Field evaluation of neem and canola oil for the selective control of the honey bee (Hymenoptera: Apidae) mite parasites Varroa jacobsoni (Acari: Varroidae) and Acarapis woodi (Acari: Tarsonemidae)

Neem oil, neem extract (neem-aza), and canola oil were evaluated for the management of the honey bee mite parasites Varroa jacobsoni (Oudemans) and Acarapis woodi (Rennie) in field experiments. Spraying neem oil on bees was more effective at controlling V. jacobsoni than feeding oil in a sucrose-based matrix (patty), feeding neem-aza in syrup, or spraying canola oil. Neem oil sprays also protected susceptible bees from A. woodi infestation. Only neem oil provided V. jacobsoni control comparable to the known varroacide formic acid, but it was not as effective as the synthetic product Apistan (tau-fluvalinate). Neem oil was effective only when sprayed six times at 4-d intervals and not when applied three times at 8-d intervals. Neem oil spray treatments had no effect on adult honey bee populations, but treatments reduced the amount of sealed brood in colonies by 50% and caused queen loss at higher doses. Taken together, the results suggest that neem and canola oil show some promise for managing honey bee parasitic mites, but the negative effects of treatments to colonies and the lower efficacy against V. jacobsoni compared with synthetic acaricides may limit their usefulness to beekeepers.     

Plague management of prairie dog colonies: degree and duration of deltamethrin flea control

Plague is a flea‐borne disease of mammalian hosts. On the grasslands of western North America, plague stifles populations of Cynomys spp. prairie dogs (PDs). To manage plague, PD burrows are treated with 0.05% deltamethrin dust that can suppress flea numbers and plague transmission. Here, we evaluate the degree and duration of deltamethrin flea control with three PD species at six sites across four U.S. states. Data were simultaneously collected at paired plots. Burrows from one randomly assigned member of each pair were treated with deltamethrin; non‐treated plots served as experimental baselines. Flea control was strong ≤two months after treatment, remained moderate one year later, and was statistically detectable for up to two years at some sites. Flea abundance was lower in plots with higher rates of deltamethrin application. After burrow treatments, flea abundance increased over time, reaching >one per PD within 255 to 352 days. Nevertheless, annual treatments of burrows with deltamethrin provided PDs with substantial protection against plague. Even so, deltamethrin should be further evaluated and combined with other tools under an integrated approach to plague management. Integrated plague management should help to conserve PDs and species that associate with them, including the endangered black‐footed ferret (Mustela nigripes).     

Temporal and spatial changes in aphid and parasitoid populations following applications of deltamethrin in winter wheat

The spatial and temporal effects of the pyrethroid insecticide, deltamethrin, on populations of cereal aphids and their primary parasitoids and hyperparasitoids were investigated in a large scale field experiment in winter wheat. Four hectare plots were treated at the recommended field concentration or a reduced concentration representing one twentieth of field rate. A control plot was left unsprayed. Invertebrate populations were sampled at sites within a grid layout covering the whole plots, enabling the use of geostatistical analysis. Hymenopteran populations were monitored using transparent sticky traps and suction sampling. Aphid populations were recorded by visual counts. Monitoring continued for 36 days after treatment. The full rate deltamethrin treatment resulted in initial reductions of aphid populations by 78%. Primary parasitoid and hyperparasitoid populations were reduced in suction samples by 90% and 47% respectively, when corrected for control fluctuations. The reduced deltamethrin concentration caused reductions of aphid, primary parasitoid and hyperparasitoid populations of 40, 60 and 54% respectively. Aphid population recovery over the full rate plot occurred slowly and in a patchy manner following treatment. No significant reinvasion gradients were detected. Aphid population density recovered more rapidly in the reduced rate treatment; with initial evidence for increased densities at the plot centre. Significant patterns of reinvasion were initially detected for both groups of Hymenoptera in the full rate treatment, suggesting that reinvasion of the sprayed area was taking place from untreated surrounding reservoirs. It was concluded that experiments that examine pesticide impacts within small plots will lead to underestimates of effects on dispersive groups including parasitic Hymenoptera.     

