Parasitization of the cottony-cushion scale in relation to host size |
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Authors: | K Thórarinsson |
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Institution: | (1) Department of Entomology, University of California, 95616 Davis, CA, USA;(2) Present address: Iceland Forest Research Station, Mógilsá, IS-270 Mosfellbœr, Iceland |
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Abstract: | Measurements of body length of cottony-cushion scales,Icerya purchasi Maskell, are presented. Although length increased markedly with developmental stage, the length distributions of successive
stages were found to overlap, making length an imperfect indicator of stage andvice versa. The likelihood of parasitism by the fly,Cryptochaetum iceryae (Williston), was found to increase with increasing scale size when scales of different sizes were concurrently made available
to the parasites under field conditions. Also, parasite loads (no. of parasites per parasitized host) were found to increase
with host size. The size ofC. iceryae pupae was found to depend on the developmental stage of the scale host in which pupation took place — the more developed
(larger) the host, the larger the pupa. This result suggests that parasite growth is food limited in the smaller hosts, and
that therefore its apparent preference for larger hosts is to the parasite's advantage.
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Keywords: | Biological control parasite preference body size parasite load Icerya purchasi Cryptochaetum iceryae |
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