Susceptibility and detoxifying enzyme activity in two spider mite species (Acari: Tetranychidae) after selection with three insecticides

Changes in the susceptibility and detoxifying enzyme activity were measured in laboratory strains of Banks grass mite, Oligonychus pratensis (Banks), and twospotted spider mite, Tetranychus urticae Koch, that were repeatedly exposed to three insecticides. Three strains of each mite species were exposed to one of two pyrethroids, bifenthrin, and lambda-cyhalothrin, or an organophosphate, dimethoate, for 10 selection cycles at the LC60 for each insecticide. A reference or nonselected strain of each mite species was not exposed to insecticides. After 10 cycles of exposure, susceptibility to the corresponding insecticides, bifenthrin, lambda-cyhalothrin, and dimethoate, decreased 4.5-, 5.9-, and 289.2-fold, respectively, relative to the reference strain in the respective O. pratensis strains, and 14.8-, 5.7-, and 104.7-fold, respectively, relative to the reference strain in the respective T. urticae strains. In the bifenthrin-exposed O. pratensis strain, there was a 88.9-fold cross-resistance to dimethoate. In the dimethoate-exposed T. urticae strain, there was a 15.9-fold cross-resistance to bifenthrin. These results suggest that there may be cross-resistance between dimethoate and bifenthrin. The reduced susceptibility to dimethoate remained stable for three months in the absence of selection pressure in both mites. The decrease in susceptibility in the O. pratensis strains exposed to bifenthrin, lambda-cyhalothrin, and dimethoate was associated with a 4.7-, 3.0-, and 3.6-fold increase in general esterase activity, respectively. The decrease in susceptibility in the T. urticae strains exposed to bifenthrin and lambda-cyhalothrin was associated with a 1.3- and 1.1-fold increase in general esterase activity, respectively. The mean general esterase activity was significantly higher in the pyrethroid-exposed O. pratensis and T. urticae strains than in the nonselected strain. There was no significant increase in esterase activity in the dimethoate-exposed T. urticae strain. The decrease in susceptibility to insecticides was also associated with reduced glutathione S-transferase 1-chloro-2, 4-dinitrobenzene conjugation activity, but this did not appear to be related to changes in insecticide susceptibility. These results suggest that in these mites, the general esterases may play a role in conferring resistance to pyrethroids. However, some other untested mechanism, such as target site insensitivity, must be involved in conferring dimethoate resistance.     

Fecundity in twospotted spider mite (Acari: Tetranychidae) is increased by direct and systemic exposure to imidacloprid

The effect of imidacloprid on fecundity in twospotted spider mites, Tetranychus urticae Koch, was investigated in laboratory experiments using individual females on bean leaf discs. Mites were directly exposed to spray formulations of imidacloprid or fed on discs cut from a systemically treated bean plant. Imidacloprid-treated T. urticae produced 10-26% more eggs during the first 12 d of adult life and 19-23% more during adulthood compared with a water-only treatment. Increased egg production occurred immediately after exposure and lasted for about 15 d in sprayed mites. In mites exposed to imidacloprid by ingestion, increased egg production was not apparent until after 6 d and lasted until about day 18. Longevity was significantly greater in mites that ingested imidacloprid but not in sprayed mites. The significance and importance of imidacloprid-stimulation of fecundity in T. urticae to pest management in crop systems like hops, which routinely use this insecticide, is discussed.     

Evaluation of predatory mites and Acramite for control of twospotted spider mites in strawberries in north central Florida

