plot. Each plant was split vertically and examined for ECB tunneling damage. Cavity number and length data were analyzed with SAS’s General Linear Models procedure and means were compared using DMRT.

Bioassays of insecticide drift from air assisted sprayers in an apple orchard

SUMMARYInsecticide drift from an air assisted sprayer was measured on two occasions in an orchard in Cambridgeshire. Bioassays with two day old larvae of Pieris brassicae (cabbage white butterfly) showed similar effects from Cypermethrin and carbaryl (used as a fruit thinner). Both compounds gave 50% larval mortality at 20-25 m and 10% mortality at about 50 m. The effects of wind speed and shelter are considered, and the results are discussed in relation to the effects of drift from tractor-drawn hydraulic sprayers.

Impact assessment of spray drift from silvicultural aerial applications of permethrin on aquatic invertebrates using mosquito bioassays

Permethrin (Pounce®) was applied at 70 g active ingredient per hectare by fixed-wing aircraft to a 16-ha jack and red pine plantation under application and meteorological conditions that were highly conducive for insecticide drift. Mortalities of an indicator aquatic insect species, Aedes aegypti mosquito larvae, and corresponding permethrin residues in shallow, artificial aquatic habitats, along with droplet densities on ground Kromekote® cards, were measured along five lines downwind and crosswind of the spray block. At 30, 60, 120, 180, and 240 m downwind, larval mortalities averaged 40, 39, 51, 18, and 34%; permethrin residues averaged 1.4, 1.1, 1.2, 0.6, and 0.8 μg/L; and droplet densities averaged 25, 22, 17, 14, and 10 droplets per centimeter squared, respectively. At similar distances crosswind of the block, mortalities were 60, 53, 11, 1, and 0%; residues to 180 m were 1.6, 2.6, 1.1, and 0.3 μg/L; and droplet densities were 30, 22, 12, 2, and 0.1 droplets per centimeter squared, respectively. Mortalities and residues were not high for such shallow water (6.7 cm depth), particularly beyond 120 m, and were less than or similar to the values predicted from a swath-superposition model. Impact on sensitive aquatic arthropods and stream insects in deeper water (≥25 cm), more representative of natural habitats, is predicted to be insignificant at such distances. A buffer zone of 150 m around productive water bodies (depth ≥25 cm) is suggested for aerial permethrin applications to such plantations.

Insecticide drift from ground-based, hydraulic spraying of peas and brussels sprouts: bioassays for determining buffer zones

Studies were made on insecticide spray drift from conventional hydraulic sprayers under typical agricultural conditions. A bioassay technique with 2-day-old Pieris brassicae larvae was used to assess drift of cypermethrin and triazophos from pea and brassica crops on six occasions. Earlier work had shown that this species was a suitable model for other butterflies. Replicated series of target larvae were placed downwind of the sprayed crops, and mortality data used to obtaib profiles of spray drift related to physical features such as roadways, adjacent crops and hedges. Estimates of the distances at which 50%, 20% and 10% mortality occurred were obtained graphically or by fitting logistic models to the data. Buffer zones that limited mortality to 10% or less were between 16 and 24 m for cypermethrin and 12 m for triazophos. These estimates made no allowance for control mortality of about 5%, however, they were based conservatively on short-term effects. Hedges also probably limited the full extent of drift in two instances. The wider application of these results is discussed and comparisons are made with the use of unsprayed crop headlands.

