The effect of temperature on the ovipositional biology of Boophilus annulatus (Say) was determined under laboratory conditions. Engorged females subjected to constant temperatures of 12 and 45 degrees C died without ovipositing, while females held at 15 and 40 degrees C laid eggs which did not hatch. The preoviposition period at 25-40 degrees C was 2-3 days; however, significant increases occurred at 20 degrees C (5.2 days) and at 15 degrees C (16.3 days). The number of eggs laid per female was ca. 2700 at temperatures of 25-35 degrees C, but decreased significantly at 20 degrees C (ca. 2300 eggs/female), 15 degrees C (ca. 1800 eggs/female), and at 40 degrees C (ca. 300 eggs/female). No differences were observed in the Conversion Efficiency Index (CEI) values at temperatures of 20-30 degrees C (ca. 50%), while temperatures of 15 and 40 degrees C produced the lowest CEI values at 35.6 and 4.9%, respectively. Hatch-ability of eggs was ca. 80% at temperatures of 20-35 degrees C. Incubation period of eggs ranged from 52.2 days at 20 degrees C to 16.2 days at 35 degrees C. The thermal threshold for egg development determined by linear regression was 12.9 degrees C. Females subjected to four fluctuating temperature regimens produced no differences in number of eggs/female (ca. 2400), CEI (ca. 50%), or hatchability of eggs (ca. 75%). Preoviposition period and incubation were significantly affected by a change in the thermoperiod, becoming longer in duration as the temperatures were decreased. From studying females exposed for various intervals from 0 to 105 days at 12 degrees C, indications were that the longer the exposure period the more adverse the effects were on oviposition and egg-hatch. Correspondingly, exposure of eggs to a temperature of 15 degrees C for up to 105 days gave indications that the longer the eggs remained at 15 degrees C, the lower the hatch would be after transfer back to a temperature of 25 degrees C.