Susceptible Mites Research Articles

Effect of acaricide resistance on reproductive ability of the honey bee mite Varroa destructor.

The reproduction of pyrethroid-resistant Varroa destructor mite, a brood parasite of honey bees, was observed in Weslaco, Texas, and the results compared with known susceptible mite populations from other studies. Seven Apis mellifera colonies that had mite populations resistant to the acaricide Apistan were used. Pyrethroid-resistance was confirmed when only 17% rather than 90% of mites confined in dishes containing Apistan died after 12 h of exposure. The average number of eggs laid by resistant mites invading worker and drone cells was 4.4 and 5.4 respectively. This is similar to the number of eggs laid by susceptible mites in worker (4.4-4.8) or drone (4.7-5.5) cells. Also the average number of fertilised V. destructor female mites produced by resistant mites in worker (1.0) and drone (2.1) cells were similar to the number produced by susceptible mites in worker (0.9) and drone (1.9-2.2) cells. In addition, no major differences between the resistant and susceptible mite populations were observed in either worker or drone cells when six different reproductive categories and offspring mortality rates were compared. Therefore, it appears that there is little or no reproductive fitness cost associated with pyrethroid resistance in V. destructor in Texas.

Host plant-induced changes in detoxification enzymes and susceptibility to pesticides in the twospotted spider mite (Acari: Tetranychidae).

Adult female twospotted spider mites, Tetranychus urticae Koch, reared on lima bean plants were moved to cucumber, maize, or new lima bean plants (the latter being a control) and evaluated after 24 h or 7 d for changes in susceptibility to three pesticides and in levels of related detoxification enzymes. The largest and most consistent changes were observed in mites feeding on cucumber. Susceptibility of mites on cucumber to the synthetic pyrethroids bifenthrin and lambda-cyhalothrin was greater than that of mites reared on lima bean and maize after only 24 h on the plants, and remained higher after 7 d. Mites on cucumber also were more susceptible to the organophosphate dimethoate than were mites on lima bean, but only after 7 d on the host. Susceptibility was inversely related to activities of both general esterase and glutathione S-transferase (GST) in mites on cucumber; general esterase and GST activities were 60 and 25% lower, respectively, than activities of twospotted spider mite on lima bean after 7 d of feeding. Mites on maize were slightly but significantly more susceptible than those on lima bean to bifenthrin, but not to lambda-cyhalothrin, after 7 d and to dimethoate after 24 h but not after 7 d. General esterase and GST activities in twospotted spider mite fed on maize for 24 h were 20 and 16% higher, respectively, than activities in twospotted spider mite on lima bean, but general esterase activity was 30% lower than lima bean-fed mites and GST was not different after 7 d. Thus, plant-induced changes in general esterase activity, perhaps in combination with GST activity, in twospotted spider mite appear to be inversely related to, and possibly responsible for, changes in susceptibility of twospotted spider mite to several pesticides, particularly the synthetic pyrethroids. General esterases appear to play less of a role in the detoxification of the organophosphate insecticide dimethoate.

Feeding behaviour of omethoate-resistant spider mites (Acari: Tetranychidae): a study using electrical penetration graphs

The feeding behaviour of omethoate-resistant and susceptible strains of the spider mites (Tetranychus cinnabarinus) on cowpea leaves was studied by electrical penetration graph (EPG). EPG waves of the mite feeding were divided to two forms, the high frequency (7.7-8.7 Hz) and low frequency waves (2.4-3.0 Hz), representing feeding and non-feeding behaviour respectively. The average duration of feeding periods was not significantly different between resistant and susceptible mites. However, the amplitudes of feeding waves were significantly greater in pesticide-resistant mites than susceptible mites.

