The effect of interspecific mating on sex ratios in the twospotted spider mite and the Banks grass mite (Acarina: Tetranychidae)

Mixed populations of the twospotted spider mite (TSM),Tetranychus urticae (Koch), and the Banks grass mite (BGM),Oligonychus pratensis (Banks), occur on corn and sorghum plants in late summer in the Great Plains. Interspecific matings between these arrhenotokous species occur readily in the laboratory but yield no female offspring. The effect of interspecific mating on female: male sex ratios was measured by examining the F₁ progeny of females that mated with both heterospecific and conspecific males in no-choice situations. TSM females that mated first with BGM males and then with TSM males produced a smaller percentage of female offspring than TSM females that mated only with TSM males (43.1±5.8 and 78.9±2.8% females, respectively). Similarly, BGM females mated with heterospecific males and then with conspecific males produced fewer female offspring than females mated only with BGM males (55.7±5.2 and 77.5±2.5%, respectively). Lower female: male sex ratios were produced also by BGM females that mated with TSM males after first mating with conspecifics (62.4±3.4%). In mixed populations containing males of both species, females also produced lower female: male sex ratios, but these ratios were not as low as expected based on mating propensities and progeny sex ratios observed in no-choice tests. These data suggest that interspecific mating may substantially reduce female fitness in both mite species by reducing the output of female offspring, but in mixed populations this effect is mitigated by unidentified behavioral mechanisms.     

The development of bifenthrin resistance in two-spotted spider mite (Acari: Tetranychidae) from Australian cotton

Bifenthrin (Talstar^®) was registered at the beginning of the 1993/94 season for control of Helicoverpa spp. and Tetranychus urticae in Australian cotton. Resistance was monitored in T. urticae following registration but despite the implementation of resistance management, resistance evolved in the 1996/97 cotton-growing season after only four seasons use. During the following three seasons resistance increased progressively both in level (from 1.2- to 109-fold at LC₅₀) and abundance (from 20 to 90% strains) and was linked to field control failures. The evolution of resistance has now reduced the reliability of bifenthrin for T. urticae control in Australian cotton. The impact of bifenthrin resistance in T. urticae and its continued management in Australian cotton is discussed.     

Baseline susceptibility of persea mite (Acari: Tetranychidae) to abamectin and milbemectin in avocado groves in Southern California

Persea mite, Oligonychus perseae Tuttle, Baker, and Abatiello, susceptibility to abamectin and milbemectin was evaluated in 2003 to determine baseline susceptibility levels in avocado groves in San Diego and Ventura Counties (California, USA) where more than 70% of the state’s avocado production is concentrated. Milbemectin has yet to be used in avocado production in California and abamectin has been available for use since 1999. Baseline susceptibility ratios (in relation to the most susceptible population) of five persea mite field strains to milbemectin varied 2.1- to 2.8-fold at the LC₅₀ and LC₉₀, respectively. The susceptibility of seven field strains to abamectin varied slightly more (2.1- to 3.5-fold) with one strain subjected to seven sprays over the past 4 years showing slight but significant separation of LC₅₀ and LC₉₀’s from the most susceptible strain, which is suggestive of the early stages of resistance to this product. Based on these data, baseline susceptibility levels are proposed that might be used to monitor for future persea mite resistance to these chemicals as their use in California avocado production continues.     

Chlorfenapyr resistance in two-spotted spider mite (Acari: Tetranychidae) from Australian cotton

The responses of Tetranychus urticae Koch from Australian cotton to chlorfenapyr has been monitored since the 1997–1998 growing season. Resistance was first detected in the 2001–2002 season and then increased quickly in both level and proportion of resistant strains detected. In response, the resistance management strategy for chlorfenapyr use in cotton was altered and now recommends a further restriction of use from two to one spray per season. There was no evidence of negative cross-resistance to the pyrethroid bifenthrin, but chlorfenapyr was associated with an undefined negative cross-resistance.     

Predatory behaviors of Neoseiulus californicus and Galendromus helveolus (Acari: Phytoseiidae) attacking Oligonychus perseae (Acari: Tetranychidae)

