A tool changer is disclosed for automatically removing a working tool after having been used from the spindle of a machine tool such as a vertical milling machine, transferring the used working tool to a rack which stores a plurality of working tools, picking up from the rack another working tool for the next machining operation, transferring such new working tool to the spindle, and operatively mounting such new working tool on the spindle.

Temperature and Organism Size—A Biological Law for Ectotherms?

Substantial evidence indicates that drought stress promotes outbreaks of plant-eating (phytophagous) fungi and insects. Observations and experiments show that colonization success and pervalence of such fungi as root and stalk rots, stem cankers, and sometimes wilts and foliar diseases are much higher on water-stressed plants than on normal plants (Schoeneweiss 1986). The evidence associating insects and drought is more circumstantial, consisting largely of observations that outbreaks around the world of such insects as bark beetles and leaf feeders (see Table 1) are typically preceded by unusually warm, dry weather. There is also a consistent, positive correlation between insect oubreaks and dry, nutrient-poor sites (Mattson and Haack 1987).

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The Role of Drought in Outbreaks of Plant-eating Insects

Scolytid bark beetles that colonize living conifers are frequently associated with specific fungi that are carried in specialized structures or on the body surface. These fungi are introduced into the tree during the attack process. The continuing association suggests that there is mutual benefit to the fitness of both beetles and fungi. The fungal species may benefit from the association with the beetles by transport to new host trees. Beetle species may benefit from the association with fungi by feeding on the fungi, or by the fungi contributing to the death of the host trees through mycelial penetration of host tissue, toxin release, interactions with preformed and induced conifer defenses, or the combined action of both beetles and fungi during colonization. Extensive research has been directed towards characterizing the interactions of beetle-fungal complexes with live host conifers and determining the ecological advantages for maintaining the associations. However, differences among systems and how species interact under different population and environmental conditions make it difficult to generalize about the importance of the separate biological components in successful host colonization.

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Interactions among scolytid bark beetles, their associated fungi, and live host conifers

Development, growth, and survival of Culex quinquefasciatus Say and Aedes aegypti (L.) were determined at six constant temperatures (15, 20, 25, 27, 30, 34 degrees C). The Sharpe & DeMichele four-parameter model with high-temperature inhibition described the temperature-dependent median developmental rates of both mosquito species. In both species, body size generally decreased as temperature increased. Head capsule widths in all instars in both species were significantly greater at 15 than at 30-34 degrees C. Except for the third instar of Ae. aegypti, the larval body lengths in both species were significantly greater at 15 than at 34 degrees C. All instars and pupae of both species and the adults in Cx. quinquefasciatus were significantly heavier at 15 than at 27-34 degrees C. In Cx. quinquefasciatus, survival from eclosion to adult emergence was highest in the range from 20 to 30 degrees C (85-90%) and dropped drastically at 15 (38%) and 34 degrees C (42%). In Ae. aegypti, survival to adult stage was high at 20 (92%) and 27 degrees C (90%) and lowest at 15 degrees C (3%).

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Temperature-dependent development and survival rates of Culex quinquefasciatus and Aedes aegypti (Diptera : Culicidae)

Bien que la secheresse affecte directement la physiologie et la croissance des arbres, l'impact de facteurs secondaires (insectes ravageurs, pathogenes et feu) est souvent plus important que le stress original et peut conduire a la mortalite des arbres. En 2003, une secheresse et des vagues de chaleur ont provoque des degâts importants dans les forets d'Europe centrale et occidentale. Cet article rend compte de l'impact de la secheresse et de la canicule sur les populations d'insectes forestiers dans le contexte de cet evenement exceptionnel. Les observations des fluctuations de populations des principaux insectes ravageurs des forets europeennes sont presentees et discutees en regard des connaissances actuelles et des theories des interactions entre secheresse et insectes. Nous avons recherche les effets directs et indirects de la secheresse, respectivement sur les traits d'histoire de vie et au travers des modifications physiologiques induites chez les arbres hotes. Les insectes forestiers ont ete separes en 4 groupes : xylophages, phyllophages, mineuses et suceurs de seve. L'impact du stress hydrique a ete different selon la guilde consideree. Les xylophages ont ete positivement influences par le declin de la resistance de l'hote suite a un stress hydrique prolonge. Au contraire, les phyllophages ont mieux profite de l'augmentation de l'azote dans les tissus de la plante sous un stress hydrique modere ou intermittent. Des observations de terrains ont montre l'importance du statut hydrique du sol sur le niveau de resistance des arbres contre les attaques de ravageurs. En certains sites, la secheresse de 2003 a d'ailleurs mis en evidence des choix d'essences inappropries. Cette secheresse exceptionnelle peut nous donner des indications sur les impacts des evenements climatiques extremes. Cependant les observations des performances au niveau individuel ne permettent pas de predire a long terme les dynamiques des populations, lesquelles dependent d'interactions complexes au niveau local entre facteurs biotiques et abiotiques.