Effect of seedling damage by redlegged earth mite, Halotydeus destructor, on subsequent growth and development of yellow lupin, Lupinus luteus, in the glasshouse

Redlegged earth mite (Halotydeus destructor) causes feeding damage to some pulse species at the seedling stage. To quantify the effect of this damage on subsequent plant growth and development, an experiment was conducted in the glasshouse using yellow lupin, Lupinus luteus cv. Motiv, which is highly susceptible to the mites. After emergence, plants were infested with 0, 100, 150, and 250 mites/plant, collected from the field. Fourteen days after application, mites were removed. Damage to plants was estimated at seedling stage, flowering time, and maturity. At seedling stage (on Day 14), feeding damage scores to cotyledons and true leaves were greater at higher mite densities. Damaged plants produced fewer nodules, fewer lateral roots, and less dry weight than the control. On Day 35, severely damaged plants failed to recover and on the surviving plants, cotyledons and true leaves died earlier than on the plants without damage. On Day 78, when plants were flowering, the surviving plants produced fewer nodules and branches, and less dry weight per plant than the control. The flowering time of plants with the mite treatments was delayed by up to 6 days compared with the controls. The final shoot dry weight, pod number, seed number, and seed yield per pot were significantly reduced by the mite treatments. Feeding by H. destructor on seedlings of yellow lupin caused a reduction in seed yield of 58% at the highest mite density treatment. This significant economic loss needs to be confirmed under field conditions, but it signifies the need to develop appropriate control measures for this pest.

The discrimination of cottonwood clones in a mature grove along the Oldman River in southern Alberta

In southwestern Alberta, the prairie cottonwood (Populus deltoides Bartr.), balsam poplar (Populus balsamifera L.), narrowleaf cottonwood (Populus angustifolia James), and interspecific hybrids provide the foundation of the biologically rich riparian forests. In addition to seedling-based reproduction, these cottonwoods are capable of clonal propagation, the extent of which is poorly understood. To investigate clonality in mature cottonwoods, a method for clone recognition was investigated. Between 1995 and 1997, the morphology and phenology of each tree in a mature cottonwood grove along the Oldman River were characterized. In decreasing order of utility, the characteristics most effective in revealing clones were sex, leaf shape, floral (inflorescence) phenology, and leaf phenology: flushing, senescence, and abscission. Independent traits of poplar bud gall mite (Aceria parapopuli Keifer) susceptibility and trunk architecture were less useful in clone delineation but validated the clonal determinations. Based on the analysis, the grove's 391 trunks (>10 cm diameter) included 115 genotypes, 48 single-trunked individuals, and 67 multiple-trunked clones. The clones (genets) contained from 2 to 53 trunks (ramets). It was found that 88% of trunks belonged to clonal groups, a proportion that was higher than anticipated. The extensive capacity for clonal recruitment should thus be considered in analyses of cottonwood reproductive ecology and cottonwood conservation and restoration programs.Key words: asexual reproduction, clone delineation, cottonwoods, morphology, phenology, Populus.

A Potter spray tower bioassay of two petroleum spray oils against adult female Panonychus ulmi (Koch) and Tetranychus urticae Koch (Acari: Tetranychidae)

A Potter spray tower was used to determine the susceptibility of adult female European red mites (Panonychus ulmi (Koch)) and two-spotted spider mites (Tetranychus urticae Koch) to suffocation by petroleum spray oils (PSOs). The LC95 values calculated for P. ulmi against C23 Ampol D-C-Tron NR and C21 Caltex Lovis were 104 and 165 μg cm-2, respectively. For T. urticae the values were 169 and 207 μg cm-2, respectively. The results are consistent with established relationships between PSO efficacy and increasing PSO molecular weight. The results are discussed in relation to previously reported bioassays on spider mites and to concurrent evaluations of PSOs for use in pome fruit integrated pest management programmes in Australia.

Modelling Fungal (Neozygites cf. Floridana) Epizootics in Local Populations of Cassava Green Mites (Mononychellus Tanajoa)

