Tetranychus Pacificus Research Articles

Biology and ecology ofEuseius scutalis(Athias-Henriot) (Acarina: Phytoseiidae)

The effects of some environmental factors on development and fecundity of Euseius scutalis (Athias-Henriot) were investigated. Although E. scutalis is a general feeder, pollen and Tetranychus pacificus McGregor eggs were found to be the most favorable foods. Development and fecundity were lowest on Brevipalpus lewisi McGregor. Over a variety of different temperatures and humidities, E. scutalis showed a wider range of environmental tolerances than did E. stipulates. Eggs of E. scutalis hatched at 19 percent relative humidity and immature stages developed at 35°C, indicating that this species is adapted to arid and hot areas. The rate of development varied in a quadratic manner with increase in temperature. Euseius scutalis required mating for egg production, and multiple matings were necessary for full egg production. Euseius scutalis had the greatest intrinsic rate of natural increase (0.325) and the shortest generation time (9.32 days) at 30° C, indicating this as the optimum temperature for population increase.

Laboratory and Field Investigations of Spider Mite (Acari: Tetranychidae) Resistance to the Selective Acaricide Propargite

Evaluations of spider mite, Tetranychus spp., susceptibility to propargite, initiated in response to grower concerns about potential resistance in the field, revealed 0- to 42-fold resistance in Tetranychus urticae Koch in a whole-plant residual bioassay. Surveys of spider mites collected from throughout the San Joaquin Valley in June and August 1984 indicated that propargite-resistant phenotypes exist throughout the San Joaquin Valley; 22 of 32 sites sampled in August contained individuals that survived 1,000 ppm in residual bioassays. However, resistant phenotypes were much less common in June than August; only 3 of 23 sites sampled in June had survivors of 1,000 ppm. The shift in susceptibility of populations during the season was shown to result from intraspecific increases in frequency of resistant phenotypes or interspecific shifts in spider mite species abundance, or both. Although resistant phenotypes of T. urticae and Tetranychus pacificus McGregor were discovered, no propargite-resistant Tetranychus turkestani Ugarov and Nikolski were found. Widely differing susceptibilities to propargite exist both within and between T. urticae and T. pacificus populations. A dicofol-resistant laboratory culture of T. urticae originating from the San Joaquin Valley and maintained under pressure for 2 yr possessed a 26-fold resistance to propargite. Although resistance to propargite was discovered in the laboratory, we did not observe diminished performance of propargite in field trials at a location possessing spider mites with up to 45% survivorship of the discriminating concentration of 1,000 ppm propargite.

Spider Mite Species (Acari: Tetranychidae) Response to Propargite: Basis for an Acaricide Resistance Management Program

Spider mites were collected from cotton at 36 locations in the San Joaquin Valley of California, both before propargite had been applied and again late in the season. All populations of Tetranychus turkestani Ugarov & Nikolski, the dominant early season spider mite, were susceptible to propargite. Populations of Tetranychus urticae Koch and Tetranychus pacificus McGregor exhibited a variety of responses from highly susceptible to highly resistant. These levels of resistance were defined by the range and homogeneity of response. Early season T. urticae populations were predominantly susceptible. Late-season collections of T. urticae from the same locations exhibited lower, equal, or increased tolerance to propargite, suggesting instability of resistance. Early and late-season collections of T. pacificus exhibited a consistently higher and narrower range of response to propargite than T. urticae , suggesting a possible natural tolerance to propargite. Field plots demonstrated lack of control with propargite when populations were composed of resistant T. pacificus alone. Cases of multiple resistance to propargite and dicofol were found for both T. urticae and T. pacificus.

