The chalcid Schizonotus sieboldi (Pteromalidae) - an important regulator of the leaf beetle Chrysomela vigintipunctata mass outbreak
1998
Urban, J. (Mendelova Zemedelska a Lesnicka Univ., Brno (Czech Republic))
The paper deals with the bionomy and importance of Schizonotus sieboldi (Pteromalidae) with respect to a reduction in the population density of Chrysomela vigintipunctata. S. sieboldi is a primary ectoparasite of pupae of C. vigintipunctata and those salicicolous leaf beetles which undergo their pupal stage on tree species. Its oviposition takes place on the abdominal side of the thorax, at an amount of 1 to 15 eggs, and the first generation wasps emerge in 19 days. Up to two generations develop on the monovoltine C. vigintipunctata (and usually three generations on bivoltine to trivoltine Plagiodera versicolora) within one year. Moderate protandry was observed in wasp eclosion, and the males are more abundant than the females (sexual index = 0.37). The male percentage is considerably rising with the increasing abundance of S. sieboldi. Mortality of eggs and younger larvae and pupae is lower than 5%. Mortality of older larvae is rising up to 23.5% on pupae parasitized by a higher number of wasps as a result of food competition. Malnourished wasps are tiny and live for a shorter time.
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