The fungus, Neozygitis cf. floridana is parasitic on the cassava green mite, Mononychellus tanajoa (Bondar) (Acari: Tetranychidae) in South America and may be considered for classical biological control of cassava green mites in Africa, where cassava is an important subsistence crop, cassava green mites are an imported pest and specific natural enemies are lacking. Spider mites generally have a viscous structure of local populations, a trait that would normally hamper the spread of a fungus that is transmitted by the contact of susceptible hosts with the halo of capilliconidia surrounding an infectious host. However, if infected mites search and settle to produce capilliconidia on sites where they are surrounded by susceptible mites before becoming infectious, then the conditions for maximal transmission in a viscous host population are met. Because the ratio between spider mites and the leaf area they occupy is constant, parasite-induced host searching behaviour leads to a constant per capita transmission rate. Hence, the transmission rate only depends on the number of infectious hosts. These assumptions on parasite-induced host search and constant host density lead to a simple, analytically tractable model that can be used to estimate the maximal capacity of the fungus to decimate local populations of the cassava green mite. By estimating the parameters of this model (host density, per capita transmission rate and duration of infected and infectious state) it was shown that the fungal pathogen can reduce the population growth of M. tanajoa, but cannot drive local mite populations to extinction. Only when the initial ratio of infectious to susceptible mites exceeds unity or the effective growth rate of the mite population is sufficiently reduced by other factors than the fungus (e.g. lower food quality of the host plant, dislodgement and death by rain and wind and predation), will the fungal pathogen be capable of decimating the cassava green mite population. Under realistic field conditions, where all of these growth-reducing factors are likely to operate, there may well be room for effective control by the parasitic fungus.

Genetic improvement of Amblyseius finlandicus (Acari: Phytoseiidae): laboratory selection for resistance to azinphosmethyl and dimethoate

Amblyseius finlandicus (Oudemans) was selected in the laboratory for resistance to azinphosmethyl and dimethoate by subjecting adult females to increasing concentrations of dried residues of dimethoate and azinphosmethyl on detached bean leaves. The first eight selections were done with dimethoate. Slide-dip bioassays indicated selection with dimethoate increased dimethoate resistance 1.8-fold and azinphosmethyl resistance 2.6-fold. These resistances appeared to be quite stable: a 1.2 to 1.3-fold decrease in resistance ratios was observed in a subculture after 10 months without selections. No decrease was observed after 9 months without selections in a pooled colony that consisted of both resistant and susceptible mites. The dimethoate-selected colony was subsequently selected eight times with azinphosmethyl. About 15 % of the mites survived the last selection round with 2,500 ppm, which is 2.5 times the highest recommended field rate in Finnish apple orchards. At the end of the selection program, based on slide-dip bioassays, the total increase in resistance to dimethoate was about two-fold and to azinphosmethyl about 5.4-fold compared to the unselected base colony from which the selected colony was derived. The LC50 value for azinphosmethyl was 14 times higher in the selected colony (451.3 ppm a.i.) compared to the most susceptible colony tested. A similar level of resistance to both pesticides was achieved after six azinphosmethyl selections on a mixed colony that was initiated by pooling mites from five field-collected colonies and the dimethoate-selected lines. Year-to-year variation in azinphosmethyl LC50 values of the unselected base colony was high, with values varying from 83.8 to 348.7 ppm a.i., demonstrating the need to test a reference strain in each bioassay. Results of the azinphosmethyl selections and the subsequent slide-dip bioassays suggest that the resistant strain could tolerate field rates of azinphosmethyl (300–950 ppm a.i.) used in Finnish apple orchards.

Enhanced activation is the mechanism of negative cross-resistance to Chlorpyrifos in the Dicofol-IR strain of Tetranychus urticae (Acari: Tetranychidae).

The mechanism responsible for negative cross-resistance to chlorpyrifos was examined in isogenic dicofol susceptible (Orchard-12) and resistant (Dicofol-IR) two-spotted spider mites, Tetranychus urticae Koch. The acetylcholinesterase of both strains was equally sensitive to inhibition by chlorpyrifos oxon. However, the Dicofol-IR strain showed increased oxidative activation of chlorpyrifos to chlorpyrifos oxon relative to the Orchard-12 strain, suggesting this mechanism is responsible for the observed negative cross-resistance.

