Influence of temperature on the reproductive and demographic parameters of two spider mite pests of vineyards and their natural predator

We evaluated the influence of temperature on demographic parameters of two common vineyard pests, the Pacific spider mite, Tetranychus pacificus McGregor, and the Willamette spider mite, Eotetranychus willamettei (McGregor) (Acari: Tetranychidae). Additionally, we investigated the effects of temperature on their shared predator, the western predatory mite, Galendromus occidentalis (Nesbitt) (Acari: Phytoseiidae). The intrinsic rate of increase (r _m ) was higher for T. pacificus than E. willamettei at 15 and 28??C, but similar at 22??C. G. occidentalis achieved a higher r _m than T. pacificus from 15 to 28??C, but the difference was significant only at 22??C. At 34??C, the r _m for both T. pacificus and G. occidentalis was negative, while E. willamettei did not develop at this temperature. Prey species did not affect demographic parameters of G. occidentalis. These results suggest that higher temperatures favor T. pacificus over the less damaging E. willamettei, and may also reduce the effectiveness of G. occidentalis.     

Impact of sulfur on density of <Emphasis Type="Italic">Tetranychus pacificus</Emphasis> (Acari: Tetranychidae) and <Emphasis Type="Italic">Galendromus occidentalis</Emphasis> (Acari: Phytoseiidae) in a central California vineyard

Sulfur is the oldest and most widely used fungicide in the vineyards of California, where it is used for control of powdery mildew (Uncinula necator [Schw.] Burr). For decades, sulfur use has been associated with outbreaks of Tetranychus pacificus McGregor (Acari: Tetranychidae) on cultivated grapes in the San Joaquin Valley. I undertook large-scale field studies to test this association, to evaluate the impact of sulfur on Galendromus occidentalis (Nesbit) (Acari: Phytoseiidae), a major predator of T. pacificus, and to determine if timing of sulfur applications with respect to grape bloom has an impact on T. pacificus density. The studies took place in a 32 ha vineyard in Fresno County, and all fungicide applications were made with commercial-scale equipment. In 1998 a ‘high sulfur’ treatment, a combination of wettable sulfur and sulfur dust, was compared to ‘low sulfur,’ in which demethylation inhibitor (DMI) fungicides partially substituted for sulfur. In 1999 treatments were ‘sulfur,’ ‘DMI,’ ‘sulfur pre-bloom’ (here sulfur was applied prior to grape bloom, in late May, and then DMIs were applied until mid-season) and ‘sulfur post-bloom’ (the reverse of ‘sulfur pre-bloom’). In each year, the T. pacificus population increase came after the end of fungicide applications, and results clearly show a relationship between sulfur use and T. pacificus density. In 1998, mean T. pacificus density was 2.7 times higher and mean G. occidentalis density 2.5 times higher in ‘high sulfur’ compared to ‘low sulfur.’ In 1999, the highest T. pacificus counts were in the ‘sulfur’ and ‘sulfur pre-bloom’ treatments, 4.8 times higher than ‘sulfur post-bloom’ and 2 times higher than ‘DMIs.’ Density of G. occidentalis was 2.3 times as high in ‘sulfur’ or ‘sulfur pre-bloom’ than ‘DMIs.’ The predator/prey ratio was not significantly different among treatments in 1998, but in 1999 it was highest in the ‘sulfur pre-bloom’ treatment. In 1999, density of Homeopronematus anconai (Baker) (Acari: Tydeidae) was 2.7 times higher in ‘sulfur pre-bloom’ compared to ‘sulfur,’ and higher by 2.7 times in ‘DMI’ compared to ‘sulfur post-bloom,’ suggesting a negative effect of sulfur on this tydeid. These results do not support the hypotheses that the cause of the increase in T. pacificus density is due to negative effects of sulfur on phytoseiids or tydeids. Rather, it appears that a plant-based explanation is likely, first, because of the differences in pre-bloom versus post-bloom sulfuring, and second, because of the long lag time between the end of the sulfur applications and the corresponding increase in spider mite density.     

