Spider mite resistance to acaricides

Characterization and Exploitation of Instability of Spider Mite Resistance to Acaricides... 

It appears that spider mite resistance, or, more precisely, spider mites which possess heritable, substantial reductions in susceptibility, occur to essentially all of the acaricides widely used in agriculture, and possibly for some newer classes of acaricidal compounds that have not been widely employed to-date. Therefore, for most acaricides it is not a question of whether resistance exists per se, rather it is of greatest relevance to determine if problematic frequencies of resistant mites occur at specific locations and, through research, determine what management efforts will keep frequencies of resistant pests below those which impair field performance of acaricides. 

Resistance to organotin acaricides has been reported in several populations of spider mites. After cyhexatin and fenbutatin oxide were used for 10 to 17 years on pears and apples to control mites, populations of McDaniel spider mite (Tetranychus mcdanieli), two-spotted spider mite (T. urticae), and European red mite (Panonychus ulmi) slowly began to develop strains that were resistant to these chemicals (Croft et al. 1987). 

Another agricultural development of great potential interest is based on the more recent observation that certain rather unusual triorganotin compounds have considerable acari-cidal activity. Well-known at present is the compound tri-cyclohexyltin hydroxide (trade name "Plictran") developed by Dow Chemical Company and M T Chemicals. This compound is very effective against spider mites in fruit orchards and has been found to act as well against varieties of spider mites which had developed resistance towards the usual acaricides based on organic phosphorous compounds and car-... 

Spider mites have demonstrated the ability to become resistant to essentially all categories of organic acaricides. In concert with the trend toward fewer new acaricides entering the marketplace each year, the successive loss of effectiveness of acaricides to resistance has resulted in a dearth of effective acaricides for many agricultural commodities. This problem is especially acute for tree fruit production in the northeastern United States, where resistance has been documented, or is suspected to exist, to every registered acaricide except petroleum oil. 

Clearly, we cannot manage (or study) what we cannot measure reliably. Yet, the development of reliable methods for estimation of resistance frequencies in spider mite populations has proven to be a major obstacle with a number of important acaricides. 

Dicofol resistance in spider mites, though of lesser practical importance in some agricultural systems than resistance to the organotin and organosulfur acaricides, provides a system conducive to the study of resistance dynamics. Resistance is generally manifest as a >1000-fold difference in susceptibility of resistant versus susceptible individuals to dicofol residues (12 .). ... 

Our objective is to understand the rate at which resistance to dicofol is lost in spider mite populations and then build this information into acaricide rotation programs tailored for specific cropping systems. We intend to do this by characterizing the process(es) resulting in changes in susceptibility to dicofol. We have established 3 non-exclusive hypotheses that could account for the observed differences in susceptibility of populations to dicofol. First, it it possible that differences in susceptibility are simply a direct reflection of differences in the amount of dicofol applied to orchards since the chemical was released in the early 1960 s. Second, it is possible that movement of dicofol-susceptible individuals into orchards results in declining... 

Treatment history is important for one species but not for another. However, were no other processes involved (e.g., migration or fitness), given the nearly 30 years of use of dicofol, we would expect all populations of P. ulmi. and T. urticae to be highly resistant to dicofol such a situation exists with the widespread and stable resistances of spider mites to organophosphate acaricides. Our second hypothesis, that migration of susceptible spider mites into orchards is responsible for differential susceptibility of populations, while very plausible for T. urticae, seems unlikely for P. ulmi, given the very limited availability of hosts for this species outside of commercial orchards in New York. 

Pliytopliagous mites are important pests in many cropping systems worldwide, e.g., fruits, vegetables, grapes, and ornamentals. A major problem in their control is their high reproductive potential and the extremely short life cycle, both of which facilitate rapid resistance development to many acaricides, often after only a few applications. Therefore, the history of spider mite control is a head-to-head... 

---