Demonstration of interspecific competition between two sympatric egg parasitoids of Riptortus pedestris (Fabricius) in laboratory condition

Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) acts as a facultative hyperparasitoid of Gryon japonicum (Ashmead) (Hymenoptera: Platygastridae) sympatric parasitoid of Riptortus pedestris (Fabricius) (Hemiptera: Alydidae). A longer period of host egg exploitation by both parasitoid species would be beneficial for O. nezarae, while G. japonicum tends to be successful when the parasitoids have only a short exploitation period. We demonstrated the interspecific competition by measuring parasitism in nine combinations of host densities (10, 20, and 40 eggs) and exploitation times (1, 3, and 5 days). To reflect the gregarious-solitary dichotomy of the two species, three O. nezarae and one G. japonicum mated females were compared in addition to a one-to-one competition design. We found that O. nezarae was the better competitor when exploitation time was longer than 1 day, irrespective of host density. Total parasitism rate and progeny emergence of O. nezarae were 1.6–2.8 and 4.7–7.3 times higher than for G. japonicum in three-to-one competition design, respectively. Although G. japonicum females were more effective in host finding (as shown by their higher per capita rate of parasitism when exploitation time was short), their progeny suffered high mortality from the larval interspecific competition inside multiparasitized host eggs. These results suggest that gregarious O. nezarae is the superior competitor when host eggs are available for longer period of time while solitary G. japonicum is superior when host resources are available for only a limited time.     

Biological attributes of Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) reared on refrigerated eggs of Riptortus pedestris (= clavatus) Fabricius (Hemiptera: Alydidae)

Storing host eggs at low temperatures has been used to mass rear parasitoids of stink bugs, including Riptortus pedestris Fabricius (Hemiptera: Alydidae), a major soybean pest in Korea and Japan. However, no information on the effect of cold storage on parasitization by Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae), one of the major parasitoids of R. pedestris, has been published. In this study, we examined biological attributes, including parasitism rate, development time, sex ratio, adult size, and longevity, of O. nezarae when the adult parasitoids were provided with host eggs refrigerated for 0, 15, 30, 60, and 120 days at 2.0 °C. None of the attributes of the first or second generation of O. nezarae was negatively affected by host egg refrigeration up to 30 days. In addition, O. nezarae could parasitize refrigerated host eggs successfully for the first four days of post-refrigeration period when they were kept at 26.3 °C and 78.7% RH conditions. Therefore, refrigeration of R. pedestris eggs can be a good method to mass rear O. nezarae.     

Locomotion ability variation among instars of the bean bug, Riptortus pedestris (Fabricius) (Heteroptera: Alydidae) nymphs

The nymphal locomotion ability (walking distance) of the stenophagous bean bug Riptortus pedestris (Fabricius) was studied in each instar. We measured the walking distance using two systems. The walking distance in photophase was measured for 6 h using a tracking system with a charge coupled device (CCD) camera and computer software. The daily activity of nymphs was measured by an actograph system counting the number of infrared beam intercepts. The actograph data were converted to distance using a linear regression against the data of the tracking system. The longevity of nymphs without food was also studied to estimate the potential walking distance. Using both the tracking and actograph systems, it was determined that first instars walked less than the other instars (only 10.7 m within 6 h). The second to fifth instars could move 20-25 m within 6 h, and this distance did not differ among instar. This indicates that first instars seldom move after hatching in the field. The walking distance for 24 h varied and was greatest for the third instars (80.8 m). The potential longevity of nymphs was found to increase with instar age. Potential locomotion ability (walking distance for 24 hxpotential longevity) was high in the third to fifth instars (approximately 340 m). The potential locomotion ability for the second instars was relatively low compared with the elder instars (approximately 180 m). From these results, nymphs of R. pedestris seem to adapt by identifying feeding site locations after hatching and elder instars may be able to find a novel feeding site after the degradation of previous habitat.     

Refrigerated eggs of Riptortus pedestris (Hemiptera: Alydidae) added to aggregation pheromone traps increase field parasitism in soybean

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. Approximately 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.     

Pars intercerebralis promotes oviposition in the bean bug,Riptortus pedestris (Heteroptera: Alydidae)

Effects of the pars intercerebralis (PI) on the rate of oviposition were examined in adult females of Riptortus pedestris (F.) under long-day conditions that promote reproduction. When the neurosecretory cells in the PI were surgically removed from the females, they laid significantly fewer eggs than control females. When the PI from reproductive females was transplanted to PI-removed females, the number of eggs was significantly greater than that in PI-removed females without transplantation. Therefore, we suggest that the PI neurons promote fecundity or oviposition in R. pedestris.     

