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To understand the influence of different apple varieties on the development and reproduction of the European red mite, Panonychus ulmi (Koch) (Acari: Tetranychidae), age-stage two-sex life tables of P. ulmi on 'Fuji,' 'Starkrimson Delicious,' 'Golden Delicious,' and 'Granny Smith' varieties were constructed under laboratory conditions at 23 ± 1°C, 75 ± 5% relative humidity, and a photoperiod of 16:8 (L:D) h. Results showed that total development time of immature females was shorter on Fuji than on the other varieties, and this was because of its shorter egg duration. Immature survival of P. ulmi was 74.51-78.00% among four apple varieties, and no significant differences were found. The total fecundity per female was significantly higher on Golden Delicious (34.12 eggs per female) than that on Fuji (27.15 eggs per female), Starkrimson Delicious (25.15 eggs per female), and Granny Smith (20.62 eggs per female). Based on the intrinsic rate of population increase, Fuji and Golden Delicious were more suitable than Starkrimson Delicious and Granny Smith. [ABSTRACT FROM AUTHOR]

Laboratory bioassays were conducted to characterize the activity of the insecticide spinosad against the twospotted spider mite, Tetranychus urticae Koch, and European red mite, Panonychus ulmi (Koch) (Acari: Tetranychidae). T. urticae females and larvae were individually placed on bean, Phaseolus vulgaris L. (Fabaceae), leaf disks treated with four rates of spinosad (25, 55, 121, and 266 ppm) and a water control. Significantly fewer T. urticae completed development on any spinosad rates (<15%) compared with the control (>85%), whereas spinosad exhibited no significant effects on P. ulmi development; 72.5 and 83.1% of P. ulmi completed development on apple (Malus pumila P. Mill, Rosaceae) leaf disks treated with 75 ppm spinosad and the control, respectively. T. urticae adult females placed on spinosad-treated disks had significantly higher mortality and lower oviposition rates compared with the water control; no significant mortality effects were observed until 3 d after placing adults on leaf disks. In choice tests where half of a bean leaf was treated with 55 ppm spinosad transversally or longitudinally, T. urticae females were repelled by spinosad and largely oviposited and fed on nonspinosad treated areas. Spinosad did not affect the behavior of P. ulmi females. When T. urticae females were released on potted bean plants (two-leaf stage) in which leaves received spinosad sprays on the adaxial or abaxial leaf surfaces, or complete spinosad coverage on one or two of the leaves, mite population increase lagged significantly behind those released on control plants. These results indicate that spinosad has significant acaricidal effects against T. urticae but not P. ulmi. [ABSTRACT FROM AUTHOR]

The threshold temperature for postdiapause development in overwintering eggs of the European red mite, Panonychus ulmi (Koch), was determined after exposing the eggs to various constant temperatures (5, 10, 15, 20, and 25°C) in the laboratory. The mean number of days to 50% hatch in each temperature was >120, 44.5, 22.0, 14.5, and 8.1 d, respectively. From the regression of postdiapause developmental rate to temperature, it was estimated that 50% of egg hatch coincides with the accumulation of 154.6 degree-days (DD) above the threshold of 7.4°C. In the field (1991 and 1993-1996), 50% egg hatch occurred from the end of March to 20 April after the accumulation of a mean sum of 129.4 ± 4.5 DD above the threshold of 7.4°C from 10 February onward. The starting date of 10 February for heat accumulation was chosen because earlier experiments had shown that diapause is terminated in 50% of the eggs in the first half of February. Using the theoretical sum of 154.6 DD, the predicted dates for 50% egg hatch deviated from field observations by an average of 3.7 ± 0.5 d over the 5 yr of experiments. [ABSTRACT FROM AUTHOR]

