Unsprayed Areas Research Articles

Endosulfan Resistance in Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in Australia

ABSTRACT Helicoverpa armigera larvae and adults were collected from New South Wales (NSW) and Queensland from 1974 to 1990 and laboratory cultures were established. Endosulfan was topically applied to third instar larvae of the first or second laboratory generations of the field collections and to a susceptible laboratory strain. the highest levels of endosulfan resistance (> 50‐fold) were recorded in 1974 following several years of endosulfan use in the field. Resistance was not detected from 1977 to 1983 when pyrethroids were substituted for endosulfan in the field. Since then, resistance has become widespread with the re‐introduction of endosulfan use. However, these resistance levels have remained generally low with only 5 of the 82 strains tested having resistance factors above 10‐fold. the highest level of resistance recorded after 1984 was 23‐fold and laboratory selection with endosulfan increased this to 163‐fold. From 1986 to 1990, 15–20% of individuals in populations of H. armigera from unsprayed areas of NSW were endosulfan resistant. the Helicoverpa insecticide resistance management strategy appears to have limited endosulfan resistance.

Dynamics, spread, and persistence of a single genotype of Pseudomonas syringae relative to those of its conspecifics on populations of snap bean leaflets.

A rifampin-resistant strain of Pseudomonas syringae (R10) was introduced onto bean plants grown in field plots to examine the processes of growth, spread, and survival of a single genotype relative to the dynamics of its conspecifics on populations of individual leaflets. R10 was applied to four plots (400, 200, 100, and 50 m2), each of which was centered in a quadrant of a bean field (90 by 90 m). Population sizes of the species P. syringae and of R10 were determined on each of 25 individual leaflets collected from the largest plot (A) at approximately weekly intervals during a 10-week period following application. The spread of R10 from all plots was monitored by leaf imprinting of individual leaflets collected at sites along four transects, each of which bisected two of the plots. The introduced strain was a dominant component of the species for about 5 weeks postinoculation on leaflets from plot A. Although the population sizes of R10 remained at about 5.0 to 5.5 log10 CFU per leaflet, the strain became a progressively minor component of the species as the population sizes of its conspecifics continued to increase during the latter part of the growing season. In general, a positive correlation was found for the population sizes of R10 and its conspecifics on individual leaflets collected throughout the growing season. This result suggests that large numbers of R10 early in the growing season did not exclude the colonization of bean leaflets by its conspecifics. It is apparent that the species pool comprised genotypes that were more fit than R10 under the conditions that prevailed during the latter part of the growing season. By 6 weeks postinoculation, R10 was detected at all sites sampled within the unsprayed areas of the field. However, it was present as a minor component of the species. The persistence of R10 throughout the winter and into the following growing season was monitored in plot A, which was plowed and replanted with wheat in the fall. R10 was detected on some of the samples (wheat seedlings or soil) taken at approximately monthly intervals from November to June of the following year. In June, the field was plowed and replanted with beans. We could not detect R10 on emerging bean seedlings in plot A. The results demonstrate that the successful spread and persistence of an introduced bacterium do not necessarily lead to the establishment of large populations of the bacterium in adjacent untreated areas or on its host plant in subsequent growing seasons.

Effects of DDT treatments applied for tsetse fly control on White-headed Black Chat (Thamnolaea arnoti) populations in Zimbabwe. Part II: cause of decline

