Host Preference, Suitability and Functional Response of Tetrastichus brontispae Fer. ( Hymenoptera: Eulophidae )
As a dominating natural enemy, Tetrastichus brontispae Fer. (Hymenoptera: Eulophidae) plays an important role in natural control of the pest of Brontispa longissima (Gestro) (Coleoptera: Hispidae), which has been introduced by more than 30 countries or areas. In the laboratory, the host preference, suitability and functional response of T. brontispae to B. longissima were studied. Results showed that, under conditions of (25±1) °C, (75±5) %RH and a photoperiod of 12 h(L):12 h(D), selection coefficient and average rate of parasitization were 0.227 6, 0.211 6, 0.195 1 and 77.78 %, 77.22 %, 66.67 % for host prepupae, 1 and 2 day-old pupae, respectively, which were higher than those for other instar pupae. Prepupae of B. longissima were preferred hosts, followed by 1 and 2 day-old pupae. Mature larvae just near to prepupae were selected, and 6 day-old pupae were not selected. Prepupae and pupae of B. longissima become mummies after parasitized. Host suitability studies showed that the developmental time of T. brontispae did not change after parasitizing except for the emergence rate, number of emergence and sex ratio. Determination of these parameters showed that prepupae, 1 and 2 day-old pupae of B. longissima were the most suitable host for T. brontispae development. The functional response of the parasitoid to different densities of the host was calculated as: Na=0.338 8 N/(1+0.071 5 N), indicating that the parasitoid number increased with the host density, but the parasitoid number kept constant when the host density increased to a certain range. The model of mutual interference of T. brontispae was calculated as: a=1.621 16 P-0.726 4, indicating that the parasitizing effect decreased as the parasitoid density increased.