Spatio-temporal distribution of Ricania shantungensis (Hemiptera: Ricaniidae) in chestnut fields: Implications for site-specific management

Chestnut is one of most important forest products in Korea. However, Ricania shantungensis, an invasive species, has been increasingly causing economic damage to chestnut. To increase management efficiency of R. shantungensis in chestnut fields, its spatio-temporal distributions were analyzed using spatial analysis by distance indices (SADIE) and semivariogram. Experiments were conducted by observing selected, marked, and geo-referenced trees in two commercial chestnut fields for each developmental stage (i.e., spring egg, nymph, adult, and fall egg) of R. shantungensis from 2017 to 2019. Spatial distributions of R. shantungensis were statistically (P < 0.05) aggregated except for its nymphal stage. Spatial associations of its distributions also showed the statistically (P < 0.05) positive associations regardless of years or developmental stages except for the spatial relationship between egg and nymphal stages. These results indicated that site-specific management for R. shantungensis would be applicable. In application of site-specific management for R. shantungensis, the distance of spatial dependence for nymphs, 60 m, should be considered to minimize reoccurrence possibility and additional samplings. Incorporating site-specific management into pest control program of R. shantungensis could increase its control efficiency in chestnut fields.     

Occurrence model of first instars of Ricania shantungensis (Hemiptera: Ricaniidae)

An invasive planthopper, Ricania shantungensis, is an important pest in agriculture and forestry in Korea. Best target stage for insecticide application is known to be newly hatched first instar. Thus, the objective of the present study was to predict the occurrence of first instars of R. shantungensis. Effects of temperature on development and survival of R. shantungensis eggs were examined at seven constant temperatures (12.4, 16.4, 20.4, 24.8, 28.3, 32.4, and 36.9 °C). Development and survival of R. shantungensis eggs were quantitatively described by applying empirical models as a function of temperature over a wide thermal range. Lower developmental threshold, thermal constant, optimal developmental temperature, and upper developmental threshold were estimated to be 12.1 °C, 202 DD, 31 °C, and 36.9 °C, respectively. Survivorship was the highest at 23.3 °C. The models well predicted timing of field occurrences at three sites (Buyeo, Gwangyang, and Habcheon) in Korea. Therefore, results of this study would increase the prediction accuracy of R. shantungensis occurrence and management efficiency of R. shantungensis.     

Semi-field demographic performance of the invasive planthopper,Orosanga japonica (Hemiptera: Ricaniidae) on two host plants

Orosanga japonica Melichar (Hemiptera: Ricaniidae) is an invasive polyphagous pest in Iran. The planthopper damaged host plants by sap-sucking and egg laying on new twigs. This study aimed to determine the life table parameters of O. japonica on Rubus ulmifolius Schoot (elm leaf blackberry) and Melia azedarach L. (chinaberry) under field conditions in Rudsar (North of Iran) during 2019–2020. The collected life history data were analyzed based on age-stage, two-sex life table theory. The results showed that the incubation period of O. japonica was too long (≈ 270 days) on both host plants. The nymphs emerged from mid-May 2020. The planthopper had five nymphal stages under field conditions. The nymphal duration was 41.39 ± 0.56 days and 38.13 ± 0.62 days on R. ulmifolius and M. azedarach, respectively. The total preadult survival rates were 53.2% and 51.7% on R. ulmifolius and M. azedarach, respectively. Based on the results, a significant shorter total developmental time was observed on M. azedarach. When adults emerged in late July, they laid eggs after 26.05 days and 26.75 days on R. ulmifolius and M. azedarach, respectively. The fecundity on M. azedarach (131.69 egg/female) was significantly higher than that on R. ulmifolius. However, the life table parameters were all not significantly different on the two host plants. The intrinsic rate of increase (r) were 0.0097 ± 0.0005 day⁻¹ and 0.0105 ± 0.0006 day⁻¹ on R. ulmifolius and M. azedarach, respectively. Generally, these findings could be helpful to establish an efficient management strategy for this exotic pest.     