Food supply, breeding success and DDT residue accumulation were investigated as possible causes for the decline of White-headed Black Chat populations in woodland sprayed for tsetse fly control. Gut contents from 21 birds were examined. A variety of invertebrates had been eaten, but ants, especiallyCamponotus spp. (Formicidae: Formicinae),Pheidole spp. (Myrmicinae), and termites, especiallyOdontotermes spp. (Isoptera: Termitidae), predominated in the dry season. In the early rains, more beetles (Coleoptera (predominantly Curculionidae)) and fewer termites were eaten. Ant and termite activity at sprayed sites in the study area was as great as or greater than that at unsprayed sites. Ants (Camponotus spp.) from sprayed sites held mean residue levels of 8.71 µg g(-1) dry weight (max. 218 µg g(-1) dry weight) total DDT, of which 67% was unaltered DDT. Termites and beetles had mean residue levels of 3.32 µg g(-1) dry weight (max. 14 µg g(-1) dry weight) and 0.92 µg g(-1) dry weight (max. 8 µg g(-1) dry weight) total DDT, of which 44% and 37% was unaltered DDT, respectively. Fledging success of White-headed Black Chats in adjacent sprayed and unsprayed areas was similar. Residues of DDT, DDD and DDE were found in all 23 chat carcasses examined. Birds collected in the dry season (July) from an area sprayed one month before contained up to 2206 µg DDT, 367 µg DDD and 578 µg DDE, g(-1) extractable lipid (86, 17 and 27 µg g(-1) dry weight, respectively). On average, residue levels were 50 times higher than in birds from the unsprayed area, and 4 times higher than in birds taken from another, recently sprayed area in the early rains (November). It is concluded that DDT spraying did not reduce availability of prey or fledging success. Initial population decline in sprayed areas was due to a lethal accumulation of DDT residues from prey, especiallyCamponotus spp. ants. Possible reasons for continued decline for 2-3 years after spraying, are discussed.

Spatial and Temporal Genetic Variation in Populations of the Whitefly Bemisia Tabaci (Genn.) in Israel and Colombia: an Interim Report

Intensive investigations of genetic variation within and among populations of the whitefly, Bemisia tabaci , are under way in Israel and in Colombia. A polymorphic esterase (EST), which seems to be controlled by a Mendelian locus, has two alleles in sufficiently high frequencies to be useful as a genetic marker. The analysis of more than 10,000 individual adult whiteflies shows genetic differences among localities in the frequencies of the fast ( F ) and slow ( S ) alleles. These differences seem to be related to the intensity of insecticide use against the whitefly. The frequency of F is high in unsprayed areas and in control laboratory populations, but is close to zero in heavily-sprayed agricultural areas. The frequency of Fon cotton in agricultural areas is high in winter and spring, but decreases dramatically in the summer (coincidental with the onset of pest-control activities on cotton). A similar temporal pattern on untreated Lantana may be due to migration of adults from agricultural fields. There was no indication of differentiation of populations on different host plants. In Colombia, the difference in EST patterns in different States are very pronounced, suggestive of geographical races. Small samples from Florida, California and Kenya indicate that B. tabaci in different countries may be genetically distinct.

Behavioural variation of Anopheles arabiensis (Diptera: Culicidae) populations in Natal, South Africa

AbstractAnopheles arabiensis Patton populations occur in those areas of Natal in which intra-domiciliary DDT is used for mosquito vector control and in the unsprayed areas. Indoor resting collections from the unsprayed area showed a human blood index >90%, in contrast to the indoor collections from the sprayed area where only 31% had fed on man. In exit trap collections from the sprayed area, 66% had fed on man. These trends of a high human blood index in the exit trap collections and a low human blood index in the indoor resting catches were unaffected, despite the close proximity of a cattle kraal to the majority of homesteads.

Management of cereal aphid (Hemiptera: Aphididae) populations and their natural enemies in winter wheat by alternate strip spraying with a selective insecticide

AbstractThe effect on aphid population development of creating natural enemy refuges by spraying only alternate strips of winter wheat with the aphid-specific insecticide pirimicarb at 140 g a.i./ha was compared with those in an unsprayed and a completely sprayed block in south-eastern England. The numbers of Sitobion avenae (F.), Metopolophium dirhodum (Walker) and Rhopalosiphum padi (L.) increased rapidly in the unsprayed block and in the unsprayed strips to reach similar peak densities in early August. Natural enemy activity was similar in these two areas, indicating negligible movement of predators and parasitoids from the sprayed strips to the unsprayed strips. Instead, aphids re-colonized the sprayed strips more quickly than the sprayed block, and the peak density in the former was similar to those in the unsprayed areas.

