The stability of tebufenpyrad resistance in two-spotted spider mite (Acari: Tetranychidae) under laboratory conditions

The successful use of chemical rotations to manage insecticide resistance requires reversion between alternate chemical applications. We tested a tebufenpyrad resistant population of Tetranychus urticae Koch after some 55 months laboratory culture without pesticide selection and found LC₅₀ level resistance had dropped from 63.29- to 2.41-fold. However, the population was still heterogeneous with LC₉₉ level resistance at 38.03-fold. It is likely that a lack of reversion contributed directly to the initial tebufenpyrad control failure. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

The influence of fenbutatin-oxide use on organotin resistance in two-spotted mite Tetranychus urticae koch (Acari: Tetranychidae)

A strain of Tetranychus urticae from pears was evaluated for cyhexatin and fenbutatin-oxide resistance after field control failure to the latter occurred. High-level fenbutatin-oxide resistance was confirmed in the field strain. Fenbutatin-oxide resistance was >1,500 fold (based on flowable powder) and 127 fold (based on emulsifiable concentrate). However, the level of cyhexatin resistance was only 9.8 fold which was similar to levels previously found. This provides a stark warning against the overuse of fenbutatin-oxide.     

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.     

Functional response of Neoseiulus barkeri Hughes on two-spotted spider mite (Acari: Tetranychidae)

Generalist predatory mites are the common phytoseiid fauna in many agroecosystems, but little attention has been paid to their potential as biological control agents. In this study, we determined the functional responses of adult females of the generalist predator Neoseiulus barkeri Hughes on eggs, larvae, and adults of the two-spotted spider mite, Tetranychus urticae Koch, in the laboratory. Predation experiments were conducted on pepper leaf discs over a 24 h period at 25±1°C, 70–80% RH and 16L:8D photoperiod. Prey densities ranged 5 to 80 eggs, or 5 to 40 larvae, or 1 to 8 female adults of T. urticae per disc. The predation rate of N. barkeri adult females on T. urticae eggs was the same as on its larvae, but the predation rate on adult females was much lower. The role of generalist predatory mites in integrated and biological control of greenhouse pests was discussed.     

Temperature-dependent fumigant activity of essential oils against twospotted spider mite (Acari: Tetranychidae)

Fumigant activity of 34 commercial essential oils was assessed on female adults and eggs of twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) at three temperatures (5, 15, and 25 degrees C). Common thyme, cinnamon, and lemongrass oils were equally effective on twospotted spider mite adults showing 85.8-100% mortality at 5 and 10 microl/liter air at 25 degrees C. At a lower temperature of 15 degrees C, lemongrass and peppermint resulted in > or =90% mortality of adults at 10 microl/liter air. Only lemongrass was relatively active at 5 microl/liter air, at 15 degrees C. At 5 degrees C, lemongrass and peppermint caused significantly higher adult mortality than controls but only at 10 microl/liter air. Common thyme oil showed the highest ovicidal activity at 5 microl/liter air at 25 degrees C. Among the main components of common thyme and lemongrass oils, citral was lethal to twospotted spider mite adults at all tested temperatures. Carvacrol, thymol, and citral caused the same inhibitory effects on the hatch of twospotted spider mite eggs at 25 degrees C. However, citral was more active than other compounds to twospotted spider mite eggs at 15 degrees C. Therefore, we conclude that citral has the best potential for development as a fumigant against twospotted spider mite on agricultural products harvested late in the growing season.     

Factors determining harem ownership in a subsocial spider mite (Acari,Tetranychidae)

Several factors which may affect harem ownership by males ofSchizotetranychus miscanthi Saitō (a new subsocial species of theSchizotetranychus celarius complex) were experimentally tested. A marking method was developed and used for studying spider mite behavior. Nest ownership (longer male residence in a nest) had little influence on the consequence of male-male combat. Furthermore, age differences in males never affected the outcome of the combats. Length of male leg I, however, appeared to be an important factor. Factors affecting variation in male leg size were examined. Length of leg I was strongly affected by host plant quality but not by male age.     

Control of phytoseiids in a spider mite mass-rearing system (Acari: Phytoseiidae,Tetranychidae)

Phytoseiid mites which contaminated the spider mite colony and interfered with the mass-rearing of spider mites were controlled by dipping in hot water. Immersion for 60 s in water of 50°C killed all stages ofAmblyseius fallacis (Garman),A. womersleyi Schicha andPhytoseiulus persimilis (Athias-Henriot) (Acari: Phytoseiidae). Only approximately 0.3% of theA. womersleyi eggs hatched, and this seems negligible. The populations ofTetranychus kanzawai Kishida andT. urticae (Koch) (Acari: Tetranychidae) were reduced. However, they recovered well. Although this treatment resulted in the withering of some soybean seedlings, the next trifoliate leaf to be produced was normal. A very satisfactory result was obtained when this technique was applied to the mass-rearing system.     

