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The principal aim of this study was to evaluate bioassay techniques and to determine suitable procedures for detection and monitoring miticide resistance in spider mites with special emphasis on the miticide propargite. Several bioassay methods were evaluated using propargite (Omite 30% wettable powder (WP)) and fenbutatin oxide (Torque 50% (WP) and 55% suspension concentrate (SC)) with twospotted spider mite (TSM) and European red mite (ERM) to document their utility and reliability or accuracy in lethal concentration (LC) estimates. For each method, two post-treatment exposure periods and mortality criteria were used. Post-treatment exposure period and mortality criteria had a significant influence on the reliability of LC estimates for all tested miticides with all bioassay methods. Twenty four hour (h) post-treatment exposure was found to be the most suitable for the slide dip and Petri dish methods while 48h was the most appropriate for the leaf disc methods. Scoring moribund mites as dead was the most satisfactory criterion for ensuring that bioassays were as simple and reliable as possible. The Petri dish residue- Potter tower method (PDR-PT) estimated the responses of TSM and ERM to propargite with high reliability. The same method did not result in similar reliability with both formulations of fenbutatin oxide. Significant mite run-off occurred with the leaf disc methods, and because of run-off the reliability of these methods cannot be fully known. The slide dip method produced poorly estimated LC values for propargite (WP) and fenbutatin oxide (WP), while the same method produced higher reliability in LC estimates for fenbutatin oxide (SC) than the PDR-PT method. The toxicity of candidate miticides was found to be method- and species-dependent, and LC values between methods within species were significantly different. Other than the bioassay method, the reliability or precision of LC estimates was found to be influenced by test design (placement of concentrations) and sample size (number of individuals tested for a whole bioassay) employed in a bioassay. Five test designs in combination with five different total sample sizes were investigated in this study using the PDR-PT method with propargite against TSM and ERM. Of the five designs tested, the symmetric-5 design (where concentrations were placed equidistantly on the log scale between the response level of 5-95% mortality) yielded more precise estimates of both the LC₅₀ and LC₉₀ than other designs. With this design, the minimum total sample size requirement was 360, but 480 was found to be more reliable. With a total sample size of ≥600, all designs were equally effective. The influence of several environmental, operational and biological factors on the toxicity of propargite to TSM and ERM using the PDR-PT method was also investigated. Propargite toxicity was found to be significantly positively correlated to temperature over a range of 10-30° C. Propargite toxicity was also positively correlated to spray volume. When different age groups of adult female TSM were exposed to propargite, toxicity was inversely correlated to adult age. The responses of field collected ERM to propargite varied month by month in an irregular pattern during a growing season (December to April). The responses of spider mites from one test to another did not vary significantly over time when tests were conducted with a reasonable number of individuals (≥80/concentration) on each occasion. Propargite residues persisted in pre-sprayed dishes for ≥30 days when stored at 4 ± 1°C and remained consistently toxic to mites throughout this period. Propargite did not induce any detectable vapour-activated toxicity in closed Petri dishes. The results of laboratory based Petri dish bioassays were poorly correlated with those obtained under semi-field conditions. Limitations of using laboratory results to determine an effective field application rate of propargite are discussed. Propargite resistance in numerous TSM and ERM strains was determined by using discriminating concentration (DC) and multiple concentration test techniques. Since the main difficulty with the DC technique was how to determine the appropriate concentration with which to differentiate between resistant and susceptible strains, several ways of selecting a DC were examined using the PDR-PT method. The selected DC (0.105% AI for TSM and 0.045% AI for ERM) identified levels of propargite resistance in different TSM and ERM strains as reliably as did the multiple concentration test. In the case of low resistance, the results of the DC tests were slightly different than those obtained from the multiple concentration tests, but for medium and high levels of resistance both techniques were equally effective. Considering the time involvement and the number of test individuals required for a multiple concentration bioassay, the DC technique would be a cost-effective approach for resistance monitoring. Despite the long history of propargite use in New Zealand, resistance in TSM-and ERM was found to occur sporadically at some locations. To investigate the dynamics of resistance, a propargite resistant TSM colony was established in the laboratory. Propargite resistance was found to develop fairly rapidly (after three months; one selection in each month) but it did not decline in the absence of selection pressure over six months (approximately 12 generations).