Greenhouse and field experiments were conducted from 2003 to 2005 to determine the effectiveness of two predatory mite species, Phytoseiulus persimilis Athias-Henriot and Neoseiulus californicus (McGregor), and a reduced-risk miticide, Acramite 50 WP (bifenazate), for control of twospotted spider mite, Tetranychus urticae Koch, in strawberries (Fragaria x ananassa Duchesne). In greenhouse tests, three treatments consisting of releases of P. persimilis, N. californicus, and an untreated control were evaluated. Both species of predatory mites significantly reduced twospotted spider mite numbers below those found in the control during the first 3 wk of evaluation. However, during week 4, twospotted spider mite numbers on the plants treated with P. persimilis increased and did not differ significantly from the control. Field studies used releases of P. persimilis and N. californicus, applications of Acramite, and untreated control plots. Both N. californicus and P. persimilis significantly reduced populations of twospotted spider mite below numbers recorded in the control plots. During the 2003-2004 field season P. persimilis took longer than N. californicus to bring the twospotted spider mite population under control (< 10 mites per leaflet). Acramite was effective in reducing twospotted spider mite populations below 10 mites per leaflet during the 2003-2004 field season but not during the 2004-2005 field season, possibly because of a late application. These findings indicate that N. californicus releases and properly timed Acramite applications are promising options for twospotted spider mite control in strawberries for growers in north Florida and other areas of the southeast.     

Physiological resistance and behavioral avoidance responses to residues of four pesticides by six spider mite populations

Six twospotted spider mite populations were assayed for their levels of physiological resistance and behavioral avoidance to residues of four synthetic pesticides. Mortality could not be estimated for bifenthrin and fenvalerate (synthetic pyrethroids) as mites effectively avoided treated surfaces, however significant between-population differences in mortality were detected for chlordimeform and cyhexatin. Considerable variation in walkoff and spindown behavioral response to sub-lethal doses of pesticides was observed among populations within compounds, and within populations among compounds. Within-compound walkoff and spindown behavioral response varied among all mite populations. Few significant between-compound correlations were significant, indicating that spider mites responded differently to the four pesticides. The hypothesis that physiological resistance is negatively correlated with behavioral avoidance was tested. Of the four possible negative correlations between physiological resistance and behavioral avoidance for chlordimeform and cyhexatin, only the correlation between cyhexatin-induced mortality and spindown response was significant. Comparisons of physiological resistance and behavioral avoidance of chlordimeform and cyhexatin by specific pairs of populations did not consistently find these two characters to be related. In a related experiment, the magnitude and direction of the correlation between physiological resistance and behavioral avoidance following selection for increased physiological tolerance to cyhexatin was compared in a highly resistant and a susceptible population of the twospotted spider mite. Mortality in the susceptible population at 2 ppm cyhexatin was similar to mortality in the resistant population at 250 ppm after 72h exposure (ca. 12%). However, at these concentrations, the resistant population exhibited much higher avoidance of the compound through walkoff response.     

Spider Mite-Induced (3S)-(E)-Nerolidol Synthase Activity in Cucumber and Lima Bean. The First Dedicated Step in Acyclic C11-Homoterpene Biosynthesis

Many plant species respond to herbivory with de novo production of a mixture of volatiles that attracts carnivorous enemies of the herbivores. One of the major components in the blend of volatiles produced by many different plant species in response to herbivory by insects and spider mites is the homoterpene 4,8-dimethyl-1,3(E), 7-nonatriene. One study (J. Donath, W. Boland [1995] Phytochemistry 39: 785-790) demonstrated that a number of plant species can convert the acyclic sesquiterpene alcohol (3S)-(E)-nerolidol to this homoterpene. Cucumber (Cucumis sativus L.) and lima bean (Phaseolus lunatus L.) both produce 4,8-dimethyl-1,3(E),7-nonatriene in response to herbivory. We report the presence in cucumber and lima bean of a sesquiterpene synthase catalyzing the formation of (3S)-(E)-nerolidol from farnesyl diphosphate. The enzyme is inactive in uninfested cucumber leaves, slightly active in uninfested lima bean leaves, and strongly induced by feeding of the two-spotted spider mite (Tetranychus urticae Koch) on both plant species, but not by mechanical wounding. The activities of the (3S)-(E)-nerolidol synthase correlated well with the levels of release of 4, 8-dimethyl-1,3(E),7-nonatriene from the leaves of the different treatments. Thus, (3S)-(E)-nerolidol synthase is a good candidate for a regulatory role in the release of the important signaling molecule 4,8-dimethyl-1,3(E),7-nonatriene.     

