Influences of two coexisting endosymbionts, CI-inducing and male-killing , on the performance of their host (Hemiptera: Delphacidae).

The small brown planthopper (Hemiptera: Delphacidae) is reported to have the endosymbiont , which shows a strong cytoplasmic incompatibility (CI) between infected males and uninfected females. In the 2000s, female-biased populations were found in Taiwan, and this sex ratio distortion was the result of male-killing induced by the infection of another endosymbiont, . infection is considered to negatively affect both and because the male-killing halves the offspring of and hinders the spread of infection via CI. could have traits that increase the fitness of infected and/or coexisting organisms because the coinfection rates of and were rather high in some areas. In this study, we investigated the influences of the infection of these two endosymbionts on the development, reproduction, and insecticide resistance of in the laboratory. Our results show that the single-infection state of had a negative influence on the fertility of , while the double-infection state had no significant influence. At late nymphal and adult stages, the abundance of was lower in the double-infection state than in the single-infection state. In the double-infection state, the reduction of density may be caused by competition between the two endosymbionts, and the negative influence of on the fertility of host may be relieved. The resistance of to four insecticides was compared among different infection states of endosymbionts, but infection did not contribute to increase insecticide resistance. Because positive influences of infection were not found in terms of the development, reproduction, and insecticide resistance of , other factors improving the fitness of -infected may be related to the high frequency of double infection in some populations.