Genetic transfer of a twospotted spider mite (Acari: Tetranychidae) repellent in tomato hybrids

Lycopersicon hirsutum Dunal is very resistant to arthropod herbivory, and research on causes of resistance has often implicated trichomes and their secretions. To better understand relationships among resistance, repellency, and 2,3-dihydrofarnesoic acid, a trichome-borne sesquiterpenoid spider mite repellent, two tomato, Lycopersicon esculentum Miller, varieties were interbred with a highly resistant, spider mite repellent accession (LA1363) of L. hirsutum. Backcross and F2 generations were produced with each tomato variety. Whole leaves of 99 hybrids were bioassayed with twospotted spider mites, Tetranychus urticae Koch, allowing selection of six hybrids (two susceptible and four resistant) for each generation of each family. When these 24 hybrids were characterized for spider mite repellency with thumbtack bioassays, two hybrids had repellent leaflets, demonstrating that repellency was genetically transferred to interspecific tomato hybrids. Leaflet washes containing trichome secretions from each of three hybrids, including the two having repellent leaflets, were repellent in bridge bioassays. For the two hybrids having repellent leaflets and leaflet washes, removal of trichome secretions by dipping leaflets in methanol eliminated leaflet repellency. 2,3-Dihydrofarnesoic acid was present in trichome secretions of the hybrids having leaflet repellency, and it also was present in secretions of other hybrids, indicating that its presence is essential, but not sufficient for leaflet repellency. With regard to resistance, 16 of the hybrids tested had been identified as resistant in a whole leaf bioassay, but only two had repellent leaflets, indicating that other mechanisms of resistance are present in the resistant L. hirsutum parent.     

Approaches for sampling the twospotted spider mite (Acari: Tetranychidae) on clementines in Spain

Tetranychus urticae Koch (Acari: Tetranychidae) is an important pest of clementine mandarins, Citrus reticulata Blanco, in Spain. As a first step toward the development of an integrated crop management program for clementines, dispersion patterns of T. urticae females were determined for different types of leaves and fruit. The study was carried out between 2001 and 2003 in different commercial clementine orchards in the provinces of Castelló and Tarragona (northeastern Spain). We found that symptomatic leaves (those exhibiting typical chlorotic spots) harbored 57.1% of the total mite counts. Furthermore, these leaves were representative of mite dynamics on other leaf types. Therefore, symptomatic leaves were selected as a sampling unit. Dispersion patterns generated by Taylor's power law demonstrated the occurrence of aggregated patterns of spatial distribution (b > 1.21) on both leaves and fruit. Based on these results, the incidence (proportion of infested samples) and mean density relationship were developed. We found that optimal binomial sample sizes for estimating low populations of T. urticae on leaves (up to 0.2 female per leaf) were very large. Therefore, enumerative sampling would be more reliable within this range of T. urticae densities. However, binomial sampling was the only valid method for estimating mite density on fruit.     

Development of two spotted spider mite (Acari: Tetranychidae) populations on strawberry and raspberry cultivars

Five strawberry (Fragaria sp.) and five raspberry (Rubus ideaus L.) cultivars were evaluated for resistance to two spotted spider mite (Tetranychus urticae Koch.). Two methods of assessing the development of two spotted mite populations using detached leaves were compared. The number of eggs laid and mites which developed were compared. The strawberry cvs Hapil and Pegasus had significantly greater development of two spotted mite populations than the cvs Rhapsody, Symphony and Elsanta. The raspberry cv. Joan Squires had higher populations of two spotted mite whilst the raspberry cv. Leo the least, when compared with cvs Glen Clova, Glen Moy and Glen Prosen. Differences were observed in oviposition sites and mite distribution when comparing raspberries with strawberries. The method of assessing the populations development of two spotted mite which involved maintaining the cut leaf stem in water may be of potential use for studying population dynamics of both two spotted mite and possible predators over extended periods of time.     

Leaf cell and tissue damage of cucumber caused by twospotted spider mite (Acari: Tetranychidae)

To quantify the damage caused by twospotted spider mite, Tetranychus urticae Koch, feeding on cucumber, Cucumis sativus L., leaf-cell and -tissue damage was assessed. On the abaxial leaf surface, adult T. urticae could feed through the spongy parenchyma and part of the palisade parenchyma of the leaf, while immature T. urticae could feed only through the sponge parenchyma. T. urticae punctured individual epidermal cells and consumed the contents of the mesophyll cells. Injured leaves had more empty space in the spongy parenchyma and fewer chloroplasts per cell. Damage also occurred even in the adjacent uninjured parenchyma cells without additional T. urticae feeding injury. Net photosynthetic rate, total chlorophyll content, and greenness of the leaf were significantly affected by feeding as quantified by mite-days. The percent loss of these parameters increased linearly or nonlinearly as mite-days increased, regardless of mite developmental stages. At 1,000 mite-days per 6 cm2, net photosynthetic rate was reduced by approximately 50 and 95%, total chlorophyll content was reduced by approximately 55 and 80%, and greenness was reduced by approximately 50 and 80% by feeding by immature and adult T. urticae, respectively.     