Acaricidal properties of a Chenopodium-based botanical

The emulsifiable concentrate UDA-245 [25% EC (vol:vol)], based on an essential oil extract from Chenopodium ambrosioides variety ambrosioides, a North American herbaceous plant, was compared with commercially available pesticides for their effectiveness to control the adult stage and egg hatch of the twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) and the European red mite, Panonychus ulmi (Koch) (Acari: Tetranychidae). After a laboratory bioassay with adult twospotted spider mites, a 0.5% concentration of UDA-245 was more effective than 0.7% (AI) of neem oil (Neem Rose Defense). After a similar bioassay with the European red mite, a 0.5% concentration UDA-245 was as effective as 0.006% (AI) of abamectin (Avid). UDA-245 at 0.5% significantly reduced egg hatch of the twospotted spider mite, 5 and 9 d after treatment and of the European red mite 6 d after treatment. Egg hatch was significantly lower using 0.006% (AI) of abamectin, 0.7% of neem oil, and 1.0% insecticidal soap than UDA-245. Residual tests indicated that UDA-245 may be persistent in the environment only for a few hours. Only 23% mortality was noted when mites were introduced on bean leaves 1 h after treatment with a 2% concentration of UDA-245. At the recommended dose of 0.5%, UDA-245 was not considered phytotoxic for most plants tested, i.e., lettuce, roses, and tomatoes. Results suggest that a greenhouse integrated pest management program using UDA-245 could effectively and selectively control mite infestations by treating "hot spots" with negligible effect on biological control agents when treating before introduction or when natural enemies are absent.     

Susceptibility of populations of Banks grass mites (Acari: Tetranychidae) suspected of developing bifenthrin resistance from three maize fields

Banks grass mite, Oligonychus pratensis (Banks), from three Texas maize fields were assayed for bifenthrin resistance following poor field control in 1995. Laboratory bioassays showed the field mites to be 3- to 23-fold more tolerant to bifenthrin than the susceptible laboratory culture. Comparison of LC₅₀ values to assays with bifenthrin from 1985 to 1993 indicated no statistically significant changes in mite resistance. However, high LC₉₀ values in 1995 suggest possible resistance development. The percentages of resistant mites from the three fields in 1995 were calculated to be 4.7%, 17.9%, and 30.9%. The Banks grass mite population exhibiting the highest level of tolerance to bifenthrin was further assayed to evaluate tolerance levels to other insecticides alone and in combination with synergists and insecticides. A high level of tolerance existed in the 1995 ‘bifenthrin–selected’ Banks grass mite strain to bifenthrin, dimeothate, and amitraz. The combination of bifenthrin or dimethoate with a synergist indicated changes in the ability of the more resistant 1995 mites to detoxify insecticides. The activity of a dimethoate + bifenthrin mixture and a three way mixture of dimethoate, bifenthrin, and piperonyl butoxide caused 5- and 38-fold increase in toxicity against the more resistant Banks grass mite. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pest response in packed table grapes to low temperature storage combined with slow-release sulfur dioxide pads in basic and large-scale tests

The effect of low temperature storage combined with slow release sulfur dioxide pads was determined in basic laboratory and large-scale commercial tests on western flower thrips, Frankliniella occidentalis Pergande; grape mealybug, Pseudococcus maritimus (Ehrhorn); Pacific spider mite, Tetranychus pacificus McGregor; twospotted spider mite, Tetranychus urticae Koch; and omnivorous leafroller, Platynota stultana Walshingham. Temperatures within the foam containers among the packed clusters decreased from ambient to 2 degrees C within approximately 1 d and ranged from 0.4 to 1.7 degrees C in all tests. Sulfur dioxide concentrations in the foam containers ranged between 0.2 and 1.6 ppm during the 1- to 6-wk storage period in basic tests and 0.5-1.1 ppm during the 1- to 8-wk storage period in the large-scale test. Western flower thrips was completely controlled by a > or =1-wk exposure. Grape mealybug mortality was > or =93% after 2-5 wk exposures and 100% after a 6-wk exposure in basic tests. Pacific spider mite and twospotted spider mite mortality was 98.0 and 99.6%, respectively, after a 6-wk exposure. Mortality of grape mealybug and twospotted spider mite increased significantly at > or =3-wk exposures and Pacific spider mite mortality increased significantly at > or =4-wk exposures. Mortality of the spider mites in general was directly related to the duration of exposure. An 8-wk exposure to low temperature storage combined with slow release sulfur dioxide pads in the large-scale test resulted in 100% mortality of western flower thrips, twospotted spider mite, and omnivorous leafroller. The treatment resulted in <8% survival of grape mealybug and <1% survival of Pacific spider mite in the large-scale test. The combination treatment offers an economical method to attain quarantine control of certain insects and mites.     

