Higher Mite Densities Research Articles

Mechanisms of interspecific competition that result in successful control of Pacific mites following inoculations of Willamette mites on grapevines.

We have successfully reduced populations of economically damaging Pacific mites by introducing another economically unimportant herbivorous mite to grapevines. Although this technique has proven successful in greenhouse and commercial applications, we had a poor understanding of why it worked. Experiments were conducted in a Zinfandel vineyard to assess the relative importance of different forms of competition between these two species and the importance of the timing of the introduction. The early season release of Willamette mites that occurred as shoots were first elongating reduced populations of Pacific mites, indicating that some form of competition occurred in this experiment. However, introductions of Willamette mites 4 weeks later did not reduce populations of Pacific mites. An early season release is essential for control. Control shoots did not receive additions of Willamette mites and had high population densities of Pacific mites. In contrast to this, Pacific mite populations were reduced on treatments with Willamette mites, regardless of whether the two species overlapped spatially or were separated by a barrier. This indicated that physical interference was not responsible, that induced resistance was involved, and that the effect was systemic throughout the shoot.

Effects of mite age, mite density, and host quality on aerial dispersal behavior in the twospotted spider mite

AbstractMite age, population density, and host leaf quality affect various life history traits in spider mites. We investigated the effects of these factors on the aerial dispersal behavior of adult female twospotted spider mites, Tetranychus urticae Koch (Acari: Tetranychidae). The proportion of adult females exhibiting the dispersal behavior dropped significantly with age following adult emergence, particularly in the first 3 days. Sixty to eighty percent of female mites 2‐days old or younger displayed the behavior under test conditions, whereas less than 20% of female mites older than 3‐days‐old showed the behavior. Younger adult females also exhibited shorter latency for the behavior, although this trend was not as clear. Leaf quality experienced during deutonymph development had no effect on the behavior adults subsequently displayed. On the other hand, adult females that fed on poor quality leaves after emergence were twice as likely to display the behavior (90% vs. 45%), and with shorter latency (37 vs. 77 min), than those that fed on high quality leaves. When newly emerged adult females encountered high mite density and dry leaves, the incidence of the behavior increased (69% vs. 47%) and latency decreased (69 vs. 93 min) compared to mites that encountered low density on well watered leaves. Our results suggest that both starvation and desiccation of adult females may enhance their dispersal behavior.

Incidence of Caloglyphus phyllophagianus (Acari: Acaridae) on Adult Phyllophaga spp. and Other Scarabaeidae (Coleoptera) in North Central Texas

Sixteen species of adult scarabs collected over 3 yr in ultraviolet light traps in Dallas County, Tex., had widely varying levels of infestation with a nonfeeding larval stage (heteromorphic deutonymph) of Caloglyphus phyllophagianus Oseto & Mayo. The beetles were the geotrupines Bolbocerosoma confusum Brown and B. pusillum Dawson & McCulloch; the dynastines Cyclocephala lurida Bland, Dyscinetus morator (F.), and Euetheola rugiceps (LeConte); the hybosorine Hybosorus illigeri Reiche; the ruteline Pelidnota punctata L.; the melolonthines Phyllophaga affabilis (Horn), P. congrua (LeConte), P. crassissima (Blanchard), P. crinita Burmeister, P. glabricula (LeConte), P. hirtiventris (Horn), P. rubiginosa (LeConte), and P. torta (LeConte); and the trogine Omorgus suberosus (F.). The distributions of deutonymphs were compared with eight theoretical distributions. In total, 8 of 23 data sets based on beetle species, sex, and year fit the negative binomial distribution; one set fit the positive binomial distribution; and one set fit the Neyman type A distribution. Also, 13 data sets fit none of the distributions, but variability in the entire range of data was described using Taylor's power law. Infestation rates ranged from zero ( Bolbocerosoma spp., D. morator , and E. rugiceps ) to 85.0% ( P. glabricula ). The highest mean mite density was 25.4 mites per beetle (maximum, 300 mites) on P. torta . Mite densities on some host species were influenced by host sex, year, and date. The relative ranking of beetle species as hosts tended to be consistent from year to year. Host size was only weakly correlated with mite density, and synchronously-reproducing host species that share habitats had widely varied levels of infestation. These facts suggest that some species may be inherently more preferred by the mites.

Sampling Mononychellus tanajoa (Acari: Tetranychidae) on cassava in Africa

AbstractDensity-specific sampling plans were developed under African conditions for the exotic spider mite, Mononychellus tanajoa (Bondar), a serious pest of cassava, Manihot esculenta. The within-plant distribution of Mononychellus tanajoa was found to favour new foliage, regardless of time of planting or plant age. Consequently, the first developed leaf near the top of the foliage was selected as the sampling unit and related to whole plant populations of M. tanajoa. The relationship between the mite population's variance and mean as measured by Taylor's Power Law proved to be stable over a range of planting dates, seasons and locations. Two binomial sampling plans, one based on Taylor's dispersion parameters and another based on direct field observations, were developed and compared. Binomial sampling, appropriate only for densities below 30 mites per leaf, was replaced by an enumerative procedure based on a ‘quick count’ protocol at higher mite densities.

