The effect of food type, photoperiod, and temperature on the behavior and growth of the wireworms,Melanotus depressus(Melsheimer) andLimonius dubitansLeConte, was examined. Germinating seeds from several potential host plants were evaluated. After 6 months in the treatments, previously starvedM. depressuslarvae had the highest growth rates when fed germinating field corn, wheat, or sorghum kernels. After 1 month's observation of larvae preconditioned to wheat only, those which continued on the same regimen showed a significant weight gain.L. dubitanslarvae which had been preconditioned to wheat kernels, however, showed a significant weight gain over a 3-month period when held on germinating wheat, soybean or corn kernels.Temperature and photoperiodic studies withM. depressuslarvae employed combinations of 2 temperatures (21°C and 27°C), 2 photoperiods (12L:12D, 14L:10D), and 6 diets (germinating wheat kernels in soil or on fibrous cotton, and 4 artificial diets on fibrous cotton). The effect of these conditions on larval feeding response, ecdyses, growth, and mortality is presented. None of the artificial media substituted adequately for the wheat-loam substrate. Similar experiments employingL. dubitanscould not be completed because of exceptionally high mortality.