Impact of natural epizootics of the fungal pathogen Neozygites floridana (Zygomycetes: Entomophthorales) on population dynamics of Tetranychus evansi (Acari: Tetranychidae) in tomato and nightshade

The tomato red spider mite, Tetranychus evansi (Acari: Tetranychidae) was recently introduced in Africa and Europe, where there is an increasing interest in using natural enemies to control this pest on solanaceous crops. Two promising candidates for the control of T. evansi were identified in South America, the fungal pathogen, Neozygites floridana and the predatory mite Phytoseiulus longipes. In this study, population dynamics of T. evansi and its natural enemies together with the influence of environmental conditions on these organisms were evaluated during four crop cycles in the field and in a protected environment on nightshade and tomato plants with and without application of chemical pesticides. N. floridana was the only natural enemy found associated with T. evansi in the four crop cycles under protected environment but only in the last crop cycle in the field. In the treatments where the fungus appeared, reduction of mite populations was drastic. N. floridana appeared in tomato plants even when the population density of T. evansi was relatively low (less than 10 mites/3.14 cm² of leaf area) and even at this low population density, the fungus maintained infection rates greater than 50%. The application of pesticides directly affected the fungus by delaying epizootic initiation and contributing to lower infection rates than unsprayed treatments. Rainfalls did not have an apparent impact on mite populations. These results indicate that the pathogenic fungus, N. floridana can play a significant role in the population dynamics of T. evansi, especially under protected environment, and has the potential to control this pest in classical biological control programs.     

A single nucleotide polymorphism in the acetylcholinesterase gene of the predatory mite Kampimodromus aberrans (Acari: Phytoseiidae) is associated with chlorpyrifos resistance

The predatory mite Kampimodromus aberrans (Oudemans) (Acari: Phytoseiidae) is one of the most important biocontrol agents of herbivorous mites in European perennial crops. The use of pesticides, such as organophosphate insecticides (OPs), is a major threat to the success of biocontrol strategies based on predatory mites in these cropping systems. However, resistance to OPs in K. aberrans has recently been reported. The present study investigated the target site resistance mechanisms that are potentially involved in OP insensitivity. In the herbivorous mite Tetranychus urticae Koch (Acari: Tetranychidae), resistance to OPs is due to a modified and insensitive acetylcholinesterase (AChE; EC: 3.1.1.7) that bears amino acid substitution F331W (AChE Torpedo numbering). To determine whether the predators and prey have evolved analogous molecular mechanisms to withstand the same selective pressure, the AChE cDNA from a putative orthologous gene was cloned and sequenced from susceptible and resistant strains of K. aberrans. No synonymous mutation coding for a G119S substitution was determined to be strongly associated with the resistant phenotype instead of the alternative F331W. Because the same mutation in T. urticae AChE was not associated with comparable levels of chlorpyrifos resistance, the role of the G119S substitution in defining insensitive AChE in K. aberrans remains unclear. G119S AChE genotyping can be useful in ecological studies that trace the fate of resistant strains after field release or in marker-assisted selection of improved populations of K. aberrans to achieve multiple resistance phenotypes through gene pyramiding. The latent complexity of the target site resistance in K. aberrans vs. that of T. urticae is also discussed in the context of data from the genome project of the predatory mite Metaseiulus occidentalis (Nesbitt) (Acari: Phytoseiidae).     

