Abstract
BackgroundEntomopathogenic nematodes (EPNs), as biological control agents, have been isolated from many regions throughout the world. Local isolates of EPNs are usually more effective for controlling indigenous insect pests as they are adapted to the local environmental conditions and the insect pest species.ResultsIn the present work, EPN isolates were searched in the soil under citrus and guava trees, and Egyptian clover at Noubaria region, Elbhaira governorate, Egypt, within two consecutive years. The EPNs were isolated from two positive soil samples of Egyptian clover (Trifolium alexandrinum) (TAN5) and guava trees (Psidium guajava) (PGN6), while the EPNs were not existent in the soil samples under citrus. Laboratory applications of the two EPNs isolates against the cotton leafworm, Spodoptera littoralis(Boisd.), and the black cutworm, Agrotis ipsilon (Hufn.) (Lepidoptera: Noctuidae), were recorded. Nematodes naturally occurring in the soil were trapped by full-grown larvae of the greater wax moth (Galleria mellonella L.). Infected larvae turned from whitish beige to dark reddish color, proofed that these isolates belong to the genus Heterorhabditis. Laboratory results revealed that the mortality rate ranges from 24 to 100% with TAN5 while from 18 to 96% with PGN6 at A. ipsilon larvae. The LC50 values of TAN5 against A. ipsilon were 1285.527 and 1560.747 IJs/cup, while those values for S. littoralis were 1339.099 and 2531.605 IJs/cup in larvae and pupae, respectively. The 3rd instar larvae of A. ipsilon and S. littoralis were more sensitive than the pupae. Production of Heterorhabditis sp. strain TAN5 was the highest in the reproduction of infective juveniles than the strain PGN6 at all concentrations.ConclusionsThe EPNs isolated from the soil samples belonged to the genus Heterorhabditis. Heterorhabditis sp. strain (TAN5) collected from the soil under Egyptian clover at Noubaria region was the highest reproduction and the most effective against both tested pests, A. ipsilon and S. littoralis larvae and pupae. EPN species would serve as an alternative to chemical pesticides and fit well in an integrated pest management program against larvae as well as adults and pupae of many economic insect pests which inhabit the soil.
Highlights
Entomopathogenic nematodes (EPNs), as biological control agents, have been isolated from many regions throughout the world
In Egypt, the initial research on EPN began in the 1970s when Dr El-Kifl worked on the biological control potential of Neoaplectana (= Steinernema) carpocapsae against the cotton leafworm, Spodoptera littoralis, one of the most economically important insect pests in Egypt
Nematode isolates Two EPNs isolates, named Trifolium alexandrinum Nubaria (TAN5) collected from the soil samples under Egyptian clover (Trifolium alexandrinum) and Psidium guajava Nubaria (PGN6) collected from the soil samples under guava trees (Psidium guajava) while the EPNs was not existent in the soil samples under citrus
Summary
Entomopathogenic nematodes (EPNs), as biological control agents, have been isolated from many regions throughout the world. Entomopathogenic nematodes (EPNs) of the families Steinernematidae and Heterorhabditidae with their associated symbiotic bacteria (Xenorhabdus and Photorhabdus, respectively) are widely distributed in soils throughout the world (Adams et al, 2006). These nematodes are pathogenic to insects, killing them within 48 hrs with the aid of their associated bacterial symbionts, and have great importance as biological control agents of many insect pests (Laznik et al, 2011). Host availability, and percentage of moisture in the soil are thought to be important in determining the distribution of nematodes inside the soil (Susurluk 2011). The surveys carried out in Egyptian soils revealed that species of heterorhabditids were more prevalent than steinernematids; research regarding their use to control other insect species was done as well (Aashaq et al, 2020)
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