Multiple origins of outbreak populations of a native insect pest in an agro-ecosystem

Native insects can become epidemic pests in agro-ecosystems. A population genetics approach was applied to analyze the emergence and spread of outbreak populations of native insect species. Outbreaks of the mirid bug, Stenotus rubrovittatus, have rapidly expanded over Japan within the last two decades. To characterize the outbreak dynamics of this species, the genetic structure of local populations was assessed using polymorphisms of the mtDNA COI gene and six microsatellite loci. Results of the population genetic analysis suggested that S. rubrovittatus populations throughout Japan were genetically isolated by geographic distance and separated into three genetic clusters occupying spatially segregated regions. Phylogeographic analysis indicated that the genetic structure of S. rubrovittatus reflected post-glacial colonization. Early outbreaks of S. rubrovittatus in the 1980s occurred independently of genetically isolated populations. The genetic structure of the populations did not fit the pattern of an outbreak expansion, and therefore the data did not support the hypothesis that extensive outbreaks were caused by the dispersal of specific pestiferous populations. Rather, the historical genetic structure prior to the outbreaks was maintained throughout the increase in abundance of the mirid bug. Our study indicated that changes in the agro-environment induced multiple outbreaks of native pest populations. This implies that, given suitable environmental conditions, local populations may have the potential to outbreak even without invasion of populations from other environmentally degraded areas.     

Changes in abundance of native and introduced parasites (Hymenoptera: Braconidae), and of the target and non-target plant bug species (Hemiptera: Miridae), during two classical biological control programs in alfalfa.

High numbers of tarnished plant bugs [Lygus lineolaris (Palisot)], were once common in alfalfa, as was a low level of parasitism (9%) by the native Peristenus pallipes (Curtis). After the bivoltine European parasite Peristenus digoneutis Loan became well established, average parasitism of the first and second generations increased to 64%, and tarnished plant bug numbers dropped by 65%. This reduced host density eventually caused a decline in total parasitism by both parasite species to 22%. A few P. digoneutis also attacked the alfalfa plant bug, Adelphocoris lineolatus (Goeze), but did not reduce this pest or increase its parasitism rate. At another location, where P. digoneutis is not established, parasitism of first generation alfalfa plant bugs, an adventive (accidently introduced) pest, was increased to 21% by the introduced univoltine parasite, Peristenus conradi Marsh, and a slight reduction in the pest may have resulted. P. digoneutis did not parasitize the meadow plant bug, Leptopterna dolabrata (L.), an adventive pest of forage grasses, so did not affect this mirid or its parasite. Neither introduced parasite eliminated the native parasites of the tarnished or alfalfa plant bugs. The narrow host ranges of the braconid parasites of mirid nymphs are contrasted with the broad host range of the native tachinid parasite [Phasia robertsoni (Towns.)] of adult mirids. The major changes in mirid abundance and their mortality by parasites that slowly occurred during this 19-year study demonstrate the need for long-term field research, to adequately document and understand these complex interactions.     

稻田穗期主要捕食性天敌对两种盲蝽集团内捕食的初步研究

【目的】集团内捕食是影响农业系统广食性天敌对靶标害虫控制作用的重要因素,全面揭示稻田广食性天敌对稻飞虱重要天敌黑肩绿盲蝽Cyrtorhinus lividipennis Reuter和中华淡翅盲蝽Tytthus chinensis(St?l)(半翅目:盲蝽科)的集团内捕食作用有助于更好地保护利用天敌。【方法】建立以两种盲蝽为猎物对象的种特异性二重定量PCR系统,检测比较不同抗性品种穗期田间主要捕食者对两种盲蝽的集团内捕食作用。【结果】(1)本研究建立的二重定量PCR具有的物种专化性,两种检测靶标灵敏度高且相似,可用于田间捕食者猎物分析;(2)感虫水稻品种上捕食者对盲蝽的捕食强度高于抗性水稻品种;不同种类捕食者对盲蝽的集团内捕食强度有显著差异;捕食者对黑肩绿盲蝽集团内捕食强度显著高于中华淡翅盲蝽。【结论】捕食性盲蝽在稻田生态系统遭遇集团内捕食,其集团内捕食强度与水稻品种抗性、捕食者种类和猎物丰富度有关。     