Diaeretiella rapae limits Myzus persicae populations after applications of deltamethrin in oilseed rape

In fall, Myzus persicae (Sulzer) (Homoptera: Aphididae) may exhibit population resurgence in winter oilseed rape in France. This resurgence may arise from pyrethroid treatments against Coleoptera (Psylliodes chrysocephala L.) that either kill parasitoids present during treatment or prevent recolonization by off-crop parasitoids. We studied the impact of Diaeretiella rapae (M'Intosh) (Hymenoptera: Braconidae) on populations of M. persicae when parasitoids were introduced on deltamethrin-treated plants at increasing intervals after treatment. Parasitoids were introduced 1, 2, 7, or 14 d posttreatment on individually caged plants infested with established populations of M. persicae. Aphids were counted 7, 14 and 21 d after parasitoid introduction. First, we observed that both the pesticide and the parasitoid reduced aphid population growth and that their effects were additive. Second, there was no mortality of parasitoids exposed to treated leaves in a device with a refuge area, and only 20% of mortality without the refuge area. Furthermore, deltamethrin residues had no effect on the reproduction of D. rapae females. Compared with the known toxicity of deltamethrin to D. rapae on glass, this low mortality may have been due to both the high liposolubility of deltamethrin (leading to a rapid diffusion of residues in the oilseed rape leaf cuticle) and to the existence of a refuge area. This work suggests that D. rapae could limit populations of M. persicae in the fall, even after pyrethroid treatment, because the presence of deltamethrin residues had little impact on the parasitoid.     

Effect of insecticides and fungicides on the interaction between members of the mite families Phytoseiidae and Stigmaeidae on citrus

The study was carried out to evaluate the effect of some insecticides and fungicides on the interaction between predacious mites of the families Phytoseiidae and Stigmaeidae on citrus. Euseius citrifolius Denmark and Muma, Euseius concordis (Chant) (Phytoseiidae), and Agistemus aff. bakeri (Stigmaeidae) were the most abundant species of predacious mites. No significant reduction of the population of stigmaeids was detected following the pesticide treatment. On the contrary, the population of those mites increased after the application of methidathion, petroleum oil, deltamethrin, cupric oxychloride and cuprous oxide, as compared to the population of those mites in the control plots. The chemicals promoting increased stigmaeid populations are some of those that promoted reduction of phytoseiid populations. A significant negative correlation was found between the numbers of phytoseiids and stigmaeids on citrus leaves immediately before treatments, and 33, 50, 83 and 105 days after treatment. A clear negative linear correlation between the number of predacious mites from both families was detected for benomyl, cupric oxychloride, cuprous oxide, thiophanate methyl, and control. Phytoseiid-stigmaeid interaction on citrus orchard is discussed.     

Importance of plant extract formulations in managing different pests attacking beans in new reclaimed area and under storage conditions

Field evaluation of some botanical formulations like Neem Azal T/S, Neem Azal T/S + TS/fort and petroleum ether extract of Curcuma longa for the management of different pests attacking broad bean crop in a new reclaimed area at El- Noubaria and under storage conditions has been carried out. All tested formulations could be considered efficient in controlling Aphis craccivora infesting broad bean under field conditions. As to the leafminer, the number of living Liriomyza trifolii larvae decreased significantly compared to non-treated control. The number of living larvae continued to decrease until seven days post-treatment after which an increase in their number was noticed after 14 days post-treatment. Neem Azal T/S + additive (TS/fort) ranked first in comparison to other treatments for the control of aphids and leafminers attacking broad bean in the field either by killing, deterrent or antifeedant effect. The yield of treated crop increased significantly in comparison to the control. Another spray was used before harvesting the crop with the same formulations for protection of the stored crop. Neem Azal T/S with adjuvant (TS/fort) protected broad bean seeds from weevil attack for one year. Petroleum ether extract of C. longa could protect the stored crops for two months only. The percentage weight loss in one kg stored seeds treated in the field with Neem formulation + adjuvant was very small compared with those seeds treated with petroleum ether extract of C. longa and control.     