Bayberry Whitefly Control on Lemons, 1982

Abstract Plots were located in Irvine, Calif, and were three rows of trees; evaluations came from the middle row. Tree spacing was 14 by 22 ft. Experimental design was randomized block with three blocks. Trees were short (ca. 12 ft) and there was considerable overlap in the spray pattern from 2.5 to 5.5 ft above ground. Each treatment was evaluated by counting the number of adult whiteflies on eight terminals from each of five trees per plot. This test also evaluated the rates of Pounce as well as the inclusion of oil or Citrufilm (Helena Chemical Co., Memphis, Tenn.) and the transformed data (logx+1) were analysed by two-way analysis of variance (ANOVA) and Duncan’s multiple range test. Three unsprayed control plots were included in the experiment but not in the randomized complete block. They were located 10 rows away from the main experiment to prevent them from becoming a source of reinfestation to any of the insecticide treated plots and to avoid the effect of insecticide drift into the unsprayed plots. The precount, based on pooling samples from 826 terminals on 18 and 20 Oct. was 13.3 adults per terminal. At the time of the test, the whitefly adult population was in a period of natural decline so that by 7 weeks after insecticide application the unsprayed plots had the lowest populations. It is not certain if the cause of this decline was biological control, weather or some other factor(s). Significant interactions in ANOVA of the main effects confused the analysis on all but the 22 Nov. data so the data were evaluated by plotting the mean and standard error of each plot.

Spray droplet assessment and insecticide drift studies during the large scale aerial application of endosulfan to controlGlossina morsitansin Botswana∗

Abstract Tsetse control in the Okavango Delta of Botswana is being conducted using a night‐time drift spraying technique, the effectiveness of which is dependent on the production of the correct droplet size spectrum and on suitable meteorological conditions. A 35 e.c. formulation of endosulfan was sprayed at 5 l/min with an atomiser rotation speed of 10,000–12,000 rev/min and flying speed of approximately 70 m/s. Droplet size measurements were made by sampling on to magnesium oxide coated glass slides, and chemical assessments were made by collecting droplets on filter papers or strands of synthetic angora wool for analysis. The results showed that the method was effective, producing an aerosol cloud of 20–30 μm diam. droplets, but that airborne spray concentrations varied considerably with meteorological parameters. Insecticide drift decayed exponentially with distance downwind from the nearest spray point, but amounts recovered up to 12.5 km downwind were sufficient to kill tsetse. The wool sampler was...

Insecticide drift and reinvasion of spray blocks in aerial spraying experiments against Glossina Morsitans Centralis Machado (Diptera: Glossinidae)

AbstractThe effect of insecticide drift on Glossina morsitans centralis Machado in Botswana was assessed using two-man fly-rounds downwind of the 1700–4000 km2 aerial spraying blocks. The blocks were subjected to sequential applications of endosulfan at between 6 and 12 g/ha with a droplet v.m.d. of 30 μm. Post-spray reinvasion of flies was assessed using two-man fly-round surveys across the edge of one spray block along ideal linear habitat. Each application had an effect on the flies outside the spray block, even at a distance of 20 km downwind. The first two applications of a series had a greater effect than later ones. Total reductions of G. m. centralis after a series of 5 or 6 applications were 92·5% 7 km outside a block sprayed in 1975, 98·3% 6–12 km outside a block sprayed in 1977 and 64·2% 10–20 km outside a block sprayed in 1978. Ageing studies showed that some females 10–20 km downwind of the sprayed area survived up to five applications, and three months after the final application the population there had recovered almost to pre-spray levels. The main front of fly encroachment after spraying across the downwind edge of the 1978 block travelled at about 0·8 km/month in the first 17 months after spraying, but small numbers of flies were found well ahead of the main front. It was concluded that the situation in the drift area could be ideal for the development of insecticide resistance and that adjacent blocks sprayed in consecutive years should overlap by 10 km.

Ecology of Black Pineleaf Scale (Homoptera: Diaspididae)

The ecology of black pineleaf scale which occurs on several species of pine and Douglas fir causing defoliation, discoloration of foliage, and reduced growth is reviewed. All known outbreaks of this scale have been caused by reduction in the population of Prosphaltella parasitoid that normally keeps the scale populations at very low densities. Abnormal mortality of Prosphaltella has been found to be caused either by the presence of sorptive dusts or by drift of insecticides. High population densities of scale have been found mainly in areas of high dust fall resulting from industrial sources and roadways. No known causal relationships have been found to exist between atmospheric fluorides and the black pineleaf scale population density. Environmental improvement to conserve the Prosphaltella parasitoids appears to be the most effective control measure.