Caddisfly egg mass morphology mediates egg predation: potential costs to individuals and populations

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Testing ecological interactions between Gnomoniopsis castaneae and Dryocosmus kuriphilus

An emerging nut rot of chestnut caused by the fungus Gnomoniopsis castaneae was reported soon after the invasion of the exotic gall wasp Dryocosmus kuriphilus in Italy. The goal of this work was to assess the association between the spread of the fungal pathogen and the infestation of the pest by testing if:I) viable inoculum of G. castaneae can be carried by adults of D. kuriphilus;II) the fungal colonization is related to the number of adults inhabiting the galls;III) the fungal colonization of chestnut buds and the oviposition are associated.Fungal isolations and PCR-based molecular assays were performed on 323 chestnut galls and on their emerging D. kuriphilus adults, whose number was compared between galls colonized and not colonized by G. castaneae. To test the association between fungal colonization and oviposition, Monte Carlo simulations assuming different scenarios of ecological interactions were carried out and validated through isolation trials performed on 597 and 688 chestnut buds collected before and after oviposition, respectively.Although DNA of G. castaneae was detected in a sample of 40% of the adults developed in colonized galls, the fungus could never be isolated from insects, suggesting that the pest is an unlikely vector of viable inoculum.On average, the emerging adults were significantly more abundant from galls colonized by G. castaneae than from not colonized ones (3.76 vs. 2.54, P < 0.05), indicating a possible fungus/pest synergy.The simulations implying no interaction between G. castaneae and D. kuriphilus after fungal colonization were confirmed as the most likely. In fact, G. castaneae was present in 33.8% of the buds before oviposition, while no association was detected between fungal colonization and oviposition (odds ratio 0.98, 0.71–1.33 95% CI). These findings suggest that the fungus/pest synergy is asymmetrically favorable to the pest and occurs after oviposition.     

甘肃陇南地区银杏大蚕蛾卵寄生蜂种类调查

银杏大蚕蛾Caligula japonica（Moore）作为危害核桃、板栗、银杏等坚果类果树的重要害虫之一,已经引起国内外广泛关注。明确银杏大蚕蛾卵期寄生蜂的种类、分布和自然寄生状况,可为银杏大蚕蛾天敌的保护利用提供科学依据。本文于2018-2019年在甘肃省陇南市银杏大蚕蛾核桃危害区采集该害虫的越冬卵并带回实验室培养,收集羽化的寄生蜂并记录其种类和数量,最后通过计算寄生率确定优势天敌物种。本研究共采集银杏大蚕蛾卵块1 114个约8万粒卵,平均单株核桃树木卵块数与卵粒数分别最高可达7.5块和533.5粒;共收集到膜翅目3科5属9种银杏大蚕蛾卵期寄生蜂,其中6种为首次报道;具体为旋小蜂科7种,包括平腹小蜂属4种：麻纹蝽平腹小蜂Anastatus fulloi、甘肃平腹小蜂A. gansuensis、日本平腹小蜂A. japonicus和梅岭平腹小蜂A. meilingensis;短角平腹小蜂属2种：白跗短角平腹小蜂Mesocomys albitarsis和枯叶蛾短角平腹小蜂M. trabalae;旋小蜂属1种：Eupelmus sp.;赤眼蜂科赤眼蜂属1种：螟黄赤眼蜂Trichogramma chilonis;姬小蜂科长尾啮小蜂属1种：短梗长尾啮小蜂Aprostocetus brevipedicellus。结果表明,旋小蜂科两种短角平腹小蜂数量最多,分布最广,物种优势度指数达86以上,为陇南地区野外寄生银杏大蚕蛾卵的优势性天敌,且卵块寄生率和卵粒寄生率分别最高可达55.91%和6.77%。本研究拓宽了银杏大蚕蛾自然天敌种类并为今后开发利用寄生蜂防治该害虫提供了理论依据。     

Comparative assessments of Gonatocerus ashmeadi and the ‘new association’ parasitoid Gonatocerus tuberculifemur (Hymenoptera: Mymaridae) as biological control agents of Homalodisca vitripennis (Hemiptera: Cicadellidae)

Egg age preference, competitive ability, and behavior of Gonatocerus tuberculifemur (‘new association’ parasitoid) and Gonatocerus ashmeadi (‘old association’ parasitoid) were investigated in the laboratory to determine if one species exhibited competitive superiority. When searching concurrently for Homalodisca vitripennis egg masses, G. ashmeadi consistently outperformed G. tuberculifemur by parasitizing 25–53% more eggs under three different experimental systems in the laboratory with varying host densities, egg ages, and exposure times. G. ashmeadi parasitism in control vials containing one parasitoid ranged from 81–97% across all egg ages. G. tuberculifemur in control vials parasitized 60–66% of eggs 1 and 3 days old, and just 18% of eggs 5 days old. G. ashmeadi produced 5–16% more female offspring than G. tuberculifemur for all experimental conditions. In comparison to G. ashmeadi, G. tuberculifemur was observed off leaves with host eggs 20% more frequently and it oviposited 15% less frequently. G. ashmeadi and G. tuberculifemur when confined together allocated ∼1% of behaviors to antennating or aggressively chasing competitors off egg masses, and up to 2% of behaviors to antennating host egg masses and/or ovipositing into eggs from the opposite side of the leaf. These latter behaviors did not occur when parasitoids were confined alone with host eggs.     

