Chandra S. Prabhakar

Population genetic structure of the melon fly, Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae) based on mitochondrial cytochrome oxidase (COI) gene sequences

Population genetic structure of melon fly analysed with mitochondrial cytochrome oxidase I gene suggested that melon fly populations across the globe is homogeneous with non-significant variation of 0.000–0.003 base substitutions per site. Test isolates representing various geographic situations across the world were placed in 26 mitochondrial haplotypes based on variations associated with a maximum of three mutational steps and the predominant haplotype i.e. H1 was present in all melon fly populations except Hawaiian population. Evolution of mtCOI gene suggested that the fly could have originated some 0.4 million years ago. The present study also indicated that the B. cucurbitae population expansion is an event of post Pleistocene warm climatic conditions with small number of founder population. The invasion of B. cucurbitae in Hawaii was associated with the large population size and the global presence of the fly is associated with human mediated dispersal. The very low genetic variation suggested that the fly management might be possible by large scale sterile insect techniques programme.

Isolation and characterization of gut bacteria of fruit fly, Bactrocera tau (Walker)

Gut bacteria of fruit fly, Bactrocera tau (Walker) (Diptera: Tephritidae), were isolated and the isolates attractive to B. tau adults were characterized using morphological, biochemical and 16S rRNA analyses to determine their taxonomic position. Based upon morphological, biochemical and 16S rRNA sequences (on the basis of closest match), five gut bacterial species of B. tau were characterized as Delftia acidovorans, Pseudomonas putida, Flavobacterium sp., Defluvibacter sp. and Ochrobactrum sp., of which four bacterial isolates, viz., Delftia acidovorans, Flavobacterium sp., Defluvibacter sp. and Ochrobactrum sp. are new records from guts of the fruit fly species.

Fruit fly (Diptera: Tephritidae) diversity in cucurbit fields and surrounding forest areas of Himachal Pradesh, a north-western Himalayan state of India

During the course of studies, Bactrocera (Bactrocera) latifrons (Hendel), B. (B.) nigrofemoralis White and Tsuruta, Dacus (Callantra) longicornis Wiedemann, Dacus (Callantra) sphaeroidalis (Bezzi), Cyrtostola limbata (Hendel) and Pliomelaena udhampurensis Agarwal and Kapoor were recorded for the first time in Himachal Pradesh in a cucurbit ecosystem. Apart from these, other species viz. Bactrocera tau, Bactrocera cucurbitae, Bactrocera dorsalis, Bactrocera zonata, Bactrocera scutellaris, Bactrocera diversa and Dioxyna sororcula (Wiedemann) were also identified. Distribution records of B. (B.) dorsalis (Hendel), B. (B.) zonata (Saunders), Bactrocera (Hemigymnodacus) diversa (Coquillett), B. (Zeugodacus) cucurbitae (Coquillett), B. (Z.) scutellaris (Bezzi) and B. (Z.) tau (Walker) has been described.

Transmission and effect of sublethal infection of granulosis virus (PbGV) on Pieris brassicae Linn. (Pieridae: Lepidoptera)

A strain of granulosis virus from Pieris brassicae (Linn.) was isolated and characterized from the dry temperate region of Himachal Pradesh, India situated at an altitude of 2580 m above msl. The pest appears in the region during the summer months (May to September) and overwinters as pupae during the snow covered winter months. Carry over of virus inoculum as sublethal infections, could be an important mechanism for next season epidemics in the region. Effect of sublethal P. brassicae granulovirus infection on its host was therefore studied to understand the transmission mechanism. The third instar larvae were exposed to sublethal viral infection. The surviving larvae showed symptoms of virosis in the pupal and adult stages. The per cent pupation and adult emergence of sublethally infected larvae were significantly reduced and no adult emerged from the abnormal pupae. The mode of transmission of viruses from parents to offspring appeared to be through eggs (transovum). The emerging larvae from the eggs laid by treated females also showed symptoms of virosis. Complete mortality due to viral infection was observed at third instar stage in the offspring (F1). The amplification of granulin gene using specific primer also showed the presence of virus in F1 progenies of sublethally treated P. brassicae larvae, hence confirming vertical transmission.

