Inheritance and Biological Characterization of an Orange-nymph Mutant in Orius laevigatus (Hemiptera: Anthocoridae)

A mutation showing a distinct orange color in the nymph stages was found in Orius laevigatus (Fieber) (Hemiptera: Anthocoridae), a key biological control agent in protected crops, used to control small pests, especially thrips. A laboratory strain carrying this body color mutation ambar was established. Genetic analysis determined that the mutation (ambar) was controlled by a single autosomal recessive allele. Some biological and ecological characteristics of this orange strain were compared to a normal population. Longevity, fecundity and fertility were similar in both populations, but immature survival, development rate, body size, starvation tolerance and predation capacity were inferior in the orange strain. The utility of the orange mutant as a visible marker for biological and ecological studies of this important biological control agent is discussed.

CRISPR-mediated knockout of cardinal and cinnabar eye pigmentation genes in the western tarnished plant bug

The western tarnished plant bug, Lygus hesperus, is a key hemipteran pest of numerous agricultural, horticultural, and industrial crops in the western United States and Mexico. A lack of genetic tools in L. hesperus hinders progress in functional genomics and in developing innovative pest control methods such as gene drive. Here, using RNA interference (RNAi) against cardinal (LhCd), cinnabar (LhCn), and white (LhW), we showed that knockdown of LhW was lethal to developing embryos, while knockdown of LhCd or LhCn produced bright red eye phenotypes, in contrast to wild-type brown eyes. We further used CRISPR/Cas9 (clustered regularly interspaced palindromic repeats/CRISPR-associated) genome editing to generate germline knockouts of both LhCd (Card) and LhCn (Cinn), producing separate strains of L. hesperus characterized by mutant eye phenotypes. Although the cardinal knockout strain Card exhibited a gradual darkening of the eyes to brown typical of the wild-type line later in nymphal development, we observed bright red eyes throughout all life stages in the cinnabar knockout strain Cinn, making it a viable marker for tracking gene editing in L. hesperus. These results provide evidence that CRISPR/Cas9 gene editing functions in L. hesperus and that eye pigmentation genes are useful for tracking the successful genetic manipulation of this insect.

Biology, Ecology, and Pest Management of the Tarnished Plant Bug, Lygus lineolaris (Palisot de Beauvois) in Southern Row Crops

Simple Summary

The tarnished plant bug, Lygus lineolaris, is a polyphagous, sap-feeder that causes significant economic damage in several field crops, especially cotton (Gossypium hirsutum L.) in the mid-southern United States. In 2020, it was reported that 4.8 million acres of cotton were infested by Lygus spp. in the United States. A broad host range, polyphagous feeding behavior and high mobility of this pest along with resistance development to conventional pesticides helped them establish as a significant pest of concern for cotton growers in the mid-south. Since the publication of a review by Layton (2000) on damage caused by Lygus lineolaris, many new research studies have been published on the Lygus biology, ecology, and integrated pest management strategies. A comprehensive review paper that summarizes these latest research developments and Lygus management strategies will be useful for researchers and cotton growers. In this review, we report and discuss the latest developments in Lygus research and the new control strategies that have been developed in the last two decades.

Abstract

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), (Hemiptera: Miridae) is considered the most damaging pest of cotton (Gossypium hirsutum L.) in the mid-southern United States, although it is established throughout the United States, southern Canada, and northern Mexico. The introduction of transgenic crops for the control of moths in the Heliothine complex and eradication of the boll weevil, Anthonomus grandis, from much of the United States led to greatly reduced pesticide use in cotton fields, which allowed L. lineolaris to emerge as a new primary pest of cotton in the mid-southern United States. Since the publication of a review by Layton (2000) on damage caused by Lygus lineolaris, many new studies have been published on the changes in host range, population dynamics, sampling methods and thresholds, cultural practices, sex pheromones and attractant blends, novel pesticides and insecticide resistance mechanisms, olfactory and feeding behaviors, introduction of biological control agents, host-plant resistance mechanisms, and new molecular and genetic tools for integrated pest management of Lygus species in cotton and other important crops. Here, we review and discuss the latest developments in L. lineolaris research in the last two decades.

Characterisation of white and yellow eye colour mutant strains of house cricket, Acheta domesticus

Two eye-colour mutant strains, white (W) and yellow (Y) of house cricket Acheta domesticus were established in our laboratory. We phenotyped and genotyped the mutants, performed genetic crossings and studied the eye structure and pigment composition using light and electron microscopy and biochemical analysis. We show that W and Y phenotypes are controlled by a single autosomal recessive allele, as both traits are metabolically independent. The analysis of the mutants`eye structure showed a reduced number of dark pigment granules while simultaneously, and an increased amount of light vacuoles in white eye mutants was observed. Significant differences in eye pigment composition between strains were also found. The Y mutant had a lower number of ommochromes, while the W mutant had a lower number of ommochromes and pteridines. This indicates that mutated genes are involved in two different, independent metabolic pathways regulating tryptophan metabolism enzymes, pigment transporter granules or pigment granule formation.

karmoisin and cardinal ortholog genes participate in the ommochrome synthesis of Nilaparvata lugens (Hemiptera: Delphacidae)