Predatory behaviors of Neoseiulus californicus (McGregor) and Galendromus helveolus (Chant) attacking Oligonychus perseae Tuttle, Baker and Abbatiello on avocado leaves were videotaped and analyzed. Behaviors were recorded for “fresh” predators that were used ≤ 48 hr post receipt from a commercial insectary and “cold stored” predators that were maintained at 12°C for ≈ 14 days. Fresh and cold stored G. helveolus were observed to attack O. perseae only after invading webbed nests. Conversely, fresh and cold stored N. californicus employed three different modes of predatory attack: (1) intercepting and attacking migrant O. perseae outside of web nests; (2) attacking prey through nest webbing; or (3) invading and attacking O. perseae inside nests. Predatory efficacy of both N. californicus and G. helveolus was reduced following cold storage, as both species engaged in certain predatory behaviors less frequently in comparison to predators that were not stored at low temperatures. Our observed results for N. californicus and G. helveolus attacking O. perseae are interpreted in relation to the chaetotaxy hypothesis, which proposes that phytoseiid invasion efficiency and propensity of webbed nests is facilitated by dorsal setal lengths. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Aerial dispersal of European red mites (Acari: Tetranychidae) in commercial apple orchards

Aerial dispersal of European red mite, Panonychus ulmi (Koch), in commercial apple orchards was estimated by trapping windborne mites. Studies were conducted at four orchards in eastern New York during 1989 and 1990 and at three orchards in western New York during 1989. In each orchard mites were trapped in three locations; the interior of the orchard, at the border of the orchard and in a field or woodlot beyond the orchard. Large numbers of mites were captured, even when the numbers of mites on apple foliage were well below levels where mite injury to leaves was visible (less than five per leaf). The log numbers of mites trapped were linearly related to the log density of mites on leaves and this relationship was consistent for each year and region the study was conducted. The trap captures among the three locations in and outside an orchard were highly correlated. The implications these findings may have on metapopulation dynamics and resistance to acaricide dynamics are discussed.     

Chlorophyll fluorescence and leaf chlorophyll content of bean leaves injured by spider mites (Acari: Tetranychidae)

The use of chlorophyll fluorescence as a method for detecting and monitoring plant stress arising from Tetranychus urticae (Koch) feeding injury was investigated. The effect of mite density (1–32 mites per 1.5 cm² of leaf) and the duration of the feeding period (1–5 days) on the chlorophyll fluorescence parameters of bean (Phaseolus vulgaris) leaves were examined. Changes in chlorophyll fluorescence parameters were dependent both on mite density and duration of feeding. Decreases in F _o, the initial fluorescence and F _m, the maximum fluorescence led to a decrease in the ratio of variable to maximum fluorescence, F _v/F _m. The decrease in F _v/F _m is typical of the response of many plants to a wide range of environmental stresses and indicates a reduced efficiency of photosystem II (PSII) photochemistry. T _1/2, which is proportional to the pool size of electron acceptors on the reducing side of PSII, was also reduced in response to mite-feeding injury. The leaf chlorophyll content decreased with increasing mite density and duration of feeding but did not appear to contribute to the decrease in F _v/F _m. Chlorophyll fluorescence is an effective method for detecting and monitoring stress in T. urticae-injured bean leaves.     

Survey of natural enemies of spider mites (Acari: Tetranychidae) in citrus orchards in eastern Spain

Field surveys were conducted from 2004 to 2007 to determine the species composition and relative abundance of natural enemies associated with colonies of either the citrus red mite, Panonychus citri, or the two spotted spider mite, Tetranychus urticae, in Valencian citrus orchards (eastern Spain). Fourteen species were recorded, six phytoseiid mites and eight insect predators. Two of them are reported for the first time on citrus in Spain and two more are first reports as predators associated with T. urticae. The community of predators associated with T. urticae and P. citri was almost identical, and the Morisita–Horn index of similarity between both natural enemy complexes was close to one, suggesting that predators forage on both pest species. Quantifying the presence of many known spider mites predators in Valencian citrus orchards is an important first step towards spider mite control. A challenge for future studies will be to establish conservation and/or augmentation management strategies for these predators, especially to improve T. urticae biological control.     

Demography of the cereal rust mite Abacarus hystrix (Acari: Eriophyoidea) on quack grass

Demography parameters of the cereal rust mite Abacarus hystrix (Nalepa) on quack grass were studied to investigate its potential capacity of population increase in conditions of initially low density. The experiment was maintained under laboratory conditions at a constant temperature of 19.5-20.5 degrees C and 94 +/- 1% RH. Life-history data were used to calculate duration of developmental stages, survival of adults and rates of population increase. A new method of estimation of age-dependent fecundity is proposed. On average, eggs required 7.98 (n = 33, 95% CI: 7.68-8.21) days to develop into adults. Life expectancy of females was longer than that of males (9.72 and 5.41 days, respectively). The mean sex ratio, expressed as the proportion of females, was 0.80 (n = 122, CI: 0.71-0.86). The reproductive output for females was age-dependent and daily egg production reached a peak (3.83 eggs/day, CI: 2.50-5.15) on the 5th day, and then decreased steeply. The net reproductive rate (R0) was 10.12 female progeny per female per generation, the generation time (T) was 11.31 days, the intrinsic rate of increase (r) was 0.20 female progeny per female per day, and the finite rate of increase (lambda) was 1.23 female progeny per day. These estimates showed that A. hystrix has a great potential capacity for rapid population increase when colonising new hosts and its density is low. Therefore, we conclude that the population of the cereal rust mite on quack grass may rapidly build up to very high densities and can be a reservoir population, which may easily disperse and infest other, including cultivated, grasses.     

