Factors affecting the larvipositional activity of Oestrus ovis gravid females (Diptera: oestridae).

Observations of fly strikes or larvipositions (n=68 in 21 days of observation) were carried out in a herd of goats during the spring in Baja California Sur, Mexico in order to identify the climatic conditions favoring larviposition activity of gravid Oestrus ovis L. flies, as well as to investigate whether a mixture of some potentially useful compounds was involved in this behavior. Hand-caught, tethered flies (n=43) were either exposed or unexposed to a combination of carbon dioxide, humidity, 1-octen-3-ol, butyric, propionic, acetic acid and acetone released from movable sheep and goat dummies under open field and cage conditions. Fly strikes occurred at temperatures greater than 20 degrees C, but mainly between 25 and 28 degrees C and from 116 to 838W m(-2) of solar irradiance. Few or no strikes were seen under moderate or strong wind, but did occur in a wide range of relative humidity. The chemicals applied did not improve the capacity of animal dummies to induce the flies to larviposit, but very irregular behavior was observed. Fourteen larvipositions were made on the dummies lacking chemical stimuli, so visual ability and movement by the dummies was very important in stimulation of the flies. Temperature appeared to be the main factor determining fly activity, but wind and solar irradiance also played important roles. Characteristics of O. ovis larviposition are discussed.