Effects of Aerial Applications of Fenitrothion on Bird Populations of a Scottish Pine Plantation

(1) Fenitrothion, an organophosphorus insecticide, has been used in Scotland to control outbreaks of pine beauty moth (Panolisflammea D. & S.) in lodgepole pine (Pinus contorta Loud.) plantations. Fenitrothion is applied at 300 g ha' from helicopters using ultra-low-volume techniques. This study (1982-84) investigated the effects of spraying on five species of passerine birds in two 70 ha plots, which were compared with two neighbouring unsprayed plots. (2) Annual changes in breeding-bird populations, as measured by Common Bird Census techniques, were not affected by fenitrothion. (3) Changes in the numbers of singing birds from 5 days before until 5 days after spraying were either not significantly different or were inconsistent between sprayed and unsprayed plots. (4) There were no differences in coal tits (Parus ater L.) breeding in nestboxes between sprayed and unsprayed plots, nor in the proportion of broods hatched or fledged, clutch size, or brood size at hatching or fledging. (5) Residues of fenitrothion were detected in two coal tit nestlings found dead within 4 days after spraying, but not in six others found 10-16 days later. (6) Regression analyses of nestling growth in weight, wing and tarsus measurements did not reveal significant effects of spraying, although a non-significant trend for slower growth resulting in a lower final weight was indicated for nestlings in sprayed plots. (7) Visiting rates by parent coal tits to their nests and the diets of their nestlings were examined using camera nestboxes. The differences between nests in unsprayed and sprayed areas were complex and could have been caused by factors other than spraying.

Persistence characteristics of operationally sprayed fenitrothion in nearby unsprayed areas of a conifer forest ecosystem in New Brunswick

Abstract Persistence characteristics of operationally sprayed fenitrothion were investigated in various substrates sampled from neighbouring unsprayed areas in New Brunswick. Air, water, sediment, aquatic plants, fish, balsam fir [Abies balsamea (L.) Mill] foliage, forest soil and litter samples were collected from random sampling locations selected within 200 m from the operational spray blocks. The same substrates were resampled from the same plots and from the same locations about a year later just prior to the commencement of the operational spraying. Control samples were collected from an unsprayed site, near Sault Ste. Marie, Ontario. All samples were analysed for fenitrothion, by gas‐liquid chromatography. Except the fish samples all the substrates collected during the time of operational spraying contained low but detectable levels of fenitrothion. When collected a year later prior to the operational spray program, only balsam fir showed any detectable levels (detection limit, 0.01 ppm) of the che...

A field trial of microencapsulated deltamethrin, a synthetic pyrethroid, for malaria control

The synthetic pyrethroid deltamethrin was evaluated as a 15 mg/m 2 residual application of a microencapsulated formulation for efficacy in malaria control in a 50 km 2 area of north-eastern Zimbabwe. Results were compared with very large contiguous DDT sprayed (2 g/m 2) and unsprayed areas. A total of 3544 rooms were sprayed with deltamethrin. No significant side effects of the insecticide on spraymen were noted. Mosquito captures were poor and inconclusive due to drought conditions, but the malaria vectors Anopheles arabiensis and An. gambiae were identified in the area, the former being 14 times more abundant than the latter in bait collections from an unsprayed area. Monthly bioassays using laboratory-reared An. arabiensis showed a higher mortality of mosquitoes exposed on roofs for up to eight months after deltamethrin application and indicated a high mortality in deltamethrin sprayed houses than in DDT sprayed houses. Tests indicated that, after eight months, up to 50% of the deltamethrin remained on the roof and 25% on the wall. Malaria transmission, evaluated by blood slide surveys at the beginning and end of the transmission season, was high in the unsprayed area, slightly less in the adjacent and incompletely isolated deltamethrin sprayed area, and absent or very low in the DDT sprayed area. The results were considered to be favourable for the use of deltamethrin in malaria control by means of residual house-spraying with the non-irritant dosage of 15 mg/m 2, but require evaluation in larger trials.