Changes in cuticular hydrocarbons in different developmental stages of the bean bug,Riptortus pedestris (Hemiptera: Alydidae)

The function of “cuticular hydrocarbons” (CHCs) in insects is to protect the body as well as chemical communication and recognition between species. Gas chromatography and mass spectrometry were used to compare the composition of CHCs in eggs, all nymph instars, and male and female adults of the bean bug, Riptortus pedestris (Hemiptera: Alydidae). CHC carbon chain numbers of each developmental stage ranged from 14 to 19 in eggs to the fourth nymph and were 24 in the last nymph. CHCs' carbon chain numbers in male and female adults increased from 16 to 23 and 16 to 27 until 6 days of age, respectively. Major components consisted of n-nonacosane in the larval stages, which changed to n-hentriacontane, n-heptacosane and 13,17-;15,19-demethyltritriacontane in adults. The major component from eggs was not identified. The major component from newly emerged adults was n-heptacosane. CHCs in different developmental stages of the bean bug consisted of n-alkanes with saturated hydrocarbons (27–63%), followed by mono or di-methyl alkanes. However, the CHCs of newly emerged female and male adults consisted mostly of methyl-alkanes. The major constituents of CHCs in the developmental stages of R. pedestris were proportionally different but showed only slight differences in composition.     

Quality assessment of Riptortus pedestris (Hemiptera: Alydidae) eggs cold-stored at different temperature and relative humidity regime

Supplementation of host resource can be more economical method for the biological control of insect pest compared to direct release of adult parasitoids. Periodical release of non-viable cold-stored eggs of Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) has been found to enhance parasitism of this pest in soybean fields. To find the optimum environmental conditions for cold storage of these host eggs, we evaluated nine different combinations of temperature (2, 6, and 10 °C) and relative humidity (high 90–95%, medium 70–75%, and low 30–35%). After 30 d of cold-storage, eggs were weighed and held at 26.6 °C and 75% relative humidity for 8 d before testing. To test the eggs’ suitability as hosts following cold storage, females of Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) were released individually onto batches of eggs, and parasitization rates and the development, emergence, sex ratio, adult longevity, and size of parasitoid progeny were examined. Eggs stored at high relative humidity showed less weight loss than those stored at low relative humidity. The number of eggs parasitized was highest (5.9/15) on eggs stored at 6 °C and high relative humidity. Developmental times and adult emergence were optimal on host eggs stored at 2 °C and high relative humidity. A significantly lower proportion of eggs produced male parasitoids when eggs were stored at 2 or 6 °C. Adult longevity was not affected by egg storage conditions, but adult size of progeny decreased in eggs stored at 10 °C. In conclusion, eggs of R. pedestris stored below 6 °C and with a high relative humidity maintained the best quality for parasitization by O. nezarae.     

Leg impairment affects the reproductive attributes of a ladybird,Menochilus sexmaculatus (Fabricius)

Natural injuries and their causes have recently garnered attention amongst researchers, however the effects of these injuries on life history traits are still sparsely investigated. In the few studies that have been conducted injuries are known to have a debilitating effect on male virility and reproductive performance. Thus the effect of leg injuries in males on mating behaviour and reproductive output in the ladybird beetle, Menochilus sexmaculatus was investigated. This is the first study on the effect of injury on any life history trait in Coccinellidae. The legs of the male were amputated at three different joints on the same side and opposite sides for one leg or two legs. These amputated males were paired with uninjured females and the mating behaviour and subsequent reproductive output was observed. Time to commence mating, latent period and mating duration in impaired males were observed and were all found to be higher than that of uninjured males. Fecundity and percent egg viability were reduced in all impaired male pairs. Males with physical disability were found to copulate for an extended duration, perhaps to ensure maximum paternity.     

Interactions between host attributes and wasp size: a laboratory evaluation of Trichogramma platneri as an augmentative biological control agent for two avocado pests

We compared egg parasitization of two sporadic pests of avocado, Persea americana Miller, by Trichogramma platneri Nagarkatti reared on Sitotroga cerealella (Oliver) (=smaller parasitoids) with those reared on Trichoplusia ni (Hübner) (= larger parasitoids) in the laboratory. Large T. platneri females invested less time than smaller parasitoids in obtaining offspring from eggs of either Amorbia cuneana Walsingham or Sabulodes aegrotata (Gueneé). Furthermore, large T. platneri invested substantially more time (ca. 3-fold) in obtaining offspring from S. aegrotata than A. cuneana eggs. These investment times positively correlated with percentage egg-load retained by a female after it had ceased exploiting a host species. This occurred even though the offspring produced by a parasitoid from either host species manifested the same size and fecundity (= quality). Host species utilization in the laboratory mirrored that observed in the avocado groves of southern California following augmentative release of commercially produced T. platneri (Oatman & Platner, 1985). Explanations for these differences in host utilization are discussed along with their implications for augmentative biological control.     

