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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