Efficiency of physical means of IPM on insect population control in greenhouse crops
The efficiency of insect screens and photoselective covering materialson insect population control was experimentally evaluated. The experiments were performed from 2000 to 2004 in three greenhouse tomato, PE-covered greenhouses of 160 m 2 total at the University of Thessaly near Volos, Greece. Concerning the insects screens, field trials were conducted two consecutivecrop seasons (winter and summer) in two adjacent greenhouses equipped with continuous roll-up side openings. The ventilation inlets of the first greenhouse were covered by an insect screen (55 by 27 mesh size, 265 μm wire diameter, 150 by 150 μm hole size and 50% porosity) while the second greenhouse was used as control. Concerning the photoselective covering materials, two UV-absorbing PE films (0 and 3% UV transmission) along with a common PE film provided by Plastika Kritis S.A. (Heraklion, Crete, Greece) were used in the three greenhouses, over a three-year experiment. Results showed that installation of an insect screen on greenhouse ventilation openings prevented aphids from flying into the greenhouse and significantly restricted the number of thrips inside the greenhouse, but it did not influence the whitefly population. With the UV-absorbing PE films, a lower number of thrips andaphids were caught in the greenhouse with 0% UV transmission than those in the other greenhouses for all the three years of experimentation. Differences in efficiency were observed between the PE films during the time of insect population control. It was found that none of the two UV-absorbing PE films tested had an adverse effect on the activity of bumble bee pollinators.Although, no significant effects of photoselective materials were found ongreenhouse microclimate, the use of insects screens significantly reduced greenhouse ventilation and increased its air temperature.