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French populations of the codling moth Cydia pomonella (L.) (Lepidoptera, Tortricidae), a major pest in apple and pear orchards, have developed resistance to different classes of insecticides including the benzoylurea diflubenzuron, a chitin synthesis inhibitor. Ovicidal tests performed on two susceptible strains and one strain selected for its resistance to diflubenzuron revealed the same order of magnitude in resistance ratios to this compound (30-fold) and two other benzoylureas teflubenzuron and flufenoxuron (22- and 11-fold, respectively). Field rates of these three compounds induced a 45-55% decrease in hatching in the resistant strain, compared to over 90% in the susceptible insects. Despite a 52-fold ovicidal resistance ratio to the juvenile hormone analog fenoxycarb, this compound induced a 85% decrease in hatching in the resistant strain. Conversely the newly hatched larvae of the resistant strain exhibited a 45 000-, 33- and 2. 1-fold resistance ratio to diflubenzuron, teflubenzuron and flufenoxuron. respectively. The latter value was not signiticant, and the field rate of flufenoxuron killed over 97% of the resistant larvae while diflubenzuron had no effect, This lack of relationship between ovicidal and larvicidal resistance may be due to different transport properties together with differential enzymatic metabolization. Our results may limit the validity of substitution instars. which approach is frequently used for resistance monitoring. More importantly for resistance management, the resistance of different target instars to each compound has to be considered when establishing control strategies.

Following reports of ethion resistant cattle ticks (Boophilus microplus (Canestrini)) in New Caledonia, a series of dosage mortality tests was undertaken in an attempt to establish the extent of this resistance. Thirty samples of B. microplus which was introduced from Australia in 1942, were taken from various locations on the main island, and the results compared with similar tests carried out using an Australian susceptible reference strain (Yeerongpilly) and an Australian resistant strain (Biarra). Larvae 6–15 days after hatching were exposed to different concentrations of ethion in olive oil for 24 h. The study showed that varying levels of ethion resistance had developed in New Caledonia, and that it was most strongly marked in tick populations from the east coast region. Some very low levels of resistance are probably of no practical importance, but the LC50 value of the most resistant population was eight times that of the Yeerongpiily reference strain. Ethion resistance has appeared on th...