Search Results (8)

The tarnished plant bug, Lygus lineolaris (TPB), (Palisot de Beauvois), and the western tarnished plant bug (WTPB), Lygus hesperus, Knight, are major agricultural pests that cause significant damage to a wide range of crops in the southeastern and southwestern United States. Flonicamid (commercial name: Carbine 50WG) is generally effective against various sap-feeding pests, including both L. hesperus and L. lineolaris. This study evaluated the toxicity of flonicamid on third-instar nymphs and adults of both Lygus species under laboratory conditions. Two bioassay methods were used: spray application to assess both contact and oral toxicity, and dipping to evaluate oral toxicity. Results showed that L. hesperus was significantly more susceptible to flonicamid than L. lineolaris across both bioassay methods. While no significant differences in toxicity were observed between spray and dipping assays, third-instar nymphs exhibited significantly higher sensitivity than adults in both species. The addition of piperonyl butoxide (PBO), a known inhibitor of cytochrome P450-monooxygenases (P450s), significantly enhanced the toxicity of flonicamid, suggesting that P450 enzyme plays a critical role in its detoxification. Sublethal exposure to flonicamid also induced increased P450 activity in both species. These findings provide valuable insights into the differences in susceptibility between L. lineolaris and L. hesperus to flonicamid and indicate that P450-mediated detoxification is critical for flonicamid metabolism. Such insights are valuable for early resistance monitoring and optimizing flonicamid application in integrated pest management programs. Full article

The polyphagous Lygus hesperus Knight is a serious pest on many crops in the western USA, including California’s central coast. Although L. hesperus adults can cause damage to broccoli and cauliflower, symptoms from their interactions with these plants are not fully characterized. Characterizing the feeding and ovipositional damage will help in the early diagnosis of the problem in the field and in greenhouses. Thus, the objective of this study was to characterize the feeding and ovipositional injury symptoms in broccoli and cauliflower after exposing 0, 1, 3, 5, and 10 adult L. hesperus to seedlings of broccoli and cauliflower for 24 h, 48 h, and 7 d. Although distorted and “blind” shoots were observed, feeding injury did not rapidly manifest into damage after 7 d post-exposure with high counts of adults on broccoli and cauliflower seedlings. The ovipositional injury was expressed as lesions that developed rapidly with a high density of adults in 24 h. The same levels of damage were observed with three or five adults to these hosts in 48 h. Significant positive correlations between the total eggs and lesions developed were observed on broccoli and cauliflower seedlings. After adult L. hesperus exposure, the growth of broccoli seedlings was reduced, but there was no effect on the growth of cauliflower seedlings. For diagnosis, data show that lesions are associated with adult L. hesperus ovipositional activity on these crops, which recommends thorough scouting and immediate application of plant protectants to reduce potential crop loss in greenhouses and in the field. Full article

Transgenic Bt crops are important tools for growers to manage insect pests, but their durability is threatened by the evolution of insect resistance. Implementing a resistance monitoring program is essential to detect and mitigate resistance. For non-high-dose Bt crops, resistance monitoring is challenging, because insect control is not complete, so targeted insects and insect damage will be present even without resistance. Given these challenges, sentinel plots have been used to monitor for insect resistance to non-high-dose crops by assessing changes in the efficacy of a Bt crop over time relative to a non-Bt control. We optimized a sentinel plot resistance monitoring approach for MON 88702 ThryvOn™ cotton, a new non-high-dose Bt product targeting two sucking pest taxa—Lygus (L. lineolaris and L. hesperus) and thrips (Frankliniella fusca and F. occidentalis)—and report here on the thrips monitoring methods and results. Quantifying thrips immatures was the best metric to characterize the impact of the trait, with at least a 40–60% average reduction of thrips immatures on ThryvOn relative to the control cotton at all sites with higher thrips densities. These data can be used within a ThryvOn resistance monitoring program and represent a case study for establishing a resistance monitoring approach for a non-high-dose trait product. Full article

In natural habitats, there is a strong evolutionary selection pressure on herbivorous insects to avoid danger and choose suitable host plants. Similar selection pressures may drive movement and choices of oviposition hosts by herbivorous insects living in agricultural cropping systems, in which insecticides are often used. In this study, we quantified movement responses and nymph emergence (collectively referred to as bio-responses) of western-tarnished plant bug (Lygus hesperus Knight (Hemiptera: Miridae)) individuals when exposed to environments associated with a perceived “risk” (experimental insecticide treatments and their corresponding controls). We introduce a novel analytical approach in which treatments (risk environments) are ranked in ascending order based on bio-responses (movement or nymph emergence). Consequently, linear regression coefficients were generated and used to interpret bio-responses of Lygus individuals in different life stages to risk environments. Initially, we predicted movement by Lygus individuals to be positively associated with environmental risk and nymph emergence to be negatively associated with environmental risk. Overall, based on a comprehensive combination of no- and two-choice bioassays, we found that: (1) In no-choice bioassays, movement parameters (both total distance moved and movement percentage) by all three life stages were lowest in low-risk environments and highest when Lygus individuals were exposed to either malathion or Grandevo. Accordingly, environments involving malathion or Grandevo were considered high-risk. (2) No-choice movement bioassays also revealed that Lygus males moved significantly more (based on comparison of regression intercepts) than other life stages, and that they responded significantly more (based on comparison of regression slopes) than conspecific females and nymphs. (3) In two-choice movement bioassays, neem elicited the most consistent movement responses by Lygus individuals, and adult life stages showed the strongest response. Two-choice movement bioassays also revealed that Lygus adults, compared to nymphs, were more likely to spend time in low-risk areas of the test arenas. (4) Nymph emergence was markedly lower in no-choice compared to two-choice bioassays, and in two-choice bioassays, Grandevo and malathion elicited especially biased nymph emergence from low-risk beans. To our knowledge, this is the first study in which movement bioassays have been used to quantify and characterize behavioral responses by Lygus life stages to environments associated with varying degrees of risk. The novel analytical approach presented in this study provides a high degree of complementarity to more traditional performance-testing methods used to evaluate responses to insecticides. Furthermore, we believe that this analytical approach can be of considerable relevance to studies of animal phenomics and behavioral studies of animals more broadly, in which adaptation and fitness parameters are examined in response to environmental risk and heterogeneity. Full article

