Graduate Thesis Or Dissertation
 

Effects of single and simultaneous challenges using DDT and a nuclear polyhedrosis virus against the variegated cutwork, Peridroma saucia (Hübner)

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  • A study of mortality, food consumption, food utilization, and polyhedral production following single and simultaneous challenges of the variegated cutworm, Peridroma saucia (Hubner), with DDT and a nuclear polyhedrosis virus was made. Fourth instar larvae were challenged topically with three levels of DDT and per os with three levels of virus, one level in each case being a zero control. This design provided nine different treatments, four involving dual challenges, and five involving single or zero level controls. X² tests were used to compare total mortality, DDT mortality, and virus mortality in each combination treatment to expected mortalities which were computed from the single dose treatment results. Results indicated that the effects of virus and DDT were additive. DDT activity was affected by the presence of virus in only two of 12 combinations studied. In both cases a significant synergistic response was noted. No definite trends over all levels tested were apparent in the data. Virus mortality was significantly increased in one combination and was reduced in another. In both cases, the differences are questionable due to the low numbers of individuals involved. All other combinations resulted in virus or DDT deaths which would be expected if each were acting independently. Single or combined treatments killed no more males than females. Consumption and utilization of a meridic diet were measured gravimetrically. Different treatments had little effect on consumption or utilization by larvae of the same ultimate fates. Healthy larvae, however, consumed six times as much food as virus killed larvae and 100 times as much as DDT killed larvae. Healthy insects digested a lower percentage of the food consumed than did infected or poisoned larvae, but they converted more of what they did digest into tissue, while sick larvae utilized more as energy. Polyhedral production by infected larvae was measured in each group. Production dropped in the combination treatments as DDT dosage increased and as virus dosage decreased, indicating the need for careful consideration of goals when applying these agents in the field.
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