Identification of aphid species (Hemiptera: Aphididae: Aphidinae) using a rapid polymerase chain reaction restriction fragment length polymorphism method based on the cytochrome oxidase subunit I gene

Abstract  The identification of immature aphids is often difficult or impossible. This can be a problem when there is a need for a rapid and accurate diagnosis of any aphid life stage, such as for quarantine inspections and horticultural surveys. A polymerase chain reaction restriction fragment length polymorphism technique is described on the mitochondrial cytochrome oxidase subunit I (COI) gene to develop a molecular identification key for immature aphids from Victoria, Australia. The restriction enzymes HpyCH4 IV, Dra I, Hinf I, Taq I and Ssp I characterised 26 haplotypes that corresponded to 25 aphid species commonly found in southern Australian aphid surveys, including the currant-lettuce aphid Nasonovia ribis-nigri (Mosley) that has recently invaded Australia, presumably from New Zealand. Overseas specimens of Aulacorthum solani (Kaltenbach) and N. ribis-nigri showed no significant sequence difference when compared with their Australian counterparts. The COI gene provides a useful marker for diagnostic aphid surveys.     

Development of methods to evaluate susceptibility of soybean aphid to imidacloprid and thiamethoxam at lethal and sublethal concentrations

The soybean aphid, Aphis glycines Matsumura (Homoptera: Aphididae), is a recent introduction (2000) from Asia and has become a serious soybean [Glycine max (L.) Merr. (Fabaceae)] pest in North America. Seed treatments using the neonicotinoid insecticides, imidacloprid and thiamethoxam, have been suggested as a method of control, and the use of these insecticides is becoming widespread. As a consequence, there is increased potential to select for resistance to these compounds. In the case of soybean aphids, baseline susceptibility to neonicotinoid insecticides and standardized methods for bioassay are lacking. A bioassay technique that uses excised soybean leaves immersed in an insecticide solution was developed to determine systemic insecticidal activity at lethal and sublethal concentrations. Mortality and population growth inhibition were evaluated after 7 days. Life table parameters were calculated by exposing 1‐day‐old aphids to three concentrations of thiamethoxam. Aphid mortality and nymph production were recorded daily until the entire cohort collapsed. Soybean aphid age‐specific survivorship, fecundity, net reproductive rate, longevity, intrinsic rate of increase, discrete daily growth rate, and life expectancy were all significantly reduced at higher thiamethoxam concentrations. Soybean aphid response to both insecticides was similar, and both compounds were very toxic with LC₅₀s of 31.3 and 16.9 ng ml^?1 and EC₅₀s of 6.3 and 5.4 ng ml^?1 for imidacloprid and thiamethoxam, respectively. These results indicate that the methods developed in this study had negligible impact on the life table estimates measured and can be used to develop a baseline of susceptibility as a benchmark for subsequent resistance monitoring. Given the rapid and widespread adoption of this new insecticide class, vigilant monitoring for changes in susceptibility will be essential to its long‐term sustainability.     

Comparison of bioassay techniques for determining baseline susceptibilities to imidacloprid for green apple aphid (Homoptera: Aphididae)

The susceptibility of a clone of green apple aphid, Aphis pomi (De Geer), to the neonicotinyl insecticide imidacloprid was determined by direct and indirect bioassay techniques. Aphid numbers were assessed on potted apple seedlings treated with various concentrations of imidacloprid, adults were dipped in test solutions as per the Food and Agriculture Organization protocol, or nymphs and adults were reared on treated apple leaf disks. Effective concentrations required to kill half of the test population (EC50) varied depending on the bioassay technique, ranging from as low as 0.064 ppm for first instars reared for 3 d on treated leaf disks to 1.79 ppm for adult apterae dipped in solutions of imidacloprid and held for 24 h on clean leaf disks. When imidacloprid was directly applied to aphids, mortality continued to increase over 3 d, but the difference was not statistically significant between day 2 (1.36 ppm) and day 3 (1.19 ppm). Toxicity of neonicotinyls to aphids is expressed rather slowly and primarily after oral ingestion. The effect of imidacloprid on reproduction of green apple aphid was also assessed for adult apterae reared on treated leaf disks. Contrary to previous reports, our results demonstrated that imidacloprid does not have a direct negative effect on the reproductive physiology of this species. Negative effects can mostly be attributed to the antifeedant activity of this compound and the protracted time to death. The results of this study contribute to a better understanding of the most suitable techniques for assessing aphid mortality after exposure to these new insecticides and provides a baseline susceptibility to imidacloprid for green apple aphid.     

