Lipids help double-stranded RNA in endosomal escape and improve RNA interference in the fall armyworm,Spodoptera frugiperda

RNA interference (RNAi) is a valuable method for understanding the gene function and holds great potential for insect pest management. While RNAi is efficient and systemic in coleopteran insects, RNAi is inefficient in lepidopteran insects. In this study, we explored the possibility of improving RNAi in the fall armyworm (FAW), Spodoptera frugiperda cells by formulating dsRNA with Cellfectin II (CFII) transfection reagent. The CFII formulated dsRNA was protected from degradation by endonucleases present in Sf9 cells conditioned medium, hemolymph and midgut lumen contents collected from the FAW larvae. Lipid formulated dsRNA also showed reduced accumulation in the endosomes of Sf9 cells and FAW tissues. Exposing Sf9 cells and tissues to CFII formulated dsRNA caused a significant knockdown of endogenous genes. CFII formulated dsIAP fed to FAW larvae induced knockdown of iap gene, growth retardation and mortality. Processing of dsRNA into siRNA was detected in Sf9 cells and Spodoptera frugiperda larvae treated with CFII conjugated ³²P-UTP labeled dsGFP. Overall, the present study concluded that delivering dsRNA formulated with CFII transfection reagent helps dsRNA escapes from the endosomal accumulation and improved RNAi efficiency in the FAW cells and tissues.     

虫螨腈对草地贪夜蛾幼虫的室内毒力及田间防效

草地贪夜蛾Spodoptera frugiperda(J. E. Smith),是一种广泛存在于美洲的杂食性农业害虫。据报道2019年1月草地贪夜蛾入侵我国云南,截止2019年6月6日,已在全国18个省份的884个县(市、区)监测到发生为害,发生面积342万亩,已经对我国粮食安全造成重大威胁。在2019年5月,在广东省广州市花都区儒林村玉米田开展喷雾和喇叭口点施虫螨腈对草地贪夜蛾幼虫的防治试验以及室内毒力测定试验。试验结果表明,虫螨腈对草地贪夜蛾2龄幼虫具有良好的毒力活性;综合考虑在草地贪夜蛾1～3龄幼虫期,用药量67.5 g.a.i/hm~2、药液量675 L/hm~2常规喷雾效果更佳;在草地贪夜蛾4～6龄幼虫期,用药量22.5 g.a.i/hm~2、药液量225 L/hm~2喇叭口点施效果更佳,且喇叭口点施可以定位定向定量地直接到达草地贪夜蛾为害部位,可减少2/3的农药使用量,达到农药减量增效的目的。该研究结果为拟定草地贪夜蛾应急防控技术方案提供技术支撑和理论依据。     

Spatio-temporal partitioning and sharing of parasitoids by fall armyworm and maize stemborers in Cameroon

Biological invasion is a global concern with species deployed out of native range, the most recent in Africa being the invasion by fall armyworm (FAW) Spodoptera frugiperda J.E. Smith (Lepidoptera: Noctuidae). One of the most mentioned ecological consequences is the capacity of invaders to change native communities' structure. Busseola fusca Fuller (Lepidoptera: Noctuidae) has long been the most destructive pests of maize in Africa. Few or no studies have attempted to look at the interaction between FAW and native maize pests over a cropping cycle for sustainable management. Maize trials were established over two cropping cycles in Cameroon to investigate the nature of such interactions and eventual sharing of parasitoids. FAW incidence decreased with maize growth, while the reverse was observed for stemborers. Few cases of co-occurrence were recorded at the later maize growth stage. There was a clear indication that FAW infestation was associated with vegetative stages, while stemborers were associated with reproductive stages. Only FAW eggs were found on abaxial and adaxial leaf surfaces, while only stemborer eggs were inside leaf sheaths. Similarly, while larvae of both groups were found in maize whorl and on ears, only FAW larvae were found in closed tassels, while only stemborers were found inside stems. These results are in favour of segregation in time and space in plant colonization by native and invasive pests, which may limit competition and exacerbates damage if no control is provided. The same egg, larval and pupal parasitoids respectively Telenomus remus, Cotesia icipe and Procerochasmias nigromaculatus emerged from isolated FAW and B. fusca eggs, larvae, and pupae. The sharing of parasitoids by both species provides a unique opportunity for augmentative biocontrol.     

The reproduction-flight syndrome and the inheritance of tethered-flight activity in the cotton-bollworm moth, Heliothis armigera

Abstract. To test the hypothesis that the flight activity of Heliothis armigera (Hiibner) (Lepidoptera: Noctuidae) conforms to the 'oogenesis-fiight syndrome', female moths from India and Malawi were flight tested on nights 2, 4 and 6 after eclosion, using a tethered-flight technique. Maximum flight activity in the Indian strain occurred on night 2, that of the Malawian strain was not significantly different on the three nights of flight. This difference is explained by the Indian females reaching reproductive maturity c . 48 h before the Malawian females. The existence of a 'reproduction-flight syndrome' was confirmed by flight testing males and females of different maturity status on the fourth night after eclosion. Immature moths flew significantly more than did either mature-virgin or mature-mated moths. The inheritance of tethered-flight activity in a late-maturing line of Malawian H. armigera was investigated. Significant estimates of heritability, by offspring on mid-parent regressions, were obtained for both the total flight time (0.39 æ 0.083) and the longest flight (0.15 ± 0.058). The significance of such tethered-flight data to noctuid migration in the field is discussed, and the conclusion drawn that the current experimental design does not index migratory flight satisfactorily.     

