Interactions between Beauveria bassiana and Trichogramma pretiosum under laboratory conditions

Knowledge about interactions among biological control agents, used in sequence or simultaneously, may help to increase their efficiency, or in the case of conservation biological control, to avoid the impairment of efficiency. The aim of this study was to evaluate the interaction between two isolates of Beauveria bassiana (Bals.) Vuill. (Hypocreales) (Unioeste 47 and Unioeste 57) and Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae), varying the timing of sprays of the fungus. Isolates were sprayed at 109 conidia ml−1 upon cards (1 × 5 cm; i.e., 2 × 105 conidia mm−2) with eggs of Anagasta kuehniella Zeller (Lepidoptera: Pyralidae) and the control group was sprayed with sterile distilled water with Tween® 80 (0.01%). First, the percentage of parasitized eggs was assessed in a choice test: females of T. pretiosum were confined with two cards, one of them treated with either of the fungus isolates, the other a water‐treated control. Second, parasitism was compared on cards sprayed at various time intervals pre‐ vs. post‐parasitism: the number of parasitized eggs was assessed, as well as the parasitoid's emergence percentage, egg‐adult period, offspring sex ratio, and the longevity of parasitizing females. Trichogramma pretiosum preferred to parasitize control eggs (65 and 72%) and parasitization of the treated eggs did not differ between fungus isolates: 35% (Unioeste 47) vs. 28% (Unioeste 57). Spraying before or after parasitizing did not affect the number of parasitized eggs, nor offspring sex ratio; however, both treatments affected the percentage of emerged adults, egg‐adult period, and longevity. These findings suggested that isolates did not interfere in the longevity of parasitizing females. When the fungus was sprayed on the various development stages of the parasitoid within the host egg, or when it was offered to the parasitoid at different times after spraying, differences in adults' longevity, parasitism, emergency period from egg to adult, and sex ratio were observed. Beauveria bassiana may be used in conjunction with this parasitoid in a program of pest control.