Control of the broad mite (Polyphagotarsonemus latus (Banks)) on organic greenhouse sweet peppers (Capsicum annuum L.) with the predatory mite, Neoseiulus cucumeris (Oudemans)

The predatory mite Neoseiulus cucumeris (Oudemans) (Acarina: Phytoseiidae) successfully controlled the broad mite Polyphagotarsonemus latus (Banks) (Acarina: Tarsonemidae) on two varieties of greenhouse-grown sweet peppers (Capsicum annuum L.). A survey of pre-plant seedlings showed that nurseries were a source of infestation for the broad mite. The predatory mites were released twice (on day 1 and 5, or 15 days later) on each plant, every second plant or every fourth plant. Broad mite populations were evaluated by sampling young leaves from the top of the plant. The effect of the broad mite on plant height, dry mass and yield was evaluated. Additionally, since N. cucumeris is known to control thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), blue sticky traps and flower sampling were used to evaluate changes in thrips populations. All three release rates of N. cucumeris significantly (P<0.05) controlled broad mite populations, but when the predatory mites were released only on every fourth plant, the overall height and yield of the plants were adversely affected by broad mites. Releasing N. cucumeris on each or every second plant was as efficacious in controlling broad mites as sulfur treatments in terms of plant height, dry mass and yield. Plants treated with sulfur, however, had significantly higher thrips populations and fruit damage.     

Lethal and sublethal effects of insecticides on the survival and reproduction of Brevipalpus yothersi (Acari: Tenuipalpidae)

The overuse of insecticides to control vector insects such as Diaphorina citri Kuwayama in citrus groves has altered the population dynamics of pest mites. Among phytophagous mites, population outbreaks of citrus leprosis mite, Brevipalpus yothersi Baker, have been increasingly intense and frequent in Brazilian citrus groves. Despite the great importance of the B. yothersi mite for citrus production, the lethal and sublethal effects of insecticides on this mite have not yet been studied. Therefore, in this study, the effects of insecticides commonly used for D. citri control on B. yothersi mortality, reproduction, and instantaneous growth rate were assessed. For this, two experiments were carried out, one under controlled conditions and another in a greenhouse. The insecticides tested were beta-cyfluthrin, bifenthrin, buprofezin, chlorpyrifos, dimethoate, pyriproxyfen, and thiamethoxam at 0 (control), 0.0625, 0.125, 0.25, 0.5, 1, and twofold the recommended insecticide concentration for D. citri control. The pyriproxyfen insecticide provided high mortality of B. yothersi even at low concentrations. Furthermore, this insecticide negatively interfered with the reproduction of this mite. Beta-cyfluthrin, bifenthrin, buprofezin, chlorpyrifos, dimethoate, and thiamethoxam, in the tested concentrations, showed low impact on citrus leprosis mite. Regarding the reproduction of the mite, no significant increase in fecundity was observed on B. yothersi females exposed to insecticide residues, regardless of the concentration tested. Therefore, the application of these insecticides in the management of pest insects is unlikely to promote an increase in the citrus leprosis mite population.

     

Microbial diversity in the predatory mite Metaseiulus occidentalis (Acari: Phytoseiidae) and its prey, Tetranychus urticae (Acari: Tetranychidae)