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Effects of drought and heat on forest insect populations in relation to the 2003 drought in Western Europe

The importance of predicting the seasonal occurrence of insects has led to the formulation of many mathematical models that describe development rates as a function of temperature. Yet many of the widely used models do not provide acceptable results for predicting development times. After a careful review of the literature, we believe the biophysical model of Sharpe and DeMichele (1977; J. Theor. Biol. 64: 649–670) is the most suitable for this purpose. This model provides an excellent description of development rates over a full range of temperatures, and can be modified easily to describe rates over a portion of that range. Herein we review the literature on modeling insect development rates, describe the Sharpe and DeMichele model, and present easy instructions for its use. A computer program, assembled from the Statistical Analysis System (SAS) Library, determines the correct number of parameters to be used in the model for a given data set, selects starting values of these parameters for nonlinear regression, and computes least-square estimates of the parameters by using Marquardt techniques.

Modeling insect development rates: a literature review and application of a biophysical model

We describe a stochastic approach for modeling insect development based on a single, temperature-independent distribution of normalized development times. We review other stochastic approaches, as well as problems encountered in modeling distributions of development time. A computer program, assembled from the Statistical Analysis System library, constructs cumulative probability distributions from frequency data on insect development times. These data are obtained from constant temperature experiments. The computer program normalizes the times of these distributions on their median time, identifies a single empirical distribution representative of all normalized distributions, and fits a cumulative Weibull function to this standard curve. The program determines the starting values of the three Weibull parameters and computes least-square estimates of these parameters using Marquardt techniques. This normalized probability function was tested against 23 data sets with good results, and can be used in population models to distribute cohort development through time under variable temperature conditions.

Modeling Distributions of Insect Development Time: a Literature Review and Application of the Weibull Function

This paper presents a rate-summation approach for modeling the development times of individuals in an insect population held under variable temperatures. The approach integrates a mechanistic poikilotherm rate function and a Weibull distribution function into a simulation model. The rate function determines the median rate of insect development per day at a given temperature, while the distribution function determines the fraction of cohort development at a given accumulated rate. When combined, the rates are accumulated under variable (field) temperatures, and become the independent variable of the distribution function for predicting the cumulative proportion of cohort development through time. The modeling approach uses a frequency distribution of field oviposition times (if available) to identify the starting times of the simulation. In this way, multiplecohort development is modeled. If desired, predictions can be compared with field development (emergence) to validate the model. This approach is presented in simplified technical language and through a computer program assembled from the Statistical Analysis System (SAS) library. Although the computer code relies on specific mathematical equations for describing development rates and the distribution of development times, the same modeling concepts are applicable using other appropriate equations.

Multiple-cohort Approach for Simulating Development of Insect Populations under Variable Temperatures

A biophysical model of southern pine beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Scolytidae), development☆

Role of host disturbance in initiation and growth of infestations of the southern pine bark beetle guild [ Dendroctonus frontalis Zimmermann, D. terebrans (Olivier), Ips calligraphus (Germar), I. grandicollis (Eichhoff), and I. avulses (Eichhoff)] was investigated. Host loblolly were disturbed at four intervals throughout the year and response of the bark beetle guild was monitored. Effects of the disturbance were evaluated by assessing tree mortality resulting from colonization by the bark beetle guild. Numerical responses of beetles to treatment and control trees were measured and the structure of the populations was defined in terms of proportions of the different species responding to the disturbance. All disturbed hosts were discovered and colonized by the bark beetle guild. Multiple-tree infestations developed from 10 of 20 treatment centers. Trees disturbed during the winter persisted as foci for beetle colonization for 133–150 days. The disturbance event did not have to coincide with seasonal development of the bark beetle guild for the hosts to be utilized for colonization. Trees in spring, summer, and fall treatments were colonized immediately after the disturbance. All species of the bark beetle guild were involved in the colonization process. However, structure of the populations (species composition and numbers) was different during the four seasonal treatments. Results of the experiment are interpreted in the context of the hypothesis that lightning, acting as a disturbance, is an integral component of the natural history of the bark beetle guild. The study provides experimental evidence to support the major tenets of the hypothesis.

Terence L. Wagner

Papers

Modeling insect development rates: a literature review and application of a biophysical model

Modeling Distributions of Insect Development Time: a Literature Review and Application of the Weibull Function

Multiple-cohort Approach for Simulating Development of Insect Populations under Variable Temperatures

A biophysical model of southern pine beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Scolytidae), development☆

Response of the Southern Pine Bark Beetle Guild (Coleoptera: Scolytidae) to Host Disturbance