Components of seasonal soybean infestation by Heliothis zea in eastern Virginia, with emphasis on multivariate analysis of field susceptibility
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The development of Heliothis zea larvae in corn and soybeans was monitored during the summers of 1974 in Isle of Wight Co. and Westmoreland Co. and 1975 in Isle of Wight Co. Several aspects of insect density and development were studied and relationships between host crops and H.zea were more clearly defined.
Previous uncertainty regarding the number of instars in eastern Virginia was resolved. Based on larval head capsule measurements taken on 830 field-collected larvae and on 360 laboratory-reared larvae, six ins tars were determined to be present in eastern Virginia from July through September (Table 4). The six instars could be distinguished on the basis of head capsule width, height, and volume, but not thickness (Table 5). Head capsule volume provided more distinct separations between third through sixth instars than head capsule width alone (Figs. 14 and 15). The difficulty in detecting first and second instars suggests that in soybeans, depletion (removal) sampling techniques based on adaptation of the shake-cloth technique could be useful in future studies. Such a change in technique would enable more precise estimates of the early instar larval densities.
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