The effect of cultivation system and soil factors on the performance of herbicides against Alopecurus myosuroides

SUMMARYAspects of chemical and cultural control of Alopecurus myosuroides (blackgrass) in winter wheat were studied on a naturally‐occurring infestation over a 3‐yr period. In two experiments a comparison was made between ploughing and direct drilling, whilst in the third experiment direct drilling alone was used. Straw was spread and burnt in each year. Herbicide treatments were: chlortoluron and isoproturon in all three experiments; diclofop‐methyl and pendimethalin in two experiments; metoxuron, terbutryne, tri‐allate, carbetamide, propyzamide, chlorsulfuron + methabenthiazuron and trifluralin + linuron in one experiment. Herbicides were applied either pre‐emergence, early post‐emergence or late postemergence to separate sub‐plots. Surface soil (0–2.5 cm) samples were collected each year from unsprayed areas and used for soil analyses and for herbicide activity studies in pot experiments.Ploughing resulted in much lower populations of A. myosuroides than direct drilling. Most herbicides gave much better control of A. myosuroides in ploughed than in direct drilled soil in field and pot experiments, regardless of application time. Diclofop‐methyl, applied early post‐emergence at 1.13 kg a.i./ha, was the only herbicide treatment in field experiments to achieve over 90% weed control in direct drilled soil. Differences in adsorption between soils given different cultivations, determined as Kd values for chlortoluron and isoproturon, were much greater than differences in organic matter.The much greater adsorptive capacity of direct drilled soil, and consequently the poorer performance of all soil‐acting herbicides, was attributed to the concentration of burnt straw residues near the soil surface.

Aerial Tests of Organophosphate Insecticides Against the Sitka Spruce Weevil, 1983

Abstract A 15-year-old, 38 ha Douglas-fir/Sitka spruce plantation within the upper Hoh River valley in western Washington was the test site for aerial spray trials of Orthene and Metasystox-R against the Sitka spruce weevil in 1982 and 1983, respectively. A helicopter equipped with a 15.25-m spray boom with 64 nozzles along its length (#325 and #228, alternated; #46 swirl plates) was used for both tests; only the #325 nozzles were used in 1983. Four 1.6 to 2.0-ha rectangular treatment plots were established at random within the plantation. Spruce stocking density was ca. 900 trees/ha, and trees ranged 2-12 m in height in 1982. In the 1982 acephate test, Kromekote spray cards recorded droplet deposition, and weevils plus spruce material from sprayed and unsprayed areas were collected subsequent to treatment for mortality and oviposition assessment. Efficacy evaluations were carried out in August of both years by scoring all spruce within 10-m radius subplots for presence or absence of visible, weevil-induced leader damage. Three subplots were randomly located at least 15 m inside each of the 4 treated plots; an equal number of subplots were similarly located in unsprayed areas.

EFFECTS OF A SPLIT APPLICATION OF SEVIN-4-OIL® ON POLLINATORS AND FRUIT SET IN A SPRUCE–FIR FOREST

AbstractCounts of four pollinating insect groups were taken in unsprayed forest localities and in areas sprayed with a split application of Sevin-4-oil® (carbaryl) for spruce budworm control. Results indicate a reduction of pollinator populations due to spraying.Fruit set, measured by fecundity ratios (fruits/flower), was determined for Cornus canadensis L., Maianthemum canadense Desf., Clintonia borealis (Ait.) Raf., and Viburnum cassinoides L. in sprayed and unsprayed areas. Fecundity values for C. canadensis and M. canadense were significantly lower in sprayed than in unsprayed areas. Fruit set of C. borealis was apparently unaffected by carbaryl spraying, but the seed/flower ratio was significantly reduced in the sprayed area. V. cassinoides fecundity values were unaffected by carbaryl application. Reductions in native bee populations probably had the greatest impact on fruit set.

