Un Taek Lim

Refrigeration of Riptortus clavatus (Hemiptera: Alydidae) eggs for the parasitization by Gryon japonicum (Hymenoptera: Scelionidae)

Abstract Gryon japonicum (Ashmead) (Hymenoptera: Scelionidae) is a solitary egg parasitoid of Riptortus clavatus (Thunberg) (Hemiptera: Alydidae) one of the most important pests in soybean in Korean and Japan. Refrigeration of R. clavatus eggs for up to 120 days was evaluated as a method of mass production of G. japonicum. The refrigeration reduced the eclosion of eggs, thus no nymph emerged after 30 days of egg refrigeration. Increased duration of host acceptance behaviors by G. japonicum and some detrimental effects on parasitism rate, developmental time, longevity, and adult size of the parasitoid were found in refrigerated host eggs. However, all the biological parameters of G. japonicum were unaffected by the refrigeration of up to 30 days. Gryon japonicum parasitized 16 and 14 host eggs daily that were refrigerated for 15 and 30 days, respectively, which did not differ from parasitization of fresh host eggs. Furthermore, refrigeration of host eggs did not reduce the reproduction of the emerged adult parasitoids and emergence and sex ratio of their progeny. Gryon japonicum also parasitized 14 and 13 refrigerated host eggs per day kept at 26.3°C and 78.7% RH for 2 and 4 days of post-refrigeration without significant reduction, respectively. These results show that refrigeration of R. clavatus eggs can be a good method for mass rearing of the parasitoid, and the host eggs killed by cold storage can be supplemented in the field to boost field parasitism.

Refrigerated Eggs of Riptortus pedestris (Hemiptera: Alydidae) Added to Aggregation Pheromone Traps Increase Field Parasitism in Soybean

ABSTRACT Riptortus pedestris (F.) (Hemiptera: Alydidae) is a key pest of soybean [Glycine max (L.) Merr.] in Korea and Japan. Aggregation pheromone traps have been used to attract R. pedestris. An aggregation pheromone, produced by males of R. pedestris, also attracts the egg parasitoid, Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae). As a new method of pest management, we propose the use of nonviable host eggs in the pheromone trap together to both trap R. pedestris and propagate parasitoids on host eggs attached to the trap. ≈Ten-thousand nonviable refrigerated host eggs were placed outside pheromone traps in three soybean fields (0.167–0.284 ha.). During the sampling period from 7 August to 8 October in 2008, statistical significance of treatment was not found in any life stage of R. pedestris population. However, significantly higher parasitism of both natural (78–91%) and refrigerated eggs (36–59%) occurred in the treatment sites, compared with control sites where parasitism was 0–62% and 16-34% on natural and refrigerated eggs, respectively. The proportion of bean pods with stink bug feeding damage was significantly reduced by 47% in the treatment sites. This study is the first trial of an integrated pest management (IPM) strategy using both nonviable host eggs and trap that simultaneously targets both the pest and its natural enemy.

Behavioral Response of Western Flower Thrips to Visual and Olfactory Cues

Behavioral responses of Frankliniella occidentalis Pergande (Thysanoptera: Thripidae) to visual and olfactory cues were assessed in a cylindrical black box and a Y-tube olfactometer. Frankliniella occidentalis preferred circular shapes to other five geometrical patterns (rectangle, triangle, inverted triangle, diamond, and modified circle imitating flower petals) in multiple choice tests. In pair wise choice tests, the thrips preferred the yellow artificial flower shape to the geometrical patterns tested. Frankliniella occidentalis stayed on the artificial flower about four times longer than on the geometrical patterns. Higher numbers of thrips responded to a combination of p-anisaldehyde and artificial flower compared to the arm with only the olfactory or the visual cue. These results suggest that shape is an important cue for F. occidentalis.

Occurrence and Control Method of Riptortus pedestris (Hemiptera: Alydidae): Korean Perspectives

Hemipteran bugs, which were previously considered as secondary pests, have currently become important pests of numerous crops. Among them, Riptortus pedestris (Fabricius) is a major species that occurs in Korea, Japan, China, and South Asian countries. Riptortus pedestris infests leguminous crops like soybean, vetches, and red clover; fruit trees like persimmon and yuju; and grains like barley, foxtail millet, broomcorn, and sorghum. Riptortus pedestris causes the greatest damage to soybean, as it is the most suitable host for the bug. Feeding damage during pod formation significantly reduces the yield of soybean. Currently, 17 insecticides, including diazinon and etofenprox, are registered for the control of hemipteran bugs in Korea, and growers apply insecticides two to three times on a regular basis. Aggregation pheromone traps are widely used as a monitoring tool and partial control measure. The aggregation pheromone of R. pedestris attracts conspecific adults and nymphs and is used for food exploitation rather than sexual attraction. In addition, the pheromone serves as a kairomone for egg parasitoids such as Gryon japonicum (Ashmead) and Ooencyrtus nezarae Ishii. As a new method of pest management, nonviable host eggs were included in the pheromone trap to catch R. pedestris and propagate parasitoids. As a part of cultural practices, resistant soybean varieties with specific color and size of pod and control of flowering time through the alteration of planting date can be used. For the effective management of R. pedestris in the near future, development of cultural practices that can support natural control factors and the use of multiple control tactics are needed.

