Relative impact of spider predation and cover crop on population dynamics of Erythroneura variabilis in a raisin grape vineyard

Experimental and correlative evidence has steadily mounted over the past 30 years implicating spiders in the suppression of insect herbivore pests in crop fields. A large body of evidence has also shown that increasing agroecosystem vegetation diversity often influences the abundance of herbivores and their natural enemies. In previous experiments, the abundance of several species of spiders on grapevines in a raisin grape vineyard was twofold enhanced in vineyard plots vegetationally diversified with a cover crop. A concomitant reduction in the abundance of the leafhopper pest Erythroneura variabilis Beamer was observed on grapevines in the diversified plots, but a causal relationship was not established. In the present study, we simultaneously manipulated spider densities (in open‐vine spider exclusion and vine‐shoot enclosures) and ground cover to determine their relative impact on E. variabilis population dynamics. Open‐vine spider exclusion resulted in an average 35% increase in the density of E. variabilis the greatest effect with occurring during the first and second leafhopper generations. The negative impact of spiders on E. variabilis densities was corroborated with vine‐shoot enclosure experiments. Under the conditions of the present study, the cover crop per se did not affect the dynamics of E. variabilis populations on grapevines, despite a 1.6‐fold increase in spider densities on vines in cover crop plots, compared with vines in bare ground plots, probably due to insufficient spider enhancement and low overall E. variabilis abundance during the summer months. The cover crop had little effect on vine macronutrient status (and presumably vine water status). While this study provided further support for the hypothesis that vegetation diversity can enhance spider abundance, this enhancement does not always lead to lower pest densities, thus underscoring the complexity and variability that exists in interactions involving cover crop, spiders, and crop plants and their herbivore pests.     

Immigration of Phytoseiid Mites from Surrounding Uncultivated Areas into a Newly Planted Vineyard

This study reports (1) a faunistic survey of phytoseiid mites observed inside a vine plot and in neighbouring vegetation (other vine plots and uncultivated areas) and (2) dispersal of phytoseiid mites into the plot studied. These data aim to raise some hypotheses concerning natural colonisation of a vineyard by predatory mites. The study was carried out over 3 years (1999, 2000 and 2001) in an experimental plot planted with two cultivars (Grenache and Syrah) and with Sorbus domestica in a framework of agroforestry investigations. Phytoseiid mites were collected in both cultivated and uncultivated areas surrounding the experimental plot, and their dispersal into the plot studied using “aerial” traps. Densities remained quite low compared to previous studies. The main species encountered in the uncultivated areas and in the traps was Typhlodromus phialatus. Despite the low numbers of phytoseiid mites trapped, densities of phytoseiid mites into the vine field increased during 3 years. Typhlodromus phialatus, the species mainly found in the neighbouring uncultivated areas, was rarely found in vineyards. Another morphologically close species was predominant on vines: Typhlodromus exhilaratus. However, Kampimodromus aberrans the main phytoseiid mite species in vineyards of Southern France was not found in the present survey. Hypotheses for this colonisation process are discussed.     

Agroforestry management and phytoseiid communities in vineyards in the South of France

This study deals with the long-term effect of agroforestry management (trees within vine crops) on communities of phytoseiid mites. Several plots were considered: vineyards co-planted with Sorbus domestica or Pinus pinea, monocultures of vines and monocultures of S. domestica or P. pinea. All vine plots included two vine cultivars, Syrah and Grenache. Phytoseiid mites have been surveyed in these plots during several years within the previous 10 years. In 2010, samplings were again carried out in these same plots, from May to September, twice a month. Significantly higher densities of Phytoseiidae were observed on the cultivar Syrah (0.85 phytoseiids per leaf) than on Grenache (0.26 phytoseiids per leaf). Furthermore, significantly higher phytoseiid mite densities were observed in the monocultural grapevine plot than in the two co-planted ones. The main species found was Typhlodromus (Typhlodromus) exhilaratus in all vine plots considered. However, Kampimodromus aberrans was observed in the grapevine plots co-planted with the two trees, but never in the monocultural vine plot. Surprisingly, this phytoseiid species was not found on the co-planted trees, nor in the neighbouring uncultivated vegetation. Several hypotheses are discussed to explain such an unexpected distribution. Furthermore, contrary to what has been observed previously, agroforestry management did not seem to favour phytoseiid mite development, especially on the Grenache cultivar. Again, some hypotheses are developed to explain such observations and density modifications.     