Pheromonal cross-attraction in true bugs (Heteroptera): attraction of Piezodorus hybneri (Pentatomidae) to its pheromone versus the pheromone of Riptortus pedestris (Alydidae)

We investigated the attractiveness of a synthetic form of the pheromone of the soybean stink bug, Piezodorus hybneri (Gmelin), under field conditions, and compared it with that of (E)-2-hexenyl (E)-2-hexenoate, a pheromone component of a competitor, Riptortus pedestris (Fabricius). Many adult stink bugs were attracted to traps baited with 100 mg of the synthetic pheromone (1: 1: one mixture of β-sesquiphellandrene, (R)-15-hexadecanolide, and methyl (Z)-8-hexadecenoate), but few were attracted to 1 or 10 mg. More than twice as many females as males were attracted to this male-produced pheromone. None of the individual pheromone components (30 mg) attracted conspecifics. In summer (June-July), when field P. hybneri were not in diapause, (E)-2-hexenyl (E)-2-hexenoate was more attractive to P. hybneri than the synthetic pheromone. The sex ratio of the adults attracted to the synthetic pheromone was highly female-biased, yet almost equal numbers of both sexes were attracted to (E)-2-hexenyl (E)-2-hexenoate. Most females attracted to both attractants were mated and had mature ovaries. However, adults attracted to (E)-2-hexenyl (E)-2-hexenoate were likely to have less food in their stomach than those attracted to the synthetic pheromone. In late autumn (October-November), when the bugs were in reproductive diapause, both attractants attracted many sexually immature female and male adults that had well-developed fat body. The synthetic pheromone also attracted a large number of conspecific nymphs. These results suggest that P. hybneri pheromone and R. pedestris pheromone component, respectively, have different functions for P. hybneri. The male-produced pheromone system of P. hybneri seems to be sex-related but to have other roles.     

Fruits of apple and sweet persimmon are not essential food sources for Riptortus pedestris (Hemiptera: Alydidae) which causes fruit-spotting

Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) has recently become an important fruit-spotting bug of apple and sweet persimmon trees in Korea. Although fruits of cultivated species are unsuitable food for some fruit-spotting bugs, the dietary importance of fruits of apple and sweet persimmon for R. pedestris is unknown. We evaluated harvested fruits of apple and sweet persimmon with or without soybean seeds as a food source for R. pedestris by investigating nymphal development time, immature mortality, preovipositional period, fecundity, and adult size in the laboratory. No first instars of R. pedestris that were fed only apple or sweet persimmon fruits became third instar nymphs. When supplemented with soybean seeds, both fruits supported nymphal development and reproduction of R. pedestris. However, fruits combined with soybean seeds were not a better diet than soybean seeds only. Therefore, apples and sweet persimmons are not essential food sources for the development and the reproduction of R. pedestris. These results suggest that R. pedestris may not reproduce on fruit trees, thus explaining the absence of eggs and nymphs of this bug on fruit trees in orchards. Management of nearby vegetation of fruit orchards would be important for reducing damage by adult R. pedestris.     

Insecticidal and biological efficacy of two vegetable oils against Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae) under laboratory conditions

Bioefficacy of two vegetable oils, namely ethyl oleate and Acorus calamus, were conducted against the pulse beetle Callosobruchus maculatus (Fabr.) under a constant temperature of 29 ± 1 °C and a relative humidity of 65 ± 5% R.H. Four concentrations (0.125, 0.25, 0.5 and 1.0%) of each oil were used against the adult and tested their latent effect on the immature stages of the beetle. The results obtained show insecticidal effect of both ethyl oleate and A. calamus oil; however, A. calamus oil proved to be more toxic to the adults at all the concentrations tested in comparison to the ethyl oleate oil. As the concentration of the oils decreased, the percentage mortality decreased. The obtained results concentrated on biological efficacy of the oils tested against the adults. Both oils affected the longevities of both male and female C. maculatus adults in comparison to the control. The oviposition periods of the adult female were affected significantly in comparison to the control. A. calamus oil prohibited oviposition completely at high concentrations of 0.5 and 1.0% and caused complete sterility to the females. Lower concentrations decreased the oviposition period greatly and reduced the number of eggs laid in comparison to the control. Ethyl oleate had an inconsiderable latent effect on the incubation period as well as the percentage of hatching of the resulting eggs. A. calamus oil decreased the percentage of egg hatchability with serious increase in the percent sterility. The two tested oils had slight extension in either larval or pupal stage of the resulting progeny of C. maculatus. Both oils show oviposition deterrency towards C. maculatus adults. The oviposition deterrent index was 100% when mung bean seeds were treated with A. calamus oil. The bruchid females laid all eggs on control seeds and no eggs were laid on treated seeds.     

