The two-spotted spider mite, Tetranychus urticae Koch is a major pest that feeds on >1,100 plant species. Many perennial crops including hop (Humulus lupulus) are routinely plagued by T. urticae infestations. Hop is a specialty crop in Pacific Northwest states, where 99% of all U.S. hops are produced. To suppress T. urticae, growers often apply various acaricides. Unfortunately T. urticae has been documented to quickly develop resistance to these acaricides which directly cause control failures. Here, we investigated resistance ratios and distribution of multiple resistance-associated mutations in field collected T. urticae samples compared with a susceptible population. Our research revealed that a mutation in the cytochrome b gene (G126S) in 35% tested T. urticae populations and a mutation in the voltage-gated sodium channel gene (F1538I) in 66.7% populations may contribute resistance to bifenazate and bifenthrin, respectively. No mutations were detected in Glutamate-gated chloride channel subunits tested, suggesting target site insensitivity may not be important in our hop T. urticae resistance to abamectin. However, P450-mediated detoxification was observed and is a putative mechanism for abamectin resistance. Molecular mechanisms of T. urticae chemical adaptation in hopyards is imperative new information that will help growers develop effective and sustainable management strategies.

Experimental sources of cobalt‐60, made radioactive by neutron irradiation, have been used during recent years for investigating the radiation susceptibility of insect pests. Lethal and sterilising effects have been examined on species, strains and developmental stages to evaluate the dose levels required for commercial treatment. The technical feasibility of using radiation as an insecticide is now established. Results of research and problems of application are examined in relation to the two potential methods of controlling insect pests by irradiation; indirect control by the release of sterilised adults and the direct treatment of infested products. Application of the first method, exemplified by work on screw‐worm fly, is limited to very few species by a number of biological requirements. Direct treatment could have wider application for the control of all species infesting stored products. The most favourable products for radiation dis‐infestation are those handled in bulk at particular centres, and for this reason radiation treatment of grain has been examined in detail. The fundamental and applied problems of using γ‐radiation for this purpose are discussed and the relative merits of fumigation and radiation sterilisation are compared. It is concluded that among factors which may influence the success of radiation disinfestation, bulk handling and the incorporation of treatment into established handling procedures must receive primary consideration. γ‐Irradiation may eventually take its place as a useful means of insect control, but it is unlikely to displace conventional methods.

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