We compared the pathogenicity of the entomopathogenic nematodes Heterorhabditis bacteriophora, Steinernema glaseri, and S. scarabaei against third instars of 12 white grub species. The Japanese beetle (Popillia japonica) was highly susceptible to all nematode species. Oriental beetle [Exomala (= Anomala) orientalis], European chafer (Rhizotrogus majalis), Asiatic garden beetle (Maladera castanea), and the May/June beetles Phyllophaga crinita, Ph. congrua, and Ph. (Subgenus Phytalus) georgiana were highly susceptible to S. scarabaei but had mediocre to low susceptibility to H. bacteriophora and S. glaseri. The black turfgrass ataenius (Ataenius spretulus) was very susceptible to H. bacteriophora but had mediocre susceptibility to S. glaseri and S. scarabaei. Northern (Cyclocephala borealis) and southern masked chafer (C. lurida) had mediocre and southwestern masked chafer (C. pasadenae) and green June beetle (Cotinis nitida) had low susceptibility to all nematode species.

The role of the professional disease diagnostician has become increasingly important in turf management. Responsible turfgrass disease diagnosis must incorporate the possibility of biotic, as well as abiotic, disorders and should consist of three components: the interview, identification of the stress factor, and a management recommendation. The concept of management groups is introduced to facilitate delivery of the rapid and effective solution required by turf managers. Recent advances in diagnostics, including immunoassay, PCR kits, and distance diagnostics, have had minimal effect on turfgrass diagnostic practices to date. However, continued emphasis on the application of technology rather than knowledge-based diagnostic procedures is contributing to the demise of applied plant pathology. Nevertheless, the demand for turfgrass disease diagnostic services continues to increase, making the future for the applied plant pathologist somewhat uncertain, but full of opportunities.

A search for patterns in the success and failure of microbial insecticides in vegetable crops was conducted through review of four case studies: the use of Bacillus thuringiensis (B.t.) var. tenebrionis for control of the Colorado potato beetle, the use of B.t. var. kurstaki for control of the diamondback moth, the use of various B.t.s for control of lepidopterous pests in tomatoes and celery, and the use of a granulosis virus for control of potato tuber moth. With success defined in terms of achievement of technical goals (efficacy), commercial goals (end-user and insecticide manufacturer satisfaction) and social, or public goals (environmental and health safety), only certain of the case studies could be judged a success. These successes shared a variety of features including: (1) use of the microbial insecticide as a component, rather than as the sole agent, in an integrated crop management program; (2) unavailability of conventional insecticides, due to insecticide resistance, lack of registered products or mandatory IPM programs, provided incentive for the use of microbial insecticides; (3) modification of the expectation that microbial insecticides will perform within the chemical paradigm – fast, lethal and on contact; (4) exploitation of all possible benefits of the microbial insecticide, including safety to natural enemies, as well as efficacy against the target insect, and (5) support from large private and public institutions in the form of research, grower education, scouting programs, subsidized production, and economic and legal incentives to the use of microbial insecticides.

In previous laboratory studies, entomopathogenic nematodes andBacillus thuringiensissubspeciesjaponensis(Btj) caused additive or synergistic mortality in third-instarCyclocephala(Coleoptera: Scarabaeidae) grubs when the nematodes were applied at least 7 days afterBtj.This type of mortality was observed forC. hirta,a species that is not very susceptible toBtj,and forC. pasadenae,a species that has intermediate susceptibility toBtj.In the present study, this observation was confirmed for third-instarAnomala orientalis,a species that is highly susceptible toBtj.In greenhouse and field studies, additive or synergistic interactions between nematodes andBtjwere observed for all three scarab species. The interactions were variable, and to achieve acceptable grub control, high concentrations ofBtjhad to be applied. A subsequent greenhouse experiment showed that young third-instarC. pasadenaewere more susceptible toBtjthan older third instars. In addition the interaction between nematodes andBtjwas also more synergistic in the younger than in the older third instars. In a field test against a population ofC. hirtaconsisting of late second and early third instars, combinations of nematodes andBtjat economic application rates provided acceptable control levels whether applied simultaneously or with a 4-day delay betweenBtjand nematode application. Our observations suggest that curative control of white grubs is possible with combinations of entomopathogenic nematodes andBtjif the applications are done when populations consist of second and early third instars.