Insecticide resistance and detoxifying enzyme activity in the principal bancroftian filariasis vector, Culex quinquefasciatus, in northeastern India

The insecticide resistance status of Culex quinquefasciatus Say (Diptera: Culicidae) to DDT and deltamethrin across army cantonments and neighbouring villages in northeastern India was investigated. In India, DDT is still the insecticide of choice for public health programmes. In military stations, pyrethroids, especially deltamethrins, are used for insecticide‐treated nets (ITNs). Recent information on the levels of resistance to DDT and deltamethrin in mosquito populations of northeastern India is scare. Continued monitoring of insecticide resistance status, identification of the underlying mechanisms of resistance in local mosquito populations and the establishment of a baseline data bank of this information are of prime importance. Insecticide susceptibility assays were performed on wild‐caught adult female Cx. quinquefasciatus mosquitoes to the discriminating doses recommended by the World Health Organisation (WHO) to DDT (4%) and deltamethrin (0.05%). Across all study sites, mortality as a result of DDT varied from 11.9 to 50.0%, as compared with 91.2% in the susceptible laboratory strain (S‐Lab), indicating that Cx. quinquefasciatus is resistant to DDT. The species was found to be 100% susceptible to deltamethrin in all study sites except Benganajuli and Rikamari. Knock‐down times (KDT) in response to deltamethrin varied significantly between study sites (P < 0.01) from 8.3 to 17.8 min for KDT₅₀ and 37.4 to 69.5 min for KDT₉₀. All populations exceeded the threshold level of alpha‐esterase, beta‐esterase and glutathion S‐transferase (GST) established for the S‐Lab susceptible strain, and all populations had 100% elevated esterase and GST activity, except Missamari and Solmara. Beta‐esterase activity in Field Unit II (96.9%) was less than in any of the other populations. Benganajuli had the highest activity level for all the enzymes tested. There was a significant correlation between all enzyme activity levels and insecticide resistance phenotype by populations (P < 0.05). The results presented here provide the first report and baseline information of the insecticide resistance status of Cx. quinquefasciatus in northeastern India, and associated information about biochemical mechanisms that are essential for monitoring the development of insecticide resistance in the area.     

Survivorship,growth and self-thinning in Banksia ericifolia

High-density (dense) and low-density (sparse) plots were set up in naturally sown monospecific stands of Banksia ericifolia in coastal heath, 3 years after fire. This was done both in high-growth and low-growth areas. Plant mortality was recorded quarterly, and two harvests were made at 6 and 9 years to sample growth. Density-independent mortality at an exponential rate was observed in the low-growth treatments at both densities, and in the high-growth sparse treatment. Growth level affected mortality, with the half-life of populations in the high-growth sparse plots being double that of populations in the low-growth plots. Density-dependent mortality (self-thinning) was seen only in the high-growth dense plots. Seasonal effects on mortality were slight; maximum mortality was observed in the spring-summer period in plots subject to density-independent mortality, and in the winter-spring quarter in plots that had self-thinned. Yields in the high-growth plots and the low-growth dense plots were high for heath vegetation. The self-thinning populations did not exceed White's (1985) upper boundary for thinning lines of log intercept (K) = 5 on standardized axes. The data suggested a log intercept value in the range 4.8–4.9 in the high-growth stands assuming a thinning-line slope of – 1.5. Banksia ericifolia (a large shrub/small tree) has a high mean plant weight per given thinning density compared with trees, where an upper limit of log K= .4 has been suggested by White (1985). The volume of canopy space per plant in B. ericifolia is not unusual compared with other species. The amount of biomass packed into a given volume of canopy space was high in this Banksia, achieved by having leaves with a low ratio of area to weight (specific leaf area, SLA). For given values of density, leaf area index and proportion of shoot as leaf, plants with a low SLA will be several times heavier than plants with a high SLA. This achieves a high biomass to volume ratio without an erectophile canopy and may explain the high intercept seen for thinning lines of conifers.     

