Beet Webworm Loxostege Sticticalis Research Articles

Male Ventroposterior Brush Display Increases the Sexual Receptivity of Females in the Gregarious Beet Webworm Loxostege sticticalis (Lepidoptera: Crambidae)

Males of many moths possess scent organs, ranging from simple scales and hair-tufts to complex glands. Males of the gregarious beet webworm Loxostege sticticalis (Lepidoptera: Crambidae) display their ventroposterior brushes (VPBs), located on the eighth abdominal sternite, toward adjacent females and usually maintain this posture until sexually receptive females become available, or the arrival of photophase. The peak period of male L. sticticalis VPB display during the scotophase broadly coincides with that of mating. Our experiments revealed that females exposed to male VPB display increased their calling behavior and were more likely to mate than those exposed to males that did not display their VPBs. Volatile chemicals provide the only reliable sensory modality for intersexual communication in L. sticticalis because all behavioral assays were conducted in a sealed darkroom, thereby eliminating a role for visual signals, and no vibratory signals occurred during VPB displaying. Therefore, odors released from the VPB of male L. sticticalis may act as aphrodisiac signals to conspecific females in order to enhance female receptivity and increase his mating success. Our study indicates that chemical communication in these gregarious moths apparently involves mutually stimulating interactions between female attractant and male courtship pheromones.

DETECTION OF WOLBACHIA IN LARVAE OF LOXOSTEGE STICTICALIS (PYRALOIDEA: CRAMBIDAE) IN EUROPEAN AND ASIAN PARTS OF RUSSIA

Beet webworm Loxostege sticticalis is a notorious pest widely distributed on the territory of Eurasia. Its outbreaks cause severe damage to crops in Russia and China. Here Wolbachia infection is reported for the first time in L. sticticalis. Larvae were sampled in Rostov, Saratov, Irkutsk Regions and Republic of Buryatia in 2005–2013. Primers targeting the wsp gene were used for the PCR screening of Wolbachia. Among 148 larvae, 35 were Wolbachia positive. Wolbachia prevalence rate ranged from 21 to 40 % in the Asian and from 0 to 47 % in the European part of Russia. The combined sample subsets were compared for European versus Asian part of Russia and 2005–2009 versus 2010–2013 timeframes. The prevalence rates of Wolbachia were not significantly different between two parts of Russia, but the endosymbiont presence (estimated for the total dataset) increased with time within the observation period.

Biodiversity of beet webworm microsporidia in Eurasia

The beet webworm Loxostege sticticalis (LS) has eruptive type of population dynamics and high migratory activity. The LS outbreaks are therefore difficult to predict and the pest belongs to the category of highly dangerous pests. However, during periods of depressions this insect is not observed within the most of its range and is very susceptible to infection by pathogens, including various species of microsporidia, some of which are not specific parasites of the order Lepidoptera. The distribution of LS microsporidia in Eurasia is quite extensive. During the study period of LS from 2003 to 2019, we have found 6 species of microsporidia. The parasite list includes not only species known for Lepidoptera such as Nosema sp. and Vairimorpha thomsoni, but also Vairimorpha (Nosema) ceranae as the typical pathogen from Apis mellifera, as well as Endoreticulatus cf poecilimonae, a pathogen similar to Endoreticulatus poecilimonae from Poecilimon thoracicus. Moreover, two isolates from the genus Tubulinosema identified in LS belong to the group of parasites with a very wide host range, including humans. In laboratory experiments, LS proved high sensitivity to microsporidia N. pyrausta from Ostrinia nubilalis and N. tyriae from Tyria jacobaeae. Its susceptibility to Paranosema locustae from Locusta migratoria has also been discovered.

