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Naturally occurring covert infections in lepidopteran populations can involve multiple viruses with potentially different transmission strategies. In this study, we characterized covert infection by two RNA viruses, Spodoptera exigua iflavirus 1 (SeIV-1) and Spodoptera exigua iflavirus 2 (SeIV-2) (family Iflaviridae) that naturally infect populations of Spodoptera exigua, and examined their influence on susceptibility to patent disease by the nucleopolyhedrovirus Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV) (family Baculoviridae). The abundance of SeIV-1 genomes increased up to ten-thousand-fold across insect developmental stages after surface contamination of host eggs with a mixture of SeIV-1 and SeIV-2 particles, whereas the abundance of SeIV-2 remained constant across all developmental stages. Low levels of SeIV-2 infection were detected in all groups of insects, including those that hatched from surface-decontaminated egg masses. SeIV-1 infection resulted in reduced larval weight gain, and an unbalanced sex ratio, whereas larval developmental time, pupal weight, and adult emergence and fecundity were not significantly affected in infected adults. The inoculation of S. exigua egg masses with iflavirus, followed by a subsequent infection with SeMNPV, resulted in an additive effect on larval mortality. The 50% lethal concentration (LC50) of SeMNPV was reduced nearly 4-fold and the mean time to death was faster by 12 h in iflavirus-treated insects. These results suggest that inapparent iflavirus infections may be able to modulate the host response to a new pathogen, a finding that has particular relevance to the use of SeMNPV as the basis for biological pest control products.

Plant secondary metabolites are crucial in affecting the interactions between insect herbivores and entomoviruses. However, there is limited knowledge regarding the impact of such metabolites on the susceptibility of insect herbivores to entomoviruses. In this study, we adopted the allicin, caterpillars ( Spodoptera exigua ) and nucleopolyhedrovirus (SeMNPV) as a system, and found that allicin significantly increased the mortality of S. exigua larvae infected with SeMNPV by 36.03–59.45% when infected with the virus at a concentration of 2.12 × 10 3 OB·mL −1 . Furthermore, NPV-infected larvae together treated with allicin inhibited the growth and development of larvae, comparing to individual NPV-infected larvae. Notably, we observed a significant enrichment of differentially expressed genes involved in the cytochrome P450-mediated metabolism pathway between the NPV-infected and allicin combined with NPV-treated groups. The silencing of CYP340AA1 through RNA interference significantly increased the mortality of larvae infected with SeMNPV. This investigation indicates that allicin might be a potential candidate for improving the performance of the NPV against insect herbivores and identifies that CYP340AA1 gene is important in this process.

Host behavioural manipulation is a common strategy used by parasites to enhance their survival and/or transmission. Baculoviruses induce hyperactivity and tree-top disease (pre-death climbing behaviour) in their caterpillar hosts. However, little is known about the underlying mechanisms of this behavioural manipulation. A previous study showed that the baculovirus Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV) induced tree-top disease at 3 days post infection in third instar S. exigua larvae and that light plays a key role in triggering this behaviour. Here we investigated the temporal requirements for the presence of light to trigger this behaviour and found that light from above was needed between 43 and 50 h post infection to induce tree-top disease. Infected larvae that were not exposed to light from above in this period finally died at low positions. Exposure to light prior to this period did not affect the final positions where larvae died. Overall we conclude that light in a particular time frame is needed to trigger SeMNPV-induced tree-top disease in S. exigua larvae.

