Abstract: The effect of Wolbachia on biology and olfactory response of its new host, Trichogramma confusum, was studied after successful interspecific horizontal transfer of Wolbachia from T. pretiosum to uninfected T. confusum by sharing the same host egg. The results showed that Wolbachia infection could induce incomplete thelytokous parthenogenesis of T. confusum and therefore enhanced the female proportion of its new host, but meanwhile caused a physiological cost by curtailing longevity and reducing fecundity of its new host. The female percentage in progeny of the newly infected virgin female and its subsequent generations (F₁-F₅) were 79.17%, 76.60%, 68.66%, 72.58%, 68.15% and 64.06%, respectively, showing a decreasing tendency with the increasing of generations after horizontal transferring and gradually approaching that of the uninfected and mated T. confusum (63.85%). The average longevity of newly infected virgin female and F₁－F₅ females was 4.33, 5.50, 5.60, 6.68, 7.32 and 7.50 days, respectively, shorter than that of the longevity of uninfected and mated T. confusum(7.59 days). The fecundity of the newly infected virgin female and F₁-F₅ females was 11.33, 70.00, 86.41, 93.90, 102.92 and 124.38 eggs per female, respectively, all except F₅ generation significantly less than 134.8 eggs per female, the fecundity of the uninfected and mated female. The olfactory response of the newly Wolbachia-infected T. confusum to the diamondback moth (DBM), Plutella xylostella, was tested by using a four-armed olfactometer under laboratory conditions. The results indicated that Wolbachia had a slightly negative effect on T. confusum by interfering their olfactory response. For the uninfected T. confusum and the Wolbachia donor species T. pretiosum, their adults were detained significantly longer time in the treated areas than in the control area and showed a very strong olfactory response to hexane extract of abdominal scales and eggs of DBM. The retention time of F₂ and F₃ adults of the Wolbachia-infected T. confusum was longer in the treated area of hexane extract of abdominal scales of DBM than in the control area, but it did not reach to a significant level. The retention time of F₂ adults was longer in the treated area of hexane extract of DBM eggs than in the control area, but it also did not reach to a remarkable level. However, the retention time of F₄-F₆ adults of the Wolbachia-infected T. confusum was significantly longer in the treated areas of above two hexane extracts than in the control area, suggesting that the normal olfactory response of T. confusum to DBM was recovered with the increasing of generations after horizontal transferring of Wolbachia.

Key words: Trichogramma confusum, Wolbachia, new hosts, thelytokous parthenogenesis, physiological cost, olfactory response