Asha Thomas

Detection and Localization of Rickettsia sp in Mealybug

ABSTRACT Mealybug, Phenacoccus solenopsis Tinsley, is a sap-sucking hemipteran insect. It is an agricultural pest that is now widely distributed in India. In this study we report the presence of Rickettsia from P. solenopsis. We constructed a 16S rRNA gene library to study the bacterial diversity associated with this insect and we found that all the clones from the library were only of Candidatus Tremblaya phenacola. This study also highlights that the normal protocol adopted to study the bacterial diversity from environmental sample, by preparation of a 16S rRNA gene library, does not work when the bacterial population is highly skewed in favor of one bacteria (primary endosymbiont in this case). Hence, we used bacterial genus specific polymerase chain reaction primers to test the presence of any of the widely known secondary endosymbionts associated with insects. We tested for the presence of Cardinium, Rickettsia, Wolbachia, and Arsenophonus in P. solenopsis collected from 10 different locations across India. Only Rickettsia was detected from four locations while we were not able to find any other bacteria. We confirmed the presence of these bacteria by localizing Rickettsia and the primary endosmbiont, Candidatus Tremblaya sp. to the bacteriocyte of P. solenopsis using fluorescent in situ hybridization.

Bemisia tabaci (Hemiptera: Aleyrodidae) Species Complex From Cotton Cultivars: A Comparative Study of Population Density, Morphology, and Molecular Variations

ABSTRACT Morphological and molecular variations of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) on cotton cultivars having varying trichome density were evaluated at New Delhi, India. The study evaluates the role of host plant nature on puparia and putative species groups of the B. tabaci species complex. More specifically, the study was done to explore the host plant characters and their effect on the population density, morphology of the puparia, and to identify the putative species groups of the B. tabaci species complex occurring on cotton. Population density was observed to be higher in cultivars with less trichome density. Studies on the puparia showed statistically significant variations on different cotton cultivars (P < 0.01), which was supported by scattergraphs derived from principal components and canonical discriminant analysis. Statistical analysis revealed the influence of trichome density on population density of B. tabaci. Sequence analyses using mitochondrial cyctochrome oxidase I confirmed the presence of three putative species Asia 1, Asia II 1, and Asia II 7 on the cultivars of cotton. The current study revealed that genetic variation is not influenced the variations in the trichome density and morphological variation.

Bemisia tabaci (Hemiptera: Aleyrodidae) on Leucaena leucocephala (Fabaceae): a new host record from India and a comparative study with a population from cotton

Biology, morphometrics and analyses of non-specific esterases were carried out for populations of Bemisia tabaci (Gennadius) collected from leucaena [Leucaena leucocephala (Lam.) de Wit] in New Delhi, India and compared with those for cotton populations. The developmental periods of the egg, and the first to fourth instars of the leucaena populations were 6.7 ± 0.18,4.2 ± 0.18,3.8 ± 0.14,3.0 ± 0.0 and 5.2 ± 0.18 days, respectively, with a total life-cycle duration of 22.9 ± 0.58 days; fecundity (62.60 ± 61.53 eggs per female) and longevity (male: 13.50 ± 0.12 days, female: 16.50 ± 0.12 days) were higher than those recorded for the cotton population, with a sex ratio (male:female) of 1:3.7 in cotton and 1:4 in leucaena. Morphometrics revealed significant differences in the length of egg, second, third and fourth instars (P < 0.05). Of the 62 measurements of the puparia analysed, 70% of those of the head, 44% of those of the thorax and 51% of those of the abdomen showed significant differences between the cotton and leucaena populations. Mapping of the host association of samples onto principal component ordination showed their significant separation according to host plants, with the first three principal components accounting for 66% of the total variation. The analysis of non-specific esterases showed two bands at Rm E0.18 and E0.23 in the cotton populations but not in the leucaena populations. So far, B. tabaci is known on leucaena only from Taiwan. The present study reports it as a new host record from India in addition to documenting the biology morphometries and esterases of this and a cotton population.

