Chromosome scale genomes of two invasive Adelges species enable virtual screening for selective adelgicides

Two invasive adelgids are associated with widespread damage to several North American conifer species. Adelges tsugae, hemlock woolly adelgid, was introduced from Japan and reproduces parthenogenetically in North America, where it has rapidly decimated Tsuga canadensis and Tsuga caroliniana (eastern and Carolina hemlocks, respectively). Adelges abietis, eastern spruce gall adelgid, introduced from Europe, forms distinctive pineapple-shaped galls on several native spruce species. While not considered a major forest pest, it weakens trees and increases susceptibility to additional stressors. Broad-spectrum insecticides that are often used to control adelgid populations can have off-target impacts on beneficial insects. Whole-genome sequencing was performed on both species to aid in the development of targeted solutions that may minimize ecological impact. A. abietis was sequenced using barcoded linked-reads from 30 pooled individuals, with Hi-C scaffolding performed using data from a single individual collected from the same host plant. A. tsugae used long-read sequencing from pooled nymphs. The assembled A. tsugae and A. abietis genomes, pooled from several parthenogenetic females, are 220.75 and 253.16 Mb, respectively. Each consists of 8 autosomal chromosomes, as well as 2 sex chromosomes (X1/X2), supporting the XX-XO sex determination system. The genomes are over 96% complete based on BUSCO assessment. Genome annotation identified 11,424 and 12,060 protein-coding genes in A. tsugae and A. abietis, respectively. Comparative analysis of proteins across 31 hemipteran species and 14 arthropod outgroups identified 32,340 putative gene families. Gene family evolution analysis with CAFE revealed lineage-specific expansions in immune-related aminopeptidases (ERAP1) and juvenile hormone binding proteins (JHBP), contractions in juvenile hormone acid methyltransferases (JHAMT), and conservation of nicotinic acetylcholine receptors (nAChRs). These genes were explored as candidate families toward a long-term objective of developing adelgid-selective insecticides. Structural comparisons of proteins across 7 focal species (A. tsugae, A. abietis, Adelges cooleyi, Rhopalosiphum maidis, Apis mellifera, Danaus plexippus, and Drosophila melanogaster) revealed high conservation of nAChR and ERAP1, while JHAMT exhibited species-specific structural divergence. The potential of JHAMT as a lineage-specific target for pest control was explored through virtual screening of drugs and pesticides.