A nonlinear model for describing the larval development of the European corn borer, Ostrinia nubilalis (Hubner), was calibrated because previous work had revealed limitations of the degree-day model. The model proposed by Logan et al. in 1976 was used as a starting point. Experimental design was based on destructive sampling in order to record a large number of larvae, and on variable temperatures in order to fit the nonlinear model with few experiments and to avoid artifacts caused by constant temperatures. A calibration method was also proposed. The Logan model and the normal distributions describing the timing of the moult could be calibrated with the proposed method for temperatures ranging between 9 and 42 degrees C. The model was validated under field conditions. Validation revealed that at least 1 environmental variable, probably maize phenology, that was not taken into account by the temperature model had a strong effect on the development rate. Leasing out the infestation where this effect was maximum (infestation during the early whorl stage), the model predicted the 2nd moult with a 48-h accuracy, and the last moult with an accuracy of better than 5 d. However, predictions were only half a day better than those obtained by the degree-day model. Nevertheless, this work helped to determine precisely the range of validity for the degree-dal; concept. Further investigations are along 2 directions: testing other mathematical formulations of the relationship between development rate and temperature to determine the possible limitations of the Logan formulation, and analyzing the influence of other environmental variables once the influence of temperature has been taken into account.

Natural mortality of Ostrinia nubilalis (Hubner) larvae on corn was studied under 30 field-infestation conditions at 3 sites. High mortality occurred during; the days immediately after egg hatching when >50% of hatched larvae died, followed by a lower and more stable mortality rate. Two models, one with constant mortality rate and the other with variable mortality rate, were proposed and tested to describe this pattern. These models described the time course of larval survival rate well. The 2nd model was used to compute the European corn borer survival rate at various dates in relation to larval development. The mean mortality rate was 74% during the Ist instar, then remained similar, then decreased by 13% during the 2nd and 3rd instars and 16% during the 4th instar. A high variability in survival rate between infestations was observed as early as the Ist instar. Multiple regressions were used to model relationships between larval survival rate and environmental factors (climatic factors and infestation conditions). Phenological stage of corn at the date of infestation was the primary factor influencing the larval sun;val rate. The relationship explained >45% of the variability.

Impact of 3 control methods on larval European corn borer, Ostrinia nubilalis Hubner, dynamics on com, Zea mays (L.), was evaluated under field conditions at Versailles, France. The control methods studied were a chemical insecticide, Beauveria bassiana Vuillemin (Deuteromycotina: Hyphomycete), and a transgenic corn hybrid. The experimental study showed that B. bassiana control was similar to chemical control. The transgenic hybrid control was always very high throughout the corn cycle studied. A substantial decrease of B. bassiana and chemical control efficacy was observed with an increase in the delay between treatment and infestation. The complementary studies of B. bassiana persistence, control impact, and pathogen contact showed control-larval behavior interactions, which could explain this decrease in efficacy. To take into account the main factors that condition control efficacy, a modular and mechanistic model was proposed to describe larval dynamic and control impact. The proposed control model made it possible to integrate O. nubilalis dynamics, and thus to describe the time response of control.

Taking into account the limits of previous models proposed to predict European com borer, Ostrinia nubilalis (Hubner) infestation time, complementary research in physiology, population dynamic, and modeling was used to propose a mechanistic model to describe this phenomenon. Diapause is the main process that determines infestation time in this pest. Recent work on diapause has demonstrated the heterogeneity of this development phase. This model describes the first phase of the diapause process, wing disk development. The model proposed consists of two parts; the first component takes into account the influence of temperature as a nonlinear function and the second (normal distributions) represents the variability in development time among a population for each stage. This model has been estimated by maximum likelihood from laboratory data obtained with a destructive sampling under three variable sinusoidal temperature regimes 9-21, 12-34, and 18-42-degrees-C with a photoperiod of 12:12 (L:D) h allowing diapause induction. This unique model describes the development under these different temperature ranges with a 2% precision (0.5 d) and has been validated under field conditions. The development of populations ending their development before winter is correctly represented (10% precision). The model is not adapted to describe the population ending their development after winter. The estimated model correctly predicts diapause development for temperatures above 4-degrees-C. This report presents novel data in modeling research and demontrates a convincing correlation between laboratory and field collected data.