Microorganisms associated with the predatory mite Metaseiulus (=Typhlodromus or Galendromus) occidentalis (Nesbitt) and its prey, the two-spotted spider mite Tetranychus urticae (Koch), were assessed using a high-fidelity polymerase chain reaction (PCR) protocol and primers designed to identify Eubacteria, Archaeabacteria, iridoviruses, Helicosporidia, Cytophaga-like microorganisms, Wolbachia and its bacteriophage WO, fungi and yeast-like organisms. Sequences from four bacterial species related to Wolbachia (α-Proteobacteria), Cardinium, Bacteroidetes, and Enterobacter (γ-Proteobacteria) were obtained from M. occidentalis, and three sequences related to Wolbachia, Rickettsia, and Caulobacter (α-Proteobacteria) were obtained from T. urticae. No nucleotide differences were detected between the 16S rRNA, wspA or wspB Wolbachia sequences obtained from M. occidentalis and T. urticae, which suggest that horizontal transfer of Wolbachia could have occurred. Southern blot analyses of genomic DNA from both M. occidentalis and T. urticae using wspA probes were negative, indicating that this Wolbachia sequence is not integrated into the nuclear genome of either species. Two of the T. urticae colonies tested contained the WO bacteriophage, but none of the six M. occidentalis populations were infected. New M. occidentalis-specific forward and reverse 16S rRNA primers based on the Wolbachia, Cardinium, Bacteroidetes, and Enterobacter sequences obtained were designed and used to amplify PCR products from each of two laboratory and four field-collected samples of M. occidentalis females and eggs, indicating that these infections are widespread. Likewise, species-specific primers for T. urticae were designed for the Wolbachia, Rickettsia, and Caulobacter sequences obtained and used to evaluate T. urticae from strawberries, wine grapes, hops, almonds, and cherries from California, Washington, and Florida; all were positive for Wolbachia and Caulobacter but two of the six were negative for Rickettsia. None of the M. occidentalis colonies tested were positive for the microsporidium Oligosporidium occidentalis, which previously had been associated with a pathogenic condition in some of our laboratory colonies. The Gainesville colonies of M. occidentalis and T. urticae were negative for iridovirus, Archaeabacteria, fungi, Helicosporidia, and yeast-like organisms. So far, Wolbachia is the only symbiont that is shared by this predator and its prey.     

Demography of the twospotted spider mite,Tetranychus urticae Koch

Summary A simple life table model was constructed for Tetranychus urticae in which daily survivorship of eggs and motil stages, fecundity, and development time was altered to assess the impact of each parameter on the intrinsic rate of increase. r. Interpretation of the trade-offs focused on management considerations.A second aspect of the study concerned age and stage structure in mite populations including the time path of convergence to a stable age distribution and the effect of changes in birth and death rates on the age profile. The stable stage distributions of 7 tetranychid mite species were computed using 25 separate life tables. In spite of the wide range of r-values induced by different experimental conditions, all of the stage distributions were quite similar averaging roughly 66% eggs, 26% immatures, and 8% adults. Several population studies were cited which reported stage distributions of growing mite populations. The empirical evidence suggested that natural mite populations are often quite near this stable distribution.A practical problem involving the extent to which hormoligosis (insecticide stimulation) affects mite population growth rate was addressed using the life table model and laboratory data from controlled studies. The findings suggested that mite populations treated with insecticide may attain a 1.4- to a 4.2-fold difference in population size relative to an untreated population after 2 generations and over a 1,300-fold potential difference after 10 generations.     

Diet-dependent cannibalism in the omnivorous phytoseiid mite Amblydromalus limonicus

Amblydromalus limonicus (Garman & McGregor) (Acari: Phytoseiidae) is a commercially available predator of key pests in protected crops, particularly of thrips and whiteflies. Basic information on the developmental and reproductive performance of the predator as a function of food is largely lacking. In the present study, development, reproduction and growth rates were determined for A. limonicus on four economically important pests: Western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), greenhouse whitefly, Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae), broad mite, Polyphagotarsonemus latus (Banks) (Acari: Tarsonemidae) and two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). The life history traits of females fed on these different target prey were compared with those of females offered Carpoglyphus lactis L. (Acari: Carpoglyphidae), which is the standard food source for mass-producing this predator. Additionally, three commercially available non-prey food sources with potential for use in the mass production or as supplementary food to sustain populations of the predator in the field were tested: the commercial pollen product Nutrimite (consisting of pollen of narrow-leaved cattail, Typha angustifolia L.), frozen eggs of the Mediterranean flour moth Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) and frozen eggs of the Mediterranean fruit fly, Ceratitis capitata Wiedemann (Diptera: Tephritidae). Survival rates of immature A. limonicus were high (>94% survival) on all tested foods except on T. vaporariorum and T. urticae (76.0% and 17.1%, respectively). The fastest development was obtained when mites were fed on T. angustifolia, whereas the longest developmental times were obtained on T. urticae and T. vaporariorum. When females were offered P. latus, no reproduction was observed, despite a high prey consumption in both the juvenile and adult stages. The reproductive performance of A. limonicus fed on T. vaporariorum was significantly lower than that on F. occidentalis. Furthermore, no second generation could be obtained on a diet solely consisting of T. vaporariorum. Population growth rates were highest when A. limonicus was fed on Nutrimite, E. kuehniella or C. lactis, and exceeded those on a diet consisting of their natural prey, F. occidentalis. The phytoseiid showed cannibalistic behavior when maintained on E. kuehniella and C. capitata eggs and T. angustifolia pollen, with females consuming their own eggs. The rate of cannibalism was dependent on the food source offered, but always resulted in reduced population growth rates. This cannibalistic behavior should be taken into account when selecting food sources for mass rearing of A. limonicus or supporting its populations in the field.     

