D. L. Haynes

Entomophthora muscae (Entomophthorales: Entomophthoracae) mycosis in the onion fly, Delia antiqua (Diptera: Anthomyiidae)

Abstract Entomophthora muscae was identified as a common fungal pathogen of the onion fly, Delia antiqua , and the adult seed corn maggot, D. platura . Low infection levels also were found in populations of the cluster fly, Pollenia rudis (Diptera: Muscidae), and the tiger fly, Coenosia tigrina (Diptera: Muscidae). The disease cycle, as it affects D. antiqua in the onion agroecosystem, is described, including the etiology, symptomatology, and phenology. Natural infection levels approaching 100% were noted early in the spring and in late fall, impacting the 1st and 3rd generations of the D. antiqua population significantly. A lagged density-dependent disease response was noted at the gross population level, although more specific biological interactions may be involved in regulating the disease intensity.

Simulating the spatiotemporal dynamics of the cereal leaf beetle in a regional crop system

Abstract Previous studies of the population dynamics of the cereal leaf beetle (CLB), Oulema melanopus , have neglected spatial considerations despite the important role played by dispersal in the life history of this species. In this paper we describe a simulation model of CLB spatiotemporal dynamics. The model was used to examine qualitatively different hypotheses about dispersal in this species. The hypothesis of random diffusion, in which beetle movement is undirected, was contrasted to hypotheses of attraction to host crops and movement away from nonhosts. Model predictions were compared to field observations of beetle distribution and abundance in a 41-km 2 region of southwestern Michigan, U.S.A., in 1976 and 1977. Evaluation criteria were peak and total seasonal abundances of CLB in grain crops in the region, and densities in 69 individual fields. The random model gave satisfactory results on a regional scale, but simulated densities for individual fields were too homogeneous and were generally poorly correlated with actual densities. The alternative models performed better in most respects, although field-to-field variation in density was still too low. Without specific studies of dispersal behavior, there is no basis for selecting one hypothesis over another. The model emphasizes the importance of local features of fields in producing spatial variations in insect density. The between-field environment plays a prominent role in the dynamics of abundance and distribution of beetles in host crops. Factorial sensitivity analysis was used to examine the influence of key parameters for which there are insufficient data. A very high rate of diffusion in nonhost habitats was needed with the random model to obtain simulated peak densities in host crops as high as those observed. To reduce the density of insects in resistant wheat relative to susceptible wheat, as observed, this crop must either repel beetles or cause beetles to move randomly at a much higher rate. Simulated late-season densities in host crops were too high, suggesting either strong seasonality in the dispersal behavior of adults, or an increase in their mortality rate as the season progresses.

A systems approach to research and simulation of insect pest dynamics in the onion agro-ecosystem

Abstract The systems approach, utilizing detailed system conceptualization and iterative simulation model development, was used to help direct field and laboratory research on the population dynamics of the onion maggot, Delia antiqua (Meigen) (Diptera: Anthomyiidae) and its naturally occurring fungal pathogen Entomophthora muscae (Cohn) (Entomophthorales: Entomophthoraceae) in the onion agro-ecosystem. The structure and interconnections of this biological system, including an alternate disease host ( Delia platura , the seed corn maggot), are outlined as are additional relationships between these components of primary interest and other components closely associated within the onion agro-ecosystem. A structural approach to model development was used as a base for system design and analysis. The model structure and simulation methodology, including program verification and model validation, are described. Examples of simulation results are presented to illustrate the application of the model.

Cereal leaf beetle spatial dynamics: Simulations with a random diffusion model

Abstract An existing model simulating the spatial dynamics of the cereal leaf beetle (CLB), Oulema melanopus, was used to examine the consequences of the hypothesis that dispersal by this species is a random diffusion process. The effects of spatial and temporal manipulations of the environment on the distribution and abundance of beetles in a regional crop system were determined. Simulation experiments included converting all winter wheat to a CLB-resistant variety, altering the syncrony of insect emergence and the phenologies of winter and spring host crops, varying the absolute and relative areas of crops planted, and making systematic changes in field size, shape and location. Results highlight the importance of the interfield environment as a reservoir of dispersing insects, and the sensitivity of pest density to the synchrony of winter and spring crop growth. Cultural management practices are suggested that may reduce CLB density in cereal crops, especially if they are coordinated on a regional scale.

Laboratory transmission and in vivo incubation of Entomophthora muscae (Entomophthorales: Entomophthoracae) in the onion fly, Delia antiqua (Diptera: Anthomyiidae)

Abstract A high-moisture infection chamber was used for the in vivo transmission of Entomophthora muscae within laboratory populations of the onion fly, Delia antiqua. This cadaver-to-fly transmission procedure provided an average experimental infection rate well above 95%. Laboratory infection and temperature-dependent incubation rates of E. muscae were further examined in adult populations of D. antiqua. The time from initial exposure until host death and pathogen sporulation was accurately predicted using a second-order function of the incubation temperature. A developmental base temperature of approximately 5°C was estimated, with 105 degree-days being the average number of heat units required between host infection and death. E. muscae transmission between D. antiqua and D. platura, two insect pests typically associated with Michigan onion production, was verified under laboratory conditions.

Phenology and control of the onion maggot (Diptera: Anthomyiidae) in Michigan onion production

Abstract The phenology and control of the onion maggot, Delia antiqua (Meigen) (Diptera: Anthomyiidae), were investigated in commercial onion fields in Michigan from 1978 to 1980. First-generation emergence of adults occurred at 399 Dδ (degree-days) (4.4°C base). Second- and third-generation emergence occurred at 1142 and 1840 D°. Adult flight activity was correlated with time of damage to onion plants by 1st and 2nd generation larvae. Third-generation larvae were only observed on unharvested mature onions. Phenologies of the various life-stages are compared to development rates determined in the laboratory. Application of foliar insecticide sprays for adult control did not provide additional protection from root maggot damage where granular insecticides had been applied at planting. Recommendations for onion maggot control are discussed.

General models for simulating population growth in insects grouped both by stages and age classes

Many models have been developed in the past that are specific to a given pest population. The authors have found that the structures of these models are similar, and thus a general model structure can be identified. On the basis of this understanding, several general component models are developed that can be used to simulate the population growth of many insects of interest. Their application to agricultural pests is shown.

A SYSTEMS APPROACH TO CONTEMPORARY AGRICULTURAL PEST PROBLEMS

ABSTRACT Short and long range goals of agricultural pest management systems are discussed. Procedures are identified to achieve these goals.