Losses in livestock production due to ectoparasite infestations exceed $2.26 billion annually. Over 50 species of ectoparasites infest cattle throughout the United States. The horn fly, Haematobia irritans (L.), is the most important and widespread of the five to six major pest species of pastured cattle in the southern region. Results from the examination of production traits from cattle under ectoparasite burdens have been variable, ranging from no effect to significant reductions in weight gains. Because of this inconsistency, specific physiological and nutritional responses in cattle infested or not infested with horn flies have been examined. Data have shown significant differences in nitrogen retention, blood cortisol concentrations, vital signs, water consumption, and urine production. Implications are that total energy balance is altered when an animal is exposed to ectoparasite infestations, thereby resulting in decreased productivity.

No abstract

Although behavioral resistance remains enigmatic, an examination of the literature firmly supports the existence of behavioral resistance in both the presence and absence of the better understood and accepted physiological and biochemical mechanisms. Studies of pyrethroid resistance in the horn fly and the tobacco budworm have identified several resistance mechanisms, including behavioral adaptations, in addition to target‐site insensitivity and enhanced detoxification. The coexistence of physiological and behavioral responses neither precludes a common mechanism nor requires one. Even if a common mechanism such as knockdown resistance or enhanced detoxification is involved, this does not negate the survival benefit of either avoiding the toxicant or reducing movement to avoid exposure. Thus, behavioral resistance may be much more ubiquitous and important than previous interpretation of the literature suggests.

No abstract

Susceptible populations of horn flies, Haematobia irritans (L.), were selected with six insecticide treatment regimens: continuous use of permethrin, diazinon, or ivermectin; permethrin/diazinon (1:2) mixture; permethrin-diazinon rotation; and permethrin-ivermectin rotation. Insecticide selection was applied as low-volume sprays on steers infested with horn flies housed in environmentally controlled rooms. During the study period, horn fly populations developed an apparent resistance to all insecticide treatment regimens. Selection with permethrin, diazinon, and ivermectin resulted in development of resistance in generations 21, 31, and 30, respectively. Selection with insecticide mixtures and rotations resulted in the delay of any apparent resistance development for an additional one to seven generations. The magnitude of this resistance ranged from 1,470-fold for the single continuous use of permethrin to < 3-fold for ivermectin in the permethrin-ivermectin rotation. Compared with single continuous insecticide selections, the onset and degree of resistance development was significantly reduced by alternating and mixing insecticides.