The effect of insecticides and a plant barrier row on aphid populations and the spread of bean yellow mosaic potyvirus and subterranean clover red leaf luteovirus in Vicia faba in South Australia

The effect of the insecticides malathion, demeton-S-methyl and disulfoton, and a barley barrier row on the rate and pattern of spread of bean yellow mosaic potyvirus (BYMV) and subterranean clover red leaf luteovirus (SCRLV) in Vicia faba was investigated in field plots with artificially introduced sources of viruses and vectors. The systemic insecticide treatments reduced aphid populations in the plots and this was associated with reduced spread of SCRLV, but not of BYMV. The barley barrier did not affect aphid populations in plots; however, it reduced the spread of BYMV to rows 1 · 1 m from the source but had only a minor effect on the spread of SCRLV. Apterae rather than alates of Aulacorthum solani were implicated in the spread of SCRLV. Spread of BYMV was attributed mainly to alate migrants of Myzus persicae and Macrosiphum euphorbiae, but other aphid species and morphs which occurred in high populations at the times of most rapid virus spread may also have had an active role as vectors of BYMV.     

Mini-plot field experiments on slug control using biological and chemical control agents

In three field experiments, the rhabditid nematode Phasmarhabditis hermaphrodita was applied one or more times at the standard rate (3 × 10⁹ ha^?1) or half the standard rate to protect crops from slug damage under experimental conditions. Expt 1 was done in a field planted with the ornamental Polygonatum japonica. The treatments were: infective juveniles of the nematode at the standard field rate, metaldehyde pellets at the recommended field rate, and ioxynil (a herbicide with molluscicidal properties) at 90 mg m^?2. The treatments were repeated every 2 wk. Arion ater agg. caused most of the damage to P. japonica. There were no significant differences in damage between treatments during the 3 wk after first application, but plants on plots treated with metaldehyde or nematodes had significantly less damage than plants on untreated plots in the fourth and fifth weeks. Expts 2 and 3 were done on the same site, the first with leaf beet and the second with lettuce. The treatments in these experiments were: nematodes applied to the planted area at the standard field rate 3 days prior to planting, with or without previous application of cow manure; nematodes at half standard rate applied twice, 6 days apart, to the planted area or to the surrounding area; metaldehyde pellets and iron phosphate pellets, both applied at the recommended rate to the planted area immediately after planting. In both experiments, the two chemical molluscicides and nematodes applied once to the planted area at the standard field rate without previous application of cow manure, or twice at half standard rate, were able to reduce slug damage. Nematodes applied after manure did not reduce slug damage. None of the treatments reduced the numbers of slugs contaminating the harvested plants. Slug populations were assessed by means of soil sampling before and after Expts 2 and 3. Only after Expt 3 was there a significant effect of treatment on slug numbers, with significantly fewer in metaldehyde treated plots than in untreated plots.     

The impact of altered precipitation on spatial stratification and activity-densities of springtails (Collembola) and spiders (Araneae)

Abstract.  1. A field experiment was conducted to determine how short-term changes in moisture can alter activity-densities of spiders and springtails.
2. In a Kentucky forest 10 unfenced 4-m² plots were divided into two rainfall treatments. A clear roof over five plots excluded rainfall to simulate severe drought conditions ( drought treatment). Water was sprayed on the five uncovered plots at a rate equal to two times the long-term mean in order to establish the high-rainfall treatment. Activity-densities of Collembola and spiders were measured using pitfall traps designed to sample the top, middle, and bottom layers of leaf litter. The experiment ran from 20 July to 23 September 2001.
3. Overall (i.e. litter layers pooled) activity-density (mean number trapped each sampling date) of Collembola was ≈ 60% lower in drought plots than in plots receiving increased precipitation. Surprisingly, overall spider activity-density was ≈ 1.6 times greater in the drought plots.
4. Differences in rainfall affected the spatial stratification of Collembola and spiders in strikingly different ways. Activity-densities of neither group differed between drought and high-rainfall treatments in the bottom litter layer. Collembola activity-density was three times greater in the top and middle litter layers in high-rainfall plots than in drought plots. In contrast, spider activity-density did not differ between treatments in the top layer, but activity-density was decreased by 50% in the middle layer of high-rainfall plots compared with drought plots.
5. Three Collembola families (Sminthuridae, Tomoceridae, and Entomobryidae) accounted for most of the Collembola pattern. The spider response was due to altered activity-density of one family of wandering spider, the Gnaphosidae.     

