INSECTÐSYMBIONT INTERACTIONS Transinfection ofWolbachia in Planthoppers: Nymphal Injection of CulturedWolbachia and Infection Dynamics

Wolbachia species are intracellular symbionts that cause reproductive alterations in arthropods. Transinfection experiments have been performed in many arthropod species to elucidate the interaction betweenWolbachia and a new host. To ease transinfection of this bacterium to new arthropodhosts,we introduced two techniques: nymphal injection insteadof embryonic injection and the use of a cultured source of Wolbachia instead of direct transfer from donors to recipients. Wolbachia in the small brown planthopper Laodelphax striatellus was cultivated in a cell line and injected into the nymphal body cavity of the brown planthopperNilaparvata lugens together with the cells. By using these techniques, two transinfected planthopper lines were obtained. In one line, Wolbachia disappeared after several generations; in the other line,Wolbachiawas retained for 7 yr. Infection rates in this latter transinfected line were 80% in early generations after transinjection but decreased to 10% through 40Ð60 generations. Subsequent selection forWolbachia-infected females in this line did not increase the infection rate as a temporary effect. Thus, this transinfected line of N. lugens showed cytoplasmic incompatibility, although the incompatibility level was lower than in L. striatellus, the original host. Themethodof transinfectionpresentedherein is useful for transmitting intracellular symbionts between small arthropod hosts.