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Abstract
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Combination of different pest biocontrol agents in integrated pest management programs is
amongst the most promising methods for enhancing control efficiency. In addition to increasing
the virulence, combination use of biocontrol agents has impact on developing resistance
phenomenon. In recent years plant extractions have been extensively screened for their potential
as insecticide. In this research, combination effects of aqueous extracts of Achillea mellefolium
and Marrubium vulgare with three species of entomopathogenic nematodes (EPN),
Heterorhabditis bacteriophora, Steinernema feltiae and S. carpocapsae have been evaluated
against an important potato key pest, Phthorimaea operculella, potato tuber moth (PTM).
Aqueous extract of plant foliage prepared using maceration method. Foliage were washed with
distilled water and dried in room temperature followed by maceration method. Extraction
completed by rotary evaporation of solvent in 40ºC and 250 rpm. Last instar larvae of Great Wax
Moth, Galleria mellonella, were used for mass rearing of EPNs. Sublethal doses including LC10,
LC30 of EPNs and LC10, LC30, LC50 of plants aqueous extracts were determined and then
involved in further bioassay by loading combination treatments on a leaf area of potato. The kind
of interactions, between EPNs and plants determined by the procedure described by Finney
(1964) [2]. A chi-square test were developed according to method developed by Koppenhöfer
and Kaya (1997) and results were compared to the tabulated X2 for df=1. Interaction results
obtained were completely different regarding two plant extracts. Nearly in all combination
treatments of EPNs and A. mellefolium aqueous extracts, a synergistic effect were recorded, but
for EPNs and M. vulgare combinations, all interactions had an antagonistic or additive effects.
Statistical parameters were: S. feltiae and A. mellefolium,: MNA (LC10 & LC10)= 50%, D=30%,
P<0.005, MNA (LC30 & LC10)= 88%, D=59%, P<0.005; S. carpocapsae and A. mell
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