The effects of sowing date and choice of insecticide on cereal aphids and barley yellow dwarf virus epidemiology in northern England

During the mid-1980s, Sitobion avenae became recognised as an important vector of barley yellow dwarf virus (BYDV) in the Vale of York. A field trial at the University of Leeds Farm, North Yorkshire, was carried out during the autumn/winter of 1984-85 to evaluate different control procedures against S. avenae-transmitted BYDV and to investigate its epidemiology. Winter barley was sown on three dates in September, and plots were sprayed with either deltamethrin, demeton-S-methyl or pirimicarb on one of three dates between mid-October and mid-November, making a factorial design. Rhopalosiphum padi, the main vector of BYDV in southern England, were rarely found during the experiment, but the numbers of S. avenae were much higher, reaching a peak of 21% of plants infested in the unsprayed plots of the first sowing date. Single applications of each insecticide reduced populations of S. avenae to zero. Some treatments, particularly in the early sown plots and those treated with pirimicarb, however, did allow some recolonisation, and thus led to increased virus incidence and decreased yields. Sprays applied before the end of the migration of S. avenae were more efficient at controlling BYDV if the insecticide was persistent, otherwise a spray after this period, in November, was more effective. Virus incidence, although reduced by sprays, was generally low in plots sown on 18 and 27 September. In contrast, about 11% of plants were infected in unsprayed plots sown on 6 September and a small yield benefit was obtained with insecticidal treatments. Enzyme-linked immunosorbent assay (ELISA) of plants taken from the plots indicated that MAV- and PAV-like strains were present, and were most likely to have been transmitted by S. avenae.     

Orchard selection for resistance to a synthetic pyrethroid in organophosphate—resistant Typhlodromus pyri in the UK

Organophosphate resistant Typhlodromus pyri were exposed to deltamethrin in replicated orchard plots from 1986–90. Treatments of 6.3, 3.1, 1.7 and 0.8 g active ingredient (ai) ha^?1 deltamethrin were applied 14 times over the 5‐year period; a 12.5 g ai ha^?1 treatment was discontinued in 1989 after eight applications. Few phytoseiids were found in the plots receiving the two highest rates of deltamethrin. Bioassays at the end of the five‐year period showed a progressive increase in LC₅₀ from the untreated strain (0.40 ppm ai) to the strain that had been exposed to 3.1 g ai ha^{‐1 1} (1.50 ppm ai) indicating a four‐fold increase in resistance in these selected mites.     

The incidence of rosette disease in groundnut in relation to plant density and its effect on yield

Trials are described in which the relationships between plant density, rosette disease incidence and the yield and quality of groundnuts were investigated on sprayed and unsprayed groundnut plants. During growth, the number and percentage of sprayed and unsprayed plants showing symptoms of rosette disease was significantly greater at low plant populations than at high. At harvest, in general on unsprayed plots the numbers attacked were also greater at low plant populations, but on the sprayed plots the results were inconsistent. The percentage attack at harvest was much lower on sprayed plots at all plant populations. Menazon used as a seed dressing did not affect the incidence of the disease but used as a spray it significantly reduced the amount of disease found. The spray was applied at a rate of 294 g a.i./ha, four times at 10-day intervals, the first spray being applied 10 days from germination. Spraying controlled secondary spread of the virus within the crop and appeared to reduce the severity of early attack. There was a marked improvement of yields and quality of nuts from sprayed plots. Plant density did not affect quality of the groundnuts obtained, but yields per ha were highest on both sprayed and unsprayed plots at the highest plant densities (seed rate up to 134 kg/ha).     

