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Distribution of cabbage root flies in brassica crops
Author(s) -
FINCH By S.,
SKINNER G.
Publication year - 1973
Publication title -
annals of applied biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.677
H-Index - 80
eISSN - 1744-7348
pISSN - 0003-4746
DOI - 10.1111/j.1744-7348.1973.tb01331.x
Subject(s) - biology , brassica , biological dispersal , crop , pest analysis , agronomy , distribution (mathematics) , horticulture , demography , population , mathematics , mathematical analysis , sociology
SUMMARY Changes in the distribution of adult cabbage root flies were determined in 0–05‐0‐4 ha brassica plots during 1970 and 1971 using yellow water‐traps. The three generations of flies occurred at similar times in both years and the numbers caught generally decreased from the first to the third generation. In resident populations, the numbers of males and females declined by 70 and 40% respectively, between the second and third generations. When there was no decline, immigration presumably compensated for flies trapped or otherwise lost. The results confirmed that male cabbage root fly movement is trivial, that wind has little effect on distribution at a brassica plot and that females move into the crop independently of males. They failed to confirm that females aggregate markedly at hedgerows or fences, that they spend little time in the crop or that they regularly return to hedgerows. Differences in the dispersal behaviour of the male and female flies were reflected in the numbers caught. Some males dispersed actively during the first 2 weeks after emergence but many were displaced slowly downwind. Once at a plot, wind appeared to have little effect on distribution of young males, but older males tended to shelter just downwind of the hedge. Relatively few males were caught near hedges but they tended to aggregate along the crop‐interfaces, particularly during the first generation. Plot size did not appear to influence the pattern of fly distribution greatly. Females dispersed more actively than males and were generally more uniformly distributed through the crops even during periods of immigration. Gravid females entered an isolated plot without accompanying males, inferring that they are migratory and mate near the site of emergence. Female distribution was not related to the stage of ovarial development except during maximum oviposition when those that had laid some eggs visited the hedgerow. Aged females became progressively easier to capture and usually died in the crop.