Impact of twospotted spider mite (Acari: Tetranychidae) on growth and productivity of glasshouse cucumbers

Experiments were conducted to assess the damage of the glasshouse cucumber by twospotted spider mite, Tetranychus urticae Koch, and to investigate when the economic yield begins to decrease after T. urticae infestations. To assess the damage, dry matter partitioning in the cucumber plant was quantified and plant growth analyses were conducted at four different T. urticae infestation levels. T. urticae infestations decreased leaf productivity by reducing the total number of leaves per plant. Approximately 14% reductions of total leaf areas could result in significant yield loss. The decreased leaf productivity by T. urticae feeding caused biomass reductions and altered the pattern of dry matter partitioning in the plant; damaged plants accumulated more dry matter in the leaf, and partitioning of dry matter to fruits was hindered. The economic yield of cucumber began to significantly decrease as early as 4 wk after heavy mite infestations. This study also showed the seasonal differences in T. urticae-cucumber damage interactions among mite infestation levels.     

Linkage between one of the polygenic hexythiazox resistance genes and an etoxazole resistance gene in the twospotted spider mite (Acari: Tetranychidae)

Genetic linkage between hexythiazox and etoxazole resistance loci was analyzed by crossing experiments. Two strains, one resistant (R) and the other susceptible (S) to both chemicals were established from field-collected Tetranychus urticae Koch (Acari: Tetranychidae) populations that were further selected in the laboratory. To analyze the recombination rate of the loci associated with resistance, we tested the ovicidal effects of a mixed solution of hexythiazox and etoxazole on haploid F2 eggs laid by F1 females from an R female x S male cross. This revealed tight or complete linkage between the hexythiazox and etoxazole resistance loci. We then assessed the number of loci associated with resistance to each acaricide based on mortality in the haploid F3 progeny (eggs) of F2 females from an F1 female (R x S) x S male testcross. The mortality rate indicated that etoxazole resistance was largely controlled by a single major locus, whereas hexythiazox resistance was controlled by more than one locus. Thus, one hexythiazox resistance locus was tightly or completely linked to the etoxazole resistance locus.     

Photoperiodic control of reproductive arrest in the oak-inhabiting spider mite Schizotetranychus brevisetosus (Acari: Tetranychidae)

Experimental and Applied Acarology - Populations of Schizotetranychus brevisetosus Ehara (Acari: Tetranychidae), which live on the evergreen oak (Quercus glauca), survive the coldest months as...     

Yield loss to corn from feeding by the Banks grass mite and two-spotted spider mite (Acari: Tetranychidae)

Our research was designed to determine the effects of a mite complex consisting of the Banks grass mite (BGM),Oligonychus pratensis (Banks), and the two-spotted spider mites (TSM),Tetranychus urticae Koch, on corn yield and plant lodging. For BGM, mite days and damage rating for the whole plant and leaves in the lower third of a corn plant had the best correlation with corn yield. The best correlation with yield for TSM was plant damage ratings. The percentage loss per unit for most independent variables (mite densities, mite days, or percentage of the leaf area damaged on a plant) was very similar for BGM and TSM. Therefore, the same economic threshold can be used for either mite species. When TSM fed on corn in the dent growth stage, yield was not reduced, and their feeding did not influence corn plant lodging.     

Genetic basis of resistances to chlorfenapyr and etoxazole in the two-spotted spider mite (Acari: Tetranychidae)

We studied the genetic basis of resistance to two new acaricides, chlorfenapyr and etoxazole, which have different chemical structures and modes of action in the two-spotted spider mite, Tetranychus urticae Koch. The resistance ratios calculated from the LC50s of resistant and susceptible strains were 483 for chlorfenapyr and >100,000 for etoxazole. Mortality caused by the two acaricides in F1 progeny from reciprocal crosses between the resistant and susceptible strains indicated that the modes of inheritance of resistance to chlorfenapyr and etoxazole were completely dominant and completely recessive, respectively. Mortality in F2 progeny indicated that for both acaricides, the resistance was under monogenic control. Repeated backcross experiments indicated a linkage relationship among the two acaricide resistances and malate dehydrogenase, although phosphoglucoisomerase was not linked with them. The recombination ratio between the resistances was 14.8%. From this result, we suggest that heavy spraying of the two acaricides will lead to apparent cross-resistance as a consequence of crossing over; the two resistance genes are so close to each other that it would be difficult to segregate them once they came together on the same chromosome.     

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.