Grasshopper response to a 40-year experimental burning and mowing regime, with recommendations for invertebrate conservation management

Grasshopper assemblages were sampled in 44 plots in each of three adjacent sites in a 40-year-old southern tall grassland experimental area in South Africa. Specific plots received particular mowing and/or burning treatments over the 40-year period. Grasshopper responses to vegetation type, and to different burning and mowing practices, were site-specific, despite the close proximity of sites. This suggests that grasshopper assemblage composition is not entirely deterministic and depends on the trajectory of plant succession. Grasshopper species richness and abundance decreased from annually to triennially burnt plots, and increased in plots mown once per year to plots mown three times per year. Burning in the first week of August (winter) was more favourable for grasshopper assemblages than burning in autumn or after the first spring rains. Mean grasshopper species richness was highest in plots mown after the first spring rains, and the mean number of individuals was highest i n plots mown early in summer. When annually burnt plots were compared with annually mown plots, grasshopper abundance and species richness were highest in the burnt plots. A rotational winter burning programme, which is practical under African conditions, is recommended for the conservation of grasshoppers and other invertebrates.     

Efficacy of acaricidal tags and pour-on as prophylaxis against ticks and louping-ill in red grouse

Abstract This paper examines the efficacy of 10% lambdacyhalothrin-impregnated plastic tags and a deltamethrin pour-on preparation in protecting red grouse chicks from parasitism by ticks and subsequent infection with the louping-ill virus. In 1995, ten red grouse hens ( Lagopus lagopus scoticus ) in a free-living population in north-east Scotland were fitted with lambdacyhalothrin-impregnated plastic tags, glued to radio transmitters. Chicks of more than 10 days of age from a further ten untreated radio-collared hens were caught and fitted with individual tags to the plagium. Both treatments significantly reduced tick burdens in the short term. The number of larvae and nymphs on chicks up to 45 days was less under both treatments than on control chicks and tagged chicks had fewer nymphs than chicks from treated hens. Nevertheless, treatments did not reduce viral infection rates nor increase survival to 10 weeks, possibly explained by incomplete treatment of tagged broods and/or direct or indirect mortality due to tags. In 1996 chicks in ten broods from hens with radio transmitters were individually treated at 14 days of age at a rate of lmg/kg of chick with a deltamethrin pour-on preparation. This preparation significantly reduced the number of larvae and nymphs on grouse chicks 7–10 days after application below the number on untreated controls. At 20 days from application, however, only larval numbers were lower on treated chicks. Nevertheless louping-ill virus infection prevalences were significantly reduced at 35 days of age and survival of chicks to 10 weeks increased.     

Field evaluation of the efficacy of neem oil (Azadirachta indica A. Juss) and Beauveria bassiana (Bals.) Vuill. in cotton production

Neem oil (Azadirachta indica A. Juss) alone and combined with the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin (isolate Bb11) was applied to control cotton pests. The efficacy of these treatments was compared with that of synthetic insecticides applied either in a calendar‐based application or in the ‘Lutte Etagée Ciblée’ (LEC) strategy, consisting of using first calendar‐based (half‐dose) applications followed by threshold‐based treatments. The experiment was carried out in collaborative research with farmers in three cotton agro‐ecological zones differing in rainfall, pest prevalence, and farming practices. The neem oil and neem oil‐Bb11 treatments required 2 to 6 applications, while conventional and LEC received 6 to 8 applications. The percentage of damaged reproductive organs in plots treated with neem oil and neem oil plus Bb11 was higher than that recorded under the conventional and LEC strategy, with exception of the zone with the highest rainfall; this resulted in yields being 25% and 39% lower, respectively. Yields in the biopesticide plots were 26–42% higher and in the conventional and LEC plots 44–59% higher than those in the control plots that received only water. Overall, the LEC regime scored best, both in yield and profitability. The incidence of natural enemies was highest in the control and in the plots treated with biopesticides. Although the use of entomopathogen Bb11 and neem oil avoids many problems associated with the application of synthetic insecticides, their efficacy needs to be enhanced by improved formulation or by combining them with other pesticides.     