HOST CORRELATED MORPHOMETRIC VARIATIONS IN THE POPULATIONS OF BEMISIA TABACI (GENNADIUS) (HEMIPTERA: ALEYRODIDAE)

Abstract Morphometrics by way of univariate and multivariate statistical analyses undertaken on the four populations of Bemisia tabaci (Gennadius) from brinjal, cotton, okra and soybean from Delhi establish that these are morphologically distinct entities showing significant variations in the taxonomic characters currently in use for defining this species. Taking into account the diagnostic features of B. tabaci, and the conclusions obtained through univariate statistical analyses, 32 characters were chosen for morphometrics in case of puparia and 8 in case of adults. Both univariate and multivariate analyses concluded that these four populations vary morphologically and statistically to a significant extent in their taxonomic characters, and are thus phenotypically distinct populations. The adult and puparia morphometrics strongly confirm that populations from soybean are significantly distinct without much overlap with other three populations. Similar trend was observed in case of populations from okra and brinjal while populations from cotton alone were significantly overlapping with the other three populations. These analyses conclude that B. tabaci exhibits a wide range of host correlated, intraspecific and morphological variations. These also establish that characters from puparia are consistent and preferable for distinguishing these intraspecific populations.

Multiple Gene Markers to Understand Genetic Diversity in the Bemisia tabaci (Hemiptera: Aleyrodidae) Species Complex

Abstract The analysis of sequence variation in the mitochondrial and ribosomal regions has been shown to provide an efficient method for the identification of species in a wide range of animal taxa. In order to assess its effectiveness in the discrimination of genetic groups of Bemisia tabaci (Gennadius) species complex, populations from ten cotton cultivars were analyzed. MtCOI, and ITS1 sequences were evaluated to find out the genetic diversity through phylogenetic methods, viz., maximum likelihood and network neighbor-net analysis. Analysis of mtCOI-1 or barcoding region did not reveal significant variation. On the contrary, the mtCOI-II region revealed the presence of three B. tabaci genetic groups or subgroups corresponded with the global data. However, the ITS1 region could not discriminate these groups of the species complex. Our results indicate that more than the barcoding and ITS1 regions, mtCOI-II region or 3′ end of the gene will be more appropriate for the identification of variations among the populations of B. tabaci species complex.

Biology, morphology and DNA barcodes of Tessaratoma javanica (Thunberg) (Hemiptera: Tessaratomidae).

Tessaratoma javanica (Thunberg) (Hemiptera: Tessaratomidae) an important sucking pest of litchi is studied for supplementing information on its biology, morphometrics of life stages and mtCOI (DNA barcodes). More details generated on the study add to the description of stages namely egg, 1st to 5th nymphal instars and adults. The evaluation of morphometrics of the life stages reveal that the progression of growth is more during 2nd to 3rd nymphal stages, and these are critical as far as the growth and development is concerned. The life cycle takes about 141.7±4.25 days; eggs last for 12.81±1.4 days with 97.14±2.86% hatchability; and duration of 1st , 2nd, 3rd, 4th and 5th nymphal instars were 11.69±0.58, 7.23±0.2, 8.63±0.55, 13.04±0.55 and 26.31±0.97 days, respectively. In addition mtCOI analyses have been done employing standard 658 bp barcode fragments facilitating molecular diagnostics of the adults and other life stages and the phylogenetic tree with available sequence in the GenBank.

DNA Barcoding and Phylogenetic Relationships of Spodoptera litura and S. exigua (Lepidoptera: Noctuidae)

Abstract Spodoptera spp. (Lepidoptera: Noctuidae) are highly polyphagous pests that inflict serious damage to a wide spectrum of crops. The ability of Spodoptera spp. to thrive on diverse host plants is an adaptive advantage for their survival in the ecosystem, which is achieved by its high mobility, fecundity and capacity to develop resistance to wide spectrum of chemical insecticides. In this study, we present molecular diversity and phylogenetic relationship of S. litura (Fabricius) and S. exigua (Hübner) inferred from mitochondrial cytochrome oxidase-I (COI). Alignment of the sequences of COI from various life stages of the 2 species of Spodoptera shows that the molecular identification is independent of life stages and polymorphism of the target species. Maximum likelihood analyses of S. litura, S. exigua and S. mauritia (Boisduval) reveal that there exist significant variations among these. Spodoptera exigua showed intraspecific variations with respect to different geographic locations. Present study proves the utility of COI for identification of S. litura and S. exigua irrespective of their life stages, and also draws inferences on the phylogenetic relationships between the 3 pest species.