Response of Trichogramma pretiosum females to extracts of two plants attacked by Heliothis zea

Published source details Nordlund D.A., Chalfant R.B. & Lewis W.J. (1985) Response of Trichogramma pretiosum females to extracts of two plants attacked by Heliothis zea. Agriculture, Ecosystems & Environment, 12, 127-133.
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This study is summarised as evidence for the following.

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	Use chemicals to attract natural enemies Action Link

Use chemicals to attract natural enemies

A replicated, controlled field study (Nordlund et al. 1985) found greater corn earworm Helicoverpa zea parasitism in plots of corn Zea mays treated with tomato Solanum lycopersicum extract (38% eggs parasitised) than in control plots of corn without tomato extract (29%). Eggs were parasitised by the wasp Trichogramma pretiosum. Parasitism was similar in plots of tomato treated with corn extract (53% eggs parasitised) and controls of tomato without corn extract (54%). A greenhouse experiment found the wasp also parasitised more corn earworm eggs in pots of cowpea Vigna unguiculata treated with tomato extract (52-74% eggs parasitised) than in pots treated with corn extract (19-26%) or untreated controls (18-26%). A lab study found similar results by monitoring parasitism in petri dishes containing the extracts. Plant extracts were obtained by grinding fresh leaves. In the field study extracts were sprayed (at 2 g/plot in 10 ml of hexane) on 1 row by 3 m plots. Controls were left unsprayed. Corn and tomato extract treatments were replicated 30 and 40 times, respectively. Corn earworm eggs were placed at 0.3 m intervals, 50 parasitoid wasps were released and eggs were collected after four hours. The greenhouse trial grew cowpea in 28.8-cm pots.