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Sex ratios of Spalangia endius (Hymenoptera: Pteromalidae), in relation to current theory
Author(s) -
DONALDSON J. S.,
WALTER G. H.
Publication year - 1984
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.1365-2311.1984.tb00836.x
Subject(s) - pteromalidae , biology , sex ratio , parasitoid , mating , sex allocation , offspring , hymenoptera , zoology , demography , ecology , population , genetics , pregnancy , sociology
. 1. Spulungiu endius Walker is a solitary parasitoid of house fly puparia. 2. The sex and size of S.endius was not related to host size. 3. In the laboratory the mean sex ratio of all offspring of nine groups, each comprising twenty females, was consistently female‐biased (x = 83.5%, range 79–87%). The sex ratio in the field was less female‐biased and showed greater fluctuation (61–75%). This may be a consequence of females laying male eggs before mating, some females remaining unmated, possible shorter adult life expectancy in the field than in the laboratory, and, perhaps, the presence of conspecific females. 4. The sex ratio of offspring of individual females varied from 66% to 100% females, and males were deposited early in the oviposition sequence. 5. Although a large number of fly puparia died before adult flies or parasitoids emerged (64.5%; n = 5874), there was no differential mortality of either sex. 6. Our results fit no general sex ratio hypothesis and we conclude that (i) the genetic nature of sex ratios in these insects needs careful examination, and (ii) the prevalence of female‐biased sex ratios in solitary parasitoids needs investigation.