Transgenic insect-resistant corn affects the fourth trophic level: effects of Bacillus thuringiensis-corn on the facultative hyperparasitoid Tetrastichus howardi.
As hyperparasitoids may have a considerable influence on the control of herbivorous arthropods, analyzing the host-mediated impact of Bacillus thuringiensis-plants ("Bt-plants") on hyperparasitoids is of interest. Laboratory-scale experiments were conducted in order to assess the potential effect of Bt-corn leaf material on the facultative hyperparasitoid Tetrastichus howardi (Olliff) (Hymenoptera: Eulophidae), mediated through the herbivore Chilo partellus Swinhoe (Lepidoptera: Crambidae) and its primary parasitoid Cotesia flavipes (Cameron) (Hymenoptera: Braconidae). In the Bt-group, significantly less C. flavipes larvae per host spun cocoons and pupated than in the control, and the mean fresh weight of a single C. flavipes cocoon was significantly reduced compared to the control. All C. flavipes cocoons of one host formed cocoon clusters. T. howardi females of the Bt-group parasitized significantly less cocoon clusters than in the control. Moreover, significantly fewer C. flavipes cocoons per cocoon cluster were successfully parasitized as compared to the control. As a consequence, T. howardi females of the control had more offspring than in the Bt-group. Adult female T. howardi offspring of the Bt-group weighed significantly less than in the control, but there was no significant weight difference between males of both groups. Our results suggest that transgenic insect-resistant plants could affect hyperparasitoids indirectly. However, it remains to be determined whether facultative hyperparasitoids prefer to develop as primary or secondary parasitoids under field conditions.
Prütz
Gernot
G
Lehrstuhl für Tierökologie II, Universität Bayreuth, 95440 Bayreuth, Germany. gernot.pruetz@uni-bayreuth.de
Brink
Andreas
A
Dettner
Konrad
K
D000818:Animals; D001413:Bacillus thuringiensis / Q000472:pathogenicity*; D005260:Female; D006927:Hymenoptera / Q000254:growth & development / Q000472:pathogenicity*; D007113:Immunity, Innate; D008297:Male; D010935:Plant Diseases / Q000382:microbiology / Q000469:parasitology; D030821:Plants, Genetically Modified / Q000382:microbiology*; D012098:Reproduction; D012744:Sex Ratio; D003313:Zea mays / Q000382:microbiology*