The dispersion statistic, k, of the negative binomial distribution was calculated for Panonychus ulmi and Typhlodromus pyri; mite species present in Nelson apple orchards. Distribution data taken from 2300 leaves, taken at intervals of 7-14 days during the 1976-77 season, found P. ulmi to be contagiously distributed. Contagion became more severe as the season progressed and by later summer most sample means could not be adequately described by this distribution series. Sample data for T. pyri was well described by the negative binomial distribution in mid and late summer only. Distribution of T. pyri during early summer was random with many sample means departing from the negative binomial series. The parameter ‘b’ of Taylor’s power law was determined for both species. Using this, leaf sample size estimates for both species at varying densities and error margins (expressed as ratios of standard error to mean) were determined. The Henderson-McBurnie mite brushing machine, used in a commercial mite-monitoring service provided for Nelson orchardists, was investigated for efficiency of removal of P. ulmi and T. pyri. For all leaf samples this machine had an acceptable efficiency of removal for P. ulmi, however removal of T. pyri from leaves was low and variable. Modifying the brushing procedure to expose the leaf midrib increased removal of T. pyri but did not significantly reduce the variability of numbers removed. Estimation of mite population density using the relationship between the observed proportion of mithe infested leaves and the sample mean density was investigated. Estimation of P. Ulmi density for three leaf infestation classes was determined. A mite density of five P. Ulmi active stages per leaf was unlikely to be exceeded if less than half of the leaves in a sample were infested with mites. The results showed that the reliability of this technique decreased with increasing mite density. Examination of leaf distributions of both species throughout the season found them unlikely to occur on leaves concurrently in November and December. This suggested that T. pyri was unlikely to influence population development of P. ulmi significantly during this period. In mid and late summer T. pyri failed to disperse from leaves where P. ulmi had been effectively suppressed, to those where P. ulmi was increasing in the absence of predators, before some leaf damage occurred. The predation efficiency of an azinphosmethyl-resistant strain was investigated. It was found that azinphosmethyl-resistant T. pyri were not as effective in the control of P. ulmi as a susceptible strain not receiving azinphosmethyl. It was considered that sublethal effects of this chemical may exist which disrupted T. pyri distribution patterns in the resistant strain thereby permitting damage by European red mite.

The aim of this study was to investigate the usefulness of image analysis for studying mite behaviour. Image analysis was used to convert video recordings of mites' locomotory behaviour into a series of x,y coordinates that, when joined, closely resemble the paths of mites. The coordinates were also used to calculate walking speed, direction of travel, turning frequency, turn bias and tortuosity. Two experimental arenas were developed and used to study the movement of three mite species: 1) a leaf disc arena for two-spotted spider mite, Tetranychus urticae Koch and European red mite, Panonychus ulmi (Koch); and 2), a cover-slip/tack-trap arena for Typhlodromus pyri Scheuten. Two-spotted spider mite exhibited a change in locomotory behaviour through a 48 minute period. Mites exhibited a significant decline in distance travelled, whereas the mean stationary time (per four minute interval) more than doubled, and the duration of stationary events increased steadily over the same period. A reduction in sampling frequency of mite coordinates from one per second to one every two seconds and every four seconds produced a 5% and 12% 'loss' in path length respectively. Sample period length was shown to greatly influence the results produced for some of the mean parameters calculated, however, a reduction in sample length from 3000 to 1500 coordinates was not considered to cause a major loss in information. The influence of the inherent mite movement could not be ignored and made it difficult to make decisions on the 'best' sample length to use. Some strong correlations were found between parameters used to analyse mite locomotory behaviour. In particular, arithmetic mean vector length, speed, total stationary time and total distance travelled were significantly correlated with each other. Mean angular deviation and weighted mean vector length, which both measure the degree of clustering around the mean heading angle, were strongly negatively correlated. Parameters which differentiated between 'straight' and 'tortuous' mite movement were found to be mean meander, absolute mean turn and fractal dimensions. Mean meander was thought to be the most 'powerful', while coefficient of a straight line, a commonly used parameter for measuring tortuosity, did not significantly differentiate between the two different behaviours. Frequency distributions of turns and standard deviations of the three mite species were very similar. All three species had a slight bias to turning right (clockwise) rather than to the left (counter-clockwise) and for each species certain angles occurred more often than would be expected in a 'perfect' normal distribution. A similar pattern also occurred with the frequency distribution of two-spotted spider mite heading angles, in that angles which were expected to occur more often, did not, and vice versa. The potential to use saturated salt solutions to control relative humidity on the arena was` demonstrated and indicated that relative humidity is likely to have an important influence on mite behaviour. Two-spotted spider mites appeared to move more quickly in an attempt to escape the unfavourable, extreme (10% and 95% R.H. at 25°C) moisture conditions. All three mite species displayed a characteristic edge-walking behaviour around the arenas. However, when 'edge' and 'non-edge' behaviours were compared, mean meander was the only parameter (of the parameters tested) which gave a significant difference. Behavioural responses of European red mite and T. pyri to sub-lethal (field rate) esfenvalerate were investigated and the results indicated that these mites did not seek the unsprayed halves of the arenas during the first 48 minutes. However, significant differences in most behavioural parameters to esfenvalerate residues were found with European red mite when whole arenas were compared. Image analysis is an extremely useful research tool for studying mite behaviour because of its ability to measure many parameters quickly. Careful choice of the environmental conditions, the sampling framework, and interpretation of data is essential for meaningful results.

