INSECT DISPERSAL IN A DRYING DESERT STREAM - EFFECTS OF TEMPERATURE AND WATER-LOSS

Laboratory studies of insect behavior in microcosms were used to evalu ate the tendency of Laccophilus maculosus and Stictotarsus roffii (Col eoptera, Dytiscidae), Tropisternus ellipticus (Coleoptera, Hydrophilid ae) and Graptocorixa serrulata (Hemiptera, Corixidae) to disperse by f lying and/or crawling when periods of drought caused stream pools to c ontract in Sycamore Creek, an intermittent Sonoran Desert stream in ce ntral Arizona. The principal cues tested for dispersal behavior were l oss of water in the three beetle species, and rising water temperature in the Corixidae. Laccophilus maculosus and G. serrulata responded by flying, while S. roffii and T. elliptus responded by both flying and crawling out of the experimental aquaria. Graptocorixa serrulata was t he most sensitive to high temperatures, while L. maculosus was the mos t tolerant, surviving well at 40 degrees C. Resistance to desiccation was low in all species, and most individuals dispersed before the thir d day of complete dryness. Those remaining did not survive. We suggest that the dispersal mechanism used by the various taxa depends on body morphology and the energy cost of dispersal.