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.     

Predators ofLymantria dispar (Lep. lymantriidae) egg masses: Spatio-temporal variation of their impact during the 1988–89 pest generation in the mamora cork oak forest (Morocco)

In the Mamora cork oak forest (Morocco), oophagous predators of the gypsy mothLymantria dispar (L.) (Lepidoptera: Lymantriidae) are one of the main mortality factors influencing pest population dynamics. The predators destroy egg masses more by disrupting their cohesiveness than by predation. From 1987 to 1990, the impact of oophagous enemies significantly contributed to the collapse of a localized gypsy moth outbreak. Variation of egg mass dislocation intensity was greater between trees than among the different strata of a tree. The number of gypsy moth egg masses and egg predator attacks increased when oaks were large and unhealthy. Forest degradation probably explains why egg mass destruction rates were so high (60 to 90% of the eggs) in the infested forest. Oophagous predators find food and shelter under the dehiscent bark of unhealthy cork oaks.     

Identification of the Key Weather Factors Affecting Overwintering Success of Apolygus lucorum Eggs in Dead Host Tree Branches

Understanding the effects of weather on insect population dynamics is crucial to simulate and forecast pest outbreaks, which is becoming increasingly important with the effects of climate change. The mirid bug Apolygus lucorum is an important pest on cotton, fruit trees and other crops in China, and primarily lays its eggs on dead parts of tree branches in the fall for subsequent overwintering. As such, the eggs that hatch the following spring are most strongly affected by ambient weather factors, rather than by host plant biology. In this study, we investigated the effects of three major weather factors: temperature, relative humidity and rainfall, on the hatching rate of A. lucorum eggs overwintering on dead branches of Chinese date tree (Ziziphus jujuba). Under laboratory conditions, rainfall (simulated via soaking) was necessary for the hatching of overwintering A. lucorum eggs. In the absence of rainfall (unsoaked branches), very few nymphs successfully emerged under any of the tested combinations of temperature and relative humidity. In contrast, following simulated rainfall, the hatching rate of the overwintering eggs increased dramatically. Hatching rate and developmental rate were positively correlated with relative humidity and temperature, respectively. Under field conditions, the abundance of nymphs derived from overwintering eggs was positively correlated with rainfall amount during the spring seasons of 2009–2013, while the same was not true for temperature and relative humidity. Overall, our findings indicate that rainfall is the most important factor affecting the hatching rate of overwintering A. lucorum eggs on dead plant parts and nymph population levels during the spring season. It provides the basic information for precisely forecasting the emergence of A. lucorum and subsequently timely managing its population in spring, which will make it possible to regional control of this insect pest widely occurring in multiple crops in summer.     

Probing the effects of dietary selenised glucose on the selenium concentration,quality, and antioxidant activity of eggs and production performances of laying hens

Selenised glucose (SeGlu) is a newly invented organic selenium compound being synthesised through the selenisation reaction of glucose with NaHSe. We hypothesised that glucose could be used as a carrier for the stable low-valent organoselenium to enhance the selenium concentrations of eggs. To probe the effects of SeGlu on production performances of laying hens, egg selenium concentration, egg quality, and antioxidant indexes, 360 Hy-Line Brown laying hens were randomly assigned to three treatment groups fed with a basal diet alone or the diet supplemented with 5 or 10 mg/kg of Se from SeGlu. The results showed that SeGlu treatment not only enhanced (P < 0.001) the Se concentration in albumen and yolks, glutathione peroxidase activity, and total antioxidant capacity of eggs but also increased (P = 0.032) the Haugh unit of eggs being stored for 2 weeks, while the production performances and egg qualities of fresh eggs were not affected. Moreover, SeGlu supplementation linearly (P < 0.001) increased the scavenging ability of superoxide radicals in eggs. Briefly, SeGlu can enhance the selenium deposition and antioxidant activity of eggs, thereby meeting the nutritional requirement for Se-deficient humans.     

