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Population dynamics of the yew gall midge Taxomyia taxi and its chalcid parasitoids: a 24‐year study
Author(s) -
REDFERN M.,
CAMERON R. A. D.
Publication year - 1993
Publication title -
ecological entomology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.865
H-Index - 81
eISSN - 1365-2311
pISSN - 0307-6946
DOI - 10.1111/j.1365-2311.1993.tb01113.x
Subject(s) - cecidomyiidae , biology , gall , population density , infestation , parasitism , parasitoid , population , bionomics , midge , ecology , host (biology) , larva , demography , botany , sociology
.1 The dynamics of three populations of Taxomyia taxi (Inchbald) (Diptera: Cecidomyiidae) and its chalcid parasitoids have been studied over a 24‐year period. Most individuals have a 2‐year life cycle but some develop in 1 year. Details of within‐generation mortalities in T.taxi are used for life table analyses. 2 Mortality in the period between emergence of adult T.taxi and larval infestation of buds appears to be density‐dependent and is the largest component of overall mortality. In 2‐year life cycles, this mortality and that caused by Torymus nigritarsus (Walker) contribute equally to variance in overall mortality. In 1‐year cycles, mortality caused by Mesopolobus diffinis (Walker) is density‐dependent and accounts for most within‐gall losses. 3 T. nigritarsus , which attacks only 2‐year galls, is absent from all populations for a number of years in the middle of the study period. Its searching efficiency declines as its density and that of its host increase. 4 Densities of M.diffinis are strongly correlated with those of available hosts. Percentage parasitism of 2‐year galls is less than that of 1‐year galls, suggesting the occurrence of enemy‐free space. 5 Although there are some correlations in densities and mortality between trees, the dynamics of populations on each are frequently different. 6 An earlier analysis of 10 years' data failed to demonstrate density‐dependent effects. The extension to a 24‐year run has revealed such effects, but also demonstrates long‐term fluctuations in population densities, with corresponding changes in the balance of advantage between 1‐ and 2‐year life cycles of T.taxi.