The immune system of adult mosquitoes has received significant attention because of the ability of females to vector disease-causing pathogens while ingesting blood meals. However, few studies have focused on the immune system of larvae, which, we hypothesize, is highly robust due to the high density and diversity of microorganisms that larvae encounter in their aquatic environments and the strong selection pressures at work in the larval stage to ensure survival to reproductive maturity. Here, we surveyed a broad range of cellular and humoral immune parameters in larvae of the malaria mosquito, Anopheles gambiae, and compared their potency to that of newly-emerged adults and older adults. We found that larvae kill bacteria in their hemocoel with equal or greater efficiency compared to newly-emerged adults, and that antibacterial ability declines further with adult age, indicative of senescence. This phenotype correlates with more circulating hemocytes and a differing spatial arrangement of sessile hemocytes in larvae relative to adults, as well as with the individual hemocytes of adults carrying a greater phagocytic burden. The hemolymph of larvae also possesses markedly stronger antibacterial lytic and melanization activity than the hemolymph of adults. Finally, infection induces a stronger transcriptional upregulation of immunity genes in larvae than in adults, including differences in the immunity genes that are regulated. These results demonstrate that immunity is strongest in larvae and declines after metamorphosis and with adult age, and suggest that adaptive decoupling, or the independent evolution of larval and adult traits made possible by metamorphosis, has occurred in the mosquito lineage.

The immune and circulatory systems of mammals are functionally integrated, as exemplified by the immune function of the spleen and lymph nodes. Similar functional integration exists in the malaria mosquito, Anopheles gambiae, as exemplified by the infection-induced aggregation of hemocytes around the heart valves. Whether this is specific to mosquitoes or a general characteristic of insects remained unknown. We analyzed 68 species from 51 families representing 16 orders and found that infection induces the aggregation of hemocytes and pathogens on the heart of insects from all major branches of the class Insecta. An expanded analysis in the holometabolous mosquito, Aedes aegypti, and the hemimetabolous bed bug, Cimex lectularius, showed that infection induces the aggregation of phagocytic hemocytes on the hearts of distantly related insects, with aggregations mirroring the patterns of hemolymph flow. Therefore, the functional integration of the immune and circulatory systems is conserved across the insect tree of life.

In the holometabolous insect order Neuroptera (lacewings), the cosmopolitan Myrmeleontidae (antlions) are the most species-rich family, while the closely related Nymphidae (split-footed lacewings) are a small endemic family from the Australian-Malesian region. Both families belong to the suborder Myrmeleontiformia, within which controversial hypotheses on the interfamilial phylogenetic relationships exist. Herein, we describe the complete mitochondrial (mt) genomes of an antlion (Myrmeleon immanis Walker, 1853) and a split-footed lacewing (Nymphes myrmeleonoides Leach, 1814), representing the first mt genomes for both families. These mt genomes are relatively small (respectively composed of 15,799 and 15,713 bp) compared to other lacewing mt genomes, and comprise 37 genes (13 protein coding genes, 22 tRNA genes and two rRNA genes). The arrangement of these two mt genomes is the same as in most derived Neuroptera mt genomes previously sequenced, specifically with a translocation of trnC. The start codons of all PCGs are started by ATN, with an exception of cox1, which is ACG in the M. immanis mt genome and TCG in N. myrmeleonoides. All tRNA genes have a typical clover-leaf structure of mitochondrial tRNA, with the exception of trnS1(AGN). The secondary structures of rrnL and rrnS are similar with those proposed insects and the domain I contains nine helices rather than eight helices, which is common within Neuroptera. A phylogenetic analysis based on the mt genomic data for all Neuropterida sequenced thus far, supports the monophyly of Myrmeleontiformia and the sister relationship between Ascalaphidae and Myrmeleontidae.

Rapisma McLachlan, 1866 (Neuroptera: Ithonidae) is a rarely encountered genus of lacewings found inmontane tropical or subtropical forests in Oriental Asia. In Xizang Autonomous Region (Tibet) of China there are two sympatrically distributed species of Rapisma, i.e. Rapisma xizangense Yang, 1993 and Rapisma zayuanum Yang, 1993, in which R. xizangense is only known as male and has dull brownish body and wing coloration, while R. zayuanum is only known as female and has bright green body and wing coloration. In order to clarify the relationship between these two species, we determined the complete mitochondrial (mt) genomes of R. xizangense and R. zayuanum for the first time. The mt genomes are 15,961 and 15,984 bp in size, respectively, and comprised 37 genes (13 protein coding genes, 22 tRNA genes and 2 rRNA genes). A major noncoding (control) region was 1,167 bp in R. xizangense and 1,193 bp in R. zayuanum with structural organizations simpler than that reported in other Neuropterida species, notably lacking conserved blocks or long tandem repeats. Besides similar mitogenomic structure, the genetic distance between R. xizangense and R. zayuanum based on two rRNAs and 13 protein coding genes (PCGs) as well as the genetic distance between each of these two Tibetan Rapisma species and a Thai Rapisma species (R. cryptunum) based on partial rrnL show that R. xizangense and R. zayuanum are most likely conspecific. Thus, R. zayuanum syn. nov. is herein treated as a junior synonym of R. xizangense. The present finding represents a rare example of distinct sexual dimorphism in lacewings. This comparative mitogenomic analysis sheds new light on the identification of rare species with sexual dimorphism and the biology of Neuroptera.