Efficacy and persistence of rosemary oil as an acaricide against twospotted spider mite (Acari: Tetranychidae) on greenhouse tomato

Efficacy of rosemary, Rosmarinus officinalis L., essential oil was assessed against twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), as well as effects on the tomato, Lycopersicum esculatum Mill., host plant and biocontrol agents. Laboratory bioassay results indicated that pure rosemary oil and EcoTrol (a rosemary oil-based pesticide) caused complete mortality of spider mites at concentrations that are not phytotoxic to the host plant. The predatory mite Phytoseiulus persimilis Athias-Henriot is less susceptible to rosemary oil and EcoTrol than twospotted spider mite both in the laboratory and the greenhouse. Rosemary oil repels spider mites and can affect oviposition behavior. Moreover, rosemary oil and rosemary oil-based pesticides are nonpersistent in the environment, and their lethal and sublethal effects fade within 1 or 2 d. EcoTrol is safe to tomato foliage, flowers, and fruit even at double the recommended label rate. A greenhouse trial indicated that a single application of EcoTrol at its recommended label rate could reduce a twospotted spider mite population by 52%. At that rate, EcoTrol did not cause any mortality in P. persimilis nor did it affect their eggs. In general, EcoTrol was found to be a suitable option for small-scale integrated pest management programs for controlling twospotted spider mites on greenhouse tomato plants.     

Attraction of Phytoseiulus persimilis (Acari: Phytoseiidae) towards volatiles from various Tetranychus urticae-infested plant species

Plants infested with the spider mite Tetranychus urticae Koch, may indirectly defend themselves by releasing volatiles that attract the predatory mite Phytoseiulus persimilis Athias-Henriot. Several plants from different plant families that varied in the level of spider mite acceptance were tested in an olfactometer. The predatory mites were significantly attracted to the spider mite-infested leaves of all test plant species. No differences in attractiveness of the infested plant leaves were found for predatory mites reared on spider mites on the different test plants or on lima bean. Thus, experience with the spider mite-induced plant volatiles did not affect the predatory mites. Jasmonic acid was applied to ginkgo leaves to induce a mimic of a spider mite-induced volatile blend, because the spider mites did not survive when incubated on ginkgo. The volatile blend induced in ginkgo by jasmonic acid was slightly attractive to predatory mites. Plants with a high degree of direct defence were thought to invest less in indirect defence than plants with a low degree of direct defence. However, plants that had a strong direct defence such as ginkgo and sweet pepper, did emit induced volatiles that attracted the predatory mite. This indicates that a combination of direct and indirect defence is to some extent compatible in plant species.     

Adaptive learning in arthropods: spider mites learn to distinguish food quality

Many herbivorous arthropods have been shown to possess learning capabilities, yet fitness effects of learning are largely unknown. In this paper, we test whether two-spotted spider mites (Tetranychus urticae) learn to distinguish food quality in choice tests, and whether this results in fitness benefits. Food consisted of cucumber plants with one of three degrees of feeding damage: undamaged (no mites), mildly damaged (infested by a mite strain adapted to tomato) and heavily damaged (infested by a mite strain adapted to cucumber). Mites were subjected to one choice test in a greenhouse and three sequential choice tests on leaf disks. Thereafter, individual mite performance was measured as oviposition rate over four days. In the course of the three small-scale choice tests, preference shifted towards less damaged food. The performance tests showed that learning was adaptive: mites learned to prefer the food type that yielded the higher oviposition rate. Interestingly, innate preferences in the greenhouse tests were close to those shown after learning in the small-scale tests. Given that both strains of mites had not experienced cucumber for several years, we hypothesize that the preference in the greenhouse was due to avoidance of mite odours rather than odours of damaged plants. Through its effect on foraging behaviour, adaptive learning may promote the evolution of host plant specialization in herbivorous arthropods.     