Effect of fungicide application on activity of Neozygites fresenii (Entomophthorales: Neozygitacaea) and cotton aphid (Homoptera: Aphididae) suppression

The development of resistance in aphid populations highlights the importance of biological control as a pest management tactic. Four treatments were evaluated to determine the effects of pesticides on the population dynamics of Aphis gossypii Glover and Neozygites fresenii (Nowakowski) Batko: (1) weekly applications of the insecticide imidacloprid (Provado 1.6 F); (2) weekly applications of the fungicide chlorothalonil (Bravo 720); (3) applications of imidacloprid (Provado 1.6 F) when aphid densities exceeded 30 aphids per leaf, and (4) untreated control. Differences in aphid density among the four treatments were shown only to be significant during the 1997 growing season; however, aphid densities were greater in the chlorothalonil treatment than in the other treatments during each growing season. Percentage of N. fresenii-killed aphids was most often highest in the chlorothalonil treatment as well. The fungal epizootic caused by N. fresenii was delayed approximately 1 wk in the chlorothalonil treatment when compared with the other treatments. This delay allowed the aphids to temporarily escape suppression by the fungus and to continue to increase in density until the density-dependent effects of the epizootic overwhelmed the aphid population. N. fresenii also appeared to persist in the system when imidacloprid was in use and does appear responsible for initial aphid reductions. Treatment did not appear to have a large influence on yield outcome. Yield was variable from year to year and from location to location.     

Movement, toxicity, and persistence of imidacloprid in seedling Tabasco pepper infested with Myzus persicae (Hemiptera: Aphididae)

Application of imidacloprid to the soil in which Tabasco pepper, Capsicum frutescens L., seedlings were growing was highly effective against the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae). In just 48 h after the soil drench, aphid numbers on treated plants declined from 292.1 to 33.0 per plant, a reduction of 89%. By 72 and 96 h after the application, the reductions were 97 and 100%, respectively. Reductions in green peach aphid numbers also indicated that imidacloprid readily moved throughout the Tabasco pepper plant. Although, initial green peach aphid reductions at 24 and 48 h after imidacloprid application to soil, were greater on the lower leaves than on the upper leaves, by 72 h toxicity was high throughout the plant. At 48 h, overall green peach aphid reduction on seedlings grown in wet soil was significantly higher than that on plants growing in the drier soil. Regardless of soil moisture or leaf location, no live green peach aphids were detected on treated seedlings after 96 h. After the initial uptake period, toxicity to green peach aphid remained high for 5 wk. Under Tabasco pepper production conditions in Central America, the greatest need for aphid management is just after transplanting. Imidacloprid soil drenches before transplanting should offer the Tabasco pepper producer an extended period of aphid-free production.     