Multiple host use by the egg parasitoid Trissolcus basalis (Wollaston) in a soybean agricultural system: biological control and environmental implications

1 Species of bugs (Hemiptera: Pentatomidae and other families) that are parasitized by the egg parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae) in the soybean agricultural system on the Darling Downs in south-eastern Queensland, Australia, are reported. The degree to which eggs of each bug species are used by T. basalis is quantified, which allows assessment of the role of these alternative host species in the biological control of the green vegetable bug Nezara viridula (L.). 2 Egg masses of nine species of pentatomid bugs and one unidentified bug species were collected. Parasitism rates of egg masses of all species averaged 50–70% but were significantly lower for the more important pest species, including the green vegetable bug, than for some of the agriculturally less important species. 3 Trissolcus basalis emerged from nearly all species collected and was the major parasitoid to emerge from most species. A number of native species were parasitized heavily by T. basalis and parasitism of such species may enhance biological control of the green vegetable bug, but may also pose environmental concerns. Parasitism of predatory bugs by T. basalis may have a negative impact on the biological control of other pests, especially lepidopterous pests. 4 Although the impact of T. basalis on native and predatory host species was not directly quantified, these host species remain abundant and therefore do not appear to be affected adversely by such high rates of parasitism.     

Cephalotes clypeatus Fabricius (Hymenoptera: Formicidae): nesting habits and occurrence in animal carcass

The ecological position of the family Formicidae in animal carcasses varies from predator, when feeding on eggs, larvae and pupae of some insects to necrophagous, when the ants feed on exudates or decomposing tissues. Ants are present in human corpses subject to forensic analyses and can also be used in estimation of the post-mortem interval (PMI). Cephalotes clypeatus Fabricius is exclusively arboricolous and occurs only in the American continent. During a field study conducted in the Campus of the Universidade Estadual de Campinas, in December 2003, a laboratory mouse carcass weighing 35,9 g was placed in an iron-mesh cage, which was adequate to collect adult ants. The carcass decomposed in four days. The total of 82 specimens of C. clypeatus was collected, in the first two days of exposure. They were observed feeding on exudates, tissues of the carcass, and on Diptera larvae occurring in the carcass. This species was observed nesting in hollow branches of Senna multijuga (Rich.) H.S. Irwin & Barneby (Caesalpinaceae), which was found one-meter far from the cage. Further investigation on the biology of this Cephalotini must be performed, in order to understand the role of this species in the utilization of animal carcasses, and in the entomological succession process as well. This is the first report of C. clypeatus in animal carcasses.     

The occurrence and distribution of poly(a) ribonucleic Acid in soybean

The occurrence and distribution of poly(A) sequences in the RNA of soybean (Glycine max var. Wayne) have been studied. Only one of the two species of AMP-rich RNA contains poly(A). D-RNA does not contain detectable poly(A) sequences. The TB-RNA is the poly(A) RNA in this system. At least a part (up to 50% or more) of the mRNA in polyribosomes contains a poly(A) sequence. The poly(A) RNA is heterodisperse in size but has a mean size of approximately 18S (2,000 nucleotides) in urea and formamide gels. The poly(A) fragment resulting from ribonuclease A and T₁ digestion migrates as a broad band overlapping the 4 to 5.8S regions of the gels with a mean size of somewhat greater than 5S. No evidence was found for the occurrence of a discrete oligo(A) fragment in the poly(A) RNA; however, oligonucleotides which migrate faster than the poly(A) fraction were observed in preparations which were not bound to oligo(dT) cellulose prior to electrophoresis. This oligonucleotide region was enriched in AMP (up to about 65%) as would be expected after ribonuclease A and T₁ digestion.     