Ommochrome is the major source for eye coloration of all insect species so far examined. Phenoxazinone synthetase (PHS) has always been regarded as the terminal step enzyme for ommochrome formation, which is encoded by cardinal or karmoisin genes. Our previous study indicated that the karmoisin ortholog gene (Nl-karmoisin) product in the brown planthopper (BPH) was a monocarboxylate transporter, while not a PHS. Here, based on full-length complementary DNA, the cardinal ortholog gene in BPH (Nl-cardinal) product was predicted to be a haem peroxidase rather than a PHS. We suggest for the first time that neither karmoisin nor cardinal encodes the PHS, but whether PHS participates in BPH eye pigmentation needs further research. Nymphal RNA interference (RNAi) experiments showed that knockdown Nl-cardinal transcript led the BPH ocelli and compound eye to color change from brown to red, while knockdown Nl-karmoisin only made the ocelli present the red phenotype. Notably, not only the Nl-cardinal transcript, dscd injection (Nl-cardinal targeting double-stranded DNA (dsRNA)) also significantly reduced the Nl-karmoisin transcript by 33.7%, while dska (Nl-karmoisin targeting dsRNA) injection did not significantly change the Nl-cardinal transcript. Considering the above RNAi and quantitative real-time polymerase chain reaction results, we propose that Nl-cardinal plays a more important role in ommochrome synthesis than Nl-karmoisin, and it may be an upstream gene of Nl-karmoisin. The present study suggested that both karmoisin and cardinal ortholog genes play a role in ommochrome synthesis in a hemimetabolous insect.

RNA interference-mediated knockdown of eye coloration genes in the western tarnished plant bug (Lygus hesperus Knight)

Insect eye coloration arises from the accumulation of various pigments. A number of genes that function in the biosynthesis (vermilion, cinnabar, and cardinal) and importation (karmoisin, white, scarlet, and brown) of these pigments, and their precursors, have been identified in diverse species and used as markers for transgenesis and gene editing. To examine their suitability as visible markers in Lygus hesperus Knight (western tarnished plant bug), transcriptomic data were screened for sequences exhibiting homology with the Drosophila melanogaster proteins. Complete open reading frames encoding putative homologs for all seven genes were identified. Bioinformatic-based sequence and phylogenetic analyses supported initial annotations as eye coloration genes. Consistent with their proposed role, each of the genes was expressed in adult heads as well as throughout nymphal and adult development. Adult eyes of those injected with double-stranded RNAs (dsRNAs) for karmoisin, vermilion, cinnabar, cardinal, and scarlet were characterized by a red band along the medial margin extending from the rostral terminus to the antenna. In contrast, eyes of insects injected with dsRNAs for both white and brown were a uniform light brown. White knockdown also produced cuticular and behavioral defects. Based on its expression profile and robust visible phenotype, cardinal would likely prove to be the most suitable marker for developing gene editing methods in Lygus species.

A Comparative Study on the Population Fitness of Three Strains of Nilaparvata lugens (Hemiptera: Delphacidae) Differ in Eye Color-Related Genes

The brown planthopper, Nilaparvata lugens (Stål), is a destructive insect pest on rice throughout Asia. As a visible genetic marker, red eye mutant colony of brown planthopper is a valuable material. Here, we established the near-isogenic lines, NIL-BB and NIL-rr, through mating red eye females to brown eye brothers for eight successive generations. Biological experiments showed that NIL-BB had big fitness cost; however, NIL-rr had comparable survival and fertility parameters with BB, a normal laboratory brown planthopper strain. Significantly lower number eggs per female and egg hatchability were the key factors resulting in big fitness cost of NIL-BB. The population trend indexes of BB, NIL-rr, and NIL-BB were 52.18, 43.80, and 4.19, respectively. Real-time PCR study suggested that the poorer fertility of NIL-BB was not mediated by the differential expression of genes relating to oogenesis. The stronger fitness of NIL-rr compared with NIL-BB may be caused by the eye mutant gene or its closely linked genes having stronger compensation ability for reproduction. The comparable fitness of NIL-rr with BB indicated that NIL-rr may be used in field research. The NIL-BB strain with significantly declined fecundity and survival ability can be used as study model for the signal pathways relating to fecundity.

Transcriptome-based identification of ABC transporters in the western tarnished plant bug Lygus hesperus

ATP-binding cassette (ABC) transporters are a large superfamily of proteins that mediate diverse physiological functions by coupling ATP hydrolysis with substrate transport across lipid membranes. In insects, these proteins play roles in metabolism, development, eye pigmentation, and xenobiotic clearance. While ABC transporters have been extensively studied in vertebrates, less is known concerning this superfamily in insects, particularly hemipteran pests. We used RNA-Seq transcriptome sequencing to identify 65 putative ABC transporter sequences (including 36 full-length sequences) from the eight ABC subfamilies in the western tarnished plant bug (Lygus hesperus), a polyphagous agricultural pest. Phylogenetic analyses revealed clear orthologous relationships with ABC transporters linked to insecticide/xenobiotic clearance and indicated lineage specific expansion of the L. hesperus ABCG and ABCH subfamilies. The transcriptional profile of 13 LhABCs representative of the ABCA, ABCB, ABCC, ABCG, and ABCH subfamilies was examined across L. hesperus development and within sex-specific adult tissues. All of the transcripts were amplified from both reproductively immature and mature adults and all but LhABCA8 were expressed to some degree in eggs. Expression of LhABCA8 was spatially localized to the testis and temporally timed with male reproductive development, suggesting a potential role in sexual maturation and/or spermatozoa protection. Elevated expression of LhABCC5 in Malpighian tubules suggests a possible role in xenobiotic clearance. Our results provide the first transcriptome-wide analysis of ABC transporters in an agriculturally important hemipteran pest and, because ABC transporters are known to be important mediators of insecticidal resistance, will provide the basis for future biochemical and toxicological studies on the role of this protein family in insecticide resistance in Lygus species.