Niches and interspecific competitions of wolf spiders and mirid bug, Cyrtorhinus lividipennis under three pest management strategies in paddy fields

The duck-rice and fish-rice were two important strategies of pest management in the process of organic rice. The niches and interspecific competitions of wolf spiders and mirid bug, Cyrtorhinus lividipennis under three strategies of pest management in paddy fields were studied in order to understand the influences of different pest control methods on ecological relationships between the two main types of predators. The results of our study suggested that ducks might prey upon wolf spiders resting on the base of rice plants, thus the populations of wolf spiders decreased in duck-rice treatment. The impact of ducks on mirid bug was not significant because it preferred to congregate on the mid-part of rice plants. The temporal selectivity of wolf spiders was smaller than that of mirid bug, which meant occurrence frequency of wolf spiders was higher compared with mirid bug. In addition, competition between wolf spiders and mirid bug was significantly more intense in duck-rice or fish-rice treatment than in natural control treatment at different stages. Probably, ducks and fishes drove wolf spiders away from their original spatial niche, the base to the mid-part in rice plants, enhancing competition between wolf spiders and mirid bug in duck-rice or fish-rice treatment. Based on the results of this study, duck-rice or fish-rice, as a control pest method in the process of organic rice, should be prudentially treated.     

Niches and interspecific competitions of wolf spiders and mirid bug, Cyrtorhinus lividipennis under three pest management strategies in paddy fields

The duck-rice and fish-rice were two important strategies of pest management in the process of organic rice. The niches and interspecific competitions of wolf spiders and mirid bug, Cyrtorhinus lividipennis under three strategies of pest management in paddy fields were studied in order to understand the influences of different pest control methods on ecological relationships between the two main types of predators. The results of our study suggested that ducks might prey upon wolf spiders resting on the base of rice plants, thus the populations of wolf spiders decreased in duck-rice treatment. The impact of ducks on mirid bug was not significant because it preferred to congregate on the mid-part of rice plants. The temporal selectivity of wolf spiders was smaller than that of mirid bug, which meant occurrence frequency of wolf spiders was higher compared with mirid bug. In addition, competition between wolf spiders and mirid bug was significantly more intense in duck-rice or fish-rice treatment than in natural control treatment at different stages. Probably, ducks and fishes drove wolf spiders away from their original spatial niche, the base to the mid-part in rice plants, enhancing competition between wolf spiders and mirid bug in duck-rice or fish-rice treatment. Based on the results of this study, duck-rice or fish-rice, as a control pest method in the process of organic rice, should be prudentially treated.     

Host preferences of introduced and native parasites (Hymenoptera: Braconidae) of phytophagous plant bugs (Hemiptera: Miridae) in alfalfa-grass fields in the northeastern USA

During an eight-year field study at two widely-separated locations (NJ & DE, USA), seven species of phytophagous mirid plant bugs were found in alfalfa and alfalfa-grass fields grown for animal forage. Five species of parasites were reared from these mirids. Two parasite species introduced from Europe killed significantly higher proportions of nymphs of the two important mirid pests of alfalfa than did native parasites. The introduced Peristenus digoneutis Loan parasitized an average of 31% of first and second generation tarnished plant bugs, Lygus lineolaris, a native insect; and the introduced Peristenus conradi parasitized 22% of first generation alfalfa plant bugs, Adelphocoris lineolatus, an introduced species. In addition, Peristenus pallipes significantly parasitized nymphs of Trigonotylus caelestialium (43%) and Leptopterna dolabrata (37%); both mirids are immigrant species. Because the parasite P. pallipes significantly attacked only these two non-native mirids, and is present in Europe, it also may be an accidental introduction to North America. A native wasp, Leiophron uniformis, heavily parasitized (49%) the native garden fleahopper, Halticus bractatus. A third native species, P. pseudopallipes, occasionally parasitized a few Lygus lineolaris in alfalfa at one location. Two other mirids, Stenotus binotatus and Megaloceroea recticornis, both accidently-introduced grass-feeding species, were not parasitized by native or introduced species. It is noteworthy that the effective host ranges of all the parasites in alfalfa-grass fields were limited: four of the five parasite species significantly parasitized only one of the seven mirid species, and the other parasite significantly parasitized only two mirids. Activity of the four common parasites was correlated with the mirids' host plant: three species principally parasitized alfalfa-feeding mirids, and one species principally parasitized grass-feeding mirids.     

