Effects of Temperature and Light on the Mass Rearing of the Geminate Leafhopper, Colladonus geminatus (Van D.)

Author

Walter H. A. Wilde, Utah State University

Date of Award:

5-1-1952

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Department name when degree awarded

Entomology

Committee Chair(s)

Not Specified

Committee

G. H. Kaloostian

Committee

C. J. Sorenson

Abstract

Mass rearing experiments with Colladonus geminatus ( Van D.) conducted in an experimental greenhouse laboratory from January 30, 1952, to April 18, 1952, indicated light had important breeding effects on C. geminatus, the geminate leafhopper. A light intensity of forty foot-candles provided by a 100 watt incandescent bulb for a period of 16 hours daily was the most effective of the three light intensities and the three heat ranges tried. It was found in the expirimental cages that light had the effect of speeding up the development of the new leaf hopper generation, progeny of the overwintering adults from the reservoir cages. Check cages started January 30, and having only natural daily illumination and average greenhouse temperatures of 70 degrees F., did not respond until the last week in March, nymphal development lagging far behind that in the lighted cages. By the first week in April the check cages showed a tremendous development of leafhoppers, indicating that these cages were effective in mass rearings. Temperatures of 85 degrees F. in the top portions of two experimental heated cages gave increased rates of reproduction but not as much as in the lighted cages. The 85 degree temperature was maintained by placing 100 watt bulbs inside blackened 600 ml. flasks in the top of each cage. One serious effect of the temperature experiment was heat damage to the growing tips of the alfalfa. Insect populations in the two 100 watt lighted cages totalled 385 specimens as compared with 307 specimens in the two check cages, and 102 specimens in the two 100 watt heated cages. Check cages were not subjected to anything but regular greenhouse temperatures and daylight periods. By stimulating C. geminatus (Van D.) with these various light and temperature ranges, various effects were observed. Life cycle time from adult to adult was shortened approximately three and one-half weeks in the 100 watt light intensity series as compared to the life cycle time in the check cages. The progeny from overwintered adults began egg laying immediately with nymphs appearing March 5, four and one-half weeks after the experiment began in the lighted series of cages. Nymphs did not appear until March 31 in the check cages, almost four weeks later than in the light cages. Only two factors, light and temperature, were investigated in this experiment for the following reasons. The first reason was limitations imposed by the availability of experimental facilities. Each additional factor investigated doubled or tripled the number of cages and experimental space needed. The second reason concerned results of sugar beet leafhopper investigations in which Carter of the United States Department of Agriculture showed light and heat were important factors in mass laboratory rearings. Carter found the ovaries of the overwintering leafhoppers were not developed for egg laying until late February or early March of the following year. Heat application to these overwintering leafhoppers again stimulated ovarian development and egg laying. Because of these reasons it was decided to investigate the effects of only light and heat on the geminate leafhopper. It was shown in this experiment that temperature and light investigations require a minimum of equipment and laboratory space, thus even small laboratories can carry out mass rearing experiments using the advantages of these two mediums. Some mention should be made of the economy effected in mass rearing of experimental insects. In many projects the insects require collection over distant areas, the time of one or more entomologists, and the use of equipment and vehicles. High losses in viability after the insects are transported long distances for use in the laboratory are also noted. These mass rearing experiments should provide important biological information about C. geminatus that will effect substantial monetary savings as well as add to existing knowledge of mass rearing of insects. Freedom from natural enemies, such as predators and parasites, and independence of climatic conditions are advantageous features that are available from laboratory rearing. By experimenting with various light and temperature ranges the optimum in rearing conditions can be determined. The effects of temperature and light on the reproductive rates of different species cannot be considered without some awareness of other factors such as relative humidity and types of feeding medium. This experiment has merely served to illustrate what might be learned from further investigation into optimum rearing conditions. Large populations of mites in the rearing cages did not seem to have any deleterious effects on the rearing of the leafhoppers. In a few cases leafhoppers were noticed to be entangled in the fine webs spun by the mites but in general the leafhopper was able to break any webs with ease. Mite infestations in culture cages are tolerated for want of a suitable method of control. Such control must be specific for mites without interference with the leafhopper population.