Stability of Dicofol Resistance in Populations of European Red Mite (Acari: Tetranychidae) on Apples in Southern Ontario

Fluctuations in levels of resistance to dicofol in populations of European red mite, Panonychus ulmi (Koch), from several orchards with different frequencies of resistant individuals were compared with responses of laboratory colonies established from the same sites. Considerable variability in responses occurred in observations spaeed over 2 yr, but the frequency of dicofol-resistant individuals in these populations did not decline in the absence of selection pressure. Laboratory colonies reared through 32 generations displayed relatively constant resistance frequencies, suggesting that dicofol resistance is stable for a time equivalent to at least 3 yr in the field. Relative fecundities of mites resistant and susceptible to dicofol were examined by comparing the number of eggs laid by females from intra- and interstrain crosses, as well as the percentage hatchability, percentage survivorship, and sex ratio of the resulting progeny. Females from a 12-yr-old susceptible laboratory colony laid more eggs than females from a more recently established susceptible colony and than females from two colonies resistant to dicofoi. Resistant and susceptible mites did not differ for any of the other parameters examined. It is concluded that the absence of a reproductive detriment is a major factor in the apparent stability of resistance to dicofol in these mites. Implications of these findings for management of dicofol resistance in P. ulmi are discussed.

RESIDUAL TOXICITY OF DICOFOL, FORMETANATE HCl, PROPARGITE, HEXYTHIAZOX, AND CLOFENTEZINE TO EUROPEAN RED MITE ON PEACH

AbstractThe persistence of toxic effects of the contact acaricides dicofol, propargite, and formetanate HCl and the ovicides clofentezine and hexythiazox to the European red mite, Panonychus ulmi (Koch), were tested by bioassays of disks cut from treated peach foliage. Effects of dicofol were more persistent than propargite or formetanate HCl to susceptible mites. Mortality on dicofol-treated foliage was >50% for more than 15 days. Propargite killed >50% of females for 10 days after application, whereas the toxicity of formetanate HCl deposits declined rapidly after 7 days. Mortality of dicofol-resistant mites was less than for susceptible mites. However, resistant mites were affected (>50% killed) by dicofol residues up to 7 days old. The toxic effects of the ovicides clofentezine and hexythiazox persisted for at least 30 days and at the rates tested were approximately equally toxic.Formetanate HCl and propargite residues were less persistent (half-life 8–9 days) than the other compounds. Dicofol residues had a half-life of about 15 days but approximately 10% of residues persisted for 65 days. Residues of clofentezine and hexythiazox declined more gradually (half-life = 15–20 days) than other compounds and persisted at approximately 10% of initial residues after 65 days.

Citrus Fruit Sector Chimeras as a Genetic Resource for Cultivar Improvement

Citrus fruit with sector chimeras were collected in commercial packinghouses and from the field. Chimeric fruit from eight cultivars of sweet oranges [Citrus sinensis (L.) Osbeck], grapefruit (C. paradisi Macf.), tangelo (C. paradisi × C. reticulate Blanco), and tangors (C. reticulate × c. sinensis) were found at a frequency of 0.009% to 0.271%. Tetraploid plants obtained from one type of sector mutant (termed gigas) and albino plants obtained from another type of sector mutant confirmed that some genetic mutations observed in fruit rind can be recovered in nucellar seedlings. The gigas chimeras were identified as a source of citrus tetraploids. Several types of potentially useful sector mutants with altered rind color were observed, and plants were produced from some mutant sectors by developed seed or culture of aborted ovules. HPLC analysis of rind tissues from sectors of one chimeric fruit revealed substantial quantitative and qualitative differences in pigment composition. Propagation of plants from mutant sectors may yield cultivars with improved fruit color, altered maturation date, and reduced disease or mite susceptibility and may eventually lead to breeding of seedless triploid hybrids.

