INFLUENCE OF PLANT STRUCTURAL COMPLEXITY ON THE FORAGING SUCCESS OF TRICHOGRAMMA-MINUTUM - A COMPARISON OF SEARCH ON ARTIFICIAL AND FOLIAGEMODELS

The influence of structural complexity on the foraging success for hos t eggs (Ephestia kuehniella Zeller) by Trichogramma minutum Riley was investigated in the laboratory. Naive females were released into arena s with structurally different paper models or foliage (simple: trembli ng aspen Populus tremuloides Michx., complex: balsam fir Abies balsame a L.). Observations of individual females were made every 15 min and s earching success was measured by the number of host egg clusters found and the amount of time taken to find them, within a period of 196 min . Females found significantly more egg clusters and were quicker at fi nding them on the sample paper and foliage surfaces than on the most c omplex paper or foliage surfaces. Older females (2-3 days) were more s uccessful and searched quicker than younger (< 24 h) females on all pa per surfaces. The timed observations suggested that wasps which spent more time walking had a significantly decreased probability of finding an egg mass and were significantly slower at finding them. Females th at spent more time on paper surfaces had an increased probability of f inding an egg mass. The significance of searching differences is discu ssed in relation to the potential effects of plant surfaces on Trichog ramma movements and to the physiological readiness of the wasp.