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Insects are the most abundant animals in terrestrial ecosystems and are inhabited by symbiotic microbes that provide beneficial services to their hosts [1]. Mealybugs (Homoptera: Coccoidea: Pseudococcidae) are plantsucking scale insects affecting agricultural ecosystems and causing damage to more than 300 plant species [2-4]. Examining the ecological interactions of symbiotic microbes in agriculturally important insect-hosts may lead to novel methods of pest control and enhancement of agricultural productivity [5, 6]. Diet and the insect lineage have been proposed to exert different influences on symbiotic microbial diversity [7]. Accordingly, in this study we examined the hypothesis that the mealybug microbial ecology is strongly determined by interaction between phylogenetic constraints and nutritional requirements. To this end, we performed endomicrobial community analysis of two phylogenetically distinct mealybug species that feed concurrently on the same plant yet differ in their choice of feeding site and the processing of the plant-derived diet. 1) Papaya mealybug (PM), Paracoccus marginatus Williams and Granara de Willink, feeds frequently on phloem sap and produces large amounts of honeydew [8]. 2) Two-tailed mealybug (TM), Ferrisia virgata Cockerell, colonizes around the terminal parts of the plant, infrequently accesses the phloem sap and produces small amounts of honeydew [9]. Based on integrated molecular and morphological data, these two mealybugs have been assigned under different sub-families [10]. Pooled PM and TM samples were created from fifty individuals of each mealybug species collected from a papaya (Carica papaya) plant cv. CO8 at Agricultural College and Research Institute, Madurai (9°56'0" N and 78°7'0" E), India. The insects were surface sterilized by rinsing in sterile water, soaking in 70% ethanol and 10% bleach, with three rinses in water, for 60 sec at each step. The surface-sterilized insects were homogenized in liquid nitrogen. Whole DNA was extracted from homogenates using an Insect DNA Purification Kit (Hi-Media, India) according to the manufacturer's protocol. The extracted DNA was amplified using primers targeting the V3-V4 region of the bacterial 16S rRNA gene (primers, 341F and 518R) and fungal internal transcribed spacer (primers, ITS5F and ITS2R) [11, 12]. Sequencing was performed using the Illumina MiSeq platform at Genotypic Technology, India. Resulted sequence data were deposited in SRA archives under accession number PRJNA522349. The raw reads were processed as described elsewhere [13]. The processing of raw reads clustered at 97% identity revealed 5,881 and 2,417 bacterial operational taxonomic units (OTUs), whereas 258 and 172 fungal OTUs were identified for PM and TM, respectively. The rarefaction curve (Fig. S1) indicated the adequate sampling effort for getting the full extent of taxonomic diversity. It explains how the number of species found in a sample at any given phylogenetic level is strongly affected by the number of sequences analyzed [14]. The Shannon Mea...

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