Social insects are able to mount both group‐level and individual defences against pathogens. Here we focus on individual defences, by presenting a genome‐wide analysis of immunity in a social insect, the honey bee Apis mellifera. We present honey bee models for each of four signalling pathways associated with immunity, identifying plausible orthologues for nearly all predicted pathway members. When compared to the sequenced Drosophila and Anopheles genomes, honey bees possess roughly one‐third as many genes in 17 gene families implicated in insect immunity. We suggest that an implied reduction in immune flexibility in bees reflects either the strength of social barriers to disease, or a tendency for bees to be attacked by a limited set of highly coevolved pathogens.

Mosquitoes are vectors of parasitic and viral diseases of immense importance for public health. The acquisition of the genome sequence of the yellow fever and Dengue vector, Aedes aegypti ( Aa ), has enabled a comparative phylogenomic analysis of the insect immune repertoire: in Aa , the malaria vector Anopheles gambiae ( Ag ), and the fruit fly Drosophila melanogaster ( Dm ). Analysis of immune signaling pathways and response modules reveals both conservative and rapidly evolving features associated with different functional gene categories and particular aspects of immune reactions. These dynamics reflect in part continuous readjustment between accommodation and rejection of pathogens and suggest how innate immunity may have evolved.

The synthesis of vitellogenin and its uptake by maturing oocytes during egg maturation are essential for successful female reproduction. These events are regulated by the juvenile hormones and ecdysteroids and by the nutritional signaling pathway regulated by neuropeptides. Juvenile hormones act as gonadotropins, regulating vitellogenesis in most insects, but ecdysteroids control this process in Diptera and some Hymenoptera and Lepidoptera. The complex crosstalk between the juvenile hormones, ecdysteroids, and nutritional signaling pathways differs distinctly depending on the reproductive strategies adopted by various insects. Molecular studies within the past decade have revealed much about the relationships among, and the role of, these pathways with respect to regulation of insect reproduction. Here, we review the role of juvenile hormones, ecdysteroids, and nutritional signaling, along with that of microRNAs, in regulating female insect reproduction at the molecular level.

Background: Tribolium castaneum is a species of Coleoptera, the largest and most diverse order of all eukaryotes. Components of the innate immune system are hardly known in this insect, which is in a key phylogenetic position to inform us about genetic innovations accompanying the evolution of holometabolous insects. We have annotated immunity-related genes and compared them with homologous molecules from other species. Results: Around 300 candidate defense proteins are identified based on sequence similarity to homologs known to participate in immune responses. In most cases, paralog counts are lower than those of Drosophila melanogaster or Anopheles gambiae but are substantially higher than those of Apis mellifera. The genome contains probable orthologs for nearly all members of the Toll, IMD, and JAK/STAT pathways. While total numbers of the clip-domain serine proteinases are approximately equal in the fly (29), mosquito (32) and beetle (30), lineage-specific expansion of the family is discovered in all three species. Sixteen of the thirty-one serpin genes form a large cluster in a 50 kb region that resulted from extensive gene duplications. Among the nine Toll-like proteins, four are orthologous to Drosophila Toll. The presence of scavenger receptors and other related proteins indicates a role of cellular responses in the entire system. The structures of some antimicrobial peptides drastically differ from those in other orders of insects. Conclusion: A framework of information on Tribolium immunity is established, which may serve as a stepping stone for future genetic analyses of defense responses in a nondrosophiline genetic model insect.

We have identified 44 serine protease (SP) and 13 serine protease homolog (SPH) genes in the genome of Apis mellifera . Most of these genes encode putative secreted proteins, but four SPs and three SPHs may associate with the plasma membrane via a transmembrane region. Clip domains represent the most abundant non‐catalytic structural units in these SP‐like proteins −12 SPs and six SPHs contain at least one clip domain. Some of the family members contain other modules for protein–protein interactions, including disulphide‐stabilized structures (LDL _r A, SRCR, frizzled, kringle, Sushi, Wonton and Pan/apple), carbohydrate‐recognition domains (C‐type lectin and chitin‐binding), and other modules (such as zinc finger, CUB, coiled coil and Sina). Comparison of the sequences with those from Drosophila led to a proposed SP pathway for establishing the dorsoventral axis of honey bee embryos. Multiple sequence alignments revealed evolutionary relationships of honey bee SPs and SPHs with those in Drosophila melanogaster , Anopheles gambiae , and Manduca sexta . We identified homologs of D. melanogaster persephone, M. sexta HP14, PAP‐1 and SPH‐1. A. mellifera genome includes at least five genes for potential SP inhibitors (serpin‐1 through ‐5) and three genes of SP putative substrates (prophenoloxidase, spätzle‐1 and spätzle‐2). Quantitative RT‐PCR analyses showed an elevation in the mRNA levels of SP2, SP3, SP9, SP10, SPH41, SPH42, SP49, serpin‐2, serpin‐4, serpin‐5, and spätzle‐2 in adults after a microbial challenge. The SP41 and SP6 transcripts significantly increased after an injection of Paenibacillus larva , but there was no such increase after injection of saline or Escherichia coli . mRNA levels of most SPs and serpins significantly increased by 48 h after the pathogen infection in 1st instar larvae. On the contrary, SP1, SP3, SP19 and serpin‐5 transcript levels reduced. These results, taken together, provide a framework for designing experimental studies of the roles of SPs and related proteins in embryonic development and immune responses of A. mellifera .

Closing the Vector Circle: The genome sequence of Culex quinquefasciatus offers a representative of the third major genus of mosquito disease vectors for comparative analysis. In a major international effort, Arensburger et al. (p. 86 ) uncovered divergences in the C. quinquefasciatus genome compared with the representatives of the other two genera Aedes aegypti and Anopheles gambiae . The main difference noted is the expansion of numbers of genes, particularly for immunity, oxidoreductive functions, and digestive enzymes, which may reflect specific aspects of the Culex life cycle. Bartholomay et al. (p. 88 ) explored infection-response genes in Culex in more depth and uncovered 500 immune response-related genes, similar to the numbers seen in Aedes , but fewer than seen in Anopheles or the fruit fly Drosophila melanogaster . The higher numbers of genes were attributed partly to expansions in those encoding serpins, C-type lectins, and fibrinogen-related proteins, consistent with greater immune surveillance and associated signaling needed to monitor the dangers of breeding in polluted, urbanized environments. Transcriptome analysis confirmed that inoculation with unfamiliar bacteria prompted strong immune responses in Culex . The worm and virus pathogens that the mosquitoes transmit naturally provoked little immune activation, however, suggesting that tolerance has evolved to any damage caused by replication of the pathogens in the insects.