Cuticle coloration in insects is a consequence of the accumulation of pigments in a species-specific pattern. Numerous genes are involved in regulating the underlying processes of melanization and sclerotization, and their manipulation can be used to create externally visible markers of successful gene editing. To clarify the roles for many of these genes and examine their suitability as phenotypic 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 six genes (aaNAT, black, ebony, pale, tan, and yellow) were identified, with two variants for black. Sequence and phylogenetic analyses supported preliminary annotations as cuticle pigmentation genes. In accord with observable difference in color patterning, expression varied for each gene by developmental stage, adult age, body part, and sex. Knockdown by injection of dsRNA for each gene produced varied effects in adults, ranging from the non-detectable (black 1, yellow), to moderate decreases (pale, tan) and increases (black 2, ebony) in darkness, to extreme melanization (aaNAT). Based solely on its expression profile and highly visible phenotype, aaNAT appears to be the best marker for tracking transgenic L. hesperus. Full article

The pyrokinin (PK) family of insect neuropeptides, characterized by C termini consisting of either WFGPRLamide (i.e., PK1) or FXPRLamide (i.e., PK2), are encoded on the capa and pk genes. Although implicated in diverse biological functions, characterization of PKs in hemipteran pests has been largely limited to genomic, transcriptomic, and/or peptidomic datasets. The Lygus hesperus (western tarnished plant bug) PK transcript encodes a prepropeptide predicted to yield three PK2 FXPRLamide-like peptides with C-terminal sequences characterized by FQPRSamide (LyghePKa), FAPRLamide (LyghePKb), and a non-amidated YSPRF. The transcript is expressed throughout L. hesperus development with greatest abundance in adult heads. PRXamide-like immunoreactivity, which recognizes both pk- and capa-derived peptides, is localized to cells in the cerebral ganglia, gnathal ganglia/suboesophageal ganglion, thoracic ganglia, and abdominal ganglia. Immunoreactivity in the abdominal ganglia is largely consistent with capa-derived peptide expression, whereas the atypical fourth pair of immunoreactive cells may reflect pk-based expression. In vitro activation of a PK receptor heterologously expressed in cultured insect cells was only observed in response to LyghePKb, while no effects were observed with LyghePKa. Similarly, in vivo pheromonotropic effects were only observed following LyghePKb injections. Comparison of PK2 prepropeptides from multiple hemipterans suggests mirid-specific diversification of the pk gene. Full article

California strawberries have two major arthropod pests—the twospotted spider mite, Tetranychus urticae and the western tarnished plant bug, Lygus hesperus, which result in significant losses to the yield and quality of marketable berries. Other important insect pests that are frequently seen in strawberry include the greenhouse whitefly, Trialeurodes vaporariorum and the western flower thrips, Frankliniella occidentalis that cause varying levels of damage depending on the level of infestation. Chemical pesticides play a major role in managing these pests but not without the associated risk of pesticide resistance and environmental safety. Two field studies were conducted in commercial strawberry fields in Santa Maria, one of the strawberry growing areas in California Central Coast, to determine the efficacy of chemical, botanical and microbial pesticides in the integrated pest management (IPM) of strawberry. Chemical, botanical and microbial pesticides were evaluated against T. urticae in a small plot study in 2013 and against L. hesperus and other insect pests in a large plot study in 2015 in commercial strawberry fields. Bug vacuums were also used in the 2015 study. Results demonstrated that non-chemical alternatives can play an important role in strawberry IPM. Full article

The Gα subunits of heterotrimeric G proteins play critical roles in the activation of diverse signal transduction cascades. However, the role of these genes in chemosensation remains to be fully elucidated. To initiate a comprehensive survey of signal transduction genes, we used homology-based cloning methods and transcriptome data mining to identity Gα subunits in the western tarnished plant bug (Lygus hesperus Knight). Among the nine sequences identified were single variants of the Gαi, Gαo, Gαs, and Gα12 subfamilies and five alternative splice variants of the Gαq subfamily. Sequence alignment and phylogenetic analyses of the putative L. hesperus Gα subunits support initial classifications and are consistent with established evolutionary relationships. End-point PCR-based profiling of the transcripts indicated head specific expression for LhGαq4, and largely ubiquitous expression, albeit at varying levels, for the other LhGα transcripts. All subfamilies were amplified from L. hesperus chemosensory tissues, suggesting potential roles in olfaction and/or gustation. Immunohistochemical staining of cultured insect cells transiently expressing recombinant His-tagged LhGαi, LhGαs, and LhGαq1 revealed plasma membrane targeting, suggesting the respective sequences encode functional G protein subunits. Full article