Sublethal effects of esfenvalerate residues on pyrethroid resistant Typhlodromus pyri (Acari: Phytoseiidae) and its prey Panonychus ulmi and Tetranychus urticae (Acari: Tetranychidae)

The effect of residues of esfenvalerate on oviposition of the resistant strain of the predatory mite Typhlodromus pyri and its main prey, European red mite Panonychus ulmi and two-spotted spider mite Tetranychus urticae, were investigated. T. pyri showed a significant linear reduction in oviposition after 24h in the presence of increasing levels of esfenvalerate residue applied at the field rate. Furthermore, when given a choice, T. pyri preferred to lay eggs on residue-free surfaces. Of the two prey species, only P. ulmi showed significant avoidance of increasing levels of residues of the field rate concentration of esfenvalerate, as measured by runoff mortality, however both P. ulmi and T. urticae, when given a choice, showed a preference for esfenvalerate-free surfaces. As with the predatory mite T. pyri, both prey species showed a significant linear reduction of oviposition with increasing esfenvalerate residues and a preference to lay eggs on esfenvalerate-free surfaces. Esfenvalerate residues as high as 15X field rate were not repellent to pyrethroid-resistant T. pyri. The possible effects of these sublethal effects on predator-prey dynamics and implications for integrated mite control programmes in apple orchards are discussed.     

Comparative life-history traits of three phytoseiid mites associated with Tetranychus urticae (Acari: Tetranychidae) colonies in clementine orchards in eastern Spain: implications for biological control

The management of Tetranychus urticae, a key pest of clementine trees, is mainly based on the use of acaricides. However, more environmentally safe measures, such as biological control, are being encouraged. Life-history traits of the three most abundant phytoseiid mites associated with T. urticae on this crop (Euseius stipulatus, Phytoseiulus persimilis and Neoseiulus californicus) were studied. The experiments were performed under laboratory conditions (25°C, 80 ± 5% RH and 16:8 h (L:D)) on clementine leaves and T. urticae as prey. Euseius stipulatus could not complete its life cycle, whereas P. persimilis and N. californicus completed it satisfactorily. The estimated intrinsic rate of increase (r _m) was significantly higher for P. persimilis (0.344 day⁻¹) than for N. californicus (0.244 day⁻¹) and both were higher than the r _m value of T. urticae on clementine leaves. Implications of these results for the biological control of T. urticae in this crop are discussed.     

Prey-related odor preference of the predatory mites Typhlodromalus manihoti and Typhlodromalus aripo (Acari: Phytoseiidae)

Typhlodromalus manihoti and Typhlodromalus aripo are exotic predators of the cassava green mite Mononychellus tanajoa in Africa. In an earlier paper, we showed that the two predators were attracted to odors from M. tanajoa-infested cassava leaves. In addition to the key prey species, M. tanajoa, two alternative prey mite species, Oligonychus ossypii and Tetranychus urticae also occur in the cassava agroecosystem. Here, we used a Y-tube olfactometer to determine the attraction of the predators to odors from O. gossypii- or T. urticae-infested cassava leaves and their prey-related odor preference. T. aripo but not T. manihoti was slightly attracted to odors from O. gossypii-infested leaves. Both predator species showed a stronger response to odors from cassava leaves infested by M. tanajoa over odors from cassava leaves infested by O. gossypii. Neither predator species was attracted to odors from T. urticae-infested leaves and the predators preferred the odors from M. tanajoa-infested leaves over those from T. urticae-infested leaves. When O. gossypii was present together with M. tanajoa on the same leaves or on different sets of leaves offered together as an odor source the two predators were attracted. In contrast, after mixing non-attractive odors from T. urticae-infested leaves with attractive odors from M. tanajoa-infested leaves, neither T. aripo nor T. manihoti was attracted. Ecological advantages and disadvantages of the predators’ behavior and possible implications for biological control of M. tanajoa are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of chlorpyrifos and sulfur on spider mites (Acari: Tetranychidae) and their natural enemies