An Edible-to-insects Calcium Alginate Gel as a Carrier for Entomopathogenic Nematodes

A carrier for entomopathogenic nematodes based on an edible-to-insects calcium alginate gel was developed. The alginate system was produced by external setting through an interaction between an aqueous sodium alginate mixture and calcium ions under acidic conditions. Sodium hexa-metaphosphate was used to control gel formation. Yeast extract used in the gel as a phagostimulant for Spodoptera littoralis larvae improved the insect's relative consumption rate and digestibility. The nematodes in the gel effectively controlled the larvae in a 24-h leaf bioassay, although nematode survival in the gel was ~ 50%. Gels subjected to 31% relative humidity (RH) prior to larval feeding became desiccated and were inedible to insects. However, gels at 61% RH supported larval feeding, although the water loss from the gel due to evaporation from 200-400-mg gel cubes at this humidity exceeded 50%. The gel might be a useful delivery system for nematodes against insects infesting the plant canopy in greenhouses.     

COMPARATIVE EFFECTS OF TWO PHOTOSENSITIVE COMPOUNDS ON SUPEROXIDE DISMUTASE ACTIVITY IN SPODOPTERA LITURA LARVAE*

Abstract Superoxide dismutase activity was detected in the fourth instar larvae of cutworm Spodoptera litura and effects of the two photosensitive compounds, α-terthienyl and the synthesized compound 1-phenyl-4–(3, 4-methylene dioxy) phenyl-diacetylene (signified as compound No. 5), on superoxide dismutase activity, were compared under the specified condition. Results indicated that the near ultraviolet irradiation (300–400 nm) almost had no effect on superoxide dismutase activity in vivo in the control larvae but could decrease superoxide dismutase activity in vitro. After treatment with photosensitive compounds and near ultraviolet irradiation, superoxide dismutase activity in vitro could be enhanced by the two chemicals, with α-terthienyl more effective, while in vivo it was hardly affected by the latter compound but could be inhibited by α-terthienyl. This suggested that the larvae treated by a-terthienyl were more susceptible to light than that by the latter compound whenever in vivo or in vitro. The possible mechanisms of action of the two photo-activated compounds were discussed.     

Induction of 2-cyanoethyl-isoxazolin-5-one as an antifeedant against the tobacco cutworm (Spodoptera litura) by jasmonic acid in sweet pea leaf

ABSTRACT

Although sweet pea (Lathyrus odoratus) beans contain toxic β-aminopropionitrile, the plant itself is readily attacked by insects and is, therefore, protected through the use of pesticides. Consequently, the induction of L. odoratus resistance to insect attack via exogenous treatment is promising for pest control development. Screening of inducible elicitor effects showed that treatment of sweet pea foliage with jasmonic acid (JA) can induce antifeeding-based resistance to tobacco cutworm (Spodoptera litura) larvae. Spectroscopic analysis identified 2-cyanoethyl-isoxazolin-5-one (2-CEIX) as the antifeedant with a half-maximal effective concentration of 33.6 µmol/g fr. wt., i.e., exogenous JA treatment induced antifeeding activity due to the accumulation of 2-CEIX. Moreover, 2-CEIX-induced mortality of S. litura larvae was evaluated by a dipping test and the half-maximal lethal dose was determined to be 5.9 mg/mL. Therefore, 2-CEIX was concluded to be a suitable induced resistance target for elicitors or a lead compound for insecticide development.     

Chemical profiling of polyphenols in extracts from bark of Acacia nilotica (Linn.) and their efficacy against Spodoptera litura (Fab.)

Six different crude extracts from bark powder of an important medicinal plant, Acacia nilotica (L.) were investigated for their toxicity against Spodoptera litura (Fab.). Total phenolic content in six crude extracts was measured. Ultra-High Performance Liquid Chromatography (UHPLC) was also performed for qualitative analysis of six crude extracts which revealed the presence of 11 phenolic compounds. Bioassays conducted with all crude extracts revealed maximum adverse effect with acetone extract. Duration of larval period and total development period was found to be prolonged. Various aberrations were observed in pupae and adults in the form of wrinkled pupae, blackened pupae, bulged out head part of pupae, partially emerged adults and adults with crumpled wings. All nutritional indices viz. RGR, RCR, ECI, ECD and AD decreased with treatment. The findings indicated that A. nilotica had considerable potential in the management of this serious insect pest.     

Simultaneous monitoring of flight and oviposition of individual velvetbean caterpillar moths (by Wales, Barfield & Leppla, 1985): a critique

ABSTRACT. Flight durations of tethered female Anticarsia gemmatalis moths recorded in the laboratory were interpreted by Wales et al. as indicating a capacity for significant inter-reproductive displacements in the field. Indications that their data may not support this conclusion are discussed and evidence is presented that, in tethered Spodoptera exempta , prolonged flights starting early in the night represent migratory behaviour while those of similar durations starting after midnight do not.     

RFLP analysis of genetic variation in North American populations of the fall armyworm moth Spodoptera frugiperda (Lepidoptera: Noctuidae)

A high level of genetic variability was detected in North American fall armyworm (FA W), Spodoptera frugiperda (J. E. Smith), populations by restriction fragment length polymorphism (RFLP) analysis of genomic DNA. In nearly all cases individual larvae could be differentiated using 22 probe-enzyme combinations. Laboratory colonies formed distinct groups based on RFLP analysis. Individuals from a colony of the previously determined ‘rice strain’ formed a group showing obvious deviation in RFLP patterns from the other five populations, which included a population from a ‘com strain’ colony. The results were consistent with previous studies using allozymes which indicated that there are two genetically differentiated forms of the fall armyworm. Diagnostic markers were also found that distinguish these two groups.