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- W129256227 abstract "Natural mortality factors affecting larvae and eggs of Heliothis spp. on pigeonpea, Cajanus cajan (L.) Millsp. cv. Hunt, were investigated in a field trial at the University of Queensland farm, Pinjarra Hills. An exclusion experiment, based on similar studies conducted by Eickwort (1977) on milkweed beetles (Labidomera), was carried out. Five treatments were set up to study levels of mortality of Heliothis spp. feeding on pigeonpea: (1) cage over pigeonpea plants; (2) cage over plants with sticky stem barriers; (3) pigeonpea plants growing among weeds and grasses; (4) pigeonpea plants with stem barriers; and (5) control plants. Heliothis eggs were released on all pigeonpea plants. Mortality could then be examined under five conditions: without predators, without aerial predators, without ground predators, with heavy background vegetation, and with all predators. Pitfall traps were placed in all treatments. Laboratory tests on survival of larvae feeding on various pigeonpea plant parts were carried out. Field-collected larvae were reared to measure percentage-parasitism. The rate of egg and larval mortality in all treatments was over 90% to the late instar stage. Density independent mortality was high, and involved desiccation, dislodgement, sterility, and plant effects. Cannibalism also occurred, mainly of eggs by larvae. Density-dependent related deaths varied between treatments. Survival rate was highest on caged plants and lowest in the weeds. Ground predators had no effect on Heliothis density. Spider predation accounted for much early larval mortality in all treatments, except where plants were caged. Important spider species included Diaea sp. (Thomisidae) and Oxyopes sp. (Oxyopidae). In the laboratory Heliothis larvae survived best on buds and flowers, burrowing to emerge as 3rd instars. Parasitism of larvae was low (<10%). These results suggest that Heliothis undergoes severe mortality in the early stages of its life-cycle, suggesting that only surviving late larvae should be of concern to the pigeonpea grower. Aerial predators can contribute to reducing this late larval population, if their numbers are permitted to remain high by spraying only soft insecticides. The burrowing habit protects early larvae from predators as well as insecticidal control. If natural mortality of eggs is high, then control measures need not be implemented until the 3rd larval stage. Eggs that survive density-independent mortality will determine the level of future damage on the pigeonpea crop." @default.
- W129256227 created "2016-06-24" @default.
- W129256227 creator A5031487766 @default.
- W129256227 date "2023-10-03" @default.
- W129256227 modified "2023-10-18" @default.
- W129256227 title "Mortality factors affecting Heliothis spp. on the pigeonpea, Cajanus cajan (L.) cv. Hunt, in south east Queensland" @default.
- W129256227 doi "https://doi.org/10.14264/262036" @default.
- W129256227 hasPublicationYear "2023" @default.
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