Viral infection can regulate the cell cycle, thereby promoting viral replication. Hijacking and altering the cell cycle are important for the virus to establish and maintain a latent infection. Previously, Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV)-latently infected P8-Se301-C1 cells, which grew more slowly than Se301 cells and interfered with homologous SeMNNPV superinfection, were established. However, the effects of latent and superinfection with baculoviruses on cell cycle progression remain unknown. In this study, the cell cycle profiles of P8-Se301-C1 cells and SeMNPV or Autographa californica multiple nucleopolyhedrovirus (AcMNPV)-infected P8-Se301-C1 cells were characterized by flow cytometry. The results showed that replication-related genes MCM4, PCNA, and BAF were down-regulated (p < 0.05) in P8-Se301-C1 cells, and the S phase of P8-Se301-C1 cells was longer than that of Se301 cells. P8-Se301-C1 cells infected with SeMNPV did not arrest in the G2/M phase or affect the expression of Cyclin B and cyclin-dependent kinase 1 (CDK1). Furthermore, when P8-Se301-C1 cells were infected with SeMNPV after synchronized treatment with hydroxyurea and nocodazole, light microscopy and qRT-PCR analysis showed that, compared with unsynchronized cells and S and G2/M phase cells, SeMNPV-infected P8-Se301-C1 cells in G1 phase induced G2/M phase arrest, and the amount of virus adsorption and intracellular viral DNA replication were significantly increased (p < 0.05). In addition, budded virus (BV) production and occlusion body (OB)-containing cells were both increased at 120 h post-infection (p < 0.05). The expression of Cyclin B and CDK1 was significantly down-regulated at 48 h post-infection (p < 0.05). Finally, the arrest of SeMNPV-infected G1 phase cells in the G2/M phase increased BV production (p < 0.05) and the number of OB-containing cells. In conclusion, G1 phase infection and G2/M arrest are favorable to SeMNPV proliferation in P8-Se301-C1 cells, thereby alleviating the homologous superinfection exclusion. The results contribute to a better understanding of the relationship between baculoviruses and insect cell cycle progression and regulation.

Spodoptera exigua is a polyphagous pest of diverse crops and causes considerable economic losses. The overuse of chemical insecticides for controlling this pest results in insecticide resistance, environmental pollution and toxicity to other non-target organisms. Therefore, a sustainable and efficient way for pest management is urgently required. In this study, laboratory bioassays of eleven commonly used insecticides, the specific entomopathogen of S. exigua (Spodoptera exigua multiple nucleopolyhedrovirus, SeMNPV), and SeMNPV-insecticide combinations against the S. exigua laboratory population and two field populations were tested. Our results indicated that the two field populations had developed resistance to almost half of the tested insecticides, while SeMNPV had good virulence in all populations. Interestingly, the combined use of SeMNPV enhanced the toxicity of the tested insecticides against all populations to a different extent and considerably reduced the insecticide resistance of S. exigua field populations or even recovered the susceptibility to above insecticides. Furthermore, the field trial showed that the combined application of SeMNPV contributed to promoting the control efficacy of emamectin benzonate and chlorfenapyr. These results provide a promising efficient way for pest resistance management and an environmentally friendly approach for controlling S. exigua with the combined application of nucleopolyhedroviruses and insecticides.

Integrated Pest Management (IPM) programs are alternatives to classical pest control through the application of chemical insecticides. IPM goal is to maintain pest populations below economically injurious levels minimizing the use of chemical insecticides. In recent years, research on insect viromes has led to the discovery of many novel viral pathogens in insect pests, some of them producing covert infections that do not cause evident symptoms. However, the impact that these viruses have on the action of natural enemies employed in IPM programs is still unknown. Spodoptera exigua iflavirus 1 (SeIV1) is an RNA virus commonly found in field populations of Spodoptera exigua . In this work, we have analysed the possible impact of those viral infections on the activity of different natural enemies used for the control of this pest. Specifically, we have studied the effects of SeIV1 on susceptibility to entomopathogenic nematodes, fungi, bacteria, and parasitoids. Infections with SeIV1 showed to be compatible with the nematode Steinernema carpocapsae as the infection did not affect the susceptibility or production of new juveniles. Moreover, they are also compatible with the fungus Metarhizium brunneum as the mortality of S. exigua larvae was not affected by the viral infection. Interestingly, infections with SeIV1 increase the susceptibility to Bacillus thuringiensis formulation and increase the mortality caused by the parasitism of Hyposoter didymator . In summary, our results show that the four natural enemies tested are not negatively affected by SeIV1 and their action remains similar or enhanced by the covert infections with this iflavirus.

