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  • Author or Editor: S. M. Aly x
  • Biology and Life Sciences x
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The toxicity of Melissa officinalis L. essential oil and its formulation (Melissacide) were evaluated against eggs and females of two predatory phytoseiid mites, Typhlodromips swirskii (Athias Henriot) and Neoseiulus barkeri (Hughes), using direct spray. Results indicate that both tested materials were potent on predatory females than egg stage. Typhlodromips swirskii was proved to be more sensitive to the oil and formulation than N. barkeri.

Females mortality were (62-100%) in T. swirskii, and (46-69%) in N. barkeri, when both predatory mites were sprayed with LC50 and LC90 of the oil and Melissacide reported on Tetranychus urticae Koch. Females of both predators were suffered from reduction in food consumption when sprayed with two sublethal concentrations of Melissacide, while insignificant differences reported in daily number of eggs deposited by females of T. swirskii, when sprayed with its LC25 value of Melissacide and control.

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Seed-bone infection level of watermelon with F. oxysporum f. sp. niveum has a significant effect on wilt incidence. When high (23-31.5%) or mo­de­­rate (8.5-9.5%) seed-borne infection occurred, wilt incidence reached up to 47.5-57.5% and 45-55%, respectively. However, when low (1.5-2.5%) seed borne levels occurred wilt incidence did not increase more than 5-10%. It is recommended to use seeds of free or low infection levels of Fusarium to minimize watermelon wilt incidence.

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