An organophosphate/pyrethroid resistant strain of the phytoseiid mite Typhlodromus pyri Scheuten was imported from New Zealand in 1988 for use in biological control of European red mite, Panonychus ulmi (Koch), and apple rust mite, Aculus schlechtendali (Nalepa), in Nova Scotia. To better understand the overwintering strategy of T. pyri and the likelihood the New Zealand strain would withstand winter conditions in Canada, we measured supercooling points and mortality of diapausing females held at subzero temperatures. Mites in quartz crucibles were placed in the liquid nitrogen-cooled stage of a cryostage microscope, and temperature was lowered 1°C/min until the mites froze, as indicated by an instantaneous darkening of their body contents. Supercooling points of the New Zealand strain averaged â'18.2°C for July to September, were â'23.2°C in October, and averaged â'28.2°C in the colder months from November to March. The mean supercooling points for December 1994 did not differ from the mean for the native Nova Scotian strain. However, the mean supercooling point of the New Zealand strain for March 1995 was higher than the means for the native strain and for a T. pyri strain that was imported from Geneva, NY. New Zealand strain T. pyri taken from cloth bands affixed to orchard trees were placed on apple leaves in plastic vials and exposed to low temperatures for various periods of exposure. At â'5°C, mortality at 24 h was less for mites collected in February than for those collected in November (6% versus 44%) but at â'10°C trends were similar, reaching 100% by 24 h in both trials. For the February trial, a logistic function with a coefficient for the product of time and temperature explained 61% of the variation in mortality. If these results are applied to populations in Nova Scotian orchards, where winter temperatures of â'10°C are common, one would predict complete annihilation of the New Zealand strain. However, populations of the New Zealand strain, first released in orchards in 1988, have survived every winter since that date and have proven effective in biological control of European red mite and apple rust mite. Possible reasons for survival and increase of populations of this exotic strain of T. pyri, despite apparent susceptibility to cold-induced mortality, are discussed. [ABSTRACT FROM AUTHOR]

To assess the impact of disturbances on mite populations being regulated at low densities, the phytophagous mites Panonychus ulmi (Koch),Eotetranychus sp., Bryobia rubrioculus Scheuten, and Aculus schlechtendali Nalepa and the predaceous mites Zetzellia mali (Ewing), Amblyseius andersoni Chant, and Typhlodromus pyri Scheuten were sampled during 1996-1997 in 5 apple plots treated with azinphosmethyl (OP) (2 plots), OP + endosulfan (E) (1 plot), or were unsprayed (2 plots) in 1993-1995. P. ulmi had been regulated at very low, but differing densities by predators (OP + E > OP > unsprayed) and the numbers of predator species present were OP + E (1 species), OP (2 species), and unsprayed (3 species) during 1993-1995. During 1996-1997, plots were treated just as in 1993-1995, except that 10 of 20 trees per plot had 150-200 P. u1mi released per-tree and all 20 trees of 1 OP and 1 unsprayedplot had esfenvalerate sprayed early in 1996. We expected the peak densities of P. ulmi in 1996-1997 to reflect the earlier densities andthe diversities of predators present. Lowest peaks and the shortest outbreaks of P. ulmi in 1996-1997 were expected in the unsprayed plots with 3 predator species and the fewest P. ulmi in 1993-1995; highest peaks and longest outbreaks were expected in the OP + E plot with 1predator species and the most P. ulmi in 1993-1995. Densities in 1996-1997 supported these expectations, but with strong pesticide effects. With no esfenvalerate use, regulation of P. u1mi was as in 1993-1995, but P. ulmi was 10- to 1,000-fold denser with use of esfenvalerate. With esfenvalerate use and release of P. u1mi, they were most dense in year 1 after treatments and the outbreak lasted 2 yr before predators recovered; with esfenvalerate use and no release of P. ulmi, they were the most dense in year 2 and the oubreak lasted only 1 yr. Outbreaks of A. schlechtendali and B. rubrioculus also occurred in year2 after esfenvalerate use. [ABSTRACT FROM AUTHOR]