Impacts of silvicultural thinning treatments on beetle trap captures and tree attacks during low bark beetle populations in ponderosa pine forests of northern Arizona

Our research used a combination of passive traps, funnel traps with lures, baited trees, and surveys of long-term thinning plots to assess the impacts of different levels of stand basal area (BA) on bark beetle tree attack and on trap captures of Ips spp., Dendroctonus spp., and their predators. The study occurred at two sites in ponderosa pine, Pinus ponderosa Dougl. ex Laws., forests, from 2004 to 2007 during low bark beetle populations. Residual stand BA ranged from 9.0 to 37.0 m2/ha. More predators and bark beetles were collected in passive traps in stands of lower BA than in stands of higher BA; however, significance varied by species and site, and total number of beetles collected was low. Height of the clear panel passive traps affected trap catches for some species at some sites and years. When pheromone lures were used with funnel traps [Ips pini (Say) lure: lanierone, +03/-97 ipsdienol], we found no significant difference in trap catches among basal area treatments for bark beetles and their predators. Similarly, when trees were baited (Dendroctonus brevicomis LeConte lure: myrcene, exo-brevicomin and frontalin), we found no significant difference for days to first bark beetle attack. Surveys of long-term thinning treatments found evidence of bark beetle attacks only in unthinned plots (approximately 37 m2/ha basal area). We discuss our results in terms of management implications for bark beetle trapping and control.     

Ethirimol-sensitivity in populations of Erysiphe graminis from plots of spring barley

Barley plots, cv. Proctor were sown with either ethirimol-treated or untreated seed. At seedling emergence, plots were inoculated with isolates of Erysiphe graminis either sensitive or insensitive to ethirimol, or left uninoculated. Mildew samples taken from the coleoptile leaves of seedlings, and later from leaf 6 (next but one to the flag leaf) were compared for ethirimol sensitivity using probit analysis. Probit lines were derived using ‘Wadley's analysis’. This analysis uses the number of survivors to estimate the total number of individuals originally present. In the test for ethirimol sensitivity a count of colonies on inoculated test leaves was taken to represent survivors. Microscopic counting of the original inoculum was thus avoided. The analyses snowed that the initial leaf inoculation treatments established mildew populations in the plots, which differed considerably in ethirimol sensitivity. Some 6 wk after inoculation the levels of sensitivity in these populations remained unchanged even though inoculum coming into the experiment from external sources was often much more insensitive than the mildew in some plots. Probit lines of response to ethirimol had shallow slopes, showing that large variability exists in the pathogen for this character.     

Sub-lethal effects of deltamethrin residues on the within-crop behaviour and distribution ofCoccinella septempunctata

The behaviour and distribution of adultCoccinella septempunctata L. (Coleoptera: Coccinellidae) were recorded in two plots of winter wheat infested with the cereal aphidsSitobion avenae (F.) andMetopolophium dirhodum (Walk.) (Homoptera: Aphididae). One plot was sprayed with the pyrethroid insecticide deltamethrin at a rate of 6.25 g a.i./ha and the other was left unsprayed. Single ladybird beetles were released sequentially on the ground at the centre of the sprayed and unsprayed plots and their behaviour and position in the crop canopy were recorded at 30 second intervals for a total of 15 min per beetle. Assessments, with fresh beetles, continued for four days after spray application with a total of eighty ladybird beetles observed. The 15 min period was selected to avoid lethal effects and no ladybird beetles were killed or knocked down as a result of exposure to deltamethrin residues during this period. Significant differences were found between the overall behaviour patterns ofC. septempunctata in the untreated and deltamethrin treated plots up to three days after the spray application. Ladybird beetles exposed to deltamethrin residues were observed to walk and groom significantly more frequently and to rest significantly less frequently than those in the unsprayed plot. Significant differences were also found between the observed distribution of ladybird beetles in the sprayed and unsprayed crop canopies, with higher numbers of observations towards the bottom of the crop canopy and on the ground in the deltamethrin treated plot than in the untreated plot during the first two days after deltamethrin application. Upon the foliage itself, ladybird beetles were observed significantly more frequently on the abaxial leaf surface in the deltamethrin treated crop compared with the untreated crop. The results are discussed in terms of possible evidence for the repellency of deltamethrin toC. septempunctata and also the implications for integrated pest management of changes in predator behaviour and crop distribution resulting from sub-lethal uptake of insecticides.