Estimation of ursodeoxycholic acid in human and bear biles using Clostridium absonum 7β-hydroxysteroid dehydrogenase

Ursodeoxycholic acid was estimated in bile samples from humans and wild North American black bears using 7β-hydroxysteroid dehydrogenase purified from Clostridium absonum by Procion Red affinity chromatography. The percentage ursodeoxycholic acid was calculated by two methods: (a) 7β-hydroxyl groups were quantified using 7β-hydroxysteroid dehydrogenase and 3α-hydroxyl groups (total bile acids) were quantified using 3α-hydroxysteroid dehydrogenase. The percentage ursodeoxycholic acid was calculated on the basis of [7β-hydroxyl groups]/[3α-hydroxyl groups] × 100. (b) Bile was hydrolyzed with sodium hydroxide and subjected to thin-layer chromatography. Bands corresponding to cholic acid, chenodeoxycholic acid plus deoxycholic acid, and ursodeoxycholic acid were identified by the use of standards and Komarowsky's spray reagent. Total bile acids and total ursodeoxycholic acid were measured by elution of silica gel in unsprayed areas corresponding to the bile acid standards and quantification of the total bile acid in each eluate. Direct comparison of these methods validated the use of 7β-hydroxysteroid dehydrogenase in the estimation of ursodeoxycholic acid in the biles of black bears and of patients fed ursodeoxycholic acid for cholesterol gallstone dissolution. Relative percentages of ursodeoxycholic acid were 8–24% in four bears and 22 and 27% in the patients ingesting 500 and 750 mg ursodeoxycholic acid per day for 3 months, respectively. Predictably lower values were obtained in two control subjects and one patient ingesting 750 mg chenodeoxycholic acid per day for 3 months.

Long-Term Effects of Big Sagebrush Control on Vegetation and Soil Water

Herbaceous productivity of mountain big sagebrush (Artemisia tdnlataspp. vsyana)areasspnayed with 2,4-D(2,4-dichlorophenoxyacetic acid) was nearly twice that of untreated areas 10 years after spraying, while the number of sagebrush plants on treated areas was 4% of that before spraying. Soil at the Wyoming study site was a Youga loam (Argic Cryoboroll). On treated areas, soil water depletion from the surface 0.9 m of soil slightly exceeded that of untreated areas beginning the third year after spraying when herbaceous vegetation had fully responded to release from sagebrush competition. Water depletion in soil 0.9 m to 1.8 m deep was substantially less on sprayed areas compared to unsprayed areas. Seasonal water depletion in the surface 1.8 m of soil was reduced 31% the year of treatment, and about 7% between 5 and 11 years after treatment. Mathematical relationships were developed to predict the effect of sagebrush control on seasonal water depletion in the surface 1.8 m of soil, the surface 0.9 m of soil, and soil 0.9-1.8 m deep. Control of big sagebrush (Artemisia tridentata) with the herbicide, 2,4-D (2,4-dichlorophenoxyacetic acid) beginning in the late 1940's revolutionized management of sagebrush rangeland. Millions of acres have been sprayed to benefit livestock forage production. The response by vegetation to spraying has been investigated at numerous locations in years immediately after treatment, but information about reestablishment of big sagebrush on treated areas is less common. Both biotic and abiotic values are affected by spraying. Hydrologic impacts, for example, have received little attention compared to vegetative responses. The soil water regime may be altered when deeply rooting big sagebrush is replaced by shallower rooting herbaceous species and there is speculation that treatment can increase water yields in some locations. This paper focuses upon the responses by vegetation and soil water to big sagebrush control 6 to 11 years after treatment. Treatment responses in the first 5 years were previously reported (Sturges 1977). Vegetation Characteristics Spraying big sagebrush vegetation with 2,4-D commonly increases grass production 2 to 3 times above pretreatment levels, where adequate populations of herbaceous species are present (Hull et al. 1952, Hyder and Sneva 1956, Tabler 1968, Miller et al. 1980). Forb production is suppressed by spraying, but control of big sagebrush by burning does not greatly alter vegetative composition (Harniss and Murray 1973, Nimir and Payne 1978). Sagebrush control is not a permanent type conversion, but the time required for big sagebrush to return to pretreatment levels is quite variable. Harniss and Murray (1973) found that grass and forb production remained above preburn levels for 12 years after a mountain big sagebrush (A. tridentata spp. vaseyana) stand was burned, but was below preburn levels 30 years after treatment. The useful life of a spray project in Oregon exceeded 17 years (Sneva 1972). Sagebrush was a minor vegetation component in the first Author is research forester, Rocky Mountain Forest and Range Experiment Station, Laramie, Wyo. 82070. Station headquarters is in Fort Collins, in cooperation with Colorado State University. Portion's of the research were supported by the Bureau of Land Management, U.S. Department of the Interior. Manuscript received July 22, 1982. decade after treatment, but sagebrush density was similar to untreated vegetation in the fifteenth year. Big sagebrush reestablishment was investigated by Bartolome and Heady (1978) in another Oregon study. The age of sagebrush plants growing on sprayed areas indicated that treatment seldom killed all plants and that most reestablishment occurred in years immediately following treatment. Thilenius and Brown (1974) and Johnson (1969) investigated the return of big sagebrush to sprayed areas in Wyoming. Soil Water Withdrawal Characteristics Changes in the soil water regime that follow control of big sagebrush depend upon rooting depths of sagebrush and replacement herbaceous species and upon the depth of soil water recharge (Sturges 1977). Several studies indicate that water withdrawal in the surface meter of soil decreases slightly the first 2 years after sagebrush control. (Sonder and Alley 1961, Cook and Lewis 1963, Tabler 1968, Shown et al. 1972, Sturges 1977). Thereafter, water use by treated and untreated vegetation is similar. A substantial reduction in seasonal water withdrawal was detected at 2 Wyoming sites when mountain big sagebrush was sprayed. Tabler (1968) found that seasonal evapotranspiration decreased 14% the second year after spraying based on measurements to a 1.8 m soil depth, while Sturges (1977) detected differences of 19, 15, and 8% in the first, second, and fifth year after treatment, respectively. Treatment differences in seasonal water use were located almost entirely in soil 0.9 m to 1.8 m deep and accrued while vegetation was actively growing. No soil water study extended more than 5 years beyond the treatment year.