Cyhexatin and Propargite Resistance in Populations of Spider Mites (Acari: Tetranychidae) from California Almonds

Cyhexatin (Plictran 600 Flowable) or propargite (Omite 30 Wettable Powder) resistances or both were detected using a residual-bioassay procedure in spider mite ( Tetranychus spp.) colonies collected from California almonds. Cyhexatin-susceptible Tetranychus urticae Koch and Tetranychus pacificus McGregor responded with identical probit lines. Significant cyhexatin resistance was only detected in T. pacificus . Propargite-susceptible T. urticae were 8-fold more susceptible to propargite than the most susceptible T. pacificus colony collected. Propargite-resistant individuals of both T. urticae and T. pacificus were found. Colonies collected in the field were heterogeneous in their response to cyhexatin and propargite and contained varying frequencies of susceptible types.

Toxicity of the β-exotoxin of Bacillus thuringiensis to Tetranychus pacificus and Metaseiulus occidentalis (Acari: Tetranychidae and Phytoseiidae)

The β-exotoxin of B. thuringtensis (thuringiensin) was toxic to adult female Tetranychus pacificus (McGregor) and Metaseiulus occidentalis (Nesbitt) within 48–96 h when they were treated at rates from 0.125- to 4-fold the proposed field rate. Egg production by treated females of both species declined within 48 h. Treated larvae were unable to develop to adults. Treated eggs hatched, but larvae of both M. occidentalis and T. pacificus failed to develop. Thuringiensin is an effective but, at these rates, unselective acaricide. Because intrinsic selectivity is not present at the proposed field rates, selectivity will have to be achieved through other means if the product is to be incorporated into integrated pest management programs in which this predator is important.

Selection for Abamectin Resistance in Tetranychus urticae and T. pacificus (Acari: Tetranychidae)

Three colonies of Tetranychus urticae Koch and two colonies of Tetranychus pacificus McGregor were selected in the laboratory and greenhouse with abamectin (avermectin B10). Two selection methods were used. One challenged ability of gravid females to survive 48 h on dried residues using concentrations that resulted in 40–60% mortality. The other technique selected against all life stages on bean plants. Concentration/response bioassays were used to determine whether a selection response was achieved. The three T. urticae colonies were selected 4, 6, or 15 times. LC50’s for two of these colonies before selection ranged from 0.06 to 0.15 ppm on different dates. After selection, the T. urticae colonies LC50’s were 0.12 and 0.24 ppm (values not significantly different from those of their respective base colonies). Likewise, for the two T. pacificus colonies (selected 2 and 15 times), no response to selection occurred. LC50’s of the unselected T. pacificus base colonies ranged from 0.04 to 0.12 ppm on different dates. Selected lines had LC50’s of 0.06 and 0.08 ppm, values not significantly different from LC50’s of their base colonies. These negative results do not preclude the possibility that resistance to abamectin will develop in other populations of T. urticae or T. pacificus. Because at least one of the T. urticae and T. pacificus colonies tested was resistant to propargite, cyhexatin, and fenbutatin-oxide, we suggest that cross resistances are unlikely.

Selectivity of the Acaricides Clofentezine and Hexythiazox to the Predator Metaseiulus occidentalis (Acari: Phytoseiidae)

Two new ovicidal acaricides were tested in the laboratory to determine their relative toxicity to the predator Metaseiulus occidentalis (Nesbitt) and the Pacific spider mite, Tetranychus pacificus McGregor. Clofentezine and hexythiazox caused little mortality of adult females, larvae, or eggs of M. occidentalis . It seems unlikely that, at the proposed field rates, these ovicides will be toxic to this predator. Clofentezine is equally toxic to eggs (0–24 h old) of the spider mites T. pacificus and T. urticae Koch. However, both clofentezine and hexythiazox are less toxic to eggs of T. pacificus 49–72 h old than to younger eggs. Fecundity of M. occidentalis and T. pacificus females was significantly increased within 48 h on disks sprayed with hexythiazox at rates 0.5-fold the field rate and above.

Comparison of Feeding Damage Caused by Four Tetranychid Mite Species on Gas-exchange Rates of Almond Leaves

A dual-isotope porometer measured gas-exchange rates on almond leaves exposed to feeding damage by Panonychus citri, P. ulmi, Tetranychus pacificus , or T. urticae . The feeding injury of all four mite species caused significantly lower rates of stomatal conductance, mesophyll conductance, and photosynthesis compared with undamaged controls. No significant differences in gas-exchange rates occurred between species within either genus; however, significant differences between genera were detected. Tetranychus spp. caused lower rates of mesophyll conductance and photosynthesis when compared with Panonychus spp.