Parasitic wasp assemblages associated with native and weedy plant species in an agricultural landscape

Abstract  The establishment and maintenance of suitable habitat on-farm or in the surrounding landscape can enhance the survival of beneficial parasitic Hymenoptera, thus improving the control of pest species. Both endemic and weedy non-crop plant species across a highly modified agricultural landscape supported species-rich and abundant parasitic wasp assemblages with diverse biology and host associations. It was also shown that isolated, recently planted, single-species stands of plants can rapidly accumulate diverse assemblages of parasitoids. Chalcidoidea was the most species-rich and abundant group, egg and larval parasitoids were the most speciose and abundant guilds, and parasitoids of herbivorous insects feeding on and inside plant tissue were the most species-rich and abundant functional groups. The hymenopteran assemblages associated with the majority of plant species were dominated by three parasitoid species: a Trichogrammatidae, a Scelionidae ( Telenomus sp.) and a Eulophidae ( Ceranisus sp.), all genera that contain many important biocontrol agents of pest Lepidoptera, Hemiptera and Thysanoptera. Results show that both native and weedy plant species may potentially provide an important reservoir of mobile parasitic wasps of benefit to crop protection.     

Development of polymorphic microsatellite markers for the sorghum plant bug, Stenotus rubrovittatus (Heteroptera: Miridae)

Nine polymorphic microsatellite DNA markers from the sorghum plant bug, Stenotus rubrovittatus, were isolated and characterized. These markers were used to analyse 22 individuals from a single field population. The number of alleles at these nine loci ranged from two to 28 (mean = 11.4) and heterozygosity ranged from 0.27 to 0.86 (mean = 0.58). Stenotus rubrovittatus has shown rapid population growth in the decades since the first report in the 1980s of serious damage to a rice crop. These microsatellite markers will be of value for studying both the population genetics and population dynamics of S. rubrovittatus.     

Multiple spatial scale factors affecting mirid bug abundance and damage level in organic rice paddies

Mirid bugs, major insect pests in rice production, have dramatically expanded their range in Japan, resulting in increased economic losses especially for organic rice farmers. In this study, the within-field and landscape-scale factors affecting the bug and its damage to crops were examined in organic rice farms. Bug densities and crop damage levels showed significant positive relationships with weed densities (Schoenoplectus juncoides and Echinochloa crus-galli) within individual fields. Bug densities were negatively associated with Tetragnatha spp. and Pachygnatha clercki densities, indicating that these spiders act as biological control agents that help to decrease crop damage levels. At the landscape scale, bug densities increased with the proportion of the area that was fallow within a 400-m radius around focal fields. Fallows represent important source habitat for the bug and the spatial extent at which bug abundance was affected indicates the mobility of these insects. These results suggest that the combination of biological control by natural enemies, and weed management within individual paddies and surrounding landscapes inside a buffer zone of less than half a kilometre may be effective in controlling mirid bugs and the damage they cause in organic paddy fields.     