Three Bacillus thuringiensis strains were isolated from a specific habitat of tropical greenhouses located in the Botanical Garden of Adam Mickiewicz University in Poznań, Poland. The BG11, BG12 and BG15 strains harbour genes encoding a specific set of insecticidal proteins ( cry1Ba , cry1Ia , cry2Ab , vip3Aa )—entirely different from those found in commercial isolates, currently used as bioinsecticides. Despite high genetic similarity of the new strains, each of them produces unique Cry1Ba toxin as a main component of the parasporal crystals. Moreover, the tested entomopathogens contain genetic determinants encoding two types of chitinolytic enzymes ChiA and ChiB. The tested strains display insecticidal activity against two distinct, economically important pest insects, Cydia pomonella L. (Lepidoptera: Tortricidae) and Spodoptera exigua Hübner (Lepidoptera: Noctuidae). However, BG12 and BG15 strains are significantly more active than BG11 towards both pests. The BG12 and BG15 strains can be considered as candidates for the production of new lepidopteran-active bioinsecticides with high potential to augment the existing biocontrol strategies.

Many parasites manipulate host behavior to increase the probability of transmission. To date, direct evidence for parasitic genes underlying such behavioral manipulations is scarce. Here we show that the baculovirus Autographa californica nuclear polyhedrovirus (AcMNPV) induces hyperactive behavior in Spodoptera exigua larvae at three days after infection. Furthermore, we identify the viral protein tyrosine phosphatase (ptp) gene as a key player in the induction of hyperactivity in larvae, and show that mutating the catalytic site of the encoded phosphatase enzyme prevents this induced behavior. Phylogenetic inference points at a lepidopteran origin of the ptp gene and shows that this gene is well-conserved in a group of related baculoviruses. Our study suggests that ptp-induced behavioral manipulation is an evolutionarily conserved strategy of this group of baculoviruses to enhance virus transmission, and represents an example of the extended phenotype concept. Overall, these data provide a firm base for a deeper understanding of the mechanisms behind baculovirus-induced insect behavior.

