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In the Laboratory Bacterial Disease Effective Against Several Insects Richard D. F rye To determine their approximate susceptibility vae, except in the case of American Elm Sawfly. to Bacillus thuringiensis, several species of insects In this instance, no mortality occurred after six have been exposed to the bacterium in the labora- days and the test was terminated. tory. Larvae of these species were given food material which had been immersed in a sus- Table 2. Results of susceptibility tests. pension of spores (75 billion spores per 100 ml. of Per Cent Mortality* water). Untreated checks for each species included the same number of larvae as the treatments. Treated food and insects were confined in closed *s « containers. J0-O</> 01 All larvae used in each test were in the same *J •>g0 stage of development. All tests were conducted at |jI gd> approximately 82° F. and 45 per cent relative I- o humidity. The environment and equipment were Sunflower Moth 40 •72 92 7 72 80 15 kept as nearly sterile as possible. Banded Sunflower Moth 40 Cotoneaster Webworm 10 96 90 0 Fall Webworm 25 60 80 20 Table 1 shows the species of insects and plant Zebra Caterpillar 16 60 100 0 material used in the tests. Painted Lady 30 96 90 0 Salt Marsh Caterpillar 30 72 90 0 Imported Cu.rrantworm 25 96 88 36 Results are presented in Table 2. Time to last 144 0 0 observed death indicates the length of time from American Elm Sawfly 30 Poplar Leaf Beetle 30 72 83 57 start of test to last observed death of treated lar- •Rounded to nearest whole number. Fry e is assistant professor, Department of Entomology. Table 1. Insects and plant materials used in susceptibility tests. Order Food From Common Name Species Sunflower heads Homeosoma electellum Lepidoptera Sunflower moth Sunflower heads Phalonia hospes Lepidoptera Banded sunflower moth Cotoneaster foliage Cremona cotoneastri Lepidoptera Cotoneaster webworm Chokecherry foliage Hyphantria cunea Lepidoptera Fall webworm Cabbage foliage Ceramica pietà Lepidoptera Zebra caterpillar Sunflower foliage Vanessa cardui Lepidoptera Painted lady Sunflower foliage Estigmene acrea Lepidoptera Salt-marsh caterpillar Gooseberry foliage Nematus ribesii Hymenoptera Imported currantworm Willow foliage Cimbex americana Hymenoptera American elm sawfly Poplar foliage Poplar leaf beetle Lina scripta Coleoptera 12 Figure 1. Untreated Hyphantria cunea. Figure 2. Treated Hyphantria cunea. Figure 1 is the untreated check. Figure 2 Not Affected shows the results of bacterial treatment of the fall The test with American Elm Sawfly indicates webworm H. cunea. The difference in larval feed- that larvae of this species are not affected by the ing on treated food and untreated food is evident. bacterium. Similar results were obtained in the Very little feeding occurred on the treated food, field during 1965 when mature larvae were placed and several dead larvae can be seen. In the check, on the foilage of willow. The larvae and branches several larvae continued development into pupa- were enclosed in screen sleeve cages. Lindane tion. gave excellent control. Effectiveness From these tests, it would seem that B. thur- ingiensis is not effective against imported currant- The reaction of H. cunea to treatment was worm or the poplar leaf beetle. Any effect was typical of cases where the bacterium was effective. slight and was masked by considerable mortality When evaluating the results shown in Table 2, in the checks. per cent of mortality in both treated and untreated No attempt was made to determine the degree parts of the tests should be considered. On this of susceptibility. The results' are only relative. The basis, B. thuringiensis was effective against sun- tests described were of a preliminary nature. They flower moth, banded sunflower moth, cotoneaster are of value in that they provide evidence that in webworm, fall webworm, zebra caterpillar, painted several cases further investigation is warranted. lady, and salt-marsh caterpillar. SUMMARY In the case of fall webworm the results fall Susceptibility of the larvae of several insects somewhere between those Weiser and Veber and to the bacterium Bacillus thuringiensis varies from Vasiljevic, (as summarized by E. A. Steinhaus, 0 to 100 per cent. The degree of susceptibility was Mimeographed Series No. 4, Insect Pathol., Univ! not determined, but the tests indicate that the of California, Berkeley, 1957) whose results varied organism is not effective against imported currant- from a slight to a high degree of susceptibility. worm or the poplar leaf beetle. Preliminary tests Hall found marked susceptibility with salt marsh show that further research into insect control caterpillar. This was confirmed by E. A. Steinhaus through the use of Bacillus thuringiensis is war- (J. Insect Pathol., 2, 225-229, 1960). ranted. 13 .

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