A method to assess the effects of pesticides on the predatory mite Phytoseiulus persimilis (Acari Phytoseiidae) in the laboratory

Phytoseiulus persimilis Athias-Henriot (Acari Phytoseiidae) is a major predator of Tetranychus urticae (Acari Tetranychidae). The performance of P. persimilis in controlling T. urticae may be altered by pesticides used to manage other pests. Therefore, knowledge of the side-effects of pesticides is essential for IPM. A number of laboratory methods were suggested to evaluate pesticide side-effects on predatory mites. Most methods assess residual effects only, and a number of them are characterised by high predator escape rates from experimental units. A method aimed at evaluating the topical and residual effects of pesticides on P. persimilis is herein described. Mites were treated by microimmersion and then reared in holding cells, on bean leaves previously dipped in a pesticide solution. Three insecticides (pyrethrins, spinosad and thiamethoxam), an insecticide-acaricide (abamectin), and two fungicides (azoxystrobin and tolylfluanide) were evaluated. The strain of P. persimilis used for evaluation was collected from unsprayed vegetable plants. All the pesticides affected the survival and fecundity of P. persimilis. Pesticides did not affect the egg-hatching of P. persimilis females exposed to pesticides. Pyrethrins and abamectin proved to be more toxic than other pesticides, and thiamethoxam was more toxic than spinosad, azoxystrobin and tolylfluanide. The escape rate from experimental units was lower than 5% in all trials. Additional experiments were performed on P. persimilis eggs by dipping leaves with eggs in the pesticide solution. None of the pesticides affected egg survival. Semi-field trials conducted on potted bean plants obtained results similar to those reported in laboratory trials.     

Laboratory studies to elucidate the residual toxicity of eight insecticides to Anystis baccarum (Acari: Anystidae)

Anystis baccarum (L.) [=Anystis agilis (Banks)] (Acari: Anystidae) is a common predatory mite recently identified in apple (Malus spp.) orchards and in vineyards (Vitus spp.) in Québec, Canada. Studies of its susceptibility to pesticides used in these crops need to be carried out to encourage integrated pest management programs. A laboratory evaluation of methoxyfenozide, acetamiprid, thiamethoxam, imidacloprid, spinosad, phosmet, carbaryl, and lambda-cyhalothrin showed that residues of lambda-cyhalothrin, phosmet, and carbaryl were highly toxic in 48-h petri dish bioassays. The field rate of lambda-cyhalothrin is 0.0184 g (AI) /liter, which is 26-fold the estimated LC50 of 0.0007 g (AI) /liter) for this predator. The field rate for phosmet is 0.6000 g (AI) /liter, which is 118-fold the LC50 for phosmet, which is 0.0051 g (AI) /liter), and the field rate for carbaryl is 1.960 g (AI) /liter, which is 784-fold the estimated LC50 of 0.0025 g (AI) /liter). Five other insecticides, methoxyfenozide, acetamiprid, thiamethoxam, imidacloprid, and spinosad, were evaluated and found to be nontoxic.     