Sources of variation in the interaction between three cereal aphids (Hemiptera: Aphididae) and wheat (Poaceae)

The relative contributions of host plant, herbivore species and clone to variation in the interaction between cereal aphids and wheat were investigated using five clones each of three species, Rhopalosiphum padi (Linnaeus), Sitobion avenae (Fabricius) and Schizaphis graminum (Rondani), on seedlings of two cultivars of Triticum aestivum L. and one cultivar of Triticum durum Desf. More individuals and biomass of R. padi than of the other two species were produced on seedlings. The three wheat cultivars lost similar amounts of biomass as a result of infestation by aphids, with the amount lost depending on aphid species: S. avenae caused the lowest loss in biomass. Variation in aphid biomass production was due mostly to differences among aphid species (70%), less to the interaction between wheat type and aphid species (7%), and least to aphid clone (1%). The specific impact of the aphids on the plants ranged from 1.7 to 3.7 mg of plant biomass lost per mg of aphid biomass gained, being lowest for R. padi and highest for S. graminum. Variation in plant biomass lost to herbivory was due mostly to unknown sources of error (95%), probably phenotypic differences among individual seedlings, with 3% due to aphid species and none attributable to aphid clone. For these aphid-plant interactions, differences among aphid clones within species contributed little to variation in aphid and plant productivity; therefore, a small sample of clones was adequate for quantifying the interactions. Furthermore, one clone of each species maintained in the laboratory for about 200 parthenogenetic generations was indistinguishable from clones collected recently from the field.     

Field‐level effects of preventative management tactics on soybean aphids (Aphis glycines Matsumura) and their predators

A 2‐year field experiment was conducted in northern Illinois to evaluate the effects of host plant resistance and an insecticidal seed treatment (thiamethoxam) on soybean aphids, Aphis glycines Matsumura and their predators. Densities of soybean aphids varied between the 2 years of the experiment. During both years, resistant plants experienced fewer cumulative aphid days than susceptible plants. Populations of soybean aphids on resistant plants rarely exceeded the economic injury level of 250 soybean aphids per plant. The use of thiamethoxam reduced cumulative aphid days in 2007, but not in 2008. Although soybean aphids reached densities that were sufficient to cause yield‐loss for untreated and susceptible plants, no yield‐benefit was associated with using the two management tactics in either year. This latter finding suggests that densities of soybean aphids need to be greater and sustained for a longer period of time than what we observed if the two management tactics are expected to provide a yield‐benefit. Monitoring natural enemies revealed that densities of key aphidophagous predators were relatively unaffected by host plant resistance or thiamethoxam; the effect of these management tactics on densities of predators, as well as the effectiveness of the method used to sample predators, is discussed.     

Systemic control efficacy of neonicotinoids seeds dressing on English grain aphid (Hemiptera: Aphididae)

English grain aphid, Sitobion avenae (Fabricius) (Hemiptera: Aphididae), is an important pest of wheat (Triticum aestivum L.), and is usually controlled by intensive foliar sprays of pesticides under field conditions. In order to reduce labour costs and increase the utilization of pesticides, neonicotinoids seed treatment was studied as a simple and accurate control technology for S. avenae. We evaluated the mortality of imidacloprid, acetamiprid, thiamethoxam, clothianidin, nitenpyram and dinotefuran to the English grain aphid by seed dressing methods in the laboratory, and found that the toxicity with that LC₅₀ of clothianidin (20.97?a.i.?g/100?kg seeds) and thiamethoxam (28.84?a.i.?g/100?kg seeds) to S. avenae are higher than other neonicotinoids. LC₅₀ values of nitenpyram, imidacloprid and acetamiprid ranged between 120?a.i.?g/100?kg seeds and 210?a.i.?g/100?kg seeds. Dinotefuran showed the lowest toxicity with LC₅₀ value 565.76?a.i.?g/100?kg seeds to English grain aphid. Field plot experiments were conducted to investigate the control efficacy of neonicotinoids seed treatment for the aphid, and the effects on growth of wheat. Field observations indicated that clothianidin and thiamethoxam provided the better control efficacy on the English grain aphid than imidacloprid, and had no influence on wheat seedling emergence. These results showed that seed treatment by neonicotinoids was effective against S. avenae throughout the growth period, furthermore, thiamethoxam and clothianidin were the effective and safe alternative options for S. avenae management in the crop.     

