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Show 72 Utah Academy of Sciences, Arts and Letters [Vol. XV, to the spray applications listed above. Agicide 1 percent rotenone dust usu ally gave good results. Applications of a 0.5 percent rotenone dust did not give a significant control. The control obtained by derris and cube dusts and sprays, and the high kills secured by the "Vapo Furner," encourage the belief that with adequate equipment and readily available materials, much of the serious loss of a sea son such as 1936 might be averted. The need for local information upon pea aphid control and the fact that results in Utah seem to be somewhat in line with work reported elsewhere, induced the writers to summarize and present the above results of the 1937 experiments at this time. Biological Control Round glass or porcelain Rearing technique for individual predators. dishes, approximately 12 inches in diameter and 3 inches deep, were filled about three-fourths full of tap water. The tops of the containers then were covered with a tightly stretched piece of 20-mesh gauze, held in place by means of elastic bands. Small glass cylinders, one inch in diameter and one inch high, were used as cages. Some of these were made by cutting off the closed, glassed-in end of shell vials; others were made from glass tubing, with gauze covering the upper end. Both types of cages were satisfactory. Predators were hatched from eggs, usually in Petri dishes, then each was isolated in one of the small cylindrical glass cages with a supply of aphids for food. As a rule, fourth ins tar pea aphids only were fed to the predators in the experimental cages, although in some cages smaller nymphs were used for the first two or three days following predator hatching. The aphids sub sisted upon selected young alfalfa sprigs approximately four inches long, trimmed down until only the terminal leaf remained. The cut end of the sprig was passed through a small opening made in the gauze cover over the large jar and extended well down into the water. The small space between the sprig and the gauze was packed with cotton to prevent the predator or aphids from escaping. Advantages of above method. (1) This method permitted the han dling and observation of a number of predators within a small space, 12 to 15 small cages and an equal number of predators being kept upon each large dish. (2) Humidity was kept relatively high, which was desirable when rearing pea aphids. (3) The alfalfa sprigs remained fresh for from seven to ten days, providing a continuous food supply for the aphids upon which the predators were to feed. (4) Very few aphids died in these cages, other than those killed by the predators. A daily examination and record were made of the aphid consumption by each predator. (5) The trays were easily moved. Disadvantages, (1) Small cages occasionally were knocked over, allow ing predators to escape. (2) Recently hatched syrphid larvae occasionally crawled through the 20-mesh gauze. This did not happen when a closer mesh gauze was used. Pea aphid food for predators. During the spring and until approxi mately mid-July, pea aphids could be obtained as needed from nearby pea and After this time aphids became less plentiful in the field and alfalfa fields. it was more economical to raise the aphids in the insectary than to hunt them in the field. Two methods of rearing were used: (1) Mature wingless female aphids from alfalfa were placed on new shoots of recently potted When the alfalfa plants, reproduction under these conditions being rapid. young aphids reached the fourth instar, they were removed to cages of the predators. (2) Pea seed was planted in earthenware trays every two days. |
