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Effect of parasitoid density on the functional response and sex ratio of a cynipoid hyperparasitoidAlloxysta pleuralis [Hym.: Alloxystidae]
Authors:R. Singh  P. N. Srivastava
Affiliation:(1) Aphid-Biocontrol Laboratory, Department of Zoology, University of Gorakhpur, 273009 Gorakhpur, India;(2) Department of Zoology, Budha Post Graduate College, 274403 Kushinagar, (Deoria), India
Abstract:Experiment where variable densities (1, 2, 5, 10, 25, 50, 100 and 150) of the parasitoid (5–7 d postparasitised aphids (Aphis craccivora Koch). — parasitised by aphidiid parasitoidTrioxys indicus Subba Rao & Sharma) were exposed to individual hyperparasitoidAlloxysta pleuralis (Cameron) indicated following: (1) with increase of initial host (primary parasitoid) densities the number of hosts hyperparasitised increases sigmoidally reaching to a plateau at 50 host similar to thetype 3 functional response of Holling; the curve was described by a logistic eqution [Nhyp=44.0/(1+exp (4.0–0.16 Np))], (2) greater host mortality was recorded at lower initial host densityes (≤50); (3) the area of discovery of the hyperparasitoid is inversely density-dependent at higher host densities (≥25); and (4) the variation in host number has no significant influence on the sex ratio of F1 offspring of the hyperparasitoid which ranges between 0.56–0.67. The implications of these responses of the hyperparasitoidA. pleuralis are discussed.
Keywords:Alloxysta pleuralis    Trioxys indicus    Aphis craccivora   functional response  area of discovery  sex ratio
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