THE INFESTATION OF WINTER LETTUCE BY APHIDS AND ITS CONTROL

Observations have been made on the infestation by aphids of winter lettuce at Imperial College Field Station, Slough, for the seasons 1947–8 and 1949–54. The effects of transplanting and of the use of insecticides have been studied.
Plants drilled in September where they were to mature were ready for cutting a little earlier than those transplanted in November, but in years when aphids were numerous the drilled lettuces were heavily infested and very few of them hearted.
The infestation of young crops varied from year to year; in some winters it fell to a low level, in others it increased rapidly and persisted with serious effect on the crop. In some years lettuce mosaic virus was also prevalent. The dominant aphid species was Nusonovia ribis-nigri (Mosley).
An early and persistent attack, even in the absence of virus disease, much reduced the number of hearted plants and their average weight. A late attack by winged aphids in early spring sometimes spoilt fully hearted lettuces.
Dipping the plants in nicotine solution at the time of transplanting in November reduced aphid infestation; dusting with benzene hexachloride proved more effective.
If transplanting was delayed until February or March a relatively clean crop could be produced by insecticide treatment, but losses from fungal disease were usually high.     

Sublethal effects of selected insecticides on fecundity and wing dimorphism of green peach aphid (Hom., Aphididae)

Effects of sublethal concentrations (LC₂₅) of six insecticides (imidacloprid, rotenone, fenvalerate, abamectin, pirimicarb and azadirachtin) on fecundity and wing dimorphism of the green peach aphid, Myzus persicae (Sulzer), were studied both under laboratory and greenhouse conditions. In the laboratory, aphid reproduction reduced by 44.29% and 54.01% when rotenone and abamectin treatments were applied at sublethal dose, respectively, and sublethal fenvalerate application resulted in markedly lower average reproduction per female per day compared with control. Reproductive duration of aphid treated with abamectin significantly decreased by 44.19%. But in the greenhouse, there were no evident differences in the aphid fecundity and reproductive duration between treatments and control. Life‐table parameters also demonstrated that the six insecticides at sublethal doses did not stimulate the aphid reproductive potential. In the laboratory, after being exposed to sublethal doses of imidacloprid and fenvalerate, the proportions of alate progeny in aphid progeny were significantly higher than that of the control. In the greenhouse, percentages of alate offspring from the mother aphids treated with imidacloprid, fenvalerate and abamectin increased pronouncedly compared with control. Mortality rates of offspring in the nymphal stages from adults treated with insecticides revealed no significant changes between laboratory and greenhouse. The developmental time in days of the offspring varied in all treatments. Mechanisms of insecticide‐induced resurgence are discussed.     

Interaction between plant resistance and predation of Aphis fabae (Homoptera: Aphididae) by Coccinella septempunctata (Coleoptera: Coccinellidae)

We investigated the compatibility of host plant resistance to the black bean aphid in the faba bean crop with the use of the predatory ladybird beetle for biological control under laboratory and greenhouse conditions. Greenhouse experiments indicated that apteriform Aphis fabae reproduced on Vicia faba major (susceptible) and on 79S4 (partially resistant) cultivars at different rates. During the entire experimental period, aphids built up higher populations on V. faba major than on 79S4 cultivar. Aphid numbers on 79S4 were about 37% of those on V. faba major after 14 days. Release of a newly hatched Coccinella septempunctata larva onto each plant significantly reduced aphid density to 32.8% and 57.2% on V. faba major and 79S4 on day 14, respectively. Partial resistance combined with predation was more effective in lessening aphid numbers on faba bean than either the predator or the plant resistance alone. Laboratory tests showed that prey, A.   fabae , raised on susceptible cultivar was more suitable for the predator as food source, enhancing the development rate and fecundity than aphids fed on the partially resistant cultivar. Consumption of aphids reared on susceptible cultivar significantly increased the female fecundity and fertility of C. septempunctata by 37.7% and 33.2%, respectively, more than those fed with aphids from partially resistant cultivar. Pre-oviposition time was shortened by 4.5 days, and oviposition period was extended by 11.4 days. Feeding the predator on aphids from the partially resistant cultivar prolonged the embryonic larval developmental time and the time required from egg laying to adult emergence by 19.8, 10.1 and 32.5 h, respectively. Adult longevity was not influenced by the aphid source. The results are discussed in relation to the compatible utilisation of host plant resistance and biological control in the integrated management of aphids.     