Spider mite (Tetranychidae) outbreaks often occur following pyrethroid insecticide applications, although there is considerable variation between the response to different pyrethroids. Recent reviews suggested that differences in toxic and sub-lethal effects may be responsible and that recently developed pyrethroids, such as fluvalinate, show greater miticidal activity and cause fewer outbreaks. A comprehensive study of the toxic and sub-lethal effects of fluvalinate revealed this pyrethroid caused a range of beneficial sub-lethal effects, which esfenvalerate did not cause. These were discussed in relation to the lack of reported spider mite outbreaks with fluvalinate. At the recommended field concentration (0.1 g a.i. 1⁻¹) for spider mites the toxicity of fluvalinate was minimal to two-spotted spider mite, Tetranychus urticae Koch, but was moderately toxic to European red mite, Panonychus ulmi Koch. Larvae of both species were the more susceptible stage and fluvalinate persisted long enough in laboratory experiments to control emerging larvae, even when applied to newly laid eggs. Differences between the toxicity of four fluvalinate formulations were only detected above field concentration. The emulsifiable concentrate formulation was the most toxic to two-spotted spider mite while the wettable powder formulation was most toxic to European red mite. The main response to fluvalinate was rapid dispersal from treated areas. Both spider mite species were able to accurately detect and avoid fluvalinate residues within and between leaves. There was a high survival rate for mites which dispersed from treated areas, although their fecundity was reduced. This reduction depended on the initial amount of exposure. European red mite were comparatively more effected than two-spotted mite. The emulsifiable concentrate formulation caused the largest reductions in fecundity. Fecundity was reduced because fluvalinate prevented feeding. Two-spotted spider mite mating was inhibited on fluvalinate-treated surfaces, probably because of male intoxication, and this resulted in the production of mostly male offspring. The development rate of juvenile two-spotted spider and European red mites which remained on fluvalinate-treated surfaces was severely reduced and at the field concentration few survived to adulthood. Development rate of larvae was severely reduced by three hours exposure to fluvalinate. Prevention of feeding was also responsible for reductions in development rate. Physiological/biochemical resistance did not develop after 12 field applications or 20 applications of fluvalinate to a laboratory colony of two-spotted spider mite, but a low level of behavioural resistance developed in the laboratory colony. Fluvalinate was less active against the pyrethroid-resistant predator; Typhlodromus pyri, compared to two-spotted spider mite. But the predator showed little inclination to follow dispersing two-spotted spider mites and predation rates were lower on fluvalinate-treated surfaces and this may disrupt integrated mite control. Esfenvalerate was also relatively non-toxic to two-spotted spider mite adults, but caused more dispersal at equivalent concentrations compared to fluvalinate. Esfenvalerate residues were more easily and rapidly avoided. Larvae were also less affected by esfenvalerate compared to fluvalinate. Esfenvalerate had no effect on two-spotted spider mite fecundity and two times the concentration was required to cause the same reductions in development rate compared to fluvalinate. Esfenvalerate also prevented two-spotted spider mite mating. The greater toxicity to juveniles, reductions in oviposition, development rate, feeding and mating, in conjunction with relatively long persistence and dispersal effects were considered to prevent spider mite outbreaks with fluvalinate. Esfenvalerate had less effect on these sub-lethal parameters and combined with greater repellency and loss of density-dependent suppression, was more likely to cause outbreaks.