Eunmok Kim

Effect of Food Deprivation Period on the Development and Reproduction of Riptortus pedestris (Hemiptera: Alydidae), and Its Egg Parasitism

ABSTRACT The bean bug, Riptortus pedestris (F.) (Hemiptera: Alydidae) is one of the most important pests of soybean (Glycine max L. Merrill) in Korea and Japan. R. pedestris is known to appear early in spring when leguminous seeds such as soybean are not available. Because soybean has been reported to be the most important food source for R. pedestris development, in this study, we assessed the effect of this period of soybean deprivation during the nymphal stage on the development and reproduction of R. pedestris and on egg parasitism by its two egg parasitoids. More than 50% of the R. pedestris population tested survived on barley, even when they did not start feeding on soybean until the fourth instar. Nevertheless, R. pedestris nymphs deprived of soybean developed more slowly and became smaller adults than those provided with soybean. However, no difference was observed in the preovipositional period or fecundity between these groups. In addition, neither the hatch nor the egg parasitism rate by two egg parasitoids was affected by the presence or absence of soybeans in the nymphal diet. This study indicates that R. pedestris nymphs can develop successfully even when lacking this important food source in early life, and that adult reproduction is not affected by the quality of diet ingested during the nymphal period.

Use of aggregation pheromone traps increases infestation of adult Riptortus pedestris (Hemiptera: Alydidae) in soybean fields: Aggregation pheromone trap does not decrease soybean bug population

BACKGROUND An aggregation pheromone trap has been used for both monitoring and mass-capture of Riptortus pedestris (Fabricius) in soybean. As the traps efficacy in reducing the pest population and crop damage is unknown, we evaluated it in small experimental soybean plots using both a before/after and with/without design, and also verified our findings in commercial soybean fields. RESULTS In experimental plots, total numbers of R. pedestris on plants in the soybean plots were not affected by the trap installation until mid-August. Interestingly, the abundance of adult bugs increased (4.9-9.4 times higher) in September and October. However, compared with the counted bug population in soybean plots, the trap catch rate was low during the autumn period. In commercial fields, trap installation also did not reduce bug population from the field. Placement of traps in plots increased pod and seed damage by 2.7 and 2.2 times, respectively compared with the controls in experimental plots, although no such effect was observed in commercial fields. CONCLUSION Aggregation pheromone traps did not reduce R. pedestris populations in the field or soybean damage, and even led to an increase in the bug population during autumn. Therefore, traps should not be used as a control measure.

Seasonal Reproductive Performance and Pre-diapausing Mating Status of Female Riptortus pedestris (Hemiptera: Alydidae) Collected in Fields

Abstract Two unexplained phenomena are found in Riptortus pedestris (Fabricius) (Hemiptera: Alydidae): the first is that it tends to enter reproductive diapause much earlier in the season and to occur on host plants until late fall before finding hibernation site. The second is that they emerge in early spring when primary food sources such as leguminous plants are unavailable. To understand these phenological trends, the reproductive seasonality of both field-collected and laboratory-reared R. pedestris were compared under conditions of with/without food or access to mates. Females collected in spring or fall produced very few eggs in laboratory. But, when food sources were provided, all the bugs produced more eggs. Eggs also hatched normally except those produced by the females collected in fall. This indicates that females collected in the spring were already mated while those collected in the fall were not, most likely because they were in reproductive diapause. Similarly, when food was provided, all laboratory-reared bugs produced eggs, regardless of diapause status, with longer preoviposition period in diapausing bugs which might be due to the termination of reproductive diapause, but only eggs from mated females hatched. In conclusion, while spring reproduction (oviposition and egg hatch) of R. pedestris can occur in the presence of food resources, any lack of food can be limiting factor impeding these activities. In fall, reproduction is greatly reduced even when food resources are available, and under these conditions failure of females to become mated, due to reproductive diapause, is likely the limiting factor.