Autumnal emergence of Anagrus wasps,egg parasitoids of Empoasca vitis,from grapevine leaves and their migration towards brambles

• 1 The Anagrus‘atomus’ parasitoid group (Hymenoptera: Mymaridae), associated with Empoasca vitis (Göthe) (Homoptera: Cicadellidae), overwinters on vegetation surrounding vineyards. The emergence of parasitoid adults from grapevine leaves in autumn was studied in north‐eastern Italy, both in relation to the E. vitis egg‐laying period and to the presence of leafhoppers overwintering as eggs on Rubus bushes.
• 2 Autumnal peaks of Anagrus captured using yellow sticky traps were observed first on grapevines and then on brambles. Parasitoid captures in vineyards were observed for more than 1 month after the last first‐instar nymphs of the grape leafhoppers were noticed. Two species belonging to the A. ‘atomus’ group, Anagrus atomus and Anagrus ustulatus, were captured both on grapevines and brambles.
• 3 Parasitoids of the A.‘atomus’ group can emerge from third‐generation grape leafhopper eggs in accordance with two different development time patterns (i.e. normal or delayed). Individuals with delayed emergence required up to 2.2‐fold more time to develop from an egg to adult than individuals with normal emergence. This meant that some parasitoid adults emerged in autumn from eggs of grape leafhopper laid in August.
• 4 A delayed emergence as a result of a slower development ensures that the A.‘atomus’ parasitoid group is synchronized with the egg‐laying of leafhoppers that overwinter as eggs on Rubus spp.
• 5 Consequently, leafhoppers overwintering as eggs on brambles play a key role in the ecology of the relationship between grape leafhoppers and the A.‘atomus’ parasitoid group.

     

Spatial and temporal distribution of Empoasca vitis within a vineyard

1 The intra‐plot spatial distribution of the green leafhopper Empoasca vitis (Goethe) (Cicadellidae, Empoascini) was assessed over three successive growing seasons in a Bordeaux vineyard. Weekly measurements of adult trappings and nymphal counts were performed in a 1.7‐ha plot on 130 sampling points. 2 Statistical and geostatistical analyses revealed inconsistent spatial distributions of adults and nymphs in spring, but consistent spatial distributions in summer, which were identical every year. 3 Similarities between spatial distributions of the mobile adults and the sedentary and aggregated nymphs strongly suggest that adults disperse inside the plot to areas preferred for egg deposition. 4 The similarity of summer populations among years suggests that this insects distribution is based on (perennial) differences in plot characteristics.     

Effects of interspecific competition on development and reproduction in two giant water bugs,Diplonychus japonicus vuillefroy andDiplonychus major esaki (Hemiptera: Belostomatidae)

We studied the interpecific competition between 2 species of predatory aquatic bugs, Diplonychus japonicus and D. major by conducting a field experiment. We set up 3 types of experimental plots in the paddy fields where D. major predominated. The two plots contained single species of either D. japonicus or D. major, respectively, and one plot had both species in equal number. We compared the development and the reproductive performance between plots in each species. In D. japonicus, the number of eggs and early instar nymphs were significantly smaller in the plots containing both species than in the monospecific plots. However, the numbers of late instar nymphs and newly emerged adults were not significantly different between plots. The proportions of starved nymphs in both plots were larger than those in the D. japonicus's natural habitats. The final densities of adults in both plots were lower than those in the natural habitats. These results suggest that lower density of D. japonicus in these paddy fields is due to the lack of available food for nymphs rather than the effects of interspecific competition with D. major. In D. major, significant differences were not found in the number of eggs, each instar nymphs and adults. These results suggest that the effects of interspecific competition did not affect the reproductive performance of D. major.     