A laboratory study of the copper and nickel uptake and regulation in a copper-tolerant decapod, Cambarus bartoni (Fabricius) (Decapoda, Crustacea)

Tissue copper concentration in whole Cambarus bartoni, exposed for four weeks to 0.125, 0.25 and 0.5 mg Cu/litre and 0.2, 0.4 and 0.8 mg Ni/litre in the laboratory at 18 degrees C, showed a linear relationship with exposure time at 0.25 and 0.5 mg Cu/litre; the regression slope at 0.5 mg Cu/litre (r2 = 0.218; 0.001 less than P less than or equal to 0.05) was approximately two times higher than that at 0.25 mg Cu/litre (r2 = 0.148; 0.025 less than P less than or equal to 0.05). Regression analysis of nickel concentrations in whole crayfish as a function of exposure time showed a third degree polynomial relationship at 0.4 (y = 49.989 + 14.77x - 15.395x2 + 3.194x3) and 0.8 (y = 52.053 + 37.05x - 28.933x2 + 5.133x3) mg Ni/litre, as well as in the control (y = 49.126 + 27.253x - 23.468x2 + 4.168x3) (y = Ni concentration; x = exposure time in weeks), suggesting the occurrence of a Ni flux every 4 weeks.     

Influence of laboratory hosts on the biological attributes ofChelonus blackburni [Hym.: Braconidae]

Among 6 laboratory hosts tested, the egg-larval parasitoidChelonus blackburni Cameron completed its development in only 3;Corcyra cephalonica Stainton,Phthorimaea operculella (Zeller) andAchroia grisella (Fabricius). The parasitoid failed to develop inSpodoptera litura (Fabricius),Galleria mellonella L. andSitotroga cerealella (Olivier). The development period of the parasitoids obtained from permissive hosts correspond to the development period of their hosts. Development period ofP. operculella, A grisella andC. cephalonica were 24.7±2.0, 39.5±2.1 and 50.5±4.1 days respectively while the development period of the parasitoid reared from these hosts were 25.8±1.6, 36.4±3.5 and 42.5±3.5 days respectively. The fecundity of the parasitoids reared onA. grisella, P. operculella andC. cephalonica were 365.2±52.8, 287.9±101.9 and 248.7±50.8 respectively. The size of the parasitoids reared from the above 3 hosts also followed the similar trend. However, no significant difference was observed on the percent parasitism and the longevity of the parasitoids reared on different hosts. This study was conducted at a temperature of 24±2°C and 60±5% RH. Contribution No 46001 of Biological Control Centre (NCIPM), Bangalore.     

Field and laboratory evaluations of soybean lines against soybean aphid (Hemiptera: Aphididae)

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is a major pest of soybean, Glycine max (L.). Merr., that significantly reduces yield in northern production areas of North America. Insecticides are widely used to control soybean aphid outbreaks, but efforts are underway to develop host plant resistance as an effective alternative management strategy. Here, previously identified resistant lines were evaluated in laboratory tests against field-collected populations of soybean aphid and in field-plot tests over 2 yr in South Dakota. Six lines previously identified with resistance to soybean aphid--Jackson, Dowling, K1639, Cobb, Palmetto and Sennari--were resistant in this study, but relatively high aphid counts on Tie-feng 8 in field plots contrasted with its previously reported resistance. Bhart-PI 165989 showed resistance in one of two laboratory tests, but it had relatively large aphid infestations in both years of field tests. Intermediate levels of soybean aphid occurred in field plots on lines previously shown to have strong (Sugao Zairai, PI 230977, and D75-10169) or moderate resistance to soybean aphid (G93-9223, Bragg, Braxton, and Tracy-M). Sugao Zairai also failed to have a significant proportion of resistant plants in two laboratory tests against aphids field-collected in 2008, but it was resistant in laboratory tests with aphids collected in 2002, 2005, and 2006. Overall, results showed that lines with Rag (i.e., Jackson) or Rag1 gene (i.e., Dowling) had low aphid numbers, whereas lines with Rag2 (i.e., Sugao Zairai, Sennari) had mixed results. Collectively, responses of soybean aphid populations in laboratory and field tests in 2008 resembled a virulence pattern reported previously for biotype 3 soybean aphids, but virulence in soybean aphid populations was variable and dynamic over years of the study. These results, coupled with previous reports of biotypes virulent to Rag1, suggest that deployment of lines with a single aphid-resistance gene is limited for soybean aphid management, and that deployment strategies relying on multiple resistance genes may be needed to effectively use plant resistance against soybean aphid.