Influence of dispersal from almonds on the population dynamics and acaricide resistance frequencies of spider mites infesting neighboring cotton

Neighboring almond and cotton fields were sampled for spider mites in four locations in the San Joaquin Valley of California. The dominant species in the almonds wasTetranychus pacificus McGregor. In three cotton sites.T. pacificus was present in significantly higher densities near the almonds on at least one sampling date. In contrast.T. urticae Koch andT. turkestani Ugarov & Nikolski were equally abundant across the cotton fields. Almonds appeared to act as a continuous early-season source ofT. pacificus for cotton, with peaks in aerial dispersal from almonds occurring due to overcrowding, plant water stress, and applications of repellent acaricides. Cotton, which experienced little water stress, supported very high densities of spider mites and so acted primarily as a sink for spider-mite dispersal from almonds and other field crops throughout the growth-season. The frequencies of resistance expressed byT. pacificus andT. urticae were similar between neighboring crops, even if the acaricide had been registered for use only in almonds (cyhexatin) or cotton (dicofol). Thus, longterm acaricide selection and movement of spider mites between the two crops resulted in similar proportions of resistant individuals. In these study sites, large-scale dispersal ofT. pacificus from almonds rarely directly affected acaricide efficacy in cotton, because resistance frequencies were similar for spider mites from the two crops and because acaricide applications were usually made in cotton after dispersal from almonds was completed. In two cotton sites, field selection with dicofol was reversed by subsequent immigration of spider mites from neighboring field crops.

Control of Spider Mites on Celery, 1989

Abstract Plots were established in the portion of a celery field near Mission, Tex. which had not been harvested because of high spider mite densities and associated damage. Each plot consisted of 2 beds (4 rows) on 40 inch centers by 15 ft. Plots were arranged in a randomized complete block design with 3 replications. All acaricides were applied on 12 Dec and 20 Dec, 1988, using a CO2-pressurized backpack sprayer calibrated to deliver 69.5 gal/acre (2 flat-fan nozzles/bed; 40 psi). Acaricide treatments were evaluated by counting the number of motile adult mites on the underside of 5 randomly selected trifoliates/plot. A visual rating technique was also used with a 1 (lowest) to 5 (highest) rating, based on the relative abundance of spider mites, assigned to each of 15 randomly selected trifoliates/plot.

Influence of ground cover and herbicide treatments onTetranychus urticae populations in peach orchards

Two-spotted spider mites,Tetranychus urticae Koch, were sampled in peach orchards to quantify abundance in trees over different types of ground cover to document the dispersal of mites from orchard-floor plants to trees. Mite populations developed more quickly and with higher densities in trees over ground cover compared to bare ground, and specifically over covers of predominantly narrowleaf vetch,Vicia angustifolia Reichard. Orchard floor plants such asVicia, Geranium, Lamium, andLepidium contained relatively high densities of mites during early spring, and may have formed the source for later peach-tree infestation.

Density, Location, and Sampling of Sarcoptes scabiei (Acari: Sarcoptidae) on Experimentally Infested Pigs

Forty-eight weaned pigs were inoculated with 0 (controls), 100 (low dose), and 1,000 (high dose) itch mites, Sarcoptes scabiei (De Geer), and allowed to develop infestations for up to 10 wk. Pigs were slaughtered in sequence during the experiment to sample hides and count mites through potassium hydroxide digestion. Incipient crusted lesions occurred in ears of 4 of 16 low-dose pigs and 7 of 16 high-dose pigs, averaged less than 3 cm2 in area, and contained 86% of all females and 87% of all other mite stages found on those pigs. Crusts aside, faces had the highest mite densities among six body regions in both infested groups. Overall, high-dose pigs had higher mite populations (269 compared with 39 mites on low-dose pigs), although values were not significantly different (P = 0.13). Mite populations did not grow significantly during the 10 wk, but variance increased among pigs in each dose group. A hide-sampling plan derived from these data indicates whole-body populations could be estimated by censusing only the crusts, if present. If absent, sampling mites from the face and dorsum should provide acceptable estimates of whole-body totals of females and other stages. A sample size of 13 hides from a herd will yield an estimate of mean whole-body total with a 90% CI less than or equal to 50% of the estimated mean.