DETECTION OF MICROSPORIDIA INFECTING BEET WEBWORM LOXOSTEGE STICTICALIS (PYRALOIDEA: CRAMBIDAE) IN EUROPEAN PART OF RUSSIA IN 2006–2008

The beet webworm Loxostege sticticalis (L.) is a major insect pest that causes serious damage of agricultural crops in Russia, China and adjacent countries. Microsporidia are obligate intracellular parasites that negatively affect population density of many insect hosts including Lepidoptera. In particular, infection with microsporidia is an important mortality factor for L. sticticalis. Special methodology for the identification of microsporidia associated with terrestrial insects is required. In the present paper we report the results of screening beet webworm moths for microsporidia using two techniques, i.e. light microscopy (LM) and PCR. Adult moths were sampled in 2006–2008 in the European part of Russia: Rostov Region, Krasnodar Territory and Republic of Bashkortostan. Microsporidia infections were detected in insects collected from all sampling sites. Examination of smears by LM showed presence of microsporidian spores in 3.4 % of samples (N=98). PCR analysis of the same dataset was positive in 6.7 % of samples, including those containing and not containing spores. The higher infection rate determined by PCR is likely connected with the fact that only mature spores can be unequivocally identified by LM, whereas PCR also allows detection of otherdevelopmental stages of microsporidia. Partial sequencing of an amplicon from Krasnodar Territory showed its close relatedness to Endoreticulatus poecilomonae from Poecilimon thoracicus Fieber (Orthoptera: Tettigoniidae).

Natural infection of the beet webworm Loxostege sticticalis L. (Lepidoptera: Crambidae) with three Microsporidia and host switching in Nosema ceranae

Three species of Microsporidia were identified from a population of the beet webworm Loxostege sticticalis at prevalence rates of 35, 4, and 3%. The most prevalent parasite (Tubulinosema sp.) was similar to Tubulinosema acridophagus (99.8% ssrDNA sequence similarity) and was also isolated from the parasitoid Lydella thompsoni (Diptera, Tachinidae) that emerged from the beet webworms. In laboratory assays, spores of this Tubulinosema sp. showed an infection rate of up to 80% for both L. sticticalis and Galleria mellonella larvae. The spores were viable after 12months of storage in dried infected cadavers. The second most prevalent parasite was closely related toNosema furnacalis and Nosema granulosis (98.7% similarity). Fresh spores showed a 50% infection rate under laboratory conditions. The third most abundant parasite was identified as the honeybee pathogen Nosema ceranae (100% ssrDNA and 95-100% IGS similarity). In the laboratory, fresh spores of N. ceranae isolated from beet webworm and honey bee were infective to L. sticticalis larvae at the rates of 5 and 2%, respectively.

Molecular Characterization of a Lysozyme Gene and Its Altered Expression Profile in Crowded Beet Webworm (Loxostege sticticalis).

There is growing evidence that insects living in high-density populations exhibit an increase in immune function to counter a higher risk of disease. This phenomenon, known as density-dependent prophylaxis, has been experimentally tested in a number of insect species. Although density-dependent prophylaxis is especially prevalent in insects exhibiting density-dependent phase polyphenism, the molecular mechanism remains unclear. Our previous study demonstrated that the antibacterial activity of lysozyme is important for this process in the beet webworm Loxostege sticticalis. In this study, a lysozyme cDNA from L. sticticalis was cloned and characterized. The full-length cDNA is 1078 bp long and contains an open reading frame of 426 bp that encodes 142 amino acids. The deduced protein possesses structural characteristics of a typical c-type lysozyme and clusters with c-type lysozymes from other Lepidoptera. LsLysozyme was found to be expressed throughout all developmental stages, showing the highest level in pupae. LsLysozyme was also highly expressed in the midgut and fat body. Elevated LsLysozyme expression was observed in L. sticticalis larvae infected by Beauveria bassiana and in larvae reared under crowding conditions. In addition, the expression level of LsLysozyme in infected larvae reared at a density of 10 larvae per jar was significantly higher compared to those reared at a density of l or 30 larvae per jar. These results suggest that larval crowding affects the gene expression profile of this lysozyme. This study provides additional insight into the expression of an immune-associated lysozyme gene and helps us to better understand the immune response of L. sticticalis under crowding conditions.