Diversity of bacterial communities in the midgut of Bactrocera cucurbitae (Diptera: Tephritidae) populations and their potential use as attractants

BACKGROUND The microbiota plays an important role in insect development and fitness. Understanding the gut microbiota composition is essential for the development of pest management strategies. Midgut bacteria were isolated from nine wild B. cucurbitae populations collected from different agroecological zones of India. These isolates were further studied for attractant potential of fruit fly adults, and the chemical constituents in the supernatants of gut bacteria were analysed. RESULTS Twenty-six bacterial isolates belonging to the families Enterobacteriaceae, Bacillaceae, Micrococcaceae and Staphylococcaceae were isolated and identified on the basis of 16S rRNA gene sequence analysis. The dominant species in the midgut of melon fly were from the genera Enterobacter (34.6%), Klebsiella (19.2%), Citrobacter (7.7%), Bacillus (15.4%) and Providencia (7.7%), and 3.8% each of Micrococcus, Staphylococcus, Leclercia and Exiguobacterium. Bactrocera cucurbitae and B. dorsalis adults were significantly attracted to bacterial whole cell cultures and their supernatants in the fruit fly attraction bioassays. Bacillus cereus, Enterobacter, Klebsiella, Citrobacter and Providencia species attracted both male and females of Bactrocera species. The supernatants of Klebsiella, Citrobacter and Providencia species attracted a significantly greater number of females than males. The most abundant chemical constituents in supernatants of K. oxytoca and C. freundii were 3-methyl-1-butanol, 2-phenylethanol, butyl isocyanatoacetate, 2-methyl-1-propanol and 3-hydroxy-2-butanone, as identified by gas chromatography-mass spectrometry. CONCLUSIONS The bacterial endosymbionts associated with melon fly exhibited attractant potential which could facilitate eco-friendly insect control strategies.

Metageographic population analysis of Colletotrichum truncatum associated with chili fruit rot and other hosts using ITS region nucleotide sequences

Colletotrichum truncatum is one of the most economically important fungal pathogen causing anthracnose disease in pre and post-harvest stages of many crops worldwide. Little information is available in the literature on the genetic analysis and demographic history of this fungal pathogen. In the present study nucleotide sequence data of internal transcribed spacer (ITS) region were analyzed for C. truncatum isolates infecting chili and other crops worldwide to determine a metageographic pattern of distribution and evolution of the species. Levels of differentiation (genetic distances and FST values) among sequences of C. truncatum from 23 countries were minimal suggesting the global occurrence of a large and geographically undifferentiated population. Only 11 haplotypes were detected among 98 isolates from 24 geographically distant populations of C. truncatum. Predominant haplotype H1 which occupied a central position in the median joining network was inferred to be ancestral haplotype as it was detected at a high frequency and was shared by multiple populations. Phylogeographic pattern of the species with worldwide presence and predominance of single haplotype suggests human mediated dispersal through domestication and introduction of host plants in different parts of the world, and might have played a significant role in structuring the populations of this devastating pathogen.

Impact of Climate Change on Pest Management and Food Security

Climate change and global warming will have serious consequences for the diversity and abundance of arthropods, and the extent of losses due to insect pests, which will impact both crop production and food security. Prediction of changes in geographical distribution and population dynamics of insect pests will be useful for adapting pest management strategies to mitigate the adverse effects of climate change on crop production. Pest outbreaks might occur more frequently, particularly during extended periods of drought, followed by heavy rainfall. Some of the components of pest management such as host-plant resistance, biopesticides, natural enemies, and synthetic chemicals will be rendered less effective as a result of the increase in temperatures and UV radiation, and decrease in relative humidity. The rate of insect multiplication might increase with an increase in CO2 and temperature. Thus climate change might change the population dynamics of insect pests differently in different agro-ecosystem and ecological zones. Therefore, there is a need to take a concerted look at the likely effects of climate change on crop protection and devise appropriate measures to mitigate the effects of climate change on food security.

