R. E. Gingrich

Acquired resistance to Hypoderma lineatum: Comparative immune response of resistant and susceptible cattle

The humoral and cellular immune responses of previously infested and noninfested cattle were compared after a single experimental exposure to 1st-instar Hypoderma lineatum. No correlation was found between the development of humoral antibodies as measured by passive hemagglutination assay and resistance in cattle. However, the most resistant cattle had higher macrophage migration-inhibition activity before and 1 month after infestation than did low- or non-resistant animals, and resistant animals also had greater sensitivity to antigens from larvae as they penetrated the skin. These results suggest that acquired resistance to hypodermatosis involves a cellular component of the immune mechanism.

Differentiation of resistance in cattle to larval Hypoderma lineatum

Abstract Cattle were successively infested for 4 years with larval cattle grubs, Hypoderma lineatum, to demonstrate the acquisition of resistance. The effects of host age and dietary-induced state with Vitamin A on susceptibility to infestation and their interactions with effects from previous infestations were also determined. Cattle acquired resistance to infestation after a single infestation. This resistance was not affected by host age for at least 4 years, was not affected by a deficiency of vitamin A, and was effective in the skin and connective tissues of the host. The effects of this acquired resistance were highly variable in degree, were produced primarily during the first 90 days of infestation and increased after repeated provocation to provide nearly complete protection in some animals. Calves and yearlings had innate resistance that decreased with age, was localized in the skin, was impaired by a deficiency of Vitamin A, and resulted in a mean loss of 65–75% of the larvae in an infestation dose of up to 150. The combined effects of the 2 types of resistance reduced the grub-burden in cattle throughout their life.

Bacillus thuringiensis: Laboratory tests against four species of biting lice (mallophaga: Trichodectidae)

Abstract Four species of mammalian biting lice, Bovicola bovis, B. crassipes, B. limbata, and B. ovis, were more susceptible in the laboratory to the spore-δ-endotoxin complex of Bacillus thuringiensis than to the β-exotoxin. The relative potency of these active principles was thus reversed from that for avian biting lice. The activity of the preparations tested was not homologous with that of E-61, the international standard for δ-endotoxin activity.

A flotation procedure for producing spore-free crystals from commercial formulations of Bacillus thuringiensis var. thuringiensis

Abstract When suspensions containing crystals and spores of Bacillus thuringiensis were subjected to streams of rising bubbles in a column, the spores floated to the surface where they could be removed. Spore-free suspensions of crystals have been prepared by this method from commercial microbial concentrates.

Activity of a “thermostable exotoxin” of Bacillus thuringiensis subsp. morrisoni in the Salmonella/microsomal assay for bacterial mutagenicity☆☆☆

Abstract The purpose of this study was to employ the Salmonella /microsomal assay (Ames test) to investigate the mutagenic potential of a thermostable exotoxin of Bacillus thuringiensis subsp. morrisoni . Bacteria are ideal for the detection of infrequently occurring point mutations because the large number of organisms (200 to 400 million bacteria per plate) exposed to the mutagen at any one time increases the possibility of observing a random mutational event. The exotoxin used in this study was produced using the shaker flask fermentation procedure with mineral casein broth. A Petri dish method of bioassay using fresh bovine feces was used to determine the efficacy of the exotoxin against horn flies. The LD 50 was found to be 5.35 μl/g of feces. Five bacterial tester strains were identified and characterized for the genetic markers described by Ames et al. (B. N. Ames et al., 1975, Mutat. Res. , 31 , 347–364). Appropriate doses of the B. thuringiensis supernatant, solvent or positive control were added to agar plates. The supernatant was tested at five dose levels against all five strains of bacteria. Controls of bacteria only were included for spontaneous reversions. All treatments were performed in triplicate. The numbers of revertant colonies from each set of triplicate plates were averaged and the standard deviation calculated and compared to that found with the solvent control. The negative controls, positive controls, and sterility controls all fulfilled requirements for determination of a valid test. No detectable mutagenic activity was found for the thermostable exotoxin of B. thuringiensis morrisoni .

Thelohania tabani sp. n., a Microsporidian from larvae of the black horse fly, Tabanus atratus fabricius

Abstract A new species of Microsporidia, Thelohania tabani sp. n., is described from the black horse fly, Tabanus atratus Fabricius. This is the first report of a microsporidian from any Tabanidae. Some observations on pathology and transmission of the pathogen are also reported.

Control of the Horn Fly, Haematobia irritons, with Bacillus thuringiensis

The horn fly, one of the most common pests of cattle, causes an estimated annual loss of over 350 million dollars to producers in the United States. The adult flies are hematophagous and spend most of their lives on the host where their frequent feeding causes almost constant irritation. As few as 12–22 flies/ dairy animal (Granett and Hansens, 1956) or 46–59 flies/grazing beef animal (Granett and Hansens, 1957) can cause an economic loss, but hundreds per individual animal are common, and occasionally several thousand flies/animal can occur. Present control technologies are based on chemical insecticides, which must be applied repeatedly to reduce fly numbers to tolerable levels. There are no pathogens registered for use against horn flies. Three commercial preparations of Bacillus thuringiensis, when added to feces or fed to animals, have been found to be active against larvae of the horn fly (Gingrich, 1965). However, consecutive daily treatments were necessary to maintain complete inhibition of larval development.