Disposal of sewage effluent on forested land: Effects on groundwater

Abstract Research was conducted to investigate the effects of spraying sewage effluent on hardwood forested land at Sugarloaf Mountain, Maine. Using suction lysimeters, groundwater samples were collected throughout the summer and fall of 1979 in sprayed, near‐sprayed, and unsprayed areas. The percent removal of the constituents in the effluent ranged from 62.7 percent for sodium to 98.7 percent for orthophosphate phosphorus. Lateral movement of all constituents from the spray circles was detected.

The effects of aerial spraying of endosulfan for tsetse fly control on aquatic invertebrates in the Okavango swamps, botswana

The effects of ULV spraying of endosulfan from the air for tsetse fly control on aquatic invertebrates were studied in the Okavango delta, Northern Botswana, over a three-year period. Comparison of zooplankton numbers in a sprayed and an unsprayed lagoon revealed no changes in numbers or composition due to spraying. Major change in zooplankton numbers were associated with the rise and fall of water levels during the annual flood. Studies on invertebrate numbers in the periphyton on submerged macrophytes in sprayed and unsprayed areas revealed no differences in the major groups attributable to spraying. In the southern delta, where considerable changes in water level occur, there was a reduction in numbers of chironomid larvae during high water periods. It was concluded from these data, taken in conjunction with residue levels of the insecticide in water following spraying, that the low rates of application used were unlikely to cause substantial damage to freshwater invertebrate populations in the Okavango region.