Prevalence of Pandora neoaphidis (Zygomycetes: Entomophthorales) infecting Nasonovia ribisnigri (Hemiptera: Aphididae) on lettuce crops in Argentina

Lettuce crops, Lactuca sativa, organically produced in La Plata, Argentina, were sampled in order to determine the prevalence of fungal diseased aphids. Nasonovia ribisnigri was the only aphid detected and its occurrence was highly variable. The fungal pathogen Pandora neoaphidis (Entomophthoromycotina: Entomophthorales) was the only pathogen detected. We recorded a maximum of 34.2 aphids per plant and the highest rate of fungal prevalence was 56.6% (n = 30) (aphids infected/total aphids). Infected aphids were observed in all sampling sites. No differences of infection rates were detected between the center and the edge of crops. Host density was an important factor determining infection. The majority of host population was comprised of nymphs which were the most infected in terms of individuals per habitat unit (lettuce plant), but considering the proportion of infected aphids per stage of development, the prevalence of infection in nymphs and adults was similar.     

Characterization of nicotinic acetylcholine receptors from the insects Aphis craccivora, Myzus persicae, and Locusta migratoria by radioligand binding assays: relation to thiamethoxam action

Thiamethoxam, a new neonicotinoid insecticide acting at nicotinic acetylcholine receptors, was characterized in competition binding assays with [3-H]-imidacloprid, a specific nicotinic ligand, using membranes from the aphids Aphis craccivora and Myzus persicae, and from the locust Locusta migratoria. In all insects, Scatchard analysis suggested two binding sites for imidacloprid with Kd values in the range of 1 nM and 10 nM, respectively. The Hill values were significantly below 1 (range of 0.63 to 0.85). In contrast to imidacloprid and nicotine, the potency of thiamethoxam to displace [3-H]-imidacloprid varied considerably among these insects. Thiamethoxam was more active than nicotine on Aphis receptors but 100-fold less in Locusta, a nontarget insect. Comparable relations were found to nithiazine. In Myzus, the inhibition curve for thiamethoxam was shallow. This suggested a heterogeneous receptor population displaying a range of binding affinities to thiamethoxam in this aphid. In all three insects, the other neonicotinoid insecticides studied competed with [3-H]-imidacloprid in the same order: thiacloprid > imidacloprid > or = acetamiprid > nitenpyram. N-Methylation of imidacloprid strongly reduced the affinity to the imidacloprid site, whereas N-demethylation of thiamethoxam resulted in a comparable increase of affinity. Supplementary assays were performed with (-)-[3-H]-nicotine and [3-H]-alpha-bungarotoxin on locust membranes. Overall, the data suggested that the outstanding insecticidal properties of thiamethoxam may be due to either a different binding site on nicotinic receptors, or receptor isoforms, or specific pharmakokinetic behavior, rather than to exceptional affinity to one of the examined binding sites.     

The relationship between aphid infestations and oviposition by aphidophagous Syrphidae (Diptera)

Oviposition by aphidophagous Syrphidae varies with the size of aphid infestations and different syrphid species have different optimum aphid population sizes for oviposition. In one experiment using potted brussels sprout plants infested with Brevicoryne brassicae L., Platycheirus manicatus (Meig.) preferred about 100 aphids per plant, P. scutatus (Meig.) about 1000 aphids per plant and Syrphus ribesii (L.) about 2000 aphids per plant. These preferences were less clear in certain Platycheirus species (e.g. P. peltatus (Meig.)), than in Syrphus species (e.g. S. luniger Meig.). Once a plant has been selected for oviposition there may still be selection of suitable colonies on that plant. For a given aphid population, S. luniger preferred a small number of large aggregates to a larger number of smaller ones, whereas S. balteatus (Deg.) preferred the opposite. The tendency of the different species to select aphid populations of different sizes and distributions is likely to decrease interspecific competition.     