Effect of seasonal variation in host-plant quality on the rice leaf bug, Trigonotylus caelestialium

The rice leaf bug, Trigonotylus caelestialium (Kirkaldy) (Heteroptera: Miridae), is an important insect pest, causing pecky-rice damage in Japan. This bug has a multivoltine life cycle and feeds on various species of the Poaceae. The phenology of the host-plants differs between species and the plant quality of a single host species may change with the seasons. The fitness of the bug may be affected by these seasonal changes in host-plant quality. In the current study, the effects of such quality changes on adult and nymphal performance were examined using a population of bugs collected in Joetsu, Niigata, Japan. Rearing of newly emerged adults collected from spring to autumn from Italian rye grass, Lolium multiflorum Lam., and southern crabgrass, Digitaria ciliaris (Retz.), showed that body size and performance of adults differed between collection seasons and plant species, indicating that nymphal conditions including host-plant quality have crucial effects on their fitness. Rearing nymphs from hatching to adult emergence on various field-collected grasses under laboratory conditions showed that the performance of nymphs depends on the plant species and varies greatly with the season, within a given species. In general, nymphs performed more poorly on most of the plants collected late in the season, but they performed well on some plants unavailable early in the season. Therefore, in T. caelestialium , seasonal and spatial variations are important factors that affect fitness of nymphs and adults, and this suggests that oviposition of diapause eggs in summer is an adaptation to deteriorating food conditions.     

Indirect effects of weeds on rice plants via shared heteropteran herbivores

In agricultural ecosystems, weeds indirectly affect crops via phytophagous insects that feed on both weeds and crops. In paddy fields, heteropteran insects are among the most serious pests of rice plants. In some heteropterans, the proboscis is used to suck rice ears, inducing black spots on the grains (i.e., pecky rice). Even a low proportion of pecky rice (>0.1%) significantly decreases the market price of rice; in Japan, this problem has led to severe economic losses. Because heteropterans feed on the reproductive organs of weeds as well as rice plants, various weeds that grow around paddy fields may increase the populations of heteropterans that cause pecky rice. To clarify which types of weeds can be used by heteropterans causing pecky rice, we investigated the interactions between plants (including rice plants) and heteropterans in an agricultural landscape in Hyogo, Japan. We observed 833 individuals of 27 heteropteran species (13 families) feeding on the reproductive organs of 35 plant species (Poales: three families) including rice plants from June to October 2019. All heteropteran species were native, whereas six of 35 plant species were non-native. We found 12 heteropteran species on rice plants; nine of the 12 heteropteran species fed on weeds (a total of 32 species) as well as rice plants, whereas the other three species fed exclusively on rice plants. Heteropterans fed on native weeds throughout the growing seasons (June–October), but on non-native weeds only before rice plants bloomed (June–July). Therefore, diverse weed species that grow around paddy fields are food resources for heteropteran insects and they might indirectly increase the incidence of pecky rice.     

Field biology of Edessa rufomarginata (Hemiptera: Pentatomidae): phenology, behavior, and patterns of host plant use

Pentatomids may cause direct and indirect damage to important crop plants. Biological and ecological features of phytophagous stink bugs in natural environments, however, remain poorly documented. Here, we provide an ecological account of Edessa rufomarginata De Geer on Caryocar brasiliense (Caryocaraceae) in the Brazilian savanna. The phenology of E. rufomarginata matched that of its host plant, with immatures developing in the wet season simultaneously with the production of vegetative and reproductive plant tissue. Females do not exhibit parental care and lay eggs more frequently on larger plants. Oviposition frequency, however, does not differ between plants with and without flowers/fruits. Nymphs and adults usually feed on stem parts and more rarely on flower buds and fruits. First- and second-instar nymphs remain aggregated, but disperse as third-instar nymphs. Adults and nymphs were more abundant on mature stems of C. brasiliense compared with other plant locations. Ants visiting the plant to search for extrafloral nectar occasionally tap the abdomen of E. rufomarginata nymphs with their antennae to obtain honeydew. This is the first record of trophobiotic interactions between Edessa stinkbugs and ants, and one of the few for heteropterans. The interaction of the stink bug with other natural enemies, such as predaceous Heniartes (Reduviidae), was also observed. Given the pest status of Edessa species for crop plants, additional field studies on host plants, interaction with ants, and natural enemies in native habitats are needed for an effective management of these stink bugs in tropical agricultural systems.     