Molecular detection of Cotesia vestalis (Hymenoptera: Braconidae) in the beet webworm Loxostege sticticalis L. (Lepidoptera: Crambidae)

Genomic DNA samples from larvae of the beet webworm Loxostege sticticalis collected in the south-western Russia were used to amplify mitochondrial cytochrome oxidase unit I (COI) gene. In a small proportion of samples, the sequenced product showed considerable heterogeneity due to admixture of a minor sequence. A preliminary BLAST analysis of a 100-bp-long fragment of this minor sequence showed its maximal similarity to the COI gene region of Cotesia, a genus of braconid larval endoparasitoids of Lepidoptera. An additional primer was designed to specifically amplify ca 300 bp of the COI gene region from Braconidae. As many as seven of 25 samples were positive by PCR. Sequencing of the amplified products in all these samples showed nucleotide sequence identity to the COI region of Cotesia vestalis (Cotesia plutellae) and the presence of two molecular haplotypes among individual parasitoid samples.

The beet webworm Loxostege sticticalis L. (Lepidoptera, Crambidae) in the focus of agricultural entomology objectives: I. The periodicity of pest outbreaks

Analysis of the published data on the population dynamics of the beet webworm Loxostege sticticalis L., including its relation to solar activity, was made. The official statistical data from Russia and China testify to asynchronous outbreaks of the webworm in these countries, which suggests the existence of at least two population systems within the species range, the Euro-Siberian (Russia, Ukraine and Kazakhstan) and Central Asian (China and Mongolia) ones, geographically isolated by mountain systems (Tien Shan, Pamir, Altai, and the Sayan mountains) and deserts and bridged by the narrow East Siberian corridor. The theoretical and applied aspects of this conclusion are discussed, including the necessity for further studying of the population dynamics of this dangerous pest.

The range of the beet webworm Loxostege sticticalis L. (Lepidoptera, Pyraloidea: Crambidae) in the former USSR territory and its subdivision by the number of generations per season

The distribution limits of the beet webworm, Loxostege sticticalis L., with its sustainable development in one, two, three, or four successive generations per season in the former USSR territory were mapped for the first time using routine GIS procedures. The expected number of generations was determined based on the sum of daydegrees (above a threshold of 12°C), critical day length value (14 h), and Selyaninov’s hydrothermal index (> 0.3). The compiled map was in good agreement with that prepared for China (Luo Li-zhi and Li Guang-bo, 1993).

Photoperiodic reaction in the beet webworm Loxostege sticticalis L. (Pyraloidea, Crambidae) from eastern and western parts of its Eurasian range

The beet webworm, Loxostege sticticalis L., is a very dangerous polyphagous insect pest whose outbreaks periodically occur in southern Russia and northern China. The aim of our work was to describe the photoperiodic response of beet webworm populations from western (Krasnodar Territory and Rostov Province) and eastern [Buryatia and China (Hebei Province)] parts of the pest range. The insects were reared under constant photoperiods of 12–18 h and constant temperatures of 19–25°C. Incidence of diapause at different photoperiods did not show any considerable geographic differences, and the critical day length at which 50% of prepupae arrested their development was about 14–15 h in all the populations studied at experimental temperatures. The results obtained agree with the hypothesis on the existence of an area (or areas) where the pest survives during adverse periods and wherefrom it spreads when an outbreak begins (Saulich et al., 1983; Goryshin et al., 1986). Presumably, the larger part of the pest native habitats (to the north of the steppe zone) is occupied by temporary populations, incapable of surviving for long periods without an inflow of migrants from more southerly steppe regions.

