| Summary: | Abstract In Egypt, parasitic weed species, Orobanche crenata Forsk is one of the major constraints to the production of faba bean, which is considered the most important food legume in the country. The broomrape fly, Phytomyza orobanchia Kaltenbach (Diptera, Agromyzidae) is particularly suitable for biological control since it is oligophagous feeding in the larval stage, only on Orobanche species. The objective of the present study is to estimate the number of annual generations of P. orobanchia, using growing degree-days (GDD) in Alexandria region, Egypt. Results revealed that development of Phytomyza immature stages (from egg deposition to adult emergence) required 103.5, 90.0, 79.5, and 93.5 DD through 31, 20, 18, and 16 days for the investigated four generations, respectively. Percentage of infested Orobanche capsules positively increased with increasing accumulated degree-days. A linear model for predicting infested capsules with P. orobanchia through knowing DD was estimated. The constructed model may be used also in predicting Orobanche capsule infestation with P. orobanchia. Results also indicated that estimating the degree-days will help in predicting the occurrence of the first egg laid for P. orobanchia in O. crenata flowers in the field for the first generation and subsequent generations. Knowledge of the Phytomyza activity will provide a prediction for adult emergence and subsequent egg laying and potential damage by larvae according to infestation percent of Orobanche capsules through the successive generations. This may help the biological control programs to justify the required numbers of Phytomyza and adequate time for releases to obtain the maximum destruction of Orobanche seeds.
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