Wing polymorphism is an evolutionary feature found in a wide variety of insects, which offers a model system for studying the evolutionary significance of dispersal. In the wing-dimorphic planthopperNilaparvata lugens, the insulin/insulin-like growth factor signaling (IIS) pathway acts as a ‘master signal’ that directs the development of either long-winged (LW) or short-winged (SW) morphs via regulation of the activity of Forkhead transcription factor subgroup O (NlFoxO). However, downstream effectors of the IIS–FoxO signaling cascade that mediate alternative wing morphs are unclear. Here we found thatvestigial(Nlvg), a key wing-patterning gene, is selectively and temporally regulated by the IIS–FoxO signaling cascade during the wing-morph decision stage (fifth-instar stage). RNA interference (RNAi)-mediated silencing ofNlfoxoincreaseNlvgexpression in the fifth-instar stage (the last nymphal stage), thereby inducing LW development. Conversely, silencing ofNlvgcan antagonize the effects of IIS activity on LW development, redirecting wing commitment from LW to the morph with intermediate wing size. In vitro and in vivo binding assays indicated thatNlFoxO protein may suppressNlvgexpression by directly binding to the first intron region of theNlvglocus. Our findings provide a first glimpse of the link connecting the IIS pathway to the wing-patterning network on the developmental plasticity of wings in insects, and help us understanding how phenotypic diversity is generated by the modification of a common set of pattern elements.

A single insulin receptor (InR) gene has been identified and extensively studied in model species ranging from nematodes to mice. However, most insects possess additional copies of InR, yet the functional significance, if any, of alternate InRs is unknown. Here, we used the wing-dimorphic brown planthopper (BPH) as a model system to query the role of a second InR copy in insects. NlInR2 resembled the BPH InR homologue (NlInR1) in terms of nymph development and reproduction, but revealed distinct regulatory roles in fuel metabolism, lifespan, and starvation tolerance. Unlike a lethal phenotype derived from NlInR1 null, homozygous NlInR2 null mutants were viable and accelerated DNA replication and cell proliferation in wing cells, thus redirecting short-winged–destined BPHs to develop into long-winged morphs. Additionally, the proper expression of NlInR2 was needed to maintain symmetric vein patterning in wings. Our findings provide the first direct evidence for the regulatory complexity of the two InR paralogues in insects, implying the functionally independent evolution of multiple InRs in invertebrates.

A feminizing switch in a hemimetabolous insect provides novel insights into the diverse mechanisms of insect sex determination.

Saliva secretion is essential for successful feeding by piercing–sucking insects. Despite extensive studies of the saliva composition of phloem- and blood-feeding insects, less is known about the oral secretions of seed-feeding insects. The firebug Pyrrhocoris apterus is a polyphagous insect that feeds primarily on dry seeds of various plant species. Here, liquid chromatography‒mass spectrometry/mass spectrometry (LC‒MS/MS) was used to identify 165 P. apterus salivary proteins, including 110 gelling-specific proteins, 24 watery-specific proteins, and 31 proteins common to both groups. Transcriptomic analysis of saliva glands identified 567 potential salivary proteins, of which 87 overlapped with those detected by LC‒MS/MS. Comparative analysis showed that 98 out of 165 (59.4%) P. apterus saliva proteins were associated with extra-oral digestion and detoxification and had homologs in ten other species of arthropods examined. In addition, 67 proteins were specific to P. apterus, of which 22 proteins were defined with unknown functions. RNA interference-mediated gene silencing assays indicated that P. apterus-specific proteins were vital for P. apterus survival. Our findings shed light on the function of salivary proteins in feeding by seed-feeding insects and the evolution of feeding habits in piercing–sucking insects.

Across metazoans, the insulin/insulin-like signaling (IIS) pathway is assumed to promote organ growth. We found that genes within the IIS pathway evolved opposite roles in organ growth across wing-dimorphic insects, playing opposite roles in regulating the developmental switch between short and long wings. In the firebug, the InR-Chico-PI3K-PDK1-Tsc1/2-TORC1 cascade redirects the switch from short to long wings by inactivating IIS, whereas in the planthopper, the InR-Chico-PI3K-Akt-FoxO cascade redirects this same switch by activating IIS. Activation or inactivation of IIS results in low ecdysteroid titers in both species by regulating different genes within the ecdysteroid biosynthesis pathway, which in turn induces long wing development. Our findings reveal a negative relationship between IIS and organ growth and a mechanism for how a hormone pathway can translate opposing IIS activities into the same developmental switch across species.