ISHS


Acta
Horticulturae
Home


Login
Logout
Status


Help

ISHS Home

ISHS Contact

Consultation
statistics
index


Search
 
ISHS Acta Horticulturae 17: Symposium on Protected Growing of Vegetables

POSSIBILITIES OF USING ENCARSIA FORMOSA GAH AND ASCHERSONIA ALEURODES WEBBER IN THE CONTROL OF TRIALEURODES VAPORARIORUM WESTW

Author:   E. Hristova
DOI:   10.17660/ActaHortic.1971.17.66
Abstract:
Trialeurodes vaporariorum Westw is one of the most dangerous enemies of greenhouse vegetable crops. On account of the frequent harvests of vegetable crops, the applied means should be highly toxic for Trialeurodes vaporariorum Westw and non-toxic for man; they should not be phytotoxic for the plants and should not impart additional flavour to the fruits of the treated plants. Of all tested means only the preparations Thiodan, Bromex and Bi-58 showed high toxicity against the larves of Trialeurodes vaporariorum Westw (see tables 1 and 2). Spraying with these preparations commences with the seedlings in the autumn.

Decrease in the density of Trialeurodes vaporariorum Westw is also accomplished by using parasites. One of them is Encarsia formosa found in 1964 on tomatoes, grown in the greenhouses near the village of Zvanichevo, Pazardjik district, and on tomatoes, beans, tobacco and other plants grown in the same region in the open. In September 1964 there were up to 80 per cent parasitizing larvae on tomatoes as a result of which Trialeurodes vaporariorum Westw at that time was in a depressed state in that region. In the autumn Trialeurodes vaporariorum Westw and its parazite migrated from the field to greenhouse-grown crops. In December 1964 parasitizing on greenhouse tomatoes was 47.6 per cent, which shows that E. formosa plays a certain role in reducing the density of Trialeurodes vaporariorum Westw. This insect is an internal parasite on the larvae of Trialeurodes vaporariorum Westw. At a temperature range of 16–28°C and a relative air humidity of 60–80 per cent in the greenhouses, the parasite survives for 36–43 days and parasitizes on 60–183 or 132 larvae on the average. A single individual lays 21–161 or 101 eggs on the average (table 3). This shows that the fecundity of the parasite is greater than that of the host. The parasite's larva feeds on the internal content of the host's larva in the course of 10–16 days, eats up the internal content and the skin of the host becomes black. Then still inside, the parasite undergoes the pupal and imaginal stages. The development of E. formosa from egg to imago is completed within 21–33 days, the mass imaginal stage occurring after 24–28 days. The development of Trialeurodes vaporariorum Westw from egg to imago lasts 30–47 days. This indicates that E. formosa develops within a shorter time (fig.1). The parasite lays its eggs on larvae of second and third instar, developing into imago 4–9 days after the mass imaginal stage of Trialeurodes vaporariorum Westw occurs. Thus, while the parasite is still in the pupal stage, Trialeurodes vaporariorum Westw grows into imago and lays eggs on the leaves of plants from which larvae are hatched - the necessary food for the parasite. For that reason the accomplishment of

Download Adobe Acrobat Reader (free software to read PDF files)

17_65     17    

URL www.actahort.org      Hosted by KU Leuven      © ISHS