Dicofol Resistance in Tetranychus urticae (Acari: Tetranychidae): Cross-Resistance and Pharmacokinetics

Cross-resistance of dicofol-resistant Tetranychus urticae Koch to 21 pesticides was evaluated. Initial investigations used field-collected dicofol-resistant and susceptible colonies. Near-isogenic lines, constructed by a series of backcrosses, were used to confirm or reject determinations of cross-resistance derived from evaluations of field-collected colonies. Dicofol-resistant T. urticae showed strong positive cross-resistance to amitraz, bromopropylate, and chlorobenzilate. Moderate negative cross-resistance to ward chlorpyrifos was observed. These results suggest that amitraz, bromopropylate, and chlorobenzilate should not be used in alternation with dicofol in a resistance management program designed to exploit the instability of dicofol resistance. The uptake and distribution of (14C)-dicofol was investigated in near-isogenic lines of susceptible and resistant mites. No difference in the uptake of radiolabel was observed between strains, suggesting that decreased penetration is not a major mechanism of dicofol resistance. In vivo metabolism studies revealed greater production of water soluble metabolites and lower levels of internal dicofol in the resistant strain compared with the susceptible. Therefore, the major mechanism of resistance to dicofol appears to be increased metabolic detoxification.

Action of Insecticides to Spider Mites (Acari: Tetranychidae) on Corn in the Texas High Plains: Toxicity, Resistance, and Synergistic Combinations

Insecticide resistance within mite populations and seasonal shifts of mite infestations from a predominance of Banks grass mite, Oligonychus pratensis (Banks), to a complex which includes the two spotted spider mite, Tetranychus urticae Koch, complicate mite control in corn on the Texas high plains. Field efficacy trials from 1977 to 1987 showed that the registered insecticides did not adequately control Banks grass mite on corn. Monocrotophos was the only chemical evaluated that consistently controlled Banks grass mite for longer than 1wk under field conditions. In laboratory bioassays, we identified a high level of heterogeneity in mite susceptibility to most chemicals and higher tolerance in the twospotted spider mite. Several combinations of insecticides with a synergist and other insecticides were highly toxic to mites and could be important for improving field control. The combinations of bifenthrin + formamidine and dimethoate + pyrethroids were very toxic to mites.

Control of the Banks Grass Mite (Acari: Tetranychidae) with Bifenthrin and Propargite Applied at Different Growth Stages of Corn

Our research was designed to determine the effect of corn, Zea mays L., growth stage on susceptibility of Banks grass mite, Oligonychus praiensis (Banks), to the acaricides bifenthrin and propargite. The chemicals were applied when corn was in the following growth stages: stage 3, 12 leaves fully emerged from the whorl; stage 5, 50% pollination; and stage 7, kernels in the dough stage. An advantage of using propargite at any particular plant growth stage was not identified. In contrast, control of Banks grass mite by bifenthrin applied at 0.07 kg (AI)/ha was best at growth stage 3. Control of Banks grass mite did not differ among the growth stage treatments when bifenthrin was applied at 0.09 kg (AI)/ha. The differential susceptibility of Banks grass mite to bifenthrin applied at 0.07 kg (AI)/ha may be the result of a physiological interaction between plant biochemistry and mite susceptibility to acaricides at certain growth stages or low mite densities at application. When the effect of mite density was evaluated, we observed no difference in Banks grass mite control with bifenthrin regardless of mite abundance at application. Therefore, we conclude that better control by bifenthrin on vegetative corn at the marginal application rate of 0.07 kg (AI)/ha was probably the result of physiological effects of the plant on Banks grass mite susceptibility to the acaricide.

Toxicity of organophosphorus insecticides to diazinon-reversely-selected, pesticide-pressure-relaxed and field-resistant strains of bulb miteRhizoglyphus robini (Acari: Acaridae)

Some field strains ofRhizoglyphus robini in Taiwan, developed high multi-resistance to organophosphorus insecticides including diazinon, dimethoate, fenitrothion, malathion, methyl parathion, omethoate, parathion and prothiophos. The organophosphorus resistance of bulb mites remained stable when the pesticide pressure was relaxed. Changes of the susceptibility to several organophosphorus insecticides for a strain after relaxation of selection pressure for 3 and 27 generations were compared. Since susceptible bulb mites could not be found in the field, a reverse selection for susceptibility to diazinon was designed and conducted. Although heterogeneity was observed in the progeny of the mixed populations, the susceptibility of these reversely-selected mites increased slowly. A stable and susceptible strain was obtained after 26 generations of selection.