Effects of soil moisture and temperature on reproduction and development of twospotted spider mite (Acari: Tetranychidae) in strawberries

The effects of soil moisture and temperature on the reproduction of twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), were examined in laboratory and field tests in strawberries, Fragaria x ananassa Duchesne, in Florida. Different soil moisture levels (low, moderate, and high) were compared to determine how soil moisture affects the reproduction and development of twospotted spider mite. In addition to soil moisture, different irrigation techniques (drip versus drip/overhead) were compared to determine their effects on twospotted spider mite reproduction as well as the incidence of angular leaf spot, Xanthomonas fragaria Kennedy & King disease. Similar studies were conducted to determine how different temperatures (18, 27, and 35 degrees C) affect the reproduction and development of twospotted spider mites. In the laboratory, low soil moisture as well as temperatures >27 degrees C promoted twospotted spider mite development. A similar trend was observed in a field study with low soil moisture promoting twospotted spider mite reproduction during the early season (11 November--8 December). Irrespective of moisture levels, a significantly higher incidence of X. fragaria was recorded in treatments with drip/overhead irrigation systems compared with drip irrigation. Implications for management of soil moisture levels are discussed with respect to the abundance of twospotted spider mite and X. fragaria in strawberries.     

The composite effect of transgenic plant volatiles for acquired immunity to herbivory caused by inter-plant communications

A blend of volatile organic compounds (VOCs) emitted from plants induced by herbivory enables the priming of defensive responses in neighboring plants. These effects may provide insights useful for pest control achieved with transgenic-plant-emitted volatiles. We therefore investigated, under both laboratory and greenhouse conditions, the priming of defense responses in plants (lima bean and corn) by exposing them to transgenic-plant-volatiles (VOCos) including (E)-β-ocimene, emitted from transgenic tobacco plants (NtOS2) that were constitutively overexpressing (E)-β-ocimene synthase. When lima bean plants that had previously been placed downwind of NtOS2 in an open-flow tunnel were infested by spider mites, they were more defensive to spider mites and more attractive to predatory mites, in comparison to the infested plants that had been placed downwind of wild-type tobacco plants. This was similarly observed when the NtOS2-downwind maize plants were infested with Mythimna separata larvae, resulting in reduced larval growth and greater attraction of parasitic wasps (Cotesia kariyai). In a greenhouse experiment, we also found that lima bean plants (VOCos-receiver plants) placed near NtOS2 were more attractive when damaged by spider mites, in comparison to the infested plants that had been placed near the wild-type plants. More intriguingly, VOCs emitted from infested VOCos-receiver plants affected their conspecific neighboring plants to prime indirect defenses in response to herbivory. Altogether, these data suggest that transgenic-plant-emitted volatiles can enhance the ability to prime indirect defenses via both plant-plant and plant-plant-plant communications.     

Introduction ofPhytoseiulus persimilis for twospotted spider mite control in greenhouses in Egypt [Acari: Phytoseiidae,tetranychidae]

The exotic predaceous mite,Phytoseiulus persimilis Athias-Henriot and the 2 native onesPhytoseius finitimus Ribaga andAmblyseius gossipi Elbadry were released on greenhouse cucumber plants in Egypt to examine their efficiency to control the twospotted spider miteTetranychus urticae Koch.P. persimilis proved to be sufficiently effective for the twospotted spider mite control under greenhouse conditions in Egypt. The 2 before-mentioned native predators were lost soon after release in the greenhouse although they are key mite predators on outdoor crops in this area.      

