Damage caused by a complex of species or types of the genus Alebra in chestnut trees (Homoptera, Cicadellidae)

An unusual damage of the leaves of chestnut trees caused by species of the genus Alebra Fieber, 1872 was observed during the years 1978 to 1985. The insects were separated according to the color of the adults into three bisexual types and two unisexual color types. Although the three bisexual types do not differ in the structure of their genital apparatus, they can be differentiated on the basis of the electrophoretically detected enzyme polymorphisms. These types are symbolized by the letters A, B and D. The two unisexual types, which consist only of females are symbolized by the letters C1 and C2. However, although they are morphologically distinct, they do not differentiate electrophoretically from each other nor from type B. On the basis of the morphological characteristics type B probably corresponds to the species Alebra wahlbergi (Boheman, 1845), type D to the species Alebra albostriella (Fallen, 1826) and type A to a new species which is going to be described soon in another paper. Types B and C1 are the most numerous ones. In samples taken in three years at two different localities type B represented 62.2% to 69.0% and type C1 19.7% to 29.1%. Type D exhibited higher population densities in a shady locality whereas types A, B, C1, C2 in a sunny one. Types B, D, C1 and C2 are univoltine. Adults are present from the middle of June until the beginning of November. In contrast to this, type A is bivoltine. The first generation appears early in June and the second at the end of August. The females deposited their eggs in the bark of young branches, thus causing damage to them. Eggs are overwintering and young larvae emerged early in May. Eggs were parasitized by species of the family Mymaridae (Hymenoptera), whereas larvae and adults by species of the family Drynidae (Hymenoptera). Our results have shown that adults of the types A and D were higher parasitized than the types B and C1. Therefore, it is possible that the high population densities of types B and C1 are due to their low degree of parasitism