Effects of Aphis fabae Scop, and of its attendant ants and insect predators on yields of field beans (Vicia faba L.)

Predators (mainly coccinellid adults and larvae and syrphid larvae), although few, were important in decreasing numbers of Aphis fabae on a small plot of field beans during the early stages of infestation in a year favourable to the aphid. At the same time, ants (Lasius niger L.), attending aphids on other plants on the same plot, effectively protected the aphids from predators for about 2 weeks, enabling the attended aphids to multiply faster than the unattended. When all aphid populations started to decline, predators became more numerous and accelerated the decline on both sets of plants. Bean plants without aphids yielded fifty-six seeds per plant; those with aphids but free from ants gave seventeen; and those with ant-attended aphids, eight seeds per plant. The damage and loss of yield was caused by the large aphid populations that developed when the pods were maturing, and not by the fewer aphids present when the plants were in flower. It appears that small, temporary infestations during flowering might increase the yield of field beans.     

A new strategy for the chemical control of fig longicorn, Acalolepta vastator (Newman) (Coleoptera: Cerambycidae), infesting grapevines

Abstract  Difficulties in controlling the grapevine borer pest fig longicorn, Acalolepta vastator , were experienced. Variable results with azinphos-methyl, chlorpyrifos and methidathion applied as seasonal sprays at 2-weekly or monthly intervals, coupled with inconsistent grower spraying practices, provided unreliable control. Pest resurgence resulted in a range of new chemicals and usage strategies being tested to overcome the problem. After extensive trialling an effective strategy for control of A. vastator was developed. This involved a single application of insecticide at dormancy, and after vineyard pruning, at a much higher rate than that normally registered for crop use. Bifenthrin (Talstar 100 EC) at 1000 mL/100 L, fipronil (Regent 200 SC) at 100 mL/100 L and imidacloprid (Confidor 350 SC) at 200 mL/100 L controlled emerging adults and young. This strategy overcomes a number of problems experienced with the previous chemical application method for this pest.     

Field and laboratory tests of new insecticides against the apple maggot, Rhagoletis pomonella (Walsh) (Diptera: Tephritidae)

Laboratory bioassays and field tests were conducted to compare the effectiveness of the new insecticides, imidacloprid, indoxacarb, pyriproxyfen, spinosad, thiacloprid, and thiamethoxam, against apple maggot. The activity ranking of the compounds in reducing oviposition in laboratory bioassays was: imidacloprid, 95% reduction at 11 ppm > thiamethoxam, 91% and thiacloprid, 89% reduction at 100 ppm > spinosad, 98% reduction at 316 ppm > indoxacarb, 80% reduction at 1000 ppm > pyriproxyfen, 0% reduction at 38 ppm. In laboratory bioassays, the only insecticides that were toxic to flies at concentrations equal to or below the recommended field rates were imidacloprid, (50% of flies at 11 ppm), spinosad (90% of flies at rates > 10 ppm), and thiamethoxam (approximately 50% of flies at 32 ppm). In field trials, thiacloprid was the only material that consistently controlled apple maggot fruit infestation that was comparable to standard treatments of organophosphate insecticides. Spinosad applied at weekly intervals, and indoxacarb applied as biweekly sprays provided adequate control of apple maggot damage when infestation levels in the field were low, but were not effective in preventing damage in small plots when apple maggot pressure was high.     