Life History Characteristics of Frankliniella occidentalis and Frankliniella intonsa (Thysanoptera: Thripidae) in Constant and Fluctuating Temperatures

ABSTRACT Frankliniella occidentalis (Pergande) and Frankliniella intonsa (Trybom) are sympatric pests of many greenhouse and field crops in Korea. We compared the influence of constant (27.3°C) and fluctuating temperatures (23.8–31.5°C, with an average of 27.3°C) on the life table characteristics of F. occidentalis and F. intonsa held at a photoperiod of 16:8 (L:D) h and 45 ± 5% relative humidity. The development times of both F. occidentalis and F. intonsa were significantly affected by temperature fluctuation, species, and sex. The development time from egg to adult of F. intonsa was shorter than that for F. occidentalis at both constant and fluctuating temperatures. Survival of immature life stages was higher under fluctuating than constant temperature for both thrips species. The total and daily production of first instars was higher in F. intonsa (90.4 and 4.2 at constant temperature, and 95.7 and 3.9 at fluctuating temperatures) than that of F. occidentalis (58.7 and 3.3 at constant temperature, and 60.5 and 3.1 at fluctuating temperatures) under both constant and fluctuating temperatures. The percentage of female offspring was greater in F. intonsa (72.1–75.7%) than in F. occidentalis (57.4–58.7%) under both temperature regimes. The intrinsic rate of natural increase (rm) was higher at constant temperature than at fluctuating temperature for both thrips species. F. intonsa had a higher rm value (0.2146 and 0.2004) than did F. occidentalis (0.1808 and 0.1733), under both constant and fluctuating temperatures, respectively. The biological response of F. occidentalis and F. intonsa to constant and fluctuating temperature was found to be interspecifically different, and F. intonsa may have higher pest potential than F. occidentalis based on the life table parameters we are reporting first here.

Areal Distribution and Parasitism on Other Soybean Bugs of Trissolcus nigripedius (Hymenoptera: Scelionidae), an Egg Parasitoid of Dolycoris baccarum (Heteroptera: Pentatomidae)

From the surveys of 2005 and 2006 in Korea, Trissolicus nigripedius was found in four locations, i.e., Andong, Miryang, Namhae, and Suwon, and one of the major egg parasitoids of Dolycoris baccarum. T. nigripedius was also found to parasitize two other soybean bugs, Riptortus clavatus and Piezodous hybneri, from the field collection in 2005. Host acceptance behaviors of T. nigripedius consisting of drumming, oviposition, and marking were observed and compared on five species of soybean bugs. T. nigripedius showed the complete host acceptance behaviors on the eggs of D. baccarum, P. hybneri, and Halyomorpha halys. But T. nigripedius emerged only from the eggs of D. baccarum (96%) and P. hybneri (75%) after 24 hours of exposure. T. nigripedius did not mark on the eggs of R. clavatus and Nezara antennata during the observation of behavior, hence no egg deposition was made. However, T. nigripedius parasitized 20% and killed 30% of the eggs of R. clavatus when 24 hours were given for parasitization. T. nigripedius would be a potential biological control agent of D. baccarum and P. hybneri with ability of giving additional mortality on R. clavatus in soybean field.

Overwintering of the Citrus Leafminer, Phyllocnistis citrella (Lepidoptera: Gracillariidae), without Diapause in Florida

Abstract The citrus leafminer, Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae), is an important pest of citrus that has spread around the world. The citrus leafminer invaded Florida in 1993 and rapidly colonized all citrus-growing areas. Despite the fact that the citrus leafminer has been studied extensively, gaps in our knowledge of its biology remain. One issue is how the citrus leafminer overwinters. Citrus leafminers have been observed to overwinter in many countries, but their capacity to diapause has not been confirmed. To investigate whether P. citrella overwinters in diapause, we evaluated the ability of eggs to develop to adulthood on potted citrus trees when reared in both outdoor and growth chamber conditions. No pupae were found to be in diapause in the outdoor assessment in which three populations of citrus leafminer were reared in a shade house in Gainesville, Florida beginning on Oct 15, Nov 11, or Nov 22. Larval and pupal mortality significantly increased in the population set out on Nov 22 compared to the other populations. Adult longevity significantly increased in the last two populations compared to the Oct population. However, similar degree days were accumulated during the adult lifespan among the three populations. In the growth chamber assessments, citrus leafminers showed no arrestment in development during the pupal stage by short-day treatments. Development (days) from egg to adult was not different between short- and long-day conditions in both sexes. No signs of reproductive diapause were found from dissections of adult females reared under short- or long-day conditions. We concluded that P. citrella may overwinter on the few small flushes available during winter in mid and central Florida, and the relevance of these results for citrus IPM programs is discussed.