Factors Limiting the Utility of Homeopronematus anconai (Acari: Tydeidae) in Integrated Pest Management in San Joaquin Valley Vineyards

A survey showed that the tydeid mite Homeopronematus (Pronematus) anconai (Baker) occurs in all grape-growing areas of the San Joaquin Valley of California. High temperatures and the pesticides used in vineyards were examined as factors that might explain why H. anconai populations are low in commercial vineyards during the summer. Cyclic high temperatures and long days were not detrimental to egg hatch, development, or reproduction of H. anconai , but sulfur and three acaricides are toxic and may limit vineyard populations. Most insecticides commonly used in California vineyards were also found to be toxic. Suggestions for selective pesticide use are made in the context of the role of H. anconai as an alternate prey of Metaseiulus (Typhlodromus) occidentalis (Nesbitt), an effective predator of the Pacific spider mite, Tetranychus pacificus McGregor.

Biology ofAmblyseius citrifolius(Denmark and Muma) (Acarina—Phytoseiidae)

Descriptions of the morphological changes within each stage, of the molting and hatching processes and of the quiescent states of Amblyseius citrifolius (Denmark &; Muma) were given. The larva emerged, posterior first, from the narrow end of the egg. Hatching took ca. 8 min. The duration of the ecdysis (ca. 20 to 30 min) was approximately the same for all the stages. Quiescent states were characterized by the extended, apposed palpi, by the protruded gnathosoma, by the pale, shiny coloration of the body and by a typical response to a contact stimulus. Duration of the quiescent state ranged from ca. 9.7 to 11.3 hours. Continuous observations of behavior indicated that more than 80 percent of the time in the postembryonic stages was spent resting. Number of prey (eggs and larvae) consumed by each individual in the larval, protonymphal, and deutonymphal stages were 6.3, 17.2, and 12.0, respectively. Protonymphs averaged 3.2 minutes feeding on each prey; deutonymphs, 4.7 minutes; and larvae, 8.0 minutes. At a given temperature, different relative humidities did not seem to affect the duration of the egg stage. The eclosion rates of A. citrifolius were shown in relation to saturation deficit at 16, 20, 24, 28, and 32° C. Development from egg to adult was completed in 19.7, 7.7, 5.0, and 3.6 days at 15, 20, 25, and 30 °C, respectively. Egg, larval, protonymphal and deutonymphal stages required 27.3, 10.7, 14.1, and 15.8 degree days, respectively, to be completed. Preoviposition, oviposition, and postoviposition periods and longevity were observed at 15, 20, 25, and 30 °C. Fecundity averaged 31.3, 40.9, 49.7, and 41.3 eggs per female at 15, 20, 25, and 30 °C, respectively. Average daily egg production at 15, 20, 25, and 30 °C was .75, 1.25, 2.11, and 2.51 eggs, respectively, per female. Pollens of Pyrus kawakamii, Malephora crocea (Jacq.), and avocado, a combination of Tetranychus pacificus McGregor (eggs + larvae) plus M. crocea pollen, and T. pacificus (all stages) were the best food for oviposition and survival of A. citrifolius. Tetranychus pacificus (eggs + larvae) also was one of the best for survivorship of the predator.

Biosystematics of three taxa in theAmblyseius finlandicusgroup from south africa, with comparative life history studies (Acari: Phytoseiidae)

Abstract Hybridization tests indicated that 2 morphologically distinct populations of Amblyseius in the finlandicus species group on citrus trees from Addo and Citrusdal, South Africa, were both A. addoensis van der Merwe and Ryke. These are designated as subspecies addoensis stat. nov. and rubicolus comb. nov., respectively. A third population, from Rustenberg, was not reproductively compatible with the other 2, and was determined as A. citri van der Merwe and Ryke. Morphological data and a tabular key are included. Biological studies indicated that pollen of Malephora crocea Jacq. was a more favorable food for development and reproduction than eggs and larvae of Tetranychus pacificus McGregor. The eggs of A. citri survived at lower R. H.'s than those of the 2 subspecies of rubicolus.