Surveying native egg parasitoids and predators of the invasive Halyomorpha halys in Northern Italy

The invasive Halyomorpha halys (Heteroptera: Pentatomidae) is a key pest of fruits in the Emilia‐Romagna region of Italy. For the development of a sustainable management programme, knowledge of its native natural enemy community and its efficacy is essential. A three‐year field survey was conducted exposing H. halys egg masses in different types of habitats to investigate the efficacy of native natural enemies in reducing the H. halys populations in the Emilia‐Romagna region, where the stinkbug was first detected in 2012. Over the first year of the study, sentinel eggs from laboratory cultures were stapled to the underside of leaves in various host trees, whereas in following years H. halys adults were directly caged on branches in sleeve cages to allow natural oviposition. Over the examined years, low rates of parasitism (1%–3%) and predation (2%–5%) were observed. Parasitism was caused exclusively by the generalist parasitoid Anastatus bifasciatus.     

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.     

Effect of temperature on woodwasp (Sirex noctilio F.) development and parasitism by the entomopathogenic nematode,Deladenus siricidicola

The woodwasp, Sirex noctilio, is a significant global pest of exotic pine plantations in the Southern Hemisphere and now threatens native pine forests in North America. Management in Australia relies on biocontrol using the nematode, Deladenus (= Beddingia) siricidicola (Bedding), which infects and sterilises females who then further disperse the nematode. This pest is spreading into warmer regions in Australia and South America and coupled with the threat of global climate change, there is uncertainty as to how increasing temperatures will affect the biocontrol program. S. noctilio within nematode-inoculated wood were reared at four temperatures (24, 25.3, 26.6 and 28 °C) to investigate the effects of elevated temperatures on wasp development (emergence time, sex ratio and size), development of eggs (number, size, and maturation) and infection by the nematode. At 24 °C, which reflects current field temperature, S. noctilio were bigger in size and all the eggs were normal and all were infected with nematodes. Modest rises in temperature reflecting climate change scenarios resulted in smaller sized S. noctilio, disrupted egg development and maturation, and lowered the nematode sterilisation rate in females. Reduced S. noctilio female body size and egg infection will likely compromise biocontrol by D. siricidicola in its current distribution, but disrupted egg development may act directly on the pest, limiting dispersal of S. noctilio into subtropical pine plantations and adaptation to climate change.     

Efficacy of new nematicides for managing Meloidogyne incognita in tomato crop

New non‐fumigant nematicides (fluensulfone, fluopyram and fluazaindolizine) were tested in greenhouse tomato trials aiming to evaluate its efficacy on the control of Meloidogyne incognita soil and root populations and plant produtivity. Plants of the cultivar Red Gnome were transplanted into 2,500 cm³ fibre pots inoculated with 200 eggs of M. incognita/100 cm³ of soil and treated with fluensulfone, fluopyram and fluazaindolizine, in two rates each. After eight weeks of incubation the plants were evaluated for fresh root and shoot weight, weight and number of fruits, egg mass number, population density and nematode reproduction factor. All nematicide treatments reduced the root gall index, the number of M. incognita egg masses, eggs/g root and the nematode reproduction factor when compared to the non‐treated control.     

Evaluation of oil dispersion formulation of nematophagus fungus,Pochonia chlamydosporia against root-knot nematode,Meloidogyne incognita in cucumber

Root-knot nematode, Meloidogyne incognita is considered as one of the major non-insect pests of crops. The management of these root feeders becomes highly challenging due to a strong host-parasitic relationship. Pochonia chlamydosporia is a nematophagus fungus that colonizes eggs of nematodes. This study aimed to test the efficacy of P. chlamydosporia (NAIMCC-SF0039) against M. incognita. An oil dispersion formulation of P. chlamydosporia was prepared using emulsifiers and vegetable oil. This formulation had a shelf-life of 90 days (3.3 × 10⁸ CFU/mL) at room temperature (28 ± 1 °C). The inhibitory effect of oil formulation was tested against M. incognita by inoculating it on the egg mass. We found that colonization of the gelatinous matrix occurred on the third day of inoculation followed by complete egg parasitization on the seventh day. A greenhouse trial was laid out to evaluate the biocontrol potential of P. chlamydosporia in cucumber (Cucumis sativus). The results showed that the application of talc formulation of P. chlamydosporia at the rate of 1 kg per acre during planting, followed by delivery of 1 L of oil dispersion formulation through drip lines at 30-day intervals caused the highest reduction of nematode infestation. This treatment recorded 67.9 and 57.5% reduction in egg masses and soil nematode population respectively than that of control.     