5种茶园秋冬季天敌与假眼小绿叶蝉空间关系密切程度的差异

为了明确与假眼小绿叶蝉空间关系密切的天敌种类,为合理利用和保护天敌提供科学依据。运用地学统计学分析方法计算白毫早茶园、黄山大叶种茶园、农抗早茶园、平阳特早茶园和乌牛早茶园秋冬季假眼小绿叶蝉和其主要6种天敌地统计学半变异函数的变程。使用灰色系统分析方法对计算结果进行灰色关联度分析,并对分析结果进行标准化。以标准化后的密切指数大小评判天敌与假眼小绿叶蝉空间关系的密切程度。结果是：1）、黄山大叶种茶园和农抗早茶园与假眼小绿叶蝉空间关系密切的前3位天敌是粽管巢蛛、鳞纹肖蛸和斜纹猫蛛,但位次不同。2）、白毫早茶园前3位天敌是鳞纹肖蛸、斜纹猫蛛和锥腹肖蛸,前2种与黄山大叶种和农抗早茶园相同。3）、平阳特早茶园前3位天敌是鳞纹肖蛸、粽管巢蛛和草间小黑蛛,前2种与黄山大叶种和农抗早茶园相同。4）、乌牛早茶园前3位天敌是粽管巢蛛、草间小黑蛛和三突花蟹蛛,只有粽管巢蛛与黄山大叶种和农抗早茶园相同。根据5种茶园同种天敌密切指数之和以及同种天敌位次之和评判,与假眼小绿叶蝉空间关系密切的天敌均是鳞纹肖蛸、粽管巢蛛和斜纹猫蛛。天敌位次的变化主要是害虫和天敌数量之比的比值变化。害虫个体数与某种天敌个体数之比的比值越小,天敌与害虫的跟随关系则越密切。密切原因与食饵资源短缺有关。     

Colonization of vineyards by Kampimodromus aberrans (Oudemans) (Acari: Phytoseiidae): dispersal from surrounding plants as indicated by random amplified polymorphism DNA typing

Abstract

• 1 Kampimodromus aberrans (Oudemans) is the most important predatory mite found in vineyards of southern France. This mite also occurs in surrounding uncultivated areas from where it disperses to colonize adjacent vineyards
• 2 To determine accurately origins of immigrant mites and to study their establishment in vineyards, a study using RAPD markers (Random Amplified Polymorphism DNA) was performed. Females of K. aberrans were sampled on leaves collected in an experimental vineyard, and from several adjacent areas including neighbouring vine plots and natural plants, both of which harboured high densities of the mite. Samples were taken in May and July before and after major dispersal of K. aberrans into the experimental plot occurred.
• 3 For both dates, genetic distances within population were lower than between populations and three groupings of mites were observed. Strong relationships were observed between (1) females from different parts of the same experimental vineyard (variety Cabernet‐Sauvignon), (2) females from several plants in the woody margin neighbouring this experimental plot, and (3) females from two neighbouring vineyards (variety Carignan). Populations seemed to be structured and no correlation between genetic and geographical distances was observed. Hence, definitive conclusions about origins of migrants were not possible.
• 4 Once in a vineyard, mites are probably exposed to selection pressures (i.e. pesticide applications or vine variety characteristics) that largely determine differentiation of populations. Thus, despite many immigrants moving into vineyards, our study indicated that there was limited survival or reproduction of immigrants. Further studies of within vineyard selection factors and impacts on immigrant mites are needed to determine the influence of natural colonization on grape pest management.

     

Sowing of margin strips rich in floral resources improves herbivore control in adjacent crop fields

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Plant neighbours mediate bird predation effects on arthropod abundance and herbivory

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Colonization of vineyards by phytoseiid mites: their dispersal patterns in the plot and their fate

The effect of wind and woody margins on the dispersal and population dynamics of phytoseiid mites was studied in a vine plot for a period of two years. Mites were sampled in the plot and in the surrounding vegetation (crops and natural vegetation) in order to determine phytoseiid mite abundance. The surrounding vegetation was considered to be a reservoir of phytoseiids from where the vine plot could be invaded. Directional and non-directional soil and aerial traps were placed in the plot to determine predatory mite exchange between the two areas. Colonization of the plot occurred in two stages: first, mite migration into the plot, followed by their establishment. The two-year study partially clarified the first of these two stages. Kampimodromus aberrans was the main species caught in the aerial traps. Phytoseiid mite dispersal within the vine plot seemed to be affected by both wind (direction, intensity and regularity) and phytoseiid mite density in the woody margin. However, the woody margin had a large effect only over a short distance. Some observations pointed towards an effect of other reservoir areas but it was not possible to characterize these. The population density of the phytoseiid mites in the plot increased from 1996 to 1998, but these increases are much smaller than one would expect on the basis of the number of mites migrating by air in the plot. Moreover, blocks where most mites were trapped were not the blocks where densities of phytoseiid mites on vine leaves were the largest. It therefore seems likely that not all migrants were able to develop. Their settlement pattern was not determined and this could constitute a potential research focus for the future.     