Effects of Pacific Spider Mite on Physiological Processes of Almond Foliage1

Leaves of potted almond trees were exposed to varied population levels of Tetranychus pacificus McGregor. An inexpensive portable reflectance meter was used to nondestructively estimate chlorophyll concentrations of intact leaves. Chlorophyll content of the leaves was negatively correlated with the number of mite-days per leaf and positively correlated with the mean percent of unscarred surface area as determined visually. Gas exchange data were obtained under field conditions with a portable dual isotope (3H2O and 14CO2) porometer which allowed simultaneous estimation of photosynthesis and transpiration on the same intact leaves. The number of mite-days per leaf and visual estimates of damage were well correlated, negatively, with Ps and Ts rates. Photosynthetic rates were positively correlated with chlorophyll content of leaves. No gross physiological changes which could not be explained by mechanical damage were observed.

The possible role of carnitine in the selective toxicity of the miticide cycloprate

The titers of free and total carnitine were determined in selected developmental stages of mites ( Tetranychus pacificus) and several insects. In general, insects contained more total carnitine than mites, and mite eggs less than other mite stages. In contrast to mammals, these arthropods contain little free carnitine, with most carnitine present as the acetate ester. Comparing metabolism of cycloprate (hexadecyl cyclopropanecarboxylate) in different developmental stages of mites indicates that selective ovicidal toxicity may result from the production of cyclopropanecarboxylic acid and its subsequent conjugation with carnitine. Thus, O-(cyclopropylcarbonyl)carnitine is a significant metabolite in mite eggs, but not in other stages. We believe that the selective ovicidal activity of cycloprate in mites may result from sequestration of carnitine as this metabolite leading to an inability to transport long-chain fatty acids into the mitochondria causing a lethal disruption of lipid utilization.

Vineyard and Laboratory Evaluations of Methomyl, Dimethoate, and Permethrin for a Grape Pest Management Program in the San Joaquin Valley of California

The impact of dimethoate, methomyl, and permethrin upon target and nontarget arthropods was determined through laboratory and vineyard tests. All compounds controlled a leafhopper, Erythroneura elegantula Osborne, in vineyard trials. Permethrin only was tested against the grapeleaf folder, Desmia funeralis (Hübner). The impact of these 3 materials upon the nontarget mite species differed. Dramatic increases of the Pacific spider mite, Tetranychus pacificus McGregor, followed permethrin treatments in vineyards at 1,5,3,6, and 12 g AI/100 liters. Laboratory LC50 data showed that the Pacific spider mite is tolerant to low-moderate rates of permethrin while its phytoseiid predator, Metaseiulus occidentalis (Nesbitt), was extremely susceptible. The tydeid, Pronematus anconai Baker, which serves as alternate prey for M. oecidentalis was very susceptible to permethrin, but tolerated methomyl and dimethoate in laboratory trials. Methomyl treatments increased the Pacific spider mite and Eotetranychus willamettei McGregor populations in vineyards although M. oceidentalis numbers began to increase 10 days after treatment and the spider mite numbers reached were lower than in the blocks treated with permethrin. Laboratory tests showed that M. occidentalis was very susceptible to methomyl, but dimethoate resistance was found in the majority of vineyard colonies tested. Dimethoate exhibited moderate acaricidal activity against the Pacific spider mite in the vineyard.