Response of predatory mites with different rearing histories to volatiles of uninfested plants

The behavioural response of the predatory mite Phytoseiulus persimilis to volatiles from several host plants of its prey, spider mites in the genus Tetranychus, was investigated in a Y-tube olfactometer. A positive response to volatiles from tomato leaves and Lima bean leaves was recorded, whereas no response was observed to volatiles from cucumber leaves, or leaves of Solanum luteum and Solanum dulcamara.Different results were obtained for predators that differed in rearing history. Predators that were reared on spider mites (Tetranychus urticae) on Lima bean leaves did respond to volatiles from Lima bean leaves, while predators that had been reared on the same spider mite species but with cucumber as host plant did not respond to Lima bean leaf volatiles. This effect is compared with the effect of rearing history on the response of P. persimilis to volatile allelochemicals of prey-infested plant leaves.     

Adaptive learning in arthropods: spider mites learn to distinguish food quality

Many herbivorous arthropods have been shown to possess learning capabilities, yet fitness effects of learning are largely unknown. In this paper, we test whether two-spotted spider mites (Tetranychus urticae) learn to distinguish food quality in choice tests, and whether this results in fitness benefits. Food consisted of cucumber plants with one of three degrees of feeding damage: undamaged (no mites), mildly damaged (infested by a mite strain adapted to tomato) and heavily damaged (infested by a mite strain adapted to cucumber). Mites were subjected to one choice test in a greenhouse and three sequential choice tests on leaf disks. Thereafter, individual mite performance was measured as oviposition rate over four days. In the course of the three small-scale choice tests, preference shifted towards less damaged food. The performance tests showed that learning was adaptive: mites learned to prefer the food type that yielded the higher oviposition rate. Interestingly, innate preferences in the greenhouse tests were close to those shown after learning in the small-scale tests. Given that both strains of mites had not experienced cucumber for several years, we hypothesize that the preference in the greenhouse was due to avoidance of mite odours rather than odours of damaged plants. Through its effect on foraging behaviour, adaptive learning may promote the evolution of host plant specialization in herbivorous arthropods. This revised version was published online in July 2006 with corrections to the Cover Date.     

Experience with methyl salicylate affects behavioural responses of a predatory mite to blends of herbivore-induced plant volatiles

Many natural enemies of herbivorous arthropods use herbivore‐induced plant volatiles to locate their prey. These foraging cues consist of mixtures of compounds that show a considerable variation within and among plant–herbivore combinations, a situation that favours a flexible approach in the foraging behaviour of the natural enemies. In this paper, we address the flexibility in behavioural responses of the predatory mite Phytoseiulus persimilis Athias‐Henriot (Acari: Phytoseiidae) to herbivore‐induced plant volatiles. In particular, we investigated the effect of experience with one component of a herbivore‐induced volatile blend: methyl salicylate (MeSA). We compared the responses of three groups of predatory mites: (1) those reared from egg to adult on Tetranychus urticae Koch (Acari: Tetranychidae) on lima bean plants (Phaseolus lunatus L. that produces MeSA), (2) those reared on T. urticae on cucumber (Cucumus sativus L. that does not produce MeSA), and (3) those reared on T. urticae on cucumber in the presence of synthetic MeSA. Exposure to MeSA during the rearing period (groups 1 and 3) resulted in an attraction to the single compound MeSA in a Y‐tube olfactometer. Moreover, exposure to MeSA affected the choice of predatory mites between two volatile blends that were similar, except for the presence of MeSA. Predators reared on lima bean plants preferred the volatile blend from T. urticae‐induced lima bean (including MeSA) to the volatile blend from jasmonic‐acid induced lima bean (lacking MeSA), but predators reared on cucumber preferred the volatile blend from the latter. Predatory mites reared on cucumber in the presence of synthetic MeSA did not discriminate between these two blends. Exposure to MeSA for 3 days in the adult phase, after rearing on cucumber, also resulted in attraction to the single compound MeSA. We conclude that a minor difference in the composition of the volatile blend to which a predatory mite is exposed can explain its preferences between two odour sources.     