Characterization of Resistance to Dicofol in Spider Mites (Acari: Tetranychidae) from New York Apple Orchards

Susceptibility to dicofol of populations of Panonychus ulmi (Koch) and Tetranychus urticae Koch from New York apple orchards was estimated in 1985-1986 with a whole-plant residual bioassay. Nine of 14 P. ulmi populations collected from throughout the state in 1985 had 1,000-fold resistance to dicofol residues. Whereas susceptible mites were approximately equally affected by residual or topical exposure to dicofol, resistant mites (possessing a > 1,000-fold resistance to residual exposure) were < 15-fold resistant to topical contact with dicofol. Field trials conducted at orchard locations with P. ulmi resistant or susceptible to dicofol (as shown by bioassay results) illustrated that the resistance resulted in reduced efficacy of dicofol treatments. Advantages of the dicofol-spider mite system for evaluating resistance dynamics and resistance management strategies are described.

Genetic Analysis of Methidathion Resistance in Phytoseiulus persimilis (Acari: Phytoseiidae)

Methidathion resistance in Phytoseiulus persimilis was polyfactorially inherited. Twenty sub strains isolated from single pairs of susceptible mites and reared without selection showed a lower or a greater resistance level than the parent strain, and 10 other sub strains selected during seven generations displayed a significant increase in resistance. A direct selection for susceptibility of either susceptible or resistant strains was not possible. The nature of the genetic mechanism responsible for mediation resistance in P. persimilis is discussed, and the probable involvement of amplification of resistance genes is suggested.

Inheritance and Management of Cyhexatin and Dicofol Resistance in the European Red Mite (Acari: Tetranychidae)

Populations of European red mite, Panonychus ulmi (Koch), selected in the laboratory showed ca. 9-fold resistance to cyhexatin. Initial crosses between cyhexatin-R (resistant) and -S (susceptible) mites produced a strain showing ca. 3-fold resistance in the F1 generation. Tests with back crosses indicated that cyhexatin resistance was complex; i.e., due to more than one gene. Measurements of fecundity, life span, sex ratio, and rate of development of cyhexatin-resistant and -susceptible strains did not show any large reproductive disadvantage associated with cyhexatin resistance. In simulated population cage tests beginning with F1 mites, cyhexatin resistance was lost after four to six generations, thus providing further evidence that resistance was due to the interaction of multiple genes. Dicofol resistance in another population was ca. 15-fold. Initial test crosses between resistant and susceptible populations produced a strain similar in response to the susceptible strain. Results of back crosses indicated that resistance was probably due to a single recessive gene. Fitness tests similar to those with cyhexatin-resistant populations indicated that dicofol-resistant populations were not very different from the susceptible strain. Population cage tests with an initial population of F1 (R × S) mites showed no reversion of dicofol resistance over eight generations, suggesting that dicofol resistance was stable within a population for long periods. Crosses between cyhexatin- and dicofol-resistant strains, followed by selection with mixtures of both acaricides, produced strains showing resistance to both acaricides. Long term rotations of acaricides are suggested as a way to manage cyhexatin and dicofol resistance.

Practitioner-assessable Bioassay for Detection of Dicofol Resistance in Spider Mites (Acari: Tetranychidae)

An inexpensive, practitioner-assessable (PA) bioassay procedure for estimating frequency of dicofol-resistant spider mites, Tetranychus spp., was developed in the laboratory and evaluated in San Joaquin Valley cotton fields during 1984–85. PA assays using a discriminating concentration of 56.2 ppm readily distinguished between resistant and susceptible mites. Paired comparisons of susceptibility of spider mites from 23 field locations, as depicted by the PA bioassay and a previously validated but labor-intensive whole-plant-residual bioassay, showed that the PA bioassay can be reliably used to detect fields in which frequency of dicofol resistance is above the critical frequency of 10%. An action threshold of 80% mortality (at the discriminating concentration of 56.2 ppm) is suggested for use with the PA bioassay; dicofol should not be used at locations where mortality in PA assays is <80%. The bioassay provides a tool for taking advantage of the observed instability and limited scope of dicofol resistance in spider mites of cotton.