Response of Neoseiulus fallacis Garmen and Galendromus occidentalis Nesbitt (Acari: Phytoseiidae) to Tetranychus urticae Koch (Acari: Tetranychidae)-Damaged Hop Humulus lupulus (L.) (Urticales: Cannabaceae)

Abstract 1 The response of Neoseiulus fallacis Garmen and Galendromus occidentalis (Acari: Phytoseiidae) to Tetranychus urticae Koch (Acari: Tetranychidae)‐damaged and undamaged hop, Humulus lupulus (L.), plants was tested using a Y‐tube olfactometer. 2 Neoseiulus fallacis but not G. occidentalis was attracted to volatiles from T. urticae‐damaged hop plants when paired with undamaged plants. 3 The response of N. fallacis to these volatiles was stronger for plants severed at the soil surface than for intact plants. 4 There was no difference in the response of N. fallacis to severed or intact hop plants that had no spider mite damage, indicating that artificial wounding by severing alone does not elicit the production of attractive volatiles detectable to N. fallacis. These results are consistent with the existence of cross‐talk between signalling pathways initiated by feeding damage and artificial wounding that result in elevated levels of predator‐attracting volatiles.     

A population model for two-spotted spider mite Tetranychus urticae and its predator Metaseiulus occidentalis

A population simulation model that was developed for the fruit tree red spider mite (Panonychus ulmi Koch) and its phytoseiid predator (Amblyseius potentillae Garman) (Rabbinge, 1976) was adapted to Metaseiulus occidentalis Nesbitt and Tetranychus urticae Koch. The model uses life-table data for T. urticae and M. occidentalis and M. occidentalis' numerical and functional responses. The assumptions made in the model were tested by comparing the model outcome with the results of an independent greenhouse experiment. Sensitivity analyses were also done to evaluate the implicit assumptions of the model and to determine the relative importance of the rates and parameters used. Results of the sensitivity analysis showed that time of release is critical for rapid control of the prey population. Predator-prey release ratios and frequency of releases are relatively less important. Differences in functional and numerical response and predator dispersal rate also seem relatively less important than proper timing of releases.

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Zusammenfassung Ein Simulationsmodell, das für die Populationen der Obstbaumspinnmilbe (Panonychus ulmi Koch) und ihren Feind (Amblyseius potentillae Garman) entwickelt worden war (Rabbinge, 1976), wurde Metaseiulus occidentalis Nesbitt und Tetranychus urticae Koch angepasst. Das Modell verwendet Life-table Daten für T. urticae und M. occidentalis sowie die numerischen und funktionalen Reaktionen von M. occidentalis. Die im Modell gemachten Annahmen wurden getestet, indem das Modellergebnis mit den Resultaten eines unabhängigen Gewächshausversuchs verglichen wurde. Die Sensitivitätsanalyse zeigte, dass der Zeitpunkt der Freilassung entscheidend ist für eine rasche Begrenzung der Wirtspopulation. Das Räuber-Wirtverhältnis und die Häufigkeit der Freilassung sind weniger wichtig. Unterschiede in der numerischen und funktionalen Reaktion und die Ausbreitungsgeschwindigkeit scheinen ebenfalls weniger wichtig zu sein als der richtige Zeitpunkt der Freilassung.

     

Compatibility of sulfoxaflor and other modern pesticides with adults of the predatory mite <Emphasis Type="Italic">Amblyseius swirskii</Emphasis>. Residual contact and persistence studies

Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) is a very efficient generalist predatory mite of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) and Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), worldwide released in horticultural greenhouses. Here, the toxicity of sulfoxaflor and other ten pesticides to A. swirskii adults when applied at their maximum field rate was assessed in the laboratory in terms of mortality and reproductive performance. The duration of the harmful activity when residues were aged under greenhouse was assessed for compounds not classified as harmless in the laboratory, based on the International Organization for Biological Control (IOBC) rules. Sulfoxaflor as well as flonicamid, flubendiamide, metaflumizone, methoxyfenozide, spiromesifen, and spirotetramat were harmless, emamectin was slightly harmful and abamectin, deltamethrin and spinosad were harmful. Emamectin was short-lived and abamectin, deltamethrin and spinosad were slightly persistent under our conditions.     

