Period and intensity of Cheilosia corydon (Harris) (Diptera: Syrphidae) oviposition on ruderal plants of Carduus acanthoides L. and Carduus nutans L. (Asteraceae)

摘要

In this paper the ovipositional period and the intesity of the egg laying of Cheilosia corydon (Harris) (Diptera: Syrphidae), and the actractiveness of the ruderal plants Carduus acanthoides L. and Carduus nutans L., (Asteraceae) for the oviposition of this useful insect were researched. The ovipositional period of C. corydon under the climatic conditions of continental part of Serbia lasts from the third decade of March, during Aprile, till the early May. The ovipositional period of C. corydon on the plants of Corduus acanthoides L. and Carduus nutans L. in the region under study in 1990 lasted 38 days (from 28 March to 5 May). The biggest numbers of eggs were deposited in the period from 8 to 27 Aprile. On C. acanthoides plants the largest numbers of eggs were deposited on 14 Aprile, when 27 new eggs were registered on 7 plants (28%), which makes 7,16% in relation to the total number of deposited eggs during the whole ovipositional period. The oviposition of C. corydon on C. nutans was very intensive in the period from 12 to 24 Aprile, especially on 18 Aprile, when on 9 plants (36%) there were 47 newly deposited eggs, or 7,77% in relation to the total number of deposited eggs. In 1991, embrional period of C. corydon lasted the same as the previous year, but it started something earlier, i. e. in the beginning of the third decade of March and it lasted till the third decade of April. C. corydon deposited the largest numbers of eggs on C. acanthoides plants in the period from 5 to 10 Aprile, with the maximum on 7 April when on 5 plants (20%) the total of 23 eggs were registered or 7,23% in relation to the total number of deposited eggs. The same year, intensive oviposition on C. nutans plants was from 7 to 10 Aprile. The oviposition was especially pronounced on 9 Aprile, when 37 new eggs were found on 9 plants, which makes 8,81% of the total number of deposited eggs on this weed. C. corydon deposited considerably higher number on both plant species in 1990 (982) then in 1991 (738). C. nutans is more attractive host plant for C. corydon oviposition in relation to C. acanthoides. On 25 plants of C. acanthoides 377 eggs (38,39%) were deposited during the whole ovipositional period in 1990 (18,08 eggs on the average per plant), and on C. nutans 605 eggs (61,61%) or 24,20 eggs on the average per plant. In 1991 on the same numbers of C. acanthoides plants there were the total of 318 eggs (43,10%) which makes 12,72 eggs per plant on the average, and on C. nutans 420 eggs (16,80 per plant) or 56,90% in relation to the total number of eggs (738) deposited on both weed species. The eggs are elongated, of the average lenght of 1,3+-0,05 mm, and width 0,49+-0,03 mm.