Ground cover and floral resources in shelterbelts increase the abundance of beneficial hymenopteran families

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Effects of mowing frequency on densities of natural enemies in three Pacific Northwest pear orchards

Effects of mowing frequency on ground cover composition and on numbers of predators, parasitoids, and select phytophagous arthropods in the ground cover of three reduced‐insecticide pear orchards were determined. Concurrent samples taken in the tree canopy (with beating trays) and in the herbicide strips on the orchard floor (with pitfall traps) tested whether counts of natural enemies in these two habitats were also affected by mowing regime. A reduction in frequency of mowing from two to three times per month (= control) to once per month or once per growing season led to increased cover of grasses, broadleaf plants, and broadleaf plants in flower. Sweep net samples of natural enemies in the ground cover were dominated numerically by spiders (Araneae), parasitic Hymenoptera, and predatory Heteroptera, with lesser numbers of other taxa (Syrphidae, Neuroptera, Coccinellidae). Predators and parasitoids showed substantial increases in numbers associated with decreased mowing frequency. Sweep net counts of aphids, Lygus spp. (Heteroptera: Miridae), and leafhoppers/planthoppers, all potential prey of predators, also increased significantly with decreased mowing frequency. In the pitfall samples, only the European earwig (Forficula auricularia L.) (Dermaptera: Forficulidae) exhibited a change in counts associated with mowing treatment; numbers of earwigs in pitfall traps declined as mowing frequency decreased. For the beat tray samples, mean tray counts for most natural enemy taxa were higher in the less frequently mowed plots, but significantly (P < 0.05) so only for two taxa: spiders and a predatory mirid, Deraeocoris brevis (Uhler) (Heteroptera: Miridae). It remains to be determined whether biological control of pests in the tree canopy can be enhanced by manipulating mowing frequency. Questions raised by this study include whether there is extensive movement by natural enemies between the ground cover and tree canopy, and whether plot size affects the likelihood of showing that mowing frequency influences predator densities in the tree canopy.     

A Simulation model for the arrowhead scale (Hemiptera: Diaspididae) population dynamics on citrus trees in relation to pest-management programs

1. A mathematical model was constructed describing population dynamics of the arrowhead scale, Unaspis yanonensis Kuwana. The population occurrence patterns simulated by the model from 1971 to 1976 were relatively consistent with the actual findings in the field.
2. The effects of control tactics for this pest were examined on the basis of the model.
3. Effective timing of insecticide (petroleum oil and organophosphorous insecticide) application was indicated to be 40 days after the initial appearance of 1st-instar nymphs in both the 1st and 2nd generations of the host.
4. The number of overwintering adult females in May of the next year (i.e., the starting point of the next year's population) decreased linearly with the increment in the degree of insecticide coverage. The pest populations were expected to be kept to low densities by petroleum oil sprays alone for the 1st generation when overall, complete coverage was accomplished.
5. Examination of the effects of two introduced parasitoids, Aphytis yanonensis and Coccobius fulvus, showed that they were able to control the scale population by themselves when more than 70% parasitism was achieved. When petroleum oil was applied to overwintering adults (termed winter petroleum oil) at the degree of coverage of 0.8, host populations were reduced by ca. 60% parasitism. When the winter petroleum oil was combined either with additional petroleum oil 40 days after the initial appearance of 1st-instar nymphs of the 1st generation or with an organophosphorous insecticide 40 days after the initial appearance of 1st-instar nymphs of the 2nd generation (degree of coverage=0.8 in each case), 40% parasitism led the reduction of the pest population.
6. The most desirable control program was considered to be one in which winter petroleum oil was used every year and additional petroleum oil or an organophosphorous insecticide was also used in those years when host density was high.

