Tradeoff between triglyceride consumption and ovariole development in Plutella xylostella(L.) released in mixed-host environments

After exposure to mixed environments with multiple hosts, the frequency of flight take-offs for Plutella xylostella(L.) is known to increase with a concomitant decrease in female fecundity. The objective of the present study was to elucidate the physiological mechanism underlying the increased flight activity and decreased fecundity of P. xylostella in mixed-host environments. We measured ovariole length, and triglyceride and vitellogenin(Vg) content in P. xylostella females after they were released into different host environments consisting of either a single host(Brassica campestris, Brassica oleracea or Brassica juncea) or a mixture of all three hosts. Our results indicated that ovariole length varied significantly between female adults from different host environments. Females from the B. campestris environment had the longest ovarioles, whereas those from the mixed environment had the shortest ones. A negative correlation was found between ovariole length and the flight take-off frequency of P. xylostella adults. Additionally, there were significant differences in the triglyceride content of P. xylostella females from different host environments. Our data revealed that more triglyceride was consumed by P. xylostella female adults from B. oleracea and the mixed environments than those from environments containing only B. campestris or B. juncea. In contrast, the relative Vg content in P. xylostella females from the mixed environment was lower than that in females from the B. campestris-, B. juncea-or B. oleracea-only environments. In conclusion, the mixed environment caused increased consumption of available energy resources(triglyceride) at the cost of retarding ovarian development and decreasing the amount of Vg produced.

Identification of chorion genes and RNA interference-mediated functional characterization of chorion-1 in Plutella xylostella

Choriogenesis is the last step of insect oogenesis,a process by which the chorion polypeptides are produced by the follicular cells and deposited on the surface of oocytes in order to provide a highly specialized protective barrier to the embryo.The essential features of chorion genes have yet to be clearly understood in the diamondback moth,Plutella xylostella,a worldwide Lepidoptera pest attacking cruciferous crops and wild plants.In this study,complete sequences for 15 putative chorion genes were identified,and grouped into A and B classes.Phylogenetic analysis revealed that both classes were highly conserved and within each,branches are also species-specific.Chorion genes from each class were located in pairs on scaffolds of the P.xylostella genome,some of which shared the common promoter regulatory region.All chorion genes were highly specifically expressed in the P.xylostella adult females,mostly in the ovary with full yolk,which is a crucial period to build the shells of the eggs.RNAi-based knockdown of chorion-1,which is located on the Px_scaffold 6 alone,although had no effect on yolk deposition,resulted in smaller eggs and sharply reduced hatchability.Additionally,inhibition of PxCho-1 expression caused a less dense arrangement of the columnar layers,reduced exochorion roughness and shorter microvilli.Our study provides the foundation for exploring molecular mechanisms of female reproduction in P.xylostella,and for making use of chorion genes as the potential genetic-based molecular target to better control this economically important pest.

Antifeedant Activity and Active Ingredients Against Plutella xylostella from Momordica charantia Leaves

With the bioguided fractionation of the ethanol extracts from the leaves of Momordica charantia, we obtained two most active compounds against the feeding of the diamondback moth, Plutella xylostella larvae. The antifeedant activity of momordicine Ⅰ and momordicine Ⅱ against the second and the third instar larvae of Plutella xylostella were tested using leaf discs of cabbage in the laboratory. The results showed that momordicin Ⅰ and momordicin Ⅱ had significant antifeedant activity on the larvae of P. xylostella, and momordicin Ⅱ was more active than momordicin Ⅰ. The concentrations for 50% antifeedant effects （AFC50） of momordicin Ⅱ against the second and the third instar larvae of P. xylostella were 76.69 and 116.24μg mL^-1, whereas that of momordicin I was 144.08 and 168.42μg mL^-1, respectively. In addition, momordicin Ⅰ and momordicin Ⅱ had significant inhibitive effect on the rate of weight gain and survival of P. xylostella larvae.