Females of Riptortus pedestris (Hemiptera: Alydidae) in Reproductive Diapause are More Responsive to Synthetic Aggregation Pheromone.

Abstract Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) enters reproductive diapause under short-day length (< 13.5 h) conditions. As an apparent increase of field populations of R. pedestris has been observed during the fall when aggregation pheromone traps are placed in soybean fields, we tested the hypothesis that R. pedestris becomes more responsive to the aggregation pheromone during fall as it enters its reproductive diapause. The response of R. pedestris females—either ones collected seasonally from fields or reared in the laboratory under short-day length (10:14 [L:D] h) conditions—to the aggregation pheromone was examined using a Y-tube olfactometer. Riptortus pedestris collected in fall showed a higher response to the aggregation pheromone (74–80%) than those collected in July (40%). Females in which diapause was induced in the laboratory also showed a higher response to the pheromone than those not in diapause. In a wind tunnel assay, female bugs in laboratory-induced diapause also responded positively to the aggregation pheromone. In addition, we assessed the reproduction of females to verify their diapausing status. Diapausing females never mated with either short- or long-day-reared males, nor did they reproduce, but non-diapausing females mated with short-day-reared males at a rate of 13%. Females collected from fields during fall never mated. In a soybean field evaluation, the number of adult female R. pedestris was higher in the presence of an aggregation pheromone trap than in the absence of one. This is the first confirmation of higher response to the aggregation pheromone of both field-collected and laboratory-reared R. pedestris in reproductive diapause.

Effect of Aggregation Pheromone Trap of Riptortus pedestris (Hemiptera: Alydidae) on the Distribution and Composition of Its Egg Parasitoids

ABSTRACT The aggregation pheromone of Riptortus pedestris (F.) (Hemiptera: Alydidae) is known to attract its egg parasitoids Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) and Gryon japonicum (Ashmead) (Hymenoptera: Scelionidae). Distribution and composition of these egg parasitoids were compared in a soybean field in the presence and absence of aggregation pheromone-baited traps for two consecutive years. Three traps were installed on the edge of a soybean field, first without and then with aggregation pheromone in a before-after design, and changes in parasitism were assessed on nonviable host eggs released at distances of 9,18, 27, and 36 m from the trap. A significant interactive effect of pheromone installation and distance was found in egg parasitism by both parasitoids. Parasitism on eggs recovered from 9 m away was up to 2.2 and 3.2 times higher in presence of pheromone than without pheromone for O. nezarae and G. japonicum, respectively. Parasitism by O. nezarae was always higher than that by G. japonicum, but their relative abundance, clutch size, and sex ratio were not affected by pheromone installation, irrespective of distance from the trap. In conclusion, aggregation pheromone increases abundance of parasitoids up to 18 m from trap installation points and does not affect the relative abundance of parasitoid species.

Interspecific larval competition between two egg parasitoids in refrigerated host eggs of Riptortus pedestris (Hemiptera: Alydidae)

In a previous study, we found that soybean fields could be supplemented with refrigerated eggs of Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) to enhance parasitism. As a part of a study to evaluate the effect of host egg refrigeration on parasitism, host acceptance behavior and interspecific larval competition between Gryon japonicum (Ashmead) (Hymenoptera: Scelionidae) and Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) were studied in multiparasitized unrefrigerated and refrigerated eggs. O. nezarae showed complete host acceptance behavior when offered refrigerated host eggs that were preparasitized by G. japonicum. Adult emergence rate of O. nezarae was 43 and 74% when the interval between the first and second oviposition was 0 and 4 days, respectively, and was not different between refrigerated and unrefrigerated eggs. Refrigeration did not change host acceptance behavior of G. japonicum, but adult emergence declined from 80% in unrefrigerated eggs to 37% in refrigerated eggs that were pre-parasitized by O. nezarae on the same day. No negative effects of refrigeration on sex ratio, adult longevity, and adult size of the both parasitoids were found. Generally host egg refrigeration did not negatively affect host acceptance behavior of the both parasitoids on preparasitized eggs or larval competition between the two parasitoids in multiparasitized host eggs with exceptions in the development time and emergence rate of G. japonicum. Therefore, host egg refrigeration may not interrupt interactions between the parasitoid populations in the field.