This study was conducted between 2019-2020 in Erzincan Province Çayırlı District to reveal beneficial and harmful species and the biology of Spodoptera exigua (Hbn.) (Lepidoptera: Noctuidae), which is an important pest in sugar beet cultivation area. The study area designated as “Erzincan Çayırlı Beet Production Area” (EÇPÜA) has many beet cultivation areas. The beet production obtained from these beet fields changes according to the years, but is also noteworthy for both the region and our country. This area, sugar beet does not only bind the farmers to their field and their villages, provide work and employment opportunities to all family members, but it also is an important plant with its by-products all of which are processable. At the end of the study, five different harmful insect species belonging to the orders Orthoptera, Hemiptera, Coleoptera, Lepidoptera and 22 species [Coccinella septempunctata Linnaeus, Hippodamia variegata (Goeze), Psyllobora vigintiduopunctata (Linnaeus), Syrphus sp., Sphaerophoria scripta (Linnaeus), Sphaerophoria turkmenica Bankowska, Eristalinus aeneus (Scopoli), Tipula sp., Cotesia glomerata (Linnaeus), Exeristes roborator (Fabricius), Endromopoda phragmitidis (Perkins), Enicospilus merdarius (Gravenhorst), Exetastes laevigator (Villers), Itoplectis viduata (Gravenhorst), Exetastes laevigator (Villers), Itoplectis viduata (Gravenhorst), Lissonota (Loxonota) histrio (Fabricius,) Lissonota (Loxonota) flavovariegata Lucas, Ophion pteridis Kriechbaumer, Pimpla spuria (Gravenhorst), Scambus nigricans (Thomson), Scambus brevicornis (Gravenhorst), Sinophorus nitidus (Brischke) and Chrysoperla carnea (Stephens)] belonging to the orders Neuroptera, Coleoptera, Diptera and Hymenoptera were determined on the sugar beet plant. Among the pest species, the biology of the Spodoptera exigua (Hbn.), known as \"caradrina\" has been observed and the biological stages of the Agrotis segetum (Schiff.) which is in the secondary pest status have been followed. Damage patterns and densities of other pests (Cassida nebulosa Linnaeus, Aphis fabae (Scopoli), and Gryllotalpa gryllotalpa Linnaeus) were also tried to be revealed. Sinophorus nitidus (Brischke) collected in the study area which belonging to the family Ichneumonidae is determined as our new record for East Anatolia. Bu çalışma 2019-2020 yılları arasında Erzincan İli Çayırlı İlçesi şeker pancarı ekim alanlarında faydalı ve zararlı böcek türleri ile önemli bir zararlı olan Spodoptera exigua (Hbn.) (Lepidoptera: Noctuidae)’nın kısa biyolojisini ortaya koymak için yapılmıştır. “Erzincan Çayırlı Pancar Üretim Alanı” (EÇPÜA), olarak belirlenen çalışma bölgesi pek çok pancar ekim alanına sahiptir. Bu pancar alanlarından yıllara göre değişmekle birlikte elde edilen pancar üretimi de hem bölge hem de ülkemiz için kayda değer durumdadır. Bu bölgede şeker pancarı, çiftçileri tarlalarına ve köylerine bağlamakla kalmayıp, tüm aile bireylerine iş ve istihdam olanağı sağlayan, aynı zamanda tamamı işlenebilir yan ürünleriyle de değerli bir bitki durumundadır. Çalışma sonucunda, pancar bitkisinde Orthoptera, Hemiptera, Coleoptera ve Lepidoptera takımlarına ait beş zararlı, Neuroptera, Coleoptera, Diptera ve Hymenoptera takımlarına ait 22 yararlı tür [Coccinella septempunctata Linnaeus, Hippodamia variegata (Goeze), Psyllobora vigintiduopunctata (Linnaeus), Srypus sp., Sphaerophoria scripta (Linnaeus), Sphaerophoria turkmenica Bankowska, Eristalinus aeneus (Scopoli), Tipula sp., Cotesia glomerata (Linnaeus), Exeristes roborator (Fabricius), Endromopoda phragmitidis (Perkins), Enicospilus merdarius (Gravenhorst), Exetastes laevigator (Villers), Itoplectis viduata (Gravenhorst), Exetastes laevigator (Villers), Itoplectis viduata (Gravenhorst), Lissonota (Loxonota) histrio (Fabricius,) Lissonota (Loxonota) flavovariegata Lucas, Ophion pteridis Kriechbaumer, Pimpla spuria (Gravenhorst), Scambus nigricans (Thomson), Scambus brevicornis (Gravenhorst), Sinophorus nitidus (Brischke) and Chrysoperla carnea (Stephens)] tespit edilmiştir. Zararlı türlerin arasında halk arasında “karadrina” olarak bilinen Spodoptera exigua (Hbn.)’nın bölgedeki biyoloji ile ilgili gözlemler yapılmış, sekonder zararlı durumunda olan Agrotis segetum (Schiff.)’un biyolojik dönemleri takip edilmiştir. Tespit edilen diğer zararlıların (Cassida nebulosa Linnaeus, Aphis fabae (Scopoli) ve Gryllotalpa gryllotalpa (Linnaeus) da zarar şekilleri ve yoğunlukları belirlenmeye çalışılmıştır. Çalışma alanından atrapla toplanan yararlı türlerden Ichneumonidae familyasına ait Sinophorus nitidus (Brischke) türü çalışma bölgesi için yeni kayıttır.

The interaction between the mirid predator Engytatus varians (Distant) and a Mexican isolate (SeSIN6) of Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV) was examined under laboratory conditions. In a choice test, E. varians females and males demonstrated no preference for virus-infected Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) second instar compared with non-infected at two different post-inoculation times (48 and 72 h). Similarly, prey search time (5–6 h) did not differ significantly for each type of prey. Bioassays were performed to confirm the viability of occlusion bodies (OBs) from predator’s faces collected at 48, 96, and 144 h after exposure to virus-infected S. exigua larvae. The proportion of larval mortality was between 0.20 and 0.62 across all times and both E. varians sexes. Another experiment was performed to evaluate the dispersal of SeSIN6 OBs by physical contact with E. varians adults on tomato ( Solanum lycopersicum Miller) leaflets treated with the pathogen. Engytatus varians adults were exposed to OB-treated tomato leaflets during 24 or 48 h using a clip cage. After each exposure time, these adults were removed and placed on clean uncontaminated leaflets for periods of 4–48 h. These leaflets were then exposed to groups of S. exigua second instars in clip cages. The proportion of virus-induced larval mortality of S. exigua (ranging from 0.45 to 1.0) was significantly affected by the duration of exposure of E. varians adults on OB-treated or untreated tomato leaflets. Our results reveal the potential of E. varians as an agent for the dispersal of SeMNPV OBs.