Tubulinosema loxostegi sp.n. (Microsporidia: Tubulinosematidae) from the beet webworm Loxostege sticticalis L. (Lepidoptera: Crambidae) in Western Siberia

Adults of beet webworm Loxostege sticticalis were collected in Western Siberia in 2009 and 2010. A microsporidium was found infecting 12 of 50 moths in 2010. The parasite develops in direct contact with host cell cytoplasm, sporogony is presumably disporoblastic. The spores are ovoid, diplokaryotic, 4.2 × 2.4 μm in size (fresh), without a sporophorous vesicle. Electron microscopy showed: (a) tubules on the surface of sporoblasts and immature spores; (b) slightly anisofilar polar tube with 10–14 coils, last 2–3 coils of lesser electron density; (c) bipartite polaroplast with anterior and posterior parts composed of thin and thick lamellae, respectively; (d) an indentation in the region of the anchoring disc; (e) an additional layer of electron-dense amorphous matter on the exospore surface. The spore ultrastructure is characteristic of the genus Tubulinosema . Sequencing of small subunit and large subunit ribosomal RNA genes showed 98–99.6% similarity of this parasite to the Tubulinosema species available on Genbank. A new species Tubulinosema loxostegi sp. n. is established.

Beet Webworm (Lepidoptera: Pyralidae) Migration in China: Evidence From Genetic Markers

Genetic diversity within and among 11 geographic populations of the beet webworm Loxostege sticticalis across five provinces in the northern part of China were evaluated using amplified fragment length polymorphism (AFLP) analysis. Five AFLP primer combinations were used on 88 L. sticticalis samples from different locations, detecting a total of 384 polymorphic and 27 monomorphic fragments. Although extensive genetic diversity occurs among individuals from different geographic populations (P = 93.4%, h = 0.398, I = 0.572), the majority of the genetic diversity is within populations and not between populations (G(ST) = 0.196), which agrees well with the results of analysis of molecular variance (84% of the total genetic variation is within populations), indicating high gene flow (N(M) = 2.046) among natural populations, which are not genetically differentiated. L. sticticalis in northeastern China, northern China, and northwestern China are part of a single large metapopulation. Cluster analyses based on AFLP data were preformed to graphically show groupings between individuals and between populations. Individuals from the same region were not grouped together very well. Eleven subpopulations were clustered into six broad groups, and there was no significant correlation between geographic distance and genetic dissimilarity (r = 0.1236, P = 0.8512). Principle component analysis also indicated a lack of genetic differentiation between the 11 populations. These results indicated that, although high genetic variability existed among individuals, there was little genetic differentiation among geographic populations, which can be explained by the effects of long distance migration of the beet webworm in China and consequent gene flow.

Families of Discrete Distributions Satisfying Taylor's Power Law

Count data in entomological studies can often be described by some form of contagious distribution, such as the negative binomial, Neyman type A, or Polya-Aeppli. These are all clustered Poisson distributions (their distributional forms are given in Section 2), arising when groups of individuals occur at random (i.e., are Poissonian) and individuals within a group have their own distribution. Whilst Pahl (1969) found strong evidence that the negative binomial distribution gives good fits to his 35 samples of data on the chrysomelid beetle Paropsis atomaria, Martin and Katti (1965) fitted a number of distributions to a variety of insect, plant, and animal data, and observed, for instance, that McGuire, Brindley, and Bancroft's (1957) data on the European cornborer Pyrausta nubilalis and Beall's (1940) data on the beet webworm Loxostege sticticalis are fitted well not only by the negative binomial, but also by the Neyman type A and other distributions. In such circumstances the fits given by different distributions are often very similar and the exact choice is not critical (see Kemp and Kemp, 1965). The recent work of Tripathi, Gurland, and Bhalerao (1986) gives further guidance on the choice of appropriate distribution when this is not clearly indicated by the ecological context. The negative binomial, Neyman type A, and Polya-Aeppli distributions all have two parameters. When there are many samples of data in one data set; Anscombe (1949) and Bliss and Owen (1958) suggested fitting a model that is parsimonious in parameters, by keeping one of them constant from sample to sample. Their use of a common exponent parameter, k, when fitting families of negative binomials was criticised by Taylor, Woiwod, and Perry (1979), who considered that k is an unstable parameter whose relationship with aggregation is doubtful. Much empirical evidence has accumulated in support of Taylor's power law