Background
Entomopathogenic 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.
Results
In 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.
Conclusions
The 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.
Background
Biotic and abiotic factors influence survival, infectivity, development, reproduction, and activity of the entomopathogenic nematodes (EPNs). EPNs have been used to suppress the soil-inhabitant insects, which applied as a successful biological control agent against the black cutworm, Agrotis ipsilon (Hufnagel) (Lepidoptera/Noctuidae) larvae, and pupae.
Results
Studying the effect of different temperatures 20, 25, and 30°C ± 2, and the soil moisture content at 10, 15, and 25% on the susceptibility of two Heterorhabditis sp. strains, Egyptian strain (TAN5) and imported strain (Hb88) against the A. ipsilon 4th and 6th larval instars and 3-day-old pupae was carried out under laboratory conditions. The tested concentrations of the two strains were 30, 60, 120, 240, and 480 IJs/cm2 of soil surface. The mortality rate of 4th instar A. ipsilon larvae was high after Heterorhabditis strain TAN5 treatments at all concentrations, which ranged between (24 and 100%) and (6–100%) at 25°C and 30°C, respectively. At 20°C, Heterorhabditis strain Hb88 recorded higher mortality percentages for A. ipsilon 4th and 6th larval instars and pupae than the indigenous strain TAN5. The soil moisture content of 25% gave the highest mortality rates for the 4th instar larvae of A. ipsilon after treatments of the two strains. The Egyptian Heterorhabditis strain TAN5 was tolerant to the increase in temperature and more tolerant to the change in the water content of the soil than the imported strain Hb88 at all concentrations tested. In a semi-field experiment, Heterorhabditis strain TAN5 at concentrations between (1000–8000 IJs/cm2 of soil surface) showed mortality rates (27–95%) for 4th instar A. ipsilon larvae and (19–81%) for the 3-day-old pupae, respectively.
Conclusions
Heterorhabditis strains TAN5 can was utilized against the black cutworm of A. ipsilon at the temperatures 25 and 30°C. Heterorhabditis strains TAN5 and Hb88 can be utilized against the black cutworm of A. ipsilon at the soil moisture content from 15 to 25%. In the semi-field experiment, Heterorhabditis TAN5 and Hb88 strains were effective against larvae and pupae of A. ipsilon at high concentrations of the nematodes.
In greenhouses, tomato plants are subject to attack by several pest species. The present study aimed to investigate the compatibility of releasing the egg parasitoid, Trichogramma euproctidis (Girault) (Hymenoptera: Trichogrammatidae), and the entomopathogenic nematode, Heterorhabditis bacteriophora, strain HP88 against the tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), in commercial tomato greenhouses (Cherry and Bushra varieties) at winter plantation of 2018–2019 in Egypt. Three commercial plastic greenhouses were used. The first plastic greenhouses were treated by the two tested biological control agents (BCG), the second sprayed by certain recommended pesticides (PG), and the third used for control. Pheromone traps were used for monitoring the appearance of T. absoluta moths. The combined use of T. euproctidis and H. bacteriophora resulted to reduce the population density of the T. absoluta gradually until the end of the season in BCG. In the 17th week of treatments by T. euproctidis and H. bacteriophora, the population density of T. absoluta was estimated as leaf mines/plant (0.8 and 1.26 mines/leaf, in Cherry and Bushra varieties, respectively) in BCG. Also, in the 17th week of treatments by recommended pesticides, the population density of T. absoluta reached 12.73 mines/leaf and 18.33 mines/leaf, in CG. Early use of pesticides, by the appearance of T. absoluta infestation, could not suppress its population density that continued to increase until the end of the season in PG. Results revealed that the combination of the tested biological control agents against T. absoluta is recommended to be a main part in pest management practices in tomato greenhouses.
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