Confirmed cases of insect resistance to microbial insecticides in the field have been rare to date, primarily because the performance limitations of these products have inhibited their acceptance in mainstream agriculture. With the 1996 commercial introduction of transgenic crops that express Bacillus thuringiensis (Bt) toxins, this picture is about to change. Research conducted over the past 10 years indicates that insects are indeed capable of developing resistance to Bt toxins and Bt toxin/spore mixtures, suggesting that resistance to Bt crops is likely unless management plans to avoid it are implemented. A resistance management strategy that combines the use of high doses of Bt toxins with the use of non-treated crop refugia was implemented in Bt cotton in 1996, and will most likely be implemented for additional Bt crops in the near future.

Bioassays with MVP, a genetically engineered form of a toxin of Bacillus thuringiensis susp. kurstaki, demonstrated that a plateau in concentration response depended on the temperature and time when mortality was assessed. The presence of a plateau did not indicate resistance in diamondback moth, Plutella xylostella (L.). Comparisons of LC(50)s at 25 degrees indicated that MVP acted more slowly than a conventional B. thuringiensis subsp. kurstaki formulation (Dipel 2X). However, LT(50)s of the preparations at a given concentration did not vary substantially. AT 28 degrees C, responses were approximately equal over time. To avoid artifacts in analyses of concentration-response data, we recommend that bioassays be designed carefully to account for subtle differences in the behavior of genetically engineered versus conventional preparations of B. thuringiensis.

Our investigation of responses of Colorado potato beetle, Leptinotarsa decemlineata (Say), to Bacillus thuringiensis subsp. tenebrionis over 83 wk; diamondback moth, Plutella xylostella (L.), to B. thuringiensis subsp. kurstaki (cloned into Pseudomonas florescens) over 37 wk; and western spruce budworm, Choristoneura occidentalis Freeman, to pyrethrins and DDT over 91 generations indicated that ratios at LC(50), LC(90) and LC(99) varied among pesticides tested on the same species and among insect species tested with the same pesticide. Frequencies with which LCs were significantly different (based on bracketing of the value 1.0 by 95% CI of each ratio) compared with the standard (the lowest LC in the data set) were extremely high (>95%) in all tests except those with pyrethrins on western spruce budworm. For example, toxicity ratios for Colorado potato beetle larvae fed B. thuringiensis subsp. tenebrionis were as high as 12.8 at LC(50). 37.0 at LC(90), and 155 at LC(99) over 83 wk; the maximum upper 95% CL for a ratio were 18.6, 168, and 1,000, respectively, at these LCs. We conclude that the extent of natural variation must be investigated before biologically important changes can be identified with any certainty. The conventional practice of using ratios of one LC to another in studies to detect resistance and other biological changes may lead to erroneous conclusions if natural variation in cohorts of a population and subsequent generations of the same genetic strain are unknown.

Journal Article Activity of the M-ONE Formulation of a New Strain of Bacillus thuringiensis Against the Colorado Potato Beetle (Coleoptera: Chrysomelidae): Relationship Between Susceptibility and Insect Life Stage Get access G. W. Zehnder, G. W. Zehnder Virginia Polytechnic Institute and State University, Eastern Shore Agricultural Experiment Station, Painter, Virginia 23420 Search for other works by this author on: Oxford Academic PubMed Google Scholar W. D. Gelernter W. D. Gelernter Virginia Polytechnic Institute and State University, Eastern Shore Agricultural Experiment Station, Painter, Virginia 23420 Search for other works by this author on: Oxford Academic PubMed Google Scholar Journal of Economic Entomology, Volume 82, Issue 3, 1 June 1989, Pages 756–761, https://doi.org/10.1093/jee/82.3.756 Published: 01 June 1989 Article history Received: 27 May 1988 Accepted: 12 August 1988 Published: 01 June 1989