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

Observations of fly strikes or larvipositions (n=68 in 21 days of observati on) were carried out in a herd of goats during the spring in Baja Californi a Sur, Mexico in order to identify the climatic conditions favoring larvipo sition 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 unexpo sed to a combination of carbon dioxide, humidity, 1-octen-3-ol, butyric, pr opionic, acetic acid and acetone released from movable sheep and goat dummi es under open field and cage conditions. Fly strikes occurred at temperatur es greater than 20 degrees C, but mainly between 25 and 28 degrees C and fr om 116 to 838 W m(-2) of solar irradiance. Few or no strikes were seen unde r moderate or strong wind, but did occur in a wide range of relative humidi ty. 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 stimula tion of the flies. Temperature appeared to be the main factor determining f ly activity, but wind and solar irradiance also played important roles. Cha racteristics of O. ovis larviposition an discussed. (C) 2000 Elsevier Scien ce B.V. All rights reserved.