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Population dynamics of the Lodgepole Needle Miner, Recurvaria starki Free. (Lepidoptera: Golechiidae) in Canadian Rocky Mountain parks Stark, Ronald William

Abstract

The lodgepole needle miner, Recurvaria starki Free. has been studied intensively since 1948. Until 1953, this insect was referred to in publications as Recurvaria millerl Busck. The life history and taxonomic position of R. starki are reviewed briefly and an historical review of the research carried on since 1948 is given. A full description is given of the procedure of applying life table techniques to needle miner studies since 1954 and examples are given for selected study areas. Six sampling intervals, one egg, four larval and one pupal are deemed suitable to assess the course of the population of a single generation from the time of oviposition to moth emergence. The life tables and survivorship and death-rate curves show clearly that there are five periods in the two-year life cycle of the lodgepole needle miner during which extensive mortality may occur: (1) between egg formation and oviposition; (2) between oviposition and larval establishment; (3) during the first larval hibernation; (4) during the second larval hibernation; (5) during the spring of moth emergence. Population success is also undoubtedly affected by conditions during the adult life. Population sampling has shown that the outbreak has declined since 1948. Defoliation and increment studies have shown that the period of greatest defoliation occurred from 1940 to 1944 and that the outbreak probably began in the late 1930's. The major cause of the decline was winter temperatures, probably during the coldest month. From laboratory experiments and population sampling compared with weather records it is estimated that needle miner populations can have a high survival if extreme minima of -30°F to -40°F do not persist long enough to depress the mean monthly temperature to near 0°F. Parasitism was not a particularly important factor in the outbreak decline probably because of a greater depressant effect on parasite populations by winter temperatures. Other natural control factors are discussed as well as the possible effects of climatic factors on oviposition and fecundity. From a detailed survey of weather records since 1920 and yearly averages since 1885 it is postulated that release of the needle miner population was due to a warming trend in the climate of the region. This began in the late 1930's, reached a peak in the mid-1940's and has declined since that time. The warming trend has been noted by other authors for northern latitudes and is substantiated by the weather records of this region. It is further postulated that the climate of this part of western Canada is generally too severe for an outbreak of the lodgepole needle miner, Recurvaria starki Free, to be prolonged.

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