草地贪夜蛾成虫复眼明暗适应及黄光照射下明适应状态转化率

【目的】蛾类昆虫的趋光性与复眼明暗适应状态的转化有着直接的关系，本研究旨在阐明光照与草地贪夜蛾Spodotera frugiperda复眼明暗适应状态转化的关系。【方法】在光、暗适应条件和不同光照强度黄光照射下，在不同时间段，用相机迅速拍照，观察统计草地贪夜蛾成虫复眼的明暗适应状态及明、暗适应状态转化率。【结果】在明适应状态下，草地贪夜蛾成虫经黄光照射1 h后，随光照强度的增加，复眼明适应状态保持率逐步升高：雄成虫复眼在0.1~0.5 lx时明适应状态保持率为67.77%(有32.23%的转化为暗适应状态与中间状态)，4~6 lx时明适应状态保持率达到100%；雌成虫复眼在7~10 lx时，明适应状态保持率达98.90%。在明适应状态下，经黄光照射3 h后，草地贪夜蛾成虫复眼明适应状态保持率亦随着光照强度的增加逐步升高，在0.1~0.5 lx时雄成虫复眼明适应状态保持率为50.00%,雌成虫为32.23%；在光照强度7~10 lx时，雌雄成虫复眼明适应状态保持率分别为90.00%和100%。在暗适应状态下，草地贪夜蛾成虫经不同光照强度的黄光照射30 min后，成虫复眼向明适应状态逐渐转化：在0.1~0.5 lx光照强度时雌、雄成虫复眼明适应状态转化率均为93.33%；当光照强度达到0.6~0.9 lx时雌成虫复眼的明适应状态转化率达到100%，雄成虫复眼则在1~2 lx时达到100%。【结论】结果说明，草地贪夜蛾成虫有较强的光敏感性，且雌虫对黄光的光敏感性略强于雄虫。     

Can plants mediate the humoral immunity and biochemical metabolism of entomopathogen‐infected caterpillars?

Plant‐insect herbivore‐entomopathogen interactions are one of the hot topics in biological control and humoral immunity, and biochemical metabolism are important responses of herbivores to pathogen infection. Entomopathogens are key biocontrol agents of caterpillars, but how plants affect the responses of caterpillars to these organisms is not well understood. We studied hormonal immunity (lysozyme and phenoloxidase activities) and biochemical metabolism (total protein and lipid contents) of Beauveria bassiana‐infected beet armyworm (Spodoptera exigua) larvae that feed on five different host plants (soya bean, Chinese cabbage, edible amaranth, water convolvulus and pepper). Results indicated that plant species differentially affected lysozyme and phenoloxidase activity and lipid content, but had no effect on protein content of pathogen‐infected caterpillars. Both lysozyme and phenoloxidase activities were generally higher in entomopathogen‐infected larvae that feed on edible amaranth or water convolvulus compared with the other three plants from days 1 to 5 after treatment. Plant species did not affect in regular changes during the 5 days in the lipid content of infected or non‐infected caterpillars. Our study reveals that plants fail to affect the biochemical metabolism but plants can mediate the humoral immunity of caterpillars to defend against pathogens. This study provides insight into plant‐mediated effects on the response of herbivores to pathogens.     

Epizootics of Entomophthora aulicae in lepidopterous pests of sorghum

Entomophthora aulicae caused 48–100% mortality in Heliothis zea larvae collected from sorghum August 24–September 6, 1978, in Tift County, Georgia. The same fungus also caused 74 and 95% mortality in Celama sorghiella larvae and 19 and 40% mortality in Spodoptera frugiperda larvae collected from sorghum August 30 and September 6 in the same area. Only 2 of 94 H. virescens larvae collected from a nearby patch of pigeon peas were killed by the fungus. This is the first report of epizootics caused by E. aulicae in pests of field crops in the southeastern United States.     

The effect of natural sunlight on Spodoptera littoralis nuclear polyhedrosis virus

The effect of natural sunlight on Spodoptera littoralis (Boisduval) nuclear polyhedrosis virus (NPV) in Egypt was investigated. Wavelengths between 300 and 320 nm were shown to be responsible for almost all of the inactivation attributed to sunlight, although there was some deleterious effect of wavelengths between 320 and 400 nm and above 665 nm. When NPV was exposed to wavelengths between 400 and 665 nm in addition to wavelengths above 665 nm, no inactivation occurred. A simple linear regression equation relating solar UV dose below 320 nm to inactivation of NPV was obtained based on several experiments carried out over a 4‐year period. The survival curve follows the pattern of a single—hit, single—target model. The relationship also could be described as a bisegmented curve and it was concluded that this might be due to a proportion of the virus being inherently more stable to inactivation by sunlight or that two reactions are involved in the inactivation process.     