To quantify yield losses of corn, Zea mays (L.), caused by larvae of the European com borer, Ostrinia nubilalis (Hubner) (Lepidoptera: Pyralidae), a model describing the within-plant distribution of larvae is proposed and discussed. This paper is restricted to the interorgan and vertical distribution of larvae for pretasseling infestation. Field data collected at Versailles were used to study larval distribution and to estimate and test the model. The model proposed is based on four hypotheses deduced from field data: larval distribution in the tassel is influenced mainly by com development; distribution in the ear of fourth and fifth instars depends on infestation date; distribution of first instars in the ear is conditional upon ear appearance; and vertical distribution of larvae in vegetative organs depends on com development. For the 11 infestation conditions, the proposed mathematical model used to quantify the relations between larval distribution and main factors (com development, infestation conditions) allows the percentages of larvae in ear, tassel, and internodes to be described with a precision of 10-15%.

In order to explain and predict yield losses caused by European corn borer larvae, Ostrinia nubilalis Hbn. (Lepidoptera: Pyralidae), a mechanistic model was proposed to describe cavity appearance, their lengthwise extension, and their within-plant distribution. It integrates main dynamical processes of larvae: mortality, development and within-plant distribution. After its estimation and test under field conditions in 1988 and 1989, its validation, based upon X-ray photographs, is presented. This method allows cavity appearance and lengthwise extension to be followed without damaging the plants. This study confirms the relevance of the damage model and the rate of cavity lengthwise extension estimated with it.

The validation of a temperature-dependent model for European Corn Borer development on 3 different corn varieties (LG11, DEA and ISORA), at 4 sites in France: Avignon, Bordeaux, Colmar and Versailles, and with 2 infestation times for each site and variety, is presented. The model consist of 2 parts: a degree-day model and 4 normal distributions (fig 1). It has been estimated and tested at Versailles (table II). The validations show that the mean differences between predicted and observed data are systematically less than a week under the different experimental conditions (tables III and IV, figs 3a, 3b, 4 and 5). The model is then an appropriate representation of development for agronomical purposes (prediction of losses, pest control). Possible improvements of the model are discussed: using a non linear model between growth rate and temperature and taking into account the temperature under vegetation seem to be the most realistic ways to improve the model, considering the knowledge of European corn borer biology.

The European Corn Borer (ECB), Ostrinia nubilalis Hbn. (Lepidoptera: Pyralidae), is a major pest of maize in many countries. Yield losses caused by larvae of this insect depend mainly on the extent of cavity damage, the timing of tunnelling, and their within-plant distribution. To describe these factors, a mechanistic model of cavity appearance is proposed here. It takes into account the main biological processes which determine damage. These are the development, mortality and within-plant distribution of the ECB larvae. The model has been estimated and tested on field data collected at INRA-Versailles in France. Model fittings showed that (i) creation and lengthwise extension rates of cavities per larva depend on location and instar of the larvae, and that (ii) only instars 4 and 5 make cavities. This model described, with a high precision level, the appearance and lengthwise extension of cavities over time and their within-plant distribution for two maize varieties, several infestation dates and levels, and various climatic sequences.

The European corn borer (ECB), Ostrinia nubilalis (Hubner), is a major pest of corn in many countries. To quantify borer losses, a model describing development of the five instars of ECB for a single generation of development, tested on data collected at INRA-Versailles, France, is proposed and discussed. It consists of two parts: a degree-day model that takes into account the influence of temperature; and normal distributions that represent the variability of population development time among instars. A method of estimating the parameters of this model for field data by maximum likelihood is described. This statistical approach showed how the experimental design should be improved. For the six climatic sequences recorded, this simple model is an appropriate representation of development of the four instars sampled with enough accuracy. A validation of the model supports this conclusion. The chosen model is based on simple biological hypotheses and can be fitted under field conditions. The advantages of these two characteristics lies in the possibility of comparing laboratory and field estimations, to analyze their differences, and to determine under which environmental conditions the model is correct (i.e., validity area).

The European corn borer, Ostrinia nubilalis (Hübner), is a major pest of corn in France. Width of larval head capsules cannot be used directly to determine developmental stages of individuals because the ranges of measurements of two consecutive developmental stages overlap. A distribution model of head capsule widths of different instars, composed of five normal distributions, is fitted, and a discrimination method is proposed based on the probability of misclassification of larvae. Different infestation dates are compared during two years. Goodness-of-fit and assumptions are tested and criticized in relation to experimental conditions. It appears that statistical hypotheses are often not verified in field experiments, and that the validity of tests should be reconsidered. However, the model proposed is useful to criticize usual assumptions and to propose a practical solution.