Identification and evaluation of cultivable gut bacteria associated with peach fruit fly, Bactrocera zonata (Diptera: Tephritidae)

The aim of the present study was to identify the cultivable gut bacteria associated with peach fruit fly, Bactrocera zonata, and evaluate their potential to attract adults of B. zonata. Based on culture-dependent characterization methods and 16S rRNA gene sequence analysis, bacteria were identified as members of family Enterobacteriaceae (BZM1, Klebsiella oxytoca), Microbacteriacea (BZM2, Microbacterium spp.) and Nocardiaceae (BZM4, Rhodococcus spp.). Molecular phylogeny placed Klebsiella oxytoca within gram negative γ-proteobacteria whereas, Microbacterium spp. and Rhodococcus spp. were clustered under gram positive Actinobacteria group in family Microbacteriacea and Nocardiaceae, respectively. 16S rRNA gene sequence comparison with the available NCBI database sequences further confirmed the characterizations of bacterial symbionts. Population of these bacterial species increased significantly up to the 11th day after emergence of adults and thereafter it remains constant. Among 3 bacterial symbionts, metabolites produced from K. oxytoca had the highest attraction to the B. zonata adult females over metabolites produced from other bacteria and their combinations in field bioassay. The B. zonata adult male flies attracted to metabolites produced from each bacterial symbionts alone and their combinations were less in number with comparison to the B. zonata adult females. The present study provides the first description of the attractancy potential of metabolites produced by gut microbial community of B. zonata in open field condition. This study results may prompt the development of a female-targeted population control strategy for this fly.

Bacterial communities associated with invasive populations of Bactrocera dorsalis (Diptera: Tephritidae) in China.

The oriental fruit fly Bactrocera dorsalis (Hendel) is a destructive insect pest of a wide range of fruits and vegetables. This pest is an invasive species and is currently distributed in some provinces of China. To recover the symbiotic bacteria of B. dorsalis from different invasion regions in China, we researched the bacterial diversity of this fruit fly among one laboratory colony (Guangdong, China) and 15 wild populations (14 sites in China and one site in Thailand) using DNA-based approaches. The construction of 16S rRNA gene libraries allowed the identification of 24 operational taxonomic units of associated bacteria at the 3% distance level, and these were affiliated with 3 phyla, 5 families, and 13 genera. The higher bacterial diversity was recovered in wild populations compared with the laboratory colony and in samples from early term invasion regions compared with samples from late term invasion regions. Moreover, Klebsiella pneumoniae and Providencia sp. were two of the most frequently recovered bacteria, present in flies collected from three different regions in China where B. dorsalis is invasive. This study for the first time provides a systemic investigation of the symbiotic bacteria of B. dorsalis from different invasion regions in China.

Effect of feeding stimulants on the insecticidal properties of Pieris brassicae granulovirus (PbGV) against Pieris brassicae

Feeding stimulants (phagostimulants) increase the food uptake by the host insect larvae and thereby play a vital role in enhancing overall activity of insect viruses formulated as biopesticides. A local strain of granulovirus of Pieris brassicae (PbGV), a serious pest of cole crops worldwide, has shown potential as a biopesticide against this pest and with slight increase in its efficacy can be used successfully as a promising biocontrol agent in integrated pest management (IPM) programs of the pest. The addition of phagostimulants may enhance the efficacy but so far no specific phagostimulant for PbGV has been reported. In the present studies, some reported phagostimulants for insect viruses were tested for their impact on food utilization by host larvae and efficacy of the virus. The specified concentration of virus isolate was mixed with phagostimulants and laboratory studies were conducted to uncover their effect on consumption index (CI) and larval mortality. The studies revealed that phagostimulants, viz. boric acid and crude sugar, when mixed with PbGV, showed highest CI and larval mortality. Consumption index of 1.34, 1.49 and 1.43 mg/mg/day and corresponding larval mortality of 32.9%, 45.8% and 34.2% were recorded with the addition of 0.5% and 1% boric acid and 2% crude sugar, respectively, in PbGV. The leaf extracts of cabbage, cauliflower and broccoli at both the concentrations (1% and 2%) also enhanced the CI but were comparatively less effective than the boric acid and crude sugar. Field evaluation of PbGV alone and in combination with phagostimulants carried out at two geographically isolated locations, viz. Palampur (subtropical) and Sangla (temperate) on three cole crops (cabbage, cauliflower and broccoli) showed that boric acid was the most promising candidate for enhancing the PbGV efficacy under field conditions, followed by crude sugar.