农田景观格局变化对昆虫的生态学效应

景观格局变化是全球变化的一个重要内容。农田是由人类赖以生存所种植的人工栽培作物组成的生态系统。在该景观系统中,多种植物-害虫-天敌相互作用、相互制约,形成有机整体。研究农田景观格局对害虫和天敌种群动态影响,不仅在害虫生物防治的实践中有重要意义,而且对于揭示人类活动对生物多样性结构与功能的影响,阐明农田景观中生物多样性整合、维持机理有重大的理论意义。本文从农田景观格局的"质、量、形、度"4个方面,系统地论述了农田景观格局变化对害虫和天敌的作用,分析了农田景观的生物控制服务功能,指出了未来研究发展的方向。     

Adjacent Habitat Influence on Stink Bug (Hemiptera: Pentatomidae) Densities and the Associated Damage at Field Corn and Soybean Edges

The local dispersal of polyphagous, mobile insects within agricultural systems impacts pest management. In the mid-Atlantic region of the United States, stink bugs, especially the invasive Halyomorpha halys (Stål 1855), contribute to economic losses across a range of cropping systems. Here, we characterized the density of stink bugs along the field edges of field corn and soybean at different study sites. Specifically, we examined the influence of adjacent managed and natural habitats on the density of stink bugs in corn and soybean fields at different distances along transects from the field edge. We also quantified damage to corn grain, and to soybean pods and seeds, and measured yield in relation to the observed stink bug densities at different distances from field edge. Highest density of stink bugs was limited to the edge of both corn and soybean fields. Fields adjacent to wooded, crop and building habitats harbored higher densities of stink bugs than those adjacent to open habitats. Damage to corn kernels and to soybean pods and seeds increased with stink bug density in plots and was highest at the field edges. Stink bug density was also negatively associated with yield per plant in soybean. The spatial pattern of stink bugs in both corn and soybeans, with significant edge effects, suggests the use of pest management strategies for crop placement in the landscape, as well as spatially targeted pest suppression within fields.     

Control of western tarnished plant bug Lygus hesperus Knight (Hemiptera: Miridae) in California organic strawberries using alfalfa trap crops and tractor-mounted vacuums

A key economic pest of strawberries in California is the western tarnished plant bug, Lygus hesperus Knight (Hemiptera:Miridae). Alfalfa (Medicago sativa L.) is a highly attractive plant host to western tarnished plant bug, and we hypothesized that it can be successfully managed as a trap crop for pest suppression in strawberries. Completely randomized design trap cropping experiments were established on an organic strawberry farm from 2002 to 2004. Western tarnished plant bug adults and nymphs were significantly more abundant in alfalfa trap crops than in comparable edge strawberry rows. Over 3 experimental yr, twice-weekly summer vacuuming of alfalfa trap crops with a tractor-mounted vacuuming device reduced adult and nymph abundance by 72 and 90%, respectively, in trap crops. This summer vacuuming of alfalfa trap crops also significantly reduced damage caused by western tarnished plant bug in associated unvacuumed organic strawberries (June and July 2002, June 2003, and June and July 2004) compared with either an untreated control (2003) or the organic strawberry grower's standard whole field vacuuming treatment. Vacuuming of alfalfa trap crops reduces an organic grower's costs (tractor, tractor fuel, and driver time) by 78% compared with current whole field vacuuming practices. An economic analysis of a whole hectare model indicates that a positive return from the use of vacuumed trap crops could be realized in 2004. The overall potential positive net return for the 3 mo of vacuumed alfalfa trap crop treatments in 2004 was calculated at +$1,829/ha.     

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.     