Honey bee mortality due to tracheal mite parasitism

We demonstrate, by truncating the expected negative binomial distribution, that the tracheal mite parasite, Acarapis woodi, causes mortality in the European honey bee, Apis mellifera, but, that this mortality can be documented only during periods of low mite densities (mites per bee). At high mite densities, this technique no longer reveals mite-induced mortality. We suggest that this paradox results from a reduction in the mortality threshold at high mite densities, concealing mortality from our truncation procedures. Longitudinal comparisons of hive and forager bee cohorts, nevertheless, suggests mortality at all levels of infestation. We propose that persistent parasitism overcomes a colony's ability to compensate for losses, leading to its sudden decline and death.

Release and Evaluation of a Laboratory-Selected, Pyrethroid-Resistant Strain of the Predaceous Mite Metaseiulus occidentalis (Acari: Phytoseiidae) in Southern Oregon Pear Orchards and a Washington Apple orchard

A laboratory-selected strain of the spider mite predator Metaseiulus occidentalis (Nesbitt) was released into two southern Oregon pear orchards and a Washington apple orchard in June 1980. The permethrin and organophosphorus insecticide (OP)-resistant predators became established in all three orchards, overwintered, and survived repeated permethrin applications during 1980 and 1981. By summer 1981, the predators had spread into adjacent trees in release areas in both states. Foliage damage was substantially reduced compared with trees lacking the permethrin-OP-resistant predators in Oregon in 1981. in Washington in 1980, spider mite populations were significantly lower and M. occidentalis populations significantly higher on release trees than on control trees. In 1981, the frequency and rates of permethrin applications caused high mortality of the resistant M. occidentalis and high spider mite densities developed on all sampled trees. Permethrin resistance levels remained high in the orchard populations after two field seasons, despite the polygenic nature of this resistance. Future releases should be considered, especially where releases can be made into each tree and selective acaricides can be used to manage spider mite-predator densities until a more stable relationship occurs.

Reductions in Plant Processes by Tetranychus urticae (Acari: Tetranychidae) Feeding on Strawberry

Studies were conducted in 1980 to evaluate the effects of low and high population densities of Tetranychus urticae on photosynthesis, transpiration, productivity, and vegetative growth of strawberry plants under field conditions. All factors were significantly reduced by high mite densities. A sequenced mite-day model is presented and includes pertinent points on the population curve where the plant processes were reduced by 10%. The significance of the sequence in which the plant processes were reduced is discussed.

The thermal environment of the citrus rust mite

The distribution of citrus rust mite on individual fruit and in the whole citrus tree suggests an avoidance of solar exposure. A model of fruit temperatures as affected by solar radiation in different parts of the tree was constructed, and its predictions are compared with field temperatures and rust mite distribution patterns. The fruit temperature model is a function of latitude, time of year, time of day, fruit diameter and reflectance, position in the tree, atmospheric transmissivity and wind velocity. Where model predictions indicate unfavorable conditions, rust mite population levels were low. When the tree was divided into north-south, top-bottom quadrants, the north bottom quadrant had the most favorable temperatures and usually the most rust mites; the south bottom was also favorable and had high mite densities. The south top quadrant was least favorable often having temperatures in the lethal range, and it also had the lowest rust mite populations.

Occurrence of house dust mites, Dermatophagoides spp. (Acari: Pyroglyphidae), during the heating season.

Four sites in homes of dust-allergic patients were sampled for house dust mites. Levels of infestation in specific sites ranged from 0–3120 mites per gram of dust for Dermatophagoides spp., with considerable variation within and between homes. Greater usage of infested articles and rooms and larger household size were correlated with higher mite densities. A positive correlation was found between mite population levels in mattresses and living room furniture as compared to floors beneath them. Plastic encasement precludes mite occurrence in mattresses, but not in other locations. Use of an air filtering device did not reduce the mite population to a low level. No correlation was found between mite density and age of dwelling, dwelling type, socioeconomic level of the resident, or presence or absence of central air conditioning, and dehumidifiers.

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 .

Integrated Control: Effect on European Red Mite and Its More Important Predators1

Economic suppression of Panonychus ulmi (Koch) has been realized during the first 2 years of an integrated control study on 10 acres of apple trees in central Ohio. Naturally occurring insect predators have reduced mites during the summer and have also reduced numbers of overwintering eggs. Conversely, low predation has permitted high mite populations on scattered experimental trees, with subsequent high overwintering egg deposition resulting in high mite densities the following year. The association with low and high mite densities is reported for these predators: Leptothrips mali (Fitch), Orius insidiosus (Say), Plagiognathus politus Uhler, Chrysopa rufilabris Burmeister, C. carnea Stephens, and Stethorus punctum (LeConte). Ryania and lead arsenate were without effect on L. mali, O. insidiosus and the chrysopids. Azinophosmethyl destroyed all nymphs of L. mali and O. insidiosus , but only 45–65% of the chrysopid larvae; carbaryl eliminated L. mali nymphs.