Mite populations on grapevines in south-eastern Australia: Implications for biological control of grapevine mites (Acarina: Tenuipalpidae,Eriophyidae)

Pest and predatory mite populations were monitored over a 2 year period on grapevines in three viticultural regions of southern Australia (The Riverlands, Sunraysia and Murrumbidgee Irrigation Area [MIA]). The mite pestsBrevipalpus spp..Colomerus vitis (Pagenstecher) andCalepitrimerus vitis (Nalepa) occurred in each region with a predatory mite fauna which showed considerable interregional variation in incidence, abundance and composition. Nine species of Phytoseiidae, the dominant predatory mite family, were recorded inhabiting grapevines. In the Riverlands, mite populations were apparently suppressed by two phytoseiids (Typhlodromus doreenae Schicha,Amblyseius victoriensis (Womersley)) in vineyards on which no insecticide was used and on which sulphur and copper were used to control vine diseases. In Sunraysia and MIA, vineyards which generally had greater inputs of synthetic pesticides, particularly fungicides, five to eight phytoseiid species were recorded. However, they were less abundant and appeared to have less impact on mite (particularlyBrevipalpus spp.) populations. The population dynamics of pest and predatory mites on grapevines in southern Australia and implications for mite management based on biological control are discussed with respect to pesticide (particularly fungicide) inputs and phytoseiid biology/ecology.     

Biology and control of the broad mite,Polyphagotarsonemus latus (Banks) (Acari: Tarsonemidae)

The broad mite,Polyphagotarsonemus latus (Acari: Tarsonemidae), is an important, and in some cases recent, pest of diverse crops in tropical and subtropical regions. Infested leaves become bronzed with down-curling margins, buds are aborted and flowers distorted, shoots grow twisted and fruit may be misshapen and russeted. Injuries, presumably due to toxins, occur even after the broad mite is killed by pesticides. There is no evidence thatP. latus transmits plant viruses, but injury may be mistaken for virus or herbicide damage. The mite infests plants referable to ca 55 dicotyledone and two monocotyledone families as well as to the Cupressaceae. Changes in horticultural practices, including control measures, could have caused recent pest outbreaks. The mite may raise a generation in 1 week under optimal conditions (ca 25°C and high relative humidities) and deposit ca. 40 eggs/ female. The usual sex ratio is 1:4 male: female and reproduction is arrhenotokous. Dispersal is effected through male carriage of pharate females as well as by winds, insects (especially whiteflies) and man. Field sampling is facilitated by the pest's aggregated distribution. Control options comprise plant resistance, pesticides and biocontrol. Areas for future research include the possible emergence of sibling species or feeding strains, better understanding of the mite's reproduction, the effects of host plants on life history parameters, monitoring for pesticide resistance and exploration for additional natural enemies of the broad mite.     

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.     

Development of acaricide resistance in Pacific spider mite (<Emphasis Type="Italic">Tetranychus pacificus</Emphasis>) from California vineyards

In recent years, grape growers in California reported failures of acaricides against Tetranychus pacificus McGregor. We collected T. pacificus populations from four vineyards and tested them for resistance to bifenazate, propargite and pyridaben. In addition, we sequenced part of the cytochrome b gene of bifenazate-resistant and -susceptible T. pacificus to test for the presence of mutations reported to confer resistance to the congeneric T. urticae. None of the mutations conferring resistance to bifenazate in T. urticae were present in resistant T. pacificus. Resistance levels ranged from full susceptibility to statistically significant 11-fold resistance to pyridaben, sevenfold resistance to bifenazate and fourfold resistance to propargite compared to a susceptible population. Despite the relatively low levels of resistance detected, we estimated that under the conditions of our study the highest field rates of bifenazate and pyridaben application would cause less than 58 and 66% mortality of adult females in the most resistant populations, respectively. In contrast, field rates of propargite application would cause close to 100% mortality in the least susceptible population. These results highlight a potential link between resistance development and reduced field effectiveness for bifenazate and pyridaben. Finally, T. pacificus may be more tolerant to bifenazate and propargite than T. urticae, since the LC₅₀ values for the susceptible population of T. pacificus were several times higher than LC₅₀’s reported for susceptible T. urticae.     

