STUDIES ON ENTOMOPATHOGENIC FUNGI FOR CONTROLLING CERTAIN LEPIDOPTEROUS INSECTS ON CORN

Abstract

Survey of entomopathogenic fungi associated with com borers, the pink stem borer Sesamia cretica Led. (Noctuidae), the purple - lined corn borer, Chilo agamemnon Bles. (Crambidae) and the European com borer, Ostrinia nubilalis Hiibn (Pyraustidae) in three governorates: Qaluobia, Kafr EI­ Sheikh and Beni-Suef during 1997-1999 after harvested early, summerandNilymaizeplantings (stalks and ears). Isolating and identify these fungi on different medium PDA and SDA. The survey revealed the presence of identified fungi species associated with the three com borers; S cretica, 0 nubilalis. and C agamemnon Four entomopathogenic fungi, Beauveria bassiana, Nomuraea rileyi, Verticillium lecanii and Entomopthora sp. were isolated from the collected com borer cadavers in the three governorates. Besides, eight relatively common fungi associated with the com borers were isolated from Beni Suef (Sids region), Qaluobia and Kafr EI-Shiekh (Sakha region) governorates during 1997/98 - 1998/99. These fungi were identified as; Fusarium sp., Aspergillus jlavus, Aspergillus sp., Pseudogibellula formicarum, Alternaria sp., Penicillium sp., Mucor sp. and Trichothecium rosaum. Distribution of entomopathogenic fungi associated with com borers and survey populations of com borers (stalks and ears) in previous governorates. Susceptibility of the 1g instar (newly hatched) larvae of S. cretica to isolated fungi to estimated LC50 and LT50. Among the tested fungi, B. bassiana (B8) proved to be the most pathogenic to 1g the larval instar of S. cretica followed by N rileyi and V. lecanii. Effect of insecticides on B.bassiana (B8). Effect of insecticides on mycelial growth and spore germination was studied. Data revealed that Methomyl and Cyhalothin were promising insecticides for mixing with the fungus, since no or little inhibition occurred either at the recommended dose or at 0.25 of it Monocrotophos insecticide gave a high rate of inhibition to the tested isolate. In this respect, B. bassiana (B8) was the most tolerant isolate, at both tested doses, recording no inhibition, at any of the concentrations tested with Methomyl insecticide. Field applications of the entomopathogenic fungi B. bassiana (101 and 108 and V. lecanii (107 to evaluate the fungi in controlling S. cretica and S. exigua were carried out weekly, biweekly and monthly treatments in (Sakha) at Kafr EI-Sheikh governorate during summer and Nily plantings 1998 using two plant cultivars (maize hybrid 323 and maize variety Giza 2). Latent effects of fungal application in summer and Nily plantings on populations of com borers in stalks and ears maize plants after harvested and yield assessment was carried out The weekly treatment with B. bassiana, and V. /ecanii gave reduction of infestation and latent effect It appeared that the maize variety (Giza 2) facilitated the efficacy of both fungi more than the maize hybrid 323. The grain yield was affected by the number of fungal sprayings, fungus concentrations and maize variety. The application of fungus alone B. bassiana (108 weekly, Methomyl and Monocrotophos at recommended dose, the mixture of Methomyl at Y. recommended dose + fungus and Methomyl and Monocrotophos at Y. recommended dose were tested against com borers carried out in Kafr EI-Sheikh (Sakha region) during summer planting 1999. The treatments with Methomyl and Monocrotophos at recommended dose gave high reduction of infestation following by fungus alone, mixture of Methomyl at Y. recommended dose + fungus and Methomyl and Monocrotophos at Y. recommended dose. The maize grain yield was increased as a result of previous applications. Effect of fungi on predators after survey common predatory species associated with the com borers during 1998/1999 in Kafr EI-Sheikh (Sakha region): Coccinella udecimpunctata L, Scymnus interruptus L., Paedrus alfierii Koch, and Chrysoperla carnea. No mycosis was observed among the collected individuals of the predators.