No abstract

The size and number of aerial spray drops impinging on spruce budworm in its conifer forest habitat were determined by means of a new tracer method that uses fluorescent particles in a liquid spray. Examination of 1113 larvae affected by an experimental insecticide that had been applied to a 5000-acre (2024-ha) test area in Montana showed that 93 percent had not been contacted by any droplets larger than 50 micro in diameter. Small numbers of droplets 50 to 100 micro in diameter were found on 7 percent of the larvae, along with lethal numbers of smaller drops. No evidence was found that significant numbers of drops larger than 100 micro reached the target insects. Because about 95 percent of the spray applied to forests by current methods consist of droplets larger than 50 micro, the biologically effective portion of the drop spectrum is only a few percent. The data foreshadow a major potential reduction in insecticide requirements for the successful control of spruce budworm.

Can. Ent. 115: 815-822 (1983) Fifty Bacillus thuringiensis (B.t.) isolates representing K-1, galleriae, K-73, thuringiensis, aizawai, dendrolimus, tolworthi, kenyae, darmstadiensis, alesti, and entomocidus crystal antigen types were bioassayed against fifth-instar spruce budworm, Choristoneura fumiferana (Clem.), larvae. In addition, larvae reared on diet with and without aureomycin were tested for their susceptibility to B.t. The data indicated no significant differences in susceptibility to B.t. among insects reared on aureomycin or on aureomycin-free diet, but differences were evident in larval growth and mortality among untreated controls. None of the 50 isolates bioassayed was any more toxic to the budworm than is the strain used at present in commercial preparations of B. thuringiensis. ResumeCinquante isolats de Bacillus thuringiensis (B.t.) reprksentant les types antigkniques i l'ktat cristallisk K-1, galleriae, K-73, thuringiensis, aizawai, dendrolimus, tolworthi, kenyae, darmstadiensis, alesti et entomocidus ont CtC testks contre des larves au cinquibme stade de la tordeuse des bourgeons de l'kpinette, Choristoneura fumiferana (Clem.). De plus, la vulnkrabilitk envers B.t. des larves klevkes avec une alimentation additionnke ou exempte d'aurkomycine a kt6 exarninke. Les rksultats n'indiquent aucune diffkrence quant B la vulnkrabilitk des larves alimentkes avec ou sans aurkomycine, mais des diffkrences sont apparues au niveau de la croissance et de la mortalitk chez les lames tkmoins non traitkes. Aucun des 50 isolats testks n'ktait plus toxique pour la tordeuse que la variktk prksentement employke dans des prkparations cornrnerciales.

Bioassays of Bacillus thuringiensis (Bt.) are commonly performed by applying a serial dilution of the test sample to either foliage or artificial diet (Burges and Thompson 1971). In these assays the ingested dose is not measured directly, but is assumed to be proportional to the concentration of the sample applied to the diet. This assumption is valid only if the total amount of food ingested during the experiment is the same at all dosage levels. However, this assumption may not be true because Bt. inhibits feeding of some lepidoptera larvae (Burges and Thompson 1971). Furthermore, artificial diets usually contain nutrients and possibly antimicrobial agents which may interact with Bt.

Larval biomass of the spruce bud worm, Choristoneura fumiferana (Clem.), in balsam fir, Abies balsamea L., stands was significantly reduced following aerial applications of commercial Bacillus thuringiensis (B.t.) (Thuricide 16B®, 24B and 32BX and Dipel 85®). Treatment with Dipel vehicle (Dipel 88® without B.t.) did not affect larval biomass. Biomass reduction following the Thuricide treatment was directly related to feeding activity. These findings support published observations on the long-term effect of B.t. on budworm populations.