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