Possible role for covalent modification in the reversible activation of ecdysone 20-monooxygenase activity

Evidence is presented for the reversible activation-inactivation of the microsomal ecdysone 20-monooxygenase from fat body of the cotton leafworm, Spodoptera littoralis, in a manner commensurate with reversible changes in its phosphorylation state. The activity of the monooxygenase was higher following preincubation with fluoride (an inhibitor of phosphoprotein phosphatases) than in its absence. Preincubation with alkaline phosphatase or with cAMP-dependent protein kinase resulted in appreciable diminution or enhancement, respectively, in monooxygenase activity. Activation of ecdysone 20-monooxygenase activity could also be effected by incubation with a cytosolic fraction in the presence of cAMP, ATP, and fluoride; this activation was prevented by a cAMP-dependent protein kinase inhibitor. Similarly, inactivation of the monooxygenase was achieved by preincubation with cytosol, the effect being enhanced by Ca²⁺-calmodulin or by Mg²⁺ ions. The combined results provide indirect evidence that the microsomal ecdysone 20-monooxygenase exists in an active phosphorylated form and an inactive dephosphorylated form, interconvertible by a cAMP-dependent protein kinase and a phosphoprotein phosphatase.     

Effect of nucleopolyhedrovirus infection of Spodoptera litura larvae on host discrimination by Microplitis pallidipes

The behaviour and oviposition of solitary endoparasitoid Microplitis pallidipes Szepligeti (Hymenoptera: Braconidae) were monitored to investigate the ability of the parasitoids to distinguish between nucleopolyhedrovirus (NPV)-infected and noninfected Spodoptera litura Fabricius (Lepidoptera: Noctuidae) larvae. The results indicated that the parasitoid searching time and the time until the first parasitoid attack on infected larvae were greater than those recorded on noninfected larvae; the number of infected larvae attacked by parasitoids, the percent of first attacks and parasitism rate in infected larvae were lower than those on noninfected larvae; and these differences were all significant 3 to 5 days postexposure of the larvae to a dose of 1.6 × 10⁸ occlusion bodies (OB)· ml^?1 and significant 4 and 5 days postexposure of the larvae to a dose of 1.6 × 10⁷ OB·ml^?1. The lowest dosage (1.6 × 10⁶ OB·ml^?1) had no significant effect on the above index values. In a field cage experiment, we found that the percentage of infected larvae parasitized by M. pallidipes gradually decreased as the time after NPV inoculation (1.6 × 10⁸ OB·ml^?1) increased, and that M. pallidipes significantly preferred to oviposit in healthy larvae from day 3 to day 5 after virus inoculation. Our research concluded that this parasitoid's ability to discriminate between healthy and infected hosts increased as virus concentration increased and as the time between exposure of hosts to virus and subsequent exposure to parasitoids increased.     

Campoletis sonorensis [Hym.: Ichneumonidae] as a parasitoid ofSpodoptera frugiperda [Lep.: Noctuidae]: Host stage preference and functional response

The response of the parasitoidCampoletis sonorensis (Cameron) as a natural control agent of the fall armyworm,Spodoptera frugiperda (J. E. Smith), was evaluated at 6 host densities and 2 temperature regime. A type-II functional response was exhibited by femaleC. sonorensis in response to varying densities of all armyworn larvae at both temperatures. Significantly more larvae were parasitized at 25°C for the host densities of 60 and 75, than for the same densities at 30°C. Third instar fall armyworm larvae were found to be the preferred stage for parasitization byC. sonorensis. This research was supported by funds from HATCH project no. H-368 as allocated to the Georgia Agricultural Experiment Station.     

Spodoptera litura cyclophilin A is required for Microplitis bicoloratus bracovirus‐induced apoptosis during insect cellular immune response

Microplitis bicoloratus bracovirus (MbBV) is a polydnavirus found in the parasitic wasp M. bicoloratus. Although MbBV is a known inducer of apoptosis in host hemocytes, the mechanism by which this occurs remains elusive. In this study, we found that expression of cyclophilin A (CypA) was significantly upregulated in Spodoptera litura hemocytes at 6‐day post‐parasitization. Similar results were reported in High Five cells (Hi5 cells) infected by MbBV, suggesting that the upregulation of CypA is linked to MbBV infection in insect cells. cDNA encoding CypA was cloned from parasitized hemocytes of S. litura, and bioinformatic analyses showed that S. litura CypA belongs to the cyclophilin family of proteins. Overexpression of S. litura CypA in Hi5 cells revealed that the protein promotes MbBV‐induced apoptosis in vitro. Conversely, suppression of the expression and activity of CypA protein significantly rescued the apoptotic phenotype observed in MbBV‐infected Hi5 cells, suggesting that it plays a key role in this process. MbBV infection also promoted the cytoplasmic‐nuclear translocation of CypA in Hi5 cells. Taken together, these results suggest that MbBV infection upregulates the expression of CypA, which is required for MbBV‐mediated apoptosis. Our findings provide insight into the role that CypA plays in insect cellular immune response.