The effect of aerial insecticide spraying for spruce budworm control on the fecundity of entomophilous plants in New Brunswick

Eight entomophilous plants, Aralia nudicaulis L., Clintonia borealis (Ait.) Raf., Cornus alternifolia L., Cornus canadensis L., Cornus stolonifera Michx., Kalmia angustifolia L., Maianthemum canadense Desf., and Viburnum trilobum Marsh., all of which bloom shortly after forest spray application in New Brunswick, were shown by bagging experiments to be dependent on insect visitation for seed set. All species showed significantly lower fecundity in fenitrothion-treated than in unsprayed areas. No depression of fecundity in Clintonia borealis or Kalmia angustifolia was found associated with aminocarb (Matacil) spraying.

POLLEN REMOVAL IN CYPRIPEDIUM ACAULE (ORCHIDACEAE) IN RELATION TO AERIAL FENITROTHION SPRAYING IN NEW BRUNSWICK

AbstractMeasures of pollen removal in the orchid Cypripedium acaule Ait. provided a retrospective method for estimating the activity of bumble bee pollinators in New Brunswick spruce-fir forests. Significantly lowered activity was observed in fenitrothion-sprayed forest as compared with unsprayed control areas. The difference is probably attributable to direct mortality of bees in sprayed forest.

Feeding habits of anophelines (Diptera: Culicidae) in 1971–78, with reference to the human blood index: a review

AbstractA synoptic view is given of the data amassed by WHO, with technical assistance from the Imperial College of Science and Technology, on the origins of blood-meals in Anopheles samples collected from 1971 to 1978. Attention is focused on the proportion of each sample found to contain human blood and on the problems of interpreting from this the human blood index or degree of biting-contact with man exhibited by vector populations. The difficulties of overcoming bias in sampling, which are formidable in unsprayed areas, are further compounded where the dwellings are treated with a slow-acting residual insecticide which knocks down many engorged mosquitoes before they can be collected from their daytime resting places. There is evidence to suggest that the host-selection patterns of those vectors which are ‘opportunistic’ feeders may be heavily influenced, even from village to village or from month to month, by the changing availability of alternative hosts, particularly cattle. This suggests in turn that the possibilities of manipulating the degree of mosquito-man contact by encouraging deflection to animals (zooprophylaxis) or by measures to afford a degree of personal protection should not be under-estimated by malaria strategists. It may sometimes be found less difficult to reduce the vector’s human blood index than it is to measure it, but in view of the epidemiological importance of this parameter, suggestions are put forward for improving entomological field practice in this area. They include a quantitative survey of the biotopes available to the mosquito population as diurnal shelters, a longitudinal survey of the densities of blood-fed females per biotope, and a survey of the numbers and the respective distribution of people and domestic animals available as hosts. The work-load entailed by such a thorough form of investigation, to be repeated where necessary at different seasons of the year, underlines the necessity to concentrate efforts on a small number of localities, carefully chosen for the malaria situations they represent and the vector populations they support. A large-scale blood-meal sampling programme, confined to these selected localities, is most likely in our estimation to yield information of value for controlling malaria vectors.

THE EFFECT OF AERIAL INSECTICIDE SPRAYING ON HYMENOPTEROUS POLLINATORS IN NEW BRUNSWICK

AbstractThe effects of aerially sprayed fenitrothion (210 g/ha) and aminocarb (70 g/ha) on several hymenopteran taxa in New Brunswick are reported. Exposure cage experiments showed fenitrothion to cause as high mortality among solitary bees and vespid wasps as that previously reported for bumble bees. Exposure cage experiments under aminocarb sprays revealed no detectably increased mortality for bumble bees, but a significant effect on solitary bees. Experiments in which whole bumble bee colonies were set out in fenitrothion and aminocarb spray blocks a few days before spraying gave comparable results to those from the exposure cage experiments.A series of comparisons of bumble bee densities in sprayed and unsprayed areas confirmed our earlier finding that populations are greatly reduced after fenitrothion application. Population recovery during the rest of the season appears to be influenced by meteorological conditions. The ecological replacement of early-emerging by late-emerging Bombus species in fenitrothion spray blocks is further documented. No relationship between bee densities and aminocarb application was found.A method for retrospective assessment of pollinator activity by measuring nectar levels in Clintonia borealis was successfully carried out on a small-scale basis.