Some Problems in Using Meteorological Data to Forecast the Timing of Insect Life Cycles¹

Abstract

Sources of error in using accumulated temperatures for estimating the timing of events in insect life cycles, such as adult emergence and egg hatching, have rarely been examined in detail. There are two sources of error, one in the calculations, the other in the observations. Errors in the calculations arise from using the wrong base temperature, from using the daily arithmetic mean temperature in the calculation of the daily effective temperature on occasions when the mean is not appropriate and, occasionally, in using the linear relationship between temperature and growth where a non‐linear relationship would be more appropriate. Errors in observations arise mainly from attempts to employ standard meteorological measurements rather than measurements made from sites where the insects normally live. Temperature measurements in the soil at different depths on the flat and on north and south slopes, on the bark of trees and on the leaves of plants have been converted into estimates of insect development to demonstrate the effect of local differences in microclimate. It is strongly emphasized that day‐degrees as units of effective temperature in temperature summation calculations are physiological units of growth and not physical units of heat energy input. Les sources d'erreurs résultant de L'utilisation de la somme des températures pour prévoir le déroulement des cycles évolutifs des insectes (éclosion des adultes, ceufs, etc.) n'ont guère étéétudiées de rnanière approfondie. De L'avis de L'auteur, ces erreurs peuvent provenir de I'observation et du calcul. En ce qui concerne ce dernier, L'utilisation dune fausse température de base, résultant du recours à une moyenne arithmétique de la température quotidienne établie à tort, est préjudiciable. D'autre part, le résultat peut être faussé lorsqu'il est recouru à une relation linéaire entre la temperature et la croissance alors qu'il serait préferable de tenir compte d'une relation non linéaire. Les erreurs d'observation concernent principalement L'utilisation de données météorologiques à caracère général, au lieu de se référer à celles qui prévalent au site même où se trouve L'insecte. La détermination de la temperature du sol à des profondeurs différentes, sur terrain plat ou incline vers le nord ou le sud, ainsi que de la température de l'écorce des arbres ou des feuilles des plantes rvele L'influence du microclimat sur le développement des insectes. Il est souligné que le degre‐jour, utilisé dans les calculs de sommes de témperatures, est une unite physiologique de croissance et non une unité physique dabsorption d'énergie thermique.

Spring phenology and the response to global warming in gall-inducing sawflies

“…Temperatures in spring and summer are the most important factors determining eclosion, mating, oviposition and larval development and are of vital importance for survival for many insects. Hour-degrees accumulation above a threshold temperature (the developmental zero) is the commonest method used to estimate the dates of hatching of eggs and eclosion to adult insects (Baker 1980).…”

“…Thus, temperatures monitored by temperature loggers in the field were regressed on temperatures measured at several meteorological weather stations, and the stations giving the regression with the highest R 2 were chosen for Komagdalen and Nakkedalen, respectively. This procedure follows Baker's (1980) recommendations to start from measurements within the insect habitat (i.e. temperature loggers), then proceed to correlations with standard measurements (i.e.…”

“…To obtain temperature data in years when temperature loggers were not used, we used official meteorological stations, which provide four measurements per day, at 0100, 0700, 1300 and 1900 hours for many decades back in time, there being strong correlation between the temperatures at the field site and the nearest meteorological stations (Baker 1980;Worner 1992;Nilssen 1997). Thus, temperatures monitored by temperature loggers in the field were regressed on temperatures measured at several meteorological weather stations, and the stations giving the regression with the highest R 2 were chosen for Komagdalen and Nakkedalen, respectively.…”

“…Eclosed specimens were sexdetermined and pinned, and days needed for eclosion noted. Rate of development (1/days) was linearly regressed on rearing temperatures (9, 15, 23, 28°C) to calculate developmental zero (also called threshold temperature) (thereafter abbreviated as T 0 ) and hour-degree required (see Baker 1980). The regression can be expressed as…”

PHENOLOGY, MOVEMENT, AND WITHIN-FIELD DISTRIBUTION OF THE GRAPE BERRY MOTH, ENDOPIZA VITEANA (CLEMENS) (LEPIDOPTERA: TORTRICIDAE), IN NEW YORK VINEYARDS

“…To make predictions based on DD, grape growers would have to use data from regional weather stations. Baker (1980) warns against relying on data from weather stations for predicting phenological events because centralized weather data cannot reflect microclimatic variables affecting the development of an insect. Climatic conditions vary greatly between vineyard locations in New York and factors such as elevation, slope, proximity to lake moderation, and effective air drainage can influence the mesoclimate of vineyard sites.…”