Within-plant distribution of twospotted spider mites (Acari: Tetranychidae) on impatiens: development of a presence-absence sampling plan

The twospotted spider mite, Tetranychus urticae Koch, is an important pest of impatiens, a floricultural crop of increasing economic importance in the United States. The large amount of foliage on individual impatiens plants, the small size of mites, and their ability to quickly build high populations make a reliable sampling method essential when developing a pest management program. In our study, we were particularly interested in using spider mite counts as a basis for releasing biological control agents. The within-plant distribution of mites was established in greenhouse experiments and these data were used to identify the sampling unit. Leaves were divided into three zones according to location on the plant: inner, intermediate, and other. On average, 40, 33, and 27% of the leaves belonged to the inner, intermediate, and other leaf zones, respectively. However, because 60% of the mites consistently were found on the intermediate leaves, intermediate leaves were chosen as the sampling unit. These results lead to the development of a presence-absence sampling method for T. urticae by using Taylor coefficients generic for this pest. The accuracy of this method was verified against an independent data set. By determining numerical or binomial sample sizes for consistently estimating twospotted spider mite populations, growers will now be able to determine the number of predatory mites that should be released to control twospotted spider mites on impatiens.     

Comparative susceptibility and possible detoxification mechanisms for selected miticides in banks grass mite and two-spotted spider mite (Acari: Tetranychidae)

The susceptibility and possible detoxification mechanisms of the Banks grass mite (BGM), Oligonychus pratensis (Banks), and the two-spotted spider mite (TSM), Tetranychus urticae Koch, to selected miticides were evaluated with and without synergists. BGM was 112-fold more susceptible to the organophosphate dimethoate, and 24-fold more susceptible to both the pyrethroids bifenthrin and -cyhalothrin than TSM. The synergist triphenyl phosphate (TPP) enhanced the toxicities of bifenthrin and -cyhalothrin against BGM by 3.0- and 4.2-fold, respectively, and enhanced the toxicities of bifenthrin, -cyhalothrin, and dimethoate against TSM by 6.2-, 1.9-, and 1.7-fold, respectively. The synergist diethyl maleate (DEM) enhanced the toxicities of bifenthrin and -cyhalothrin against BGM by 2.2- and 2.9- fold, respectively, and enhanced the toxicity of bifenthrin against TSM by 4.1-fold. On the other hand, the synergist piperonyl butoxide (PBO) increased the toxicities of bifenthrin and -cyhalothrin by 6.0- and 2.6-fold, respectively, against BGM, and by 4.5- and 1.9-fold, respectively, against TSM. The significant synergism with these pyrethroids of all three tested synergists (except for DEM with -cyhalothrin against TSM) suggests that esterases, glutathione S-transferases, and cytochrome P450 monooxygenases all play important roles in their detoxification. However, the toxicity of dimethoate was not enhanced by these synergists in either mite species (except for TPP against TSM). Apparently, these metabolic enzymes play less of a role in detoxification of this organophosphate in these mites.     

The influence of host plant species on parasitism of pollen beetles (Meligethes spp.) by Phradis morionellus

We investigated the response of the specialist insect predator Oligota kashmirica benefica (Coleoptera: Staphylinidae) to volatiles from lima bean leaves infested with the spider mite Tetranychus urticae (Acari: Tetranychidae), both in a Y-tube olfactometer and in a field in Kyoto, Japan. Adult male and female predators were significantly more attracted to T. urticae-infested leaves than to clean air. Adult male and female predators were not more attracted to uninfested leaves, artificially damaged leaves, or the spider mites and their visible products when compared to clean air. In a field trap experiment, 12 adult predators were caught in three traps containing T. urticae-infested lima bean plants over 13 days, whereas no adult predators were trapped in three traps containing uninfested lima bean plants during the same period. These results showed that O. kashmirica benefica adults responded to herbivore-induced plant volatiles from T. urticae-infested lima bean leaves under both laboratory and field conditions.