Electroantennogram and behavioral responses of Cotesia plutellae to plant volatiles

Plant volatiles have been demonstrated to play an important role in regulat- ing the behavior of Cotesia plutellae, a major larval parasitoid of the diamondback moth （DBM）, Plutella xylostella, but little is currently known about the function of each volatile and their mixtures. We selected 13 volatiles of the DBM host plant, a cruciferous veg- etable, to study the electroantennogram （EAG） and behavioral responses of C. plutellae. EAG responses to each of the compounds generally increased with concentration. Strong EAG responses were to 100 μL/mL of trans-2-hexenal, benzaldehyde, nonanal and cis-3- hexenol, and 10/zL/mL of trans-2-hexenal and benzaldehyde with the strongest response provoked by trans-2-hexenal at 100μL/mL. In the Y-tube olfactometer, C. plutellae, was significantly attracted by 1μL/mL of trans-2-hexenal and benzaldehyde.β-caryophyllene, cis-3-hexenol or trans-2-hexenal significantly attracted C. plutellae at 10μL/mL, while nonanal, benzyl alcohol, cis-3-hexenol or benzyl cyanide at 100μL/mL significantly at- tracted C. plutellae. Trans-2-hexenal significantly repelled C. plutellae at 100 μL/mL. EAG of C. plutellae showed strong responses to all mixtures made of five various com- pounds with mixtures 3 （trans-2-hexenal, benzaldehyde, nonanal, cis-3-hexenol, benzyl cyanide, farnesene, eucalyptol） and 4 （trans-2-hexenal, benzaldehyde, benzyl alcohol, （R）- （＋）-limonene,β-ionone, farnesene, eucalyptol） significantly attracting C. plutellae. These findings demonstrate that the behavior of C. plutellae can be affected either by individual compounds or mixtures of plant volatiles, suggesting a potential of using plant volatiles to improve the efficiency of this parasitoid for biocontrol ofP. xylostella.

Transcriptomic analysis of epigenetic modification genes in the termite Reticulitermes speratus

Eusocial insects display a caste system in which different castes are morpho-logically and physiologically specialized for different tasks.Recent studies have revealed that epigenetic modifications,including DNA methylation and histone modification,me-diate caste determination and differentiation,longevity,and polyethism in eusocial insects.Although there has been a growing interest in the relationship between epigenetic mech-anisms and phenotypic plasticity in termites,there is ltte information about differential expression levels among castes and expression sites for these genes in termites.Here we show royaltissuc-specific expression of epigenetic modification genes in the termite Reticulitermes speratus.Using RNA-seq,we identified 74 genes,including three DNA methyltransferases,seven sirtuins,48 Trithorax group proteins,and 16 Polycomb group proteins.Among these genes,15 showed king-specific expression,and 52 showed age-dependent differential expression in kings and queens.Quantitative real-time PCR revealed that DNA methyltransferase 3 is expressed specifically in the king's testis and fat body,whereas some histone modification genes are remarkably expressed in the king's testis and queen's ovary.These findings imply that epigenetic modification plays important roles in the gamete production process in termite kings and queens.

Invasion history of Solenopsis invicta （Hymenoptera： Formicidae） in Fujian, China based on mitochondrial DNA and its implications in development of a control strategy

One of the most invasive species worldwide, Solenopsis invicta Buren, has been described in China since 2003. Recent studies have suggested that China populations are the result of introductions from the USA; however, detailed molecular studies need to be performed in order to understand the expansion and potential multiple introductions from other countries into China. As there were populations of red imported fire ant, S. invicta in different areas and with different methods of introduction, mitochondrial cytochrome oxidase Ⅰ gene was used as a marker from 12 populations in four cities in Fujian Province, China, to determine the relationship of invasion among these populations. The three most common haplotypes previously describe in invasive populations of S. invicta： H5, H22 and H36, were found in Fujian. However, frequencies in each city were different. For instance, three populations from Longyan city which invaded with waste plastics, shared haplotype H5. Populations from Xiamen city and Jinjiang city which dispersed with nursery stock, sward and scrap leather, shared haplotype H22. The population from Nanyan village of Xinluo district, Longyan city, bore haplotype H36. Mitochondrial data reveals that the invasion history of S. invicta in Fujian Province is complex, including multiple invasions probably from other provinces within China. Security measures to prevent S. invicta spreading within China are as important as from overseas.

