Normand R. Dubois

Field confirmation of a mechanism causing synergism between Bacillus thuringiensis and the gypsy moth parasitoid, Apanteles melanoscelus

Abstract In 16-ha plots aerially sprayed with single and double applications of Bacillus thuringiensis , percentage parasitism by A. melanoscelus and the number of A. melanoscelus cocoons under burlap strips were higher than in comparable untreated plots in the same area. Strong correlations occurred between percentage parasitism and caterpillar size, with plots having the smallest caterpillars being the most heavily parasitized. However, these parameters were also negatively correlated with number of caterpillars per plot. The increased numbers of parasitoid progeny, i.e., cocoons, found in treated plots showed that corresponding increases in percentage parasitism could not be due simply to improved parasitoid: host ratios. Evidence strongly suggests that the retarding effect of B. thuringiensis infection kept gypsy moth larvae small enough in the treated plots to permit A. melanoscelus females to parasitize relatively large numbers of caterpillars.

Conventional application equipment: aerial application

Chemical control of insects, diseases and weeds began in earnest with the introduction of organic pesticides in the 1940s. Chemical pesticides offer a powerful control method and, until recently, their use had been overemphasized to the detriment of research and development of cultural and biological control methods. Impacts on non-target organisms and emergence of resistance to chemical pesticides prompted the development of biopesticides as well as the implementation of integrated pest management, where pesticides are used compatibly as one of many control methods.

Bacillus thuringiensis field applications: Effect of nozzle type, drop size, and application timing on efficacy against gypsy moth

Abstract In a series of recent studies, we evaluated the influence of delivery systems, drop size and application timing on the efficacy of aerially applied Bacillus thuringiensis against gypsy moth infestations. Use of different nozzle systems including Micronair, Flat Fan or Twin Jet, did not appear to result in significant differences in Bt coverage efficiency, foliage protection or population reduction. Nor was there any significant difference in population reduction when Bt was applied at two different drop sizes with volume median diameters of 110 and 163 μm. The efficacy of different formulations on larval populations were similar when used against the younger 1st and 2nd instar but differed when treatment was delayed until the population matured to the 3rd and 4th instar stages.

Synergism between β-exotoxin and Bacillus thuringiensis subspecies kurstaki (HD-1) in gypsy moth, Lymantria dispar, larvae

Abstract Synergism was demonstrated in larvae of the gypsy moth, Lymantria dispar , fed an artificial diet containing mixtures of HD-1S-1980 (a standardized spore and crystal preparation of the HD-1 strain of Bacillus thuringiensis ) and β-exotoxin. After 5 days of exposure, the LC 50 of the B. thuringiensis mixed with 0.01 and 0.02% β-exotoxin was significantly lower than that of B. thuringiensis alone. A significant increase in larval susceptibility to B. thuringiensis was also noted with the addition of 0.001% β-exotoxin when exposure time was increased to 7 days. Minimal concentrations of B. thuringiensis β-exotoxin and exposure times where synergism was observed were 0.79 μg/ml of the HD-1S-1980 preparation with 0.01% β-exotoxin after 11 days of exposure, 0.001% β-exotoxin with 3.125 μg/ml of HD-1S-1980 also after 11 days of exposure, and with 6.25 μg/ml of HD-1S-1980 plus 0.02% β-exotoxin after 3 days of exposure.