Neonicotinoid insecticide imidacloprid causes outbreaks of spider mites on elm trees in urban landscapes

Background

Attempts to eradicate alien arthropods often require pesticide applications. An effort to remove an alien beetle from Central Park in New York City, USA, resulted in widespread treatments of trees with the neonicotinoid insecticide imidacloprid. Imidacloprid''s systemic activity and mode of entry via roots or trunk injections reduce risk of environmental contamination and limit exposure of non-target organisms to pesticide residues. However, unexpected outbreaks of a formerly innocuous herbivore, Tetranychus schoenei (Acari: Tetranychidae), followed imidacloprid applications to elms in Central Park. This undesirable outcome necessitated an assessment of imidacloprid''s impact on communities of arthropods, its effects on predators, and enhancement of the performance of T. schoenei.

Methodology/Principal Findings

By sampling arthropods in elm canopies over three years in two locations, we document changes in the structure of communities following applications of imidacloprid. Differences in community structure were mostly attributable to increases in the abundance of T. schoenei on elms treated with imidacloprid. In laboratory experiments, predators of T. schoenei were poisoned through ingestion of prey exposed to imidacloprid. Imidacloprid''s proclivity to elevate fecundity of T. schoenei also contributed to their elevated densities on treated elms.

Conclusions/Significance

This is the first study to report the effects of pesticide applications on the arthropod communities in urban landscapes and demonstrate that imidacloprid increases spider mite fecundity through a plant-mediated mechanism. Laboratory experiments provide evidence that imidacloprid debilitates insect predators of spider mites suggesting that relaxation of top-down regulation combined with enhanced reproduction promoted a non-target herbivore to pest status. With global commerce accelerating the incidence of arthropod invasions, prophylactic applications of pesticides play a major role in eradication attempts. Widespread use of neonicotinoid insecticides, however, can disrupt ecosystems tipping the ecological balance in favor of herbivores and creating pest outbreaks.     

The impact of insecticides applied in apple orchards on the predatory mite Kampimodromus aberrans (Acari: Phytoseiidae)

Kampimodromus aberrans is an effective predatory mite in fruit orchards. The side-effects of insecticides on this species have been little studied. Field and laboratory experiments were conducted to evaluate the effects of insecticides on K. aberrans. Field experiments showed the detrimental effects of etofenprox, tau-fluvalinate and spinosad on predatory mites. Spider mite (Panonychus ulmi) populations reached higher densities on plots treated with etofenprox and tau-fluvalinate than in the other treatments. Single or multiple applications of neonicotinoids caused no detrimental effects on predatory mites. In the laboratory, spinosad and tau-fluvalinate caused 100 % mortality. Etofenprox caused a significant mortality and reduced fecundity. The remaining insecticides did not affect female survival except for imidacloprid. Thiamethoxam, clothianidin, thiacloprid, chlorpyrifos, lufenuron and methoxyfenozide were associated with a significant reduction in fecundity. No effect on fecundity was found for indoxacarb or acetamiprid. Escape rate of K. aberrans in laboratory was relatively high for etofenprox and spinosad, and to a lesser extent thiacloprid. The use of etofenprox, tau-fluvalinate and spinosad was detrimental for K. aberrans and the first two insecticides induced spider mite population increases. The remaining insecticides caused no negative effects on predatory mites in field trials. Some of them (reduced fecundity and repellence) should be considered with caution in integrated pest management programs.