Gene flow in the green mirid,Creontiades dilutus (Hemiptera: Miridae), across arid and agricultural environments with different host plant species

Creontiades dilutus (Stål), the green mirid, is a polyphagous herbivorous insect endemic to Australia. Although common in the arid interior of Australia and found on several native host plants that are spatially and temporally ephemeral, green mirids also reach pest levels on several crops in eastern Australia. These host‐associated dynamics, distributed across a large geographic area, raise questions as to whether (1) seasonal fluctuations in population size result in genetic bottlenecks and drift, (2) arid and agricultural populations are genetically isolated, and (3) the use of different host plants results in genetic differentiation. We sequenced a mitochondrial COI fragment from individuals collected over 24 years and screened microsatellite variation from 32 populations across two seasons. The predominance of a single COI haplotype and negative Tajima D in samples from 2006/2007 fit with a population expansion model. In the older collections (1983 and 1993), a different haplotype is most prevalent, consistent with successive population contractions and expansions. Microsatellite data indicates recent migration between inland sites and coastal crops and admixture in several populations. Altogether, the data suggest that long‐distance dispersal occurs between arid and agricultural regions, and this, together with fluctuations in population size, leads to temporally dynamic patterns of genetic differentiation. Host‐associated differentiation is evident between mirids sampled from plants in the genus Cullen (Fabaceae), the primary host, and alternative host plant species growing nearby in arid regions. Our results highlight the importance of jointly assessing natural and agricultural environments in understanding the ecology of pest insects.     

Comparison of the effects of landscape composition on two mirid species in Japanese rice paddies

Two rice bug species, Stenotus rubrovittatus (Matsumura) and Trigonotylus caelestialium (Kirkaldy) (Hemiptera: Miridae), are major rice pests in Japan. The populations of these insects are maintained by widely distributed host plants and by a broad range of movements among resource patches. To develop an effective pest management strategy for a region where two rice bug species coexist, the impacts of the surrounding landscape and of weed-infested field boundaries on the field abundances of the two rice bug species were compared. Field abundances of the two species were estimated using the sweep-netting technique. The number of weed-infested field boundaries was also counted within a 100 m radius around 14 study paddies at three sites in Japan. The distinctive features of the surrounding landscape furnished the best predictor at a spatial scale radius of 300 m for S. rubrovittatus and at 200–300 m for T. caelestialium. The abundances of both species increased as the amounts of weed-infested area and reclaimed land increased. The size and number of sources also affected the two rice bug species. These results emphasize that adequate field boundary management can reduce the risk of high pest abundance in the fields, even when an extensive weed-infested area exists within the functional scale of the species.     

Tree Spatial Structure,Host Composition and Resource Availability Influence Mirid Density or Black Pod Prevalence in Cacao Agroforests in Cameroon

Combining crop plants with other plant species in agro-ecosystems is one way to enhance ecological pest and disease regulation mechanisms. Resource availability and microclimatic variation mechanisms affect processes related to pest and pathogen life cycles. These mechanisms are supported both by empirical research and by epidemiological models, yet their relative importance in a real complex agro-ecosystem is still not known. Our aim was thus to assess the independent effects and the relative importance of different variables related to resource availability and microclimatic variation that explain pest and disease occurrence at the plot scale in real complex agro-ecosystems. The study was conducted in cacao (Theobroma cacao) agroforests in Cameroon, where cocoa production is mainly impacted by the mirid bug, Sahlbergella singularis, and black pod disease, caused by Phytophthora megakarya. Vegetation composition and spatial structure, resource availability and pest and disease occurrence were characterized in 20 real agroforest plots. Hierarchical partitioning was used to identify the causal variables that explain mirid density and black pod prevalence. The results of this study show that cacao agroforests can be differentiated on the basis of vegetation composition and spatial structure. This original approach revealed that mirid density decreased when a minimum number of randomly distributed forest trees were present compared with the aggregated distribution of forest trees, or when forest tree density was low. Moreover, a decrease in mirid density was also related to decreased availability of sensitive tissue, independently of the effect of forest tree structure. Contrary to expectations, black pod prevalence decreased with increasing cacao tree abundance. By revealing the effects of vegetation composition and spatial structure on mirids and black pod, this study opens new perspectives for the joint agro-ecological management of cacao pests and diseases at the plot scale, through the optimization of the spatial structure and composition of the vegetation.