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Mandibular Length in Nupserha bicolor Thoms. ssp. postbrunnea Breun. (Col., Lamiidae) as the Factor in determining the Site of Oviposition in Corchorus olitorius
Published online by Cambridge University Press: 10 July 2009
Extract
Ovipositing females of Nupserha bicolor Thoms, ssp. postbrunnea Breun. cause loss of stem length in jute, Corchorus olitorius, by girdling the stem above and below a slit in which the egg is laid. The slit is made by two successive indentations of the mandibles. It is composed of a central pit and two lateral punctures. Girdling is restricted to that portion of the stem which falls within the stem-diameter range of 0·2 cm. to 0·4 cm.
A relationship exists between the length of the mandibles of the female, the depth of the stem tissue from the epidermis down to the periphery of the pith (extra-medullary tissue), and girdling and oviposition.
For girdling, the optimum ratio between the mandibular length and the depth of extra-medullary tissue as measured from the epidermal furrow and ridge of the stem (pentagonal in this region) is 1:0·80 and 1:0·99, respectively. Frequency of girdling gradually decreases in those regions of stem where the depth of extra-medullary tissue increases or decreases these ratios.
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