     

Intercropping with aromatic plants hindered the occurrence of Aphis citricola in an apple orchard system by shifting predator–prey abundances

Enhancing biological control of pests through habitat management in agricultural systems has gained increasing attention. Three different aromatic plants, ageratum (Agerarum houstonianum Mill.), French marigold (Tagetes patula L.) and basil (Ocimum basilicum L.), were chosen as intercrops for apple orchards to evaluate the effects of intercropping on Aphis citricola Van der Goot and its local natural enemies in China. We found that compared with natural vegetation, A. citricola abundance was significantly decreased by 29.26%, 35.80% and 38.28% in plots intercropped with ageratum, French marigold and basil, respectively. The number of natural enemies of A. citricola in plots intercropped with T. patula and O. basilicum were significantly higher than in plots of natural vegetation. Equally important, intercropping affected the composition of natural enemies and the population dynamics of A. citricola and its natural enemies. Annual cumulative numbers of natural enemies were significantly negatively correlated with A. citricola annual cumulative individual numbers except for O. tantillus. Our results demonstrate that intercropping with aromatic plants could be an effective method for biological control of A. citricola in apple orchards.     

Influence of hop yard ground flora on invertebrate pests of hops and their natural enemies

A 3‐year study in Washington State, USA examined the influence of hop yard ground flora both on the invertebrate pests of hops [including hop aphid (Phorodon humuli Schrank), two‐spotted spider mite (Tetranychus urticae Koch) and hop looper (Hypena humuli Harris)] and on their natural enemies. Each year half of the experimental plots were sown with a mixture of ‘insectary’ plants [including California poppy (Eschscholzia californica von Chamisso), dwarf cornflower (Centaurea cyanus L.) and buckwheat (Fagopyrum esculentum Moench)]. Season‐long average cover provided by the flowering mixture ranged from 2% to 26%, with some blooms being present for most of the season in each year. In terms of vegetation, the other main differences between cover‐cropped and control plots were in the proportions of bare soil (which was always significantly higher in control plots) and the percentage of Chenopodium album L., which was significantly higher in the cover‐cropped plots in two of the three seasons. Populations of spider mites on hop foliage were significantly lower in cover‐cropped plots than in control plots in 2 of 3 years, while mite numbers in the cones at harvest were generally low and usually did not differ between treatments. Responses of hop aphids were much more variable, with no consistent treatment effect on either leaf or cone infestations. Larval populations of hop looper tended to be higher in cover‐cropped plots in the first two generations, but usually not in the third (final) generation. Of the beneficial invertebrates, spiders and nabids consistently reached higher average densities in the ground flora of cover‐cropped plots than in control plots in all 3 years, while anthocorids, geocorids and parasitic hymenoptera reached higher mean densities in the former plots in 2 of 3 years. Adult coccinellids were higher in cover‐cropped plots only in 2006.     

Eriophyoid mite damage in Vitis vinifera (grapevine) in Australia: Calepitrimerus vitis and Colomerus vitis (Acari: Eriophyidae) as the common cause of the widespread ‘Restricted Spring Growth’ syndrome

Leaf and shoot distortions and retarded shoot growth in Vitis vinifera L. prevalent in Australian vineyards in early spring, were investigated in replicated field experiments over 3 yrs. Leaf distortion and retarded shoot growth were identified as damage due to feeding of extremely high populations of over-wintered deutogynes of Calepitrimerus vitis (Nalepa) (grape rust mite). This damage was hitherto known in Australia as Restricted Spring Growth (RSG), a syndrome comprising several growth abnormality symptoms, none with a clearly identified cause or a successful treatment. A successful treatment against C. vitis was used to selectively eliminate RSG, while C. vitis numbers were recorded using a validated trapping technique; intercepting deutogynes migrating from winter shelters in the wooden vine structure, to emerging green tissues. Severe leaf distortion was associated with >400 C. vitis deutogynes per spur, while >1000 per spur had the added effect of severely retarding shoot growth. A 43.0–47.2% shoot length reduction was recorded for Cabernet Sauvignon, 27.1–32.8% for Sauvignon Blanc, when 4–6 leaves were separated. Symptoms were most prominent up to 8–9 separated leaves, however 24.7–30.4% shoot length reduction was still evident at flowering, and 12.8% circa fruit set. C. vitis effect on vine fruitfulness, and yield parameters at fruit set, were also studied. Once successfully treated to prevent C. vitis damage, poor bud burst remained evident in some vineyards. Surveys of unburst buds from such vineyards revealed presence of Colomerus vitis (Pagenstecher) (grape bud mite). When Col. vitis numbers in unburst buds reached 100–500 per bud, apical meristems of primary, and commonly also secondary buds were dead, preventing bud burst. The remaining living scale tissue was distinctly scarred. Bud and associated shoot damage were documented. Retarded shoot growth and leaf distortion, previously attributed to RSG, are misdiagnosed C. vitis spring feeding damage. Clustered high infestations of Col. vitis can cause bud-axis necrosis, bud burst failure, shoots with short basal internodes, and short, thin, zigzagged shoots with absent fruit clusters; all previously considered RSG.This revised version was published online in May 2005 with a corrected cover date.     