Chinese species of the genus Prochiloneurus Silvestri with description of a new species(Hymenoptera: Encyrtidae)

Four species of the genus Prochiloneurus Silvestri, belonging to the family Encyrtidae of Hymenoptera, are reported from China. Among them, P. stenopterus sp. nov., which is reared as the hyperparasitoid of Phenacoccus solenopsis Tinsley （Hemiptera： Pseudococcidae）, an invasive mealybug to China, is reported as new to science. A key of the genus is provided for the recognition of the females of Chinese species. Notes on the parasitoid and hyperparasitoid of the mealybug Phenacoccus solenopsis are provided.

Estimating index of population trend by re-sampling techniques （jackknife and bootstrap） and its application to the life table study of rice leaf roller, Cnaphalocrocis medinalis （Lepidoptera： Pyralidae）

Taking a published natural population life table of rice leaf roller, Cnaphalocrocis medinalis （Lepidoptera： Pyralidae）, as an example, we estimated the population trend index, I, via re-sampling methods （jackknife and bootstrap）, determined its statistical properties and illustrated the application of these methods in determining the control effectiveness of bio- agents and chemical insecticides. Depending on the simulation outputs, the smoothed distribution pattern of the estimates of I by delete-1 jackknife is visually distinguishable from the normal density, but the smoothed pattern produced by delete-d jackknife, and logarithm- transformed smoothed patterns produced by both empirical and parametric bootstraps, matched well the corresponding normal density. Thus, the estimates of I produced by delete-1 jackknife were not used to determine the suppressive effect of wasps and insecticides. The 95% percent confidence intervals or the narrowest 95 percentiles and Z-test criterion were employed to compare the effectiveness of Trichogrammajaponicum Ashmead and insecticides （powder, 1.5% mevinphos ＋ 3% alpha-hexachloro cyclohexane） against the rice leaf roller based on the estimates of I produced by delete-d jackknife and bootstrap techniques. At a = 0.05 level, there were statistical differences between wasp treatment and control, and between wasp and insecticide treatments, if the normality is ensured, or by the narrowest 95 percentiles. However, there is still no difference between insecticide treatment and control. By Z-test criterion, wasp treatment is better than control and insecticide treatment with P-value 〈 0.01. Insecticide treatment is similar to control with P-value 〉 0.2 indicating that 95% confidence intervals procedure is more conservative. Although similar conclusions may be drawn by re-sampling techniques, such as the delta method, about the suppressive effect of trichogramma and insecticides, the normality of the estimates can be checked and guaranteed, and the correlation among sequential life stages of rice leaf roller is also considered in the estimation. Judged by the P-values from Z-test, the delta method is more conservative.

Comparing salinity tolerance in embryonic and larval development of two species of water strider, Aquarius paludum and Gerris latiabdominis （Hemiptera： Gerridae）

Water strider Aquarius paludum （Fabricius） is a cosmopolitan species colonizes mainly freshwater but occasionally brackish habitats throughout the Palearctic and Oriental regions. Water strider Gerris latiabdominis （Miyamoto） is a common species in Japan lives in temporary habitats as freshwater paddy fields. These two species often occur syntopically. We investigated differences in the developmental response to brackish water during embryonic and larval stages between the two species. Eggs were exposed to 0-1.8% NaC1 solutions within 24 h of oviposition. Larvae of G. latiabdominis were exposed to salinities of 0, 0.5%, and 0.9% from the first instar until adult emergence. Limits of NaC1 concentration for hatching were 1.3% and 1.0% for A. paludum and G. latiabdominis, respectively. The hatching rate of G. latiabdominis was lower than that ofA. paludum at salinities 〉0.9%. The period of embryonic development of G. latiabdominis was more prolonged than that ofA. paludum at a given salinity. Although the salinity tolerance of G. latiabdominis was lower than that ofA. paludum, our results suggest G. latiabdominis has the physiological capacity to expand into brackish waters. High and low salinity tolerances of A. paludum and G. latiabdominis, respectively, reflect the relatively wide range of habitat salinities utilized by A. paludum and the relatively restricted habitats preferred by G. latiabdominis. The high salinity tolerance ofA. paludum could be an important factor contributing to their cosmopolitan distribution because high tolerance to salinity means the possibility of them to be dispersed via ocean or sea to other continents and islands.