Group1_performance

Nymphal duration, adult longevity, and fertility data of Group 1

Spiroplasma density

Infection density of Spiroplasma (copy/sample

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

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

Encounter-induced hostility to neighbors in the ant Pristomyrmex pungens

Field observations have demonstrated that internest hostility is negatively correlated with the distance between nests in the Japanese queenless ant, Pristomyrmex pungens. This runs counter to the "dear enemy" phenomenon. This result led us to hypothesize the existence of encounter-induced hostility in P. pungens. We created "neighbor(s)" and "stranger(s)" by an experimental method and tested the ant's ability to discriminate the neighbors from strangers. The results indicated that the ant could distinguish the neighbors from the strangers and displayed significantly stronger hostility toward the neighbors. The recognition of neighbors was quickly established after a few encounters and was maintained for at least 10 days after the most recent encounter. Nest mates without direct encounter experience with neighbors did not show hostile behavior toward neighbors. These findings suggest that information about neighbors (probably colony odor) is not transmitted to nest mates within the colonies. Aggressiveness toward the neighbors appears to be caused and maintained on the basis of individual memories from direct contact. It may be adaptive for a species that changes nest sites frequently to discriminate strangers from neighbors and selectively attack the latter. Copyright 2003.

Take-off time of the first generation of the overwintering small brown planthopper, Laodelphax striatellus in the temperate zone in East Asia.

Overseas migration of the small brown planthopper, Laodelphax striatellus (Fallén), occurs during the winter wheat harvest season in East Asia. Knowing the take-off time of emigrating L. striatellus is crucial for predicting such migrations with a simulation technique because winds, carriers of migratory insects, change continuously. Several methods were used in China and Japan from late May to early June 2012 and again in 2013 to identify the precise timing of take-off. These methods included: a tow net trap mounted to a pole at 10 m above the ground, a helicopter-towed net trap, and a canopy trap (which also had video monitoring) set over wheat plants. Laodelphax striatellus emigrated from wheat fields mainly in the early evening, before dusk. The insects also emigrated during the daytime but rarely emigrated at dawn, showing a pattern that is unlike the bimodal emigration at dusk and dawn of two other rice planthoppers, the brown planthopper, Nilaparvata lugens (Stål), and the white-backed planthopper, Sogatella furcifera (Horváth). There was no significant difference in the temporal pattern of take-off behavior between females and males of Japanese L. striatellus populations

Current status of insecticide resistance in the small brown planthopper, Laodelphax striatellus, in Japan, Taiwan, and Vietnam

The small brown planthopper, Laodelphax striatellus, is one of the most serious pest insects of rice plants. A large migration of the insects from overseas was reported in western parts of Japan in June 2008. Insecticide resistance to imidacloprid, fipronil and BPMC was compared among local populations in these western regions after migration. The insecticides were applied to the insects using a topical application method. In some populations, the resistance status coincided with that of the immigrant insects just after migration, i.e., resistance to imidacloprid but susceptibility to fipronil. In other populations, resistance was observed not only against imidacloprid but also fipronil. It is likely that the status of the latter populations resulted from intercrossing between domestic populations of the insects and migrants. Insecticide resistance was also assessed in other areas of northern and eastern parts of Japan. In general, these populations showed relatively low resistance, although resistance to fipronil was high in the eastern part of Japan where the density of domestic populations has recently increased. Insecticide susceptibilities were also assessed in several sites in Taiwan and the northern parts of Vietnam. Although susceptibilities differed among these sites or countries, they have recently seen a decline for all three insecticides

Summary of the Japanese survey.

<p>a. The total number of <i>L</i>. <i>striatellus</i> caught in traps located at both S1 and S2 for each survey year. b. The catch number of <i>L</i>. <i>striatellus</i> female caught in the 10-m net trap at S1, the suction trap at S2 in 2012, and in the 10- and 5-m net traps and the suction trap at S1 in 2013. These traps were selected because their total numbers were large (> 100) and only days when the daily catch number was more than 10 were used to make the graph. c. The catch number of <i>L</i>. <i>striatellus male</i> caught in the five traps listed above.</p

The number of <i>L</i>. <i>striatellus</i> entering canopy traps at hourly intervals.

<p>a. The total number of insects entering canopy traps at two sites, CT1 and CT2. Insects were counted by viewing recorded video images of the trap’s entrance hole. b. The sex of trapped insects as shown in a. Insects of undetermined sex were excluded. For example, 1700 h CST corresponds to the number of insects entering the trap from 1600 to 1700 h CST.</p