The bionomics ofScolothrips sexmaculatus(Pergande) (Thysanoptera: Thripidae), an insect predator of spider mites

The biology, temperature response, and prey requirements for Scolothrips sexmaculatus were studied in the laboratory with Tetranychus pacificus as the main prey. At 26.7 C and 50% relative humidity, the mean life cycle was 8.9 (range: 7.6-10.3) days; egg, 7.2 days; 1st-stage larva, 2.8 days; 2nd-stage larva, 2.5 days; prepupa, 1.2 days; and pupa, 2.5 days. Male and female immatures developed in the same length of time, but as larvae, killed significantly different mean numbers of prey eggs, 43.0 and 56.0, respectively. Eggs of S. sexmaculatus are inserted into leaf tissue. Larval eclosion lasted a mean 7.6 min, and larvae commenced feeding a mean 40.3 min after vacating the chorion. No larval preference or nonpreference was noted for any given prey stage. Imaginal molts lasted a mean 9.1 min, and the new adult commenced feeding after a mean 92.7 min. For adult females, no preference or nonpreference was noted for any prey developmental stage. Mating was unnecessary to induce oviposition, which usually commenced on the 1st imaginal day. Unmated females produced only male progeny. Thus, S. sexmaculatus is a facultatively arrhenotokous species. Larval and adult thrips were behaviorally well adapted to preying on tetranychids which produce copious webbing. Thigmotaxes were evident in all instars, and cannibalism did not occur until prey became scarce. The lower thermal limit for incubation was between 18.3 and 23.9 C; for larval development, 12.8 and 18.3 C; for mating, 12.8 and 18.3 C; and for production of female progeny, 12.8 and 18.3 C. At 23.9 to 40.6 C, adult female thrips produced more than a mean 200 eggs during their lifetime. During the reproductive period, a mean 6.2 to 7.2 mite eggs were killed for each thrips egg laid. At 29.4 to 40.6 C, female thrips killed more than a mean 1,700 mite eggs during their lifetime. Longevity of adult females was inversely related to temperature. Production of total progeny was highest at 29.4 C, although the highest percentage of female progeny occurred at 23.9 C. Life tables were prepared from data collected at four temperatures, and intrinsic rates of natural increase were calculated therefrom. The rm values for S. sexmaculatus were 0.155, 0.232, 0.304, and 0.360 at 23.9, 29.4, 35.0, and 40.6 C, respectively. Minimums of 20 and 25 prey eggs were required for development of males and females, respectively. Mean developmental periods of both sexes were increased significantly when larvae were provided only two or three mite eggs per day. First- and 2nd-stage larvae of S. sexmaculatus effectively searched 2.45cm2 and 10.19cm2 per hr, respectively. Densities of one mite egg per 70.52cm2 and 114.59cm2 were required for development of 1st- and 2nd-stage larvae, respectively.

Toxicity of Citrus Pesticides to Some Predaceous Phytoseiid Mites1

The relative toxicity of pesticides to adult predaceous phytoseiid mites in relation to plant feeding mites was evaluated by the slide dip technique. The toxicity ratios of Typhlodromus occidentalis Nesbitt, Amblyseius hibisci (Chant), A. stipulatus Athias-Henriot, Iphiseius degenerans (Berlese), and Phytoseiulus persimilis Athias-Henriot were compared to Panonychus citri (McGregor) or Tetranychus pacificus McGregor. T. occidentalis was more resistant to many of the pesticides than the plant feeding mites; the other 4 species of predators were generally more susceptible to the pesticides than P. citri or T. pacificus . Azinphosmethyl and Vendex® (hexakis (beta, beta-dimethylphenethyl)-distannoxane) had similar order of toxicity to the 4 predaceous species as the plant feeding mites, and tricyclohexylhydroxytin was less toxic to all 5 predaceous mites than to P. citri or T. pacificus . A. hibisci eggs were exposed to concentrations of citrus pesticides by utilizing the Potter Tower sprayer. A wide range of susceptibility of both eggs and immatures was shown to exist to the various pesticides evaluated. The egg stage was relatively tolerant to a number of the pesticides evaluated. Propargite and Vendex residues were the least toxic to the immature mites.

