Efficacy of Phytomyza orobanchia Kalt. In Reducing The Seed Yield of Orobanche crenata Forsk. Under Semi-Field Conditions

• M.A.S. AI-Eryan, M.M.M. AItahtawy, H.K. El-Sherief and A.M.H. Abu-Shall
• Dept. of Economic Entomology, Faculty of Agriculture, Alexandria University, EI-Shatby, Alexandria, Egypt

Abstract

The parasitic weed Orobanche crenata Forsk., seriously, affects the faba bean crop causing significant yield losses. Biological control using the dipteran Phytomyza orobanchia Kalt. (Agromyzidae) has been promising in Eastern Europe, the former USSR and Mediterranean basin. Under semi-field conditions, P. orobanchia adults were released on pots containing faba bean plants infested with Orobanche. The applied release ratios were 1, 3, 6, 12, 24 and 48 Phytomyza pupae per Orobanche spike during the seasons of 1999, 2000 and 2001. Results revealed that the investigated release ratios gave a significant reduction in Orobanche dry weight and seed yield through the three consecutive seasons. Release of 3 Phytomyza adults per spike was enough to cause about 73.91% seed reduction during the season of 1999. This reduction increased to 97.56% during the season of 2001 in the same soil. For determining the efficacy of P. orobanchia as a biocontrol agent of O. crenata, the changes in the Orobanche seed bank in the soil was estimated. Results showed that Phytomyza efficacy, significantly, increased with increasing the number of released Phytomyza. However, it was significantly decreased by succession of the three release seasons, where the mean efficacy percentages were 61.85, 55.14 and 47.58% during the seasons 1999, 2000 and 2001, respectively. Although the effectiveness of Phytomyza releases in reducing Orobanche seed production can reach 91.73%, the already infested soil in addition to new accumulated seeds will cause further infestations over the successive seasons. This finding should be considered in the future release programms of P. orobanchia.