Growth, development and consumption by four syrphid species associated with the lettuce aphid, Nasonovia ribisnigri, in California

The lettuce aphid, Nasonovia ribisnigri Mosley, was accidentally introduced into California from Europe during the late 1990s and soon became an economic pest of Romaine lettuce along California’s central coast region. Indigenous syrphid larvae attack the lettuce aphid and are believed to be effective in the management of this invasive pest, although there have been no studies on the capacity of the syrphid larvae to kill and consume lettuce aphids. We focused on four syrphid species commonly found in central coast lettuce fields: Allograpta obliqua (Say), Eupeodes fumipennis (Thomson), Sphaerophoria sulphuripes (Thomson), and Toxomerus marginatus (Say). Laboratory feeding experiments were conducted to estimate the development times of all juvenile stages, the daily growth rate of larvae, the number of third instar aphids killed, the aphid biomass killed, and the aphid biomass consumed as measures of predator performance. Results show that during larval development E. fumipennis killed the most third-instar aphids (507 aphids, 88 mg biomass killed) and reached the largest size, followed by A. obliqua (228 aphids, 39 mg killed), S. sulphuripes (194 aphids, 31 mg killed) and T. marginatus (132 aphids, 20 mg killed). Body size alone did not account for species differences in per-capita larval consumption rates. This information is discussed in relation to the predation potential of syrphids through the short cropping cycle of lettuce, and the choice of plant species to use for floral resource provisioning to enhance the activity of syrphids needed for effective management of lettuce aphids in California’s central coast fields.     

Population level effects of cadmium and the insecticide imidacloprid to the parasitoid, Aphidius ervi after exposure through its host, the pea aphid, Acyrthosiphon pisum (Harris)

The objective of this study was to assess the influence of toxic substances with different modes of action on a two-species system: an aphid-specific parasitoid, Aphidius ervi Haliday, feeding on the pea aphid, Acyrthosiphon pisum (Harris). The instantaneous rate of population increase (r_i) was used as a measure of population level toxic effect in this study. The toxicants evaluated were imidacloprid, a nonpersistent neurotoxic insecticide, and cadmium, a chronic pollutant with a tendency to accumulate. We evaluated the effects of cadmium and imidacloprid on A. pisum and A. ervi because both toxicants can occur together in polluted areas where crops are grown. Cadmium (200 or 400 mg kg⁻¹ dry weight soil) and imidacloprid (4 or 40 g a.i. ha⁻¹) were applied to soil contained in plastic pots in which broad bean plants, Vicia faba L., were grown. Results of this study indicated that cadmium at the concentrations tested, reduced population growth rate of the pea aphid. Imidacloprid also reduced aphid growth rate, but only at the highest concentration tested (40 g a.i. ha⁻¹). Combinations of cadmium and imidacloprid had the greatest impact on aphid growth rate. Imidacloprid alone had no effect on population growth rate of the parasitoid. However, cadmium alone or in combination with imidacloprid had a negative impact on A. ervi by reducing population growth rate 77%. These results indicate that negative impacts on parasitoids may occur in areas where cadmium contamination is present and imidacloprid is used to control aphids.     

Imidacloprid increases egg production in Amblyseius victoriensis (Acari: Phytoseiidae)

The chloronicotinyl insecticide, imidacloprid, recommended for aphid control in Australian stone fruit orchards, was examined for its impact on survival and egg production in Amblyseius victoriensis Womersley. Imidacloprid at the field rate (0.0053% a.i.) was non-toxic, but repellent to A. victoriensis in laboratory bioassays. Females treated with imidacloprid showed increased egg production, producing 1.9–2.0 eggs per day compared with 1.3–1.6 eggs per day for the untreated individuals. A population of A. victoriensis in an apricot orchard was significantly reduced for 4 weeks following the application of imidacloprid. However, the population recovered after 5–6 weeks and was significantly larger (more than twice) than that in the untreated section of the orchard during weeks 9–12. The imidacloprid-mediated enhancement of the fecundity and population development of A. victoriensis is discussed with respect to integration in existing biological control programmes in the Australian stone fruit. This revised version was published online in November 2006 with corrections to the Cover Date.