Management of Grape Pests in Central California Vineyards: Toxicity of Some Commonly Used Chemicals to Tetranychus pacificus and Its Predator, Metaseiulus occidentalis

Various pesticides were evaluated over a 4-year period for efficacy against the Pacific spider mites and toxicity to Metaseiulus occidentalis Nesbitt. Based on these two characteristics and the occurrence of a favorable Tetranychus pacificus McGregor (prey) and M. occidentalis (predator) ratio (35:1 or less), tested chemicals were rated for suitability in an integrated mite management program. Chemicals such as ethion, carbophenothion, and dialifor in 1972 obtained high predator survival, low spider mite densities, and one 100% favorable T. pacificus: M. occidentalis ratio, and were rated highly suitable in an integrated control program. Treatments such as dimethoate in 1970 and 1972 and dialifor in 1970 were moderately suitable. Other chemicals including monocrotophos, methidathion, formetanate, Fundal® (N′-(4 chloro-O-tolyl-N, N′ dimethylformamidine hydrochloride)), Plictran® (tricyclohexylhydroxytin), azinphosmethyl + carbaryl, Imidan® (O,O-dimethyl phosphorodithioate S-ester with N-(mercaptomethyl) phthalimide), dialifor (low rates, 1972), Galecron® (N′-(4 chloro-O-tolyl-N,N′-dimethylformamidine), and Vendex®(distannoxane, Hexakis (betadimethyl-phenethyl)) were very toxic to the predatory mite at the rates used, and were rated poorly suitable for integrated control program, although Plictran obtained good spider mite control.

Effects of Tetranychus pacificus1 and Irrigation Practices on Yield and Quality of Grapes in North Coast Vineyards of California 2

Individual grapevines of the variety ‘Sauvignon vert’ were sampled for 3 consecutive seasons for Tetranychus pacificus McGregor to determine its effect on grape yield. We also studied the feasibility of utilizing irrigation practices and releases of the predaceous mite, Metaseiulus occidentalis (Nesbitt), to control spider mite populations. Yield, sugar content and tartaric acid content of the grapes were measured on a vine-by-vine basis at harvest. Irrigation practices had no significant effect on quantity or quality of yield, although T. pacificus populations on sprinkler-irrigated vines were reduced by about one-half the number on control vines. Except under extreme stress conditions high spider mite densities did not reduce grape quality. Yield (weight) tended to be higher in plots where spider mites were controlled by M. occidentalis .

Factors Affecting Oviposition of Stethorus picipes (Coleoptera: Coccinellidae), with Special Reference to Photoperiod1

In laboratory experiments at 21–22°C, nearly 100% Stethorus picipes Casey ♀ oviposited when reared and held as adults at a 16-h photoperiod, continuous light or continuous darkness. Only ca. 30% oviposited when reared and held as adults at a 10-h photoperiod. The reproductive-nonreproductive state of females was demonstrated as reversible by exposure to appropriate photoperiods. The results of the experiments are discussed in reference to natural populations in southern California. Mean egg production and longevity were 577 eggs and 130 days at 16-h photoperiod and 21–22°C. Oviposition response showed that eggs and larvae of Tetranychus pacificus McGregor were more favorable as food than other stages of prey.

Influence of Overhead Sprinkler Systems on Spider Mite1 Populations in North Coast Vineyards of California2

Moisture stress has been suggested as a factor predisposing cotton (Leigh 1963) and grape (Flaherty et al. 1969) to attack by spider mites. The most damaging spider mite occurring on grapes, Tetranychus pacificus McGregor, is known to reach its highest densities on distal foliage exposed to direct sunlight (Flaherty and Huffaker 1970, Kinn and Doutt 1972a), where humidity is lowest and temperatures highest (Andres 1957). It has also been claimed that spider mite populations can be reduced by irrigating with overhead sprinklers (Flaherty and Huffaker 1970). Flaherty et a1. (1971) state spider mites are drowned and removed from foliage by washing with water. Studies undertaken in North Coast vineyards during the last 2 years indicate that sprinkler irrigation can be utilized in an integrated approach to spider mite control on premium wine varieties.