In many agricultural systems spider mites are believed to be induced pests, only reaching damaging densities after pesticides decimate predator populations. Wine grapes typically receive two types of pesticides, insecticides and fungicides. Chemicals in either class could impact spider mite densities both directly through spider mite mortality, and indirectly by negatively affecting natural enemies. The impact of a broad-spectrum insecticide (chlorpyrifos) and an inorganic fungicide (sulfur) on mites and their natural enemies was monitored in replicate open-field experiments conducted in an abandoned vineyard in Washington State. In both experiments, chemicals were applied within a 2 × 2 factorial design, allowing assessment of both main and interactive effects of the two chemicals. Following typical management practices on wine grapes in Washington State, we made a single insecticide application early in the season, but repeatedly applied sulfur throughout the season. In the absence of sulfur, chlorpyrifos application led to higher spider mite densities. The main effect of chlorpyrifos appeared to be indirect, perhaps mediated through mortality of generalist phytoseiid mites; generalists appeared to be unable to recover following even a single insecticide application, while there was no evidence for harmful effects of chlorpyrifos on specialist phytoseiid mites. Sulfur had direct suppressive effects on both pest and predatory mites, although in the second experiment the suppressive effect of sulfur on spider mites was weaker when chlorpyrifos was also applied. These field experiments suggest that a complex mix of direct and indirect effects of the two chemicals impacted spider mite population dynamics in our system.     

Chemical ecology of oribatid mites III. Chemical composition of oil gland exudates from two oribatid mites, Trhypochthoniellus sp. and Trhypochthonius japonicus (Acari: Trhypochthoniidae)

The composition of oil gland exudates from two oribatid mites, Trhypochthoniellus sp. and Trhypochthonius japonicus, was studied with reference to the related species Trhypochthoniellus crassus. Trhypochthoniellus sp. contained a mixture of seven compounds; (Z,Z)-6,9-heptadecadiene, geranial, 3-hydroxybenzene-1,2-dicarbaldehyde (γ-acaridial), neryl formate, neral, (Z)-8-heptadecene and geranyl formate in decreasing order of abundance. The profile of the components from T. japonicus consisted of two types depending on the locality of sampling with unknown reason; one possessing a mixture of eight compounds [(Z,E)-farnesal, γ-acaridial, (Z,Z)-6,9-heptadecadiene, (E,E)-farnesal, (Z)-8-heptadecene and geranial in decreasing order] together with two unknown compounds, and the other composed of the same set of compounds together with 2-hydroxy-6-methylbenzaldehyde as the most abundant component. Relative abundance among common components was consistent between the two types of T. japonicus. Profiles of components differed among three species including T. crasus. The phylogenetic relationship between Oribatida and Astigmata was discussed based on secretory compounds commonly distributed between these two suborders. This revised version was published online in July 2006 with corrections to the Cover Date.     

Life-history traits of the six Panonychus species from Japan (Acari: Tetranychidae)

Six species of the genus Panonychus are known from Japan. Life-history parameters of all six species were investigated at 25 °C, and for three species two strains of different geographical origin were included. The intrinsic rate of natural increase (r _m ) ranged from 0.172/day for the P. osmanthi albino strain to 0.209/day for P. citri, while the net reproductive rate (R ₀) varied from 23.98 in the thelytokous species P. thelytokus to 46.61 in P. citri. Both values were higher in the polyphagous species (P. ulmi, P. mori and P. citri), which are considered crop pests, than those in the oligophagous species (P. thelytokus and P. osmanthi), considered non-pests. The only exception was P. bambusicola, an oligophagous non-pest species with R ₀- and r _m -values closely resembling those of the three polyphagous species. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

虱矮螨属一新种记述（蜱螨亚纲：矮螨科）

记述我国虱矮螨属Pediculaster Vitzthum1新种:开阳虱矮螨P.kaiyangensis Guo&Zhao sp.nov.,模式标本采自贵州省贵阳市开阳县中药店的远志Polygala tenuifolia Willd内,保存于贵州大学农学院昆虫研究所。     

Miticide bioassays with spider mites (Acari: Tetranychidae): effect of test design and sample size on the precision of lethal concentration estimates

The effect of interval space between the concentration (symmetric or geometric), number of concentrations and overall sample sizes were investigated using a Petri dish bioassay, the miticide propargite and two spider mites species. The precision (width of the 95% confidence intervals) of the LC₅₀ and LC₉₀ estimates was shown to be influenced by the test design and total sample size The results suggest that a symmetric five-concentration design using a minimum total sample size of 480 mites is required to produce reliable LC estimates using the Petri dish method. Asymmetric designs did not increase the reliability of LC estimates. When less than 480 test subjects are available, a symmetric three-concentration design would give adequate LC estimates, but the precision would be less than with a five-concentration design.