Effects of combining releases of non-viable host eggs with insecticide application on Riptortus pedestris population and its egg parasitoids

Our previous study demonstrated that the release of refrigerated non-viable eggs of Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) enhanced parasitism rates in soybean fields but did not result in the reduction of R. pedestris populations. This study was further conducted using an open-cage exclusion design in a soybean field in order to evaluate the compatibility of combining releases of non-viable host eggs with a single pre-harvest application of insecticide for the control of R. pedestris. Refrigerated eggs of R. pedestris were released twice in treatment plots, and fresh (< 1 day old) eggs of R. pedestris were deployed in all experimental arenas, every 6 days, for host resource and measurement of field parasitism. The releases of host eggs did not reduce the number of R. pedestris in any life stage except the adult stage on two sampling dates. However, parasitism by Gryon japonicum (Ashmead) (Hymenoptera: Scelionidae) was higher in treated plots (9–25%) than in the control plots (1–9%). Statistical significant reduction was not found in the pest population, but parasitism rates significantly increased. Pesticide application did not reduce the bug population but did affect the parasitoids population. Pest management tactics, using both artificially deployed host eggs and insecticide, are discussed.     

Soybean Cyst Nematode Population Development and its Effect on Pennycress in a Greenhouse Study

Midwest crop production is dominated by two summer annual crops grown in rotation, viz., corn (Zea mays L.) and soybean (Glycine max L.). Winter oilseed crops, such as pennycress (Thlaspi arvense L.), can provide ecosystem and economic benefits when added to the corn–soybean rotation. However, adding a new crop adds risks, such as increased pest pressure. The objectives of this study were to (i) evaluate population development of three soybean cyst nematode (SCN; Heterodera glycines) biotypes on three pennycress genotypes and susceptible soybean and (ii) determine whether SCN inoculation level influenced plant biomass. SCN population density and biomass were determined after 60 d in the greenhouse. At the inoculation level of 2,000 eggs/100 cm³ soil, the average egg density for the three pennycress genotypes was 1,959 eggs/100 cm³ soil, lower than that for the susceptible soybean ‘Sturdy’ (9,601 eggs/100 cm³ soil). At the inoculation level of 20,000 eggs/100 cm³ soil, the average egg density for the three pennycress genotypes was 6,668 eggs/100 cm³ soil, lower than that for ‘Sturdy’ (40,740 eggs/100 cm³ soil). The inoculation level did not affect plant biomass. Pennycress is an alternative host to SCN under greenhouse conditions but is a less suitable host than soybean.     

Trichogramma chilonis Ishii: A potential biological control agent of Crocidolomia pavonana in Samoa

Crocidolomia pavonana F. (Lepidoptera: Crambidae) is a major pest of Brassica crops in tropical and sub-tropical regions of Africa, Asia and the Pacific. There are no previous reports of effective natural enemies of the pest across this range but in Samoa an arrhenotokous population of the generalist egg parasitoid Trichogramma chilonis Ishii (Hymenoptera: Trichogrammatidae) frequently attacks it. This is the first record of T. chilonis in Samoa. A three-year field recruitment study showed that although C. pavonana eggs occurred at all times of the year, their abundance was greatest during drier periods. Parasitism of C. pavonana egg masses by T. chilonis was variable (0–87% of egg masses attacked) but the parasitoid was recovered from eggs collected at all times of the year and it is well established in the major Brassica growing regions of the island of Upolu. When partial lifetables were constructed for C. pavonana, the rate of egg disappearance (likely due to predation and the physical effects of rainfall) ranged from 0 to 0.839 and the marginal rate of mortality due to T. chilonis ranged from 0 to 0.474. When it was present, T. chilonis was the major mortality factor affecting C. pavonana eggs in all but one of the recruitment studies. The historical problems surrounding the identity and species status of T. chilonis are discussed and its host range and distribution in the Asia-Pacific region is reviewed briefly. Finally, the potential of this population of T. chilonis for development as a biological control agent of C. pavonana is considered.     

Suitability assessment of three Trichogramma species in the control of Mythimna separata (Lepidoptera: Noctuidae)

Mythimna separata (Walker) is a serious cosmopolitan pest. Trichogramma species have been used worldwide as biological control agents of lepidopteran pests. However, no data on the control efficiency of Trichogramma species on this pest have been reported. We evaluated the suitability of M. separata eggs for three Trichogramma species, Trichogramma dendrolimi Matsumura, T. ostriniae Pang et Chen and T. japonicum Ashmead, and compared the suitability with that of Corcyra cephalonica (Stainton) eggs. The parasitism rate, development time, emergence rate, female proportion, body size and egg load of female offspring indicated that the M. separata egg is a suitable host for the three Trichogramma species. On the other hand, the non‐emergence rate and the relationship between egg load and body size reflected that M. separata eggs are less suitable for the three Trichogramma species than C. cephalonica eggs. Egg resorption occurred in T. japonicum 4 days after emergence.