Field observations of the effects of fenitrothion and Metarhizium anisopliae var. acridum on non-target ground dwelling arthropods in the Sahel

The effect of the chemical insecticide, fenitrothion, and a mycoinsecticide based on Metarhizium anisopliae var. acridum on the activity of non-target epigeal arthropod scavengers was investigated in areas of open savannah in southeast Niger Republic, West Africa. Both insecticides were applied as full cover sprays to unreplicated 800 ha plots to assess their season-long control of Sahelian grasshoppers. Compared with control plots, fenitrothion caused an immediate but temporary reduction in grasshopper numbers, whereas M. anisopliae var. acridum provided delayed but prolonged control. Scavenging rates of pyrethroid-killed grasshoppers placed along transects in unsprayed plots and those treated with fenitrothion and M. anisopliae var. acridum at various intervals after spraying were assessed. In the fenitrothion plot, an immediate reduction in scavenging activity occurred that was still apparent after 40 days at the plot center, although recovery at the plot edges was more rapid. By contrast scavenging rates remained high over equivalent areas in the M. anisopliae var. acridum and two untreated plots. Concurrent to the scavenging study, counts of grasshopper cadavers resulting from the spray treatments were conducted. These counts revealed that the density of grasshopper cadavers remained low throughout the M. anisopliae var. acridum plot and explained <1% of the reduction in live grasshoppers resulting from treatment, compared with >20% in the fenitrothion plot. This shortfall in grasshopper cadavers resulting from the spray treatment in the M. anisopliae var. acridum plot was unexpected because in a monitoring study, fungus-killed (unlike pyrethroid-killed) grasshoppers were unattractive to scavengers and readily persisted in this plot, and thus should have become apparent. Given we did not observe significant grasshopper dispersal, the scarcity of cadavers generated in the M. anisopliae var. acridum plot, together with unquantified visual observations, suggests that predation of infected but living grasshoppers was high. Our data provide circumstantial evidence that the different effects of chemical and biological grasshopper control on grasshopper natural enemies may influence the efficacy of large-scale treatments.     

Assessing the short‐term impact of an insecticide (Deltamethrin) on predator and herbivore abundance in soybean Glycine max using a replicated small‐plot field experiment

Abstract A greater understanding of the relative impact of insecticide use on non‐target species is critical for the incorporation of natural enemies into integrated pest management strategies. Here we use a small‐plot field trial to examine the relative impact of an insecticide on herbivores and predators found in soybean (Glycine max L.), and to highlight the issues associated with calculating impact factors from these studies. The pyrethroid insecticide (Deltamethrin) caused a significant reduction in invertebrate abundance in the treated plots, and populations did not recover to pre‐treatment levels even 20 days after spraying. To assess the relative impact of the spray on arthropods we first examined the mean difference in abundance in each plot before and after spraying. All herbivores decreased in abundance in the sprayed plots but increased in the control plots after spraying. Most predators (excluding hemipterans) showed a decrease in the control plots but a proportionally greater decrease in the sprayed plots. Next we examined the corrected percentage population reduction calculated using Abbott's formula. All predators (including Araneae) experienced a greater reduction (mean 87% ± 3.54 SE) than herbivores (mean 56% ± 4.37 SE) and Araneae alone (mean 71% ± 8.12 SE). The range in values across the plots varied and made categorising overall impact subjective for some taxa. Despite the constraints associated with small‐plot trials, by using a combination of impact factors and examining community‐level response across time, we did get some indication of the likely impact of this insecticide if used in a commercial situation.