Resistance risk assessment of six pyrethroids and acephate toward the resistant adult tarnished plant bug,Lygus lineolaris

Due to rapidly developed resistance,pest management relies less on pyrethroids to control economically damaging infestations of the tarnished plant bug(TPB),Lygus lineolaris(Palisot de Beauvois)in cotton fields of Mississippi.Yet,pyrethroid resistance remains prevalent in TPB populations.This study assessed the resistance levels in adult TPB to six common pyrethroids and acephate.Resistant TBPs were collected from wild host plants in late October after harvest in the Mississippi Delta region of the United States.Based on LCso values,the field-resistant TPBs displayed higher resistance to permethrin,esfenvalerate,and bifenthrin(approximately 30 fold)and moderate resistance toα-cyhalothrin,β-cyfluthrin,5-cypermethrin,and acephate(approximately 15 fold).Further investigations showed that the inhibitors of three detoxification enzyme,triphenyl phosphate(TPP),diethyl maleate(DEM),and piperonyl butoxide(PBO)had synergistic effects on permethrin,γ-cyhalothrin,and bifenthrin in resistant TPBs.Furthermore,elevated esterase,GST,and P450 activities were significantly expressed in fieldresistant TPBs.Additionally,GST and esterase were reduced after 48 h exposure to certain pyrethroids at LCso dose.The synergistic and biochemical assays consistently indicated that P450 and esterase were involved in pyrethroid detoxification in TPBs.This study provides valuable information for the continued use of pyrethroids and acephate in controlling TPBs in cotton fields in the Mississippi Delta region of the United States.

Relative preference of Lygus hesperus （Hemiptera： Miridae） to selected host plants in the field

Information on host plant preference of agriculturally important insect pests, such as Lygus hesperus （Knight）, can be helpful in predicting its occurrence and future movement among crop and nonrop host plants. A field study was conducted during 2005 and 2006 to evaluate the host preference of Lygus to cotton and four other host plants in the Texas High Plains, including alfalfa （Medicago sativa L.）, wild sunflower （Helianthus annuus L.）, Russian thistle （Salsola iberica L.） and pigweed （Amaranthus palmeri L.）. Sampling for both nymphs and adults during 2005 （July to November） and 2006 （June to November） showed that alfalfa and Russian thistle were the two most preferred hosts out of the five hosts evaluated. Abundance of nymphs （numbers per 50 sweeps per host plant） during the sampling period also indicated the superior reproductive suitability of alfalfa and Russian thistle. Cotton appeared to be the least attractive host plant for Lygus when Russian thistle and alfalfa were available in the host mosaic. Seasonal abundance of Lygus was found to be lower during 2006 compared to 2005, which may be explained by the difference in rainfall patterns during these two years. In terms of species dominance, L. hesperus was the most dominant species in the sampled population followed by an inconsiderable fraction ofL. elisus and L. lineolaris.

Molecular cloning and comparative analysis of transcripts encoding chemosensory proteins from two plant bugs, Lygus lineolaris and Lygus hesperus

Chemosensory proteins(CSPs)are soluble carrier proteins typically characterized by a six‐helix bundle structure joined by two disulfide bridges and a conserved Cys spacing pattern(C1‐X6‐8‐C2‐X16‐21‐C3‐X2‐C4).CSPs are functionally diverse with reported roles in chemosensation,immunity,development,and resistance.To expand our molecular understanding of CSP function in plant bugs,we used recently developed transcriptomic resources for Lygus lineolaris and Lygus hesperus to identify 17 and 14 CSP‐like sequences,respectively.The Lygus CSPs are orthologous and share significant sequence identity with previously annotated CSPs.Three of the CSPs are predicted to deviate from the typical CSP structure with either five or seven helical segments rather than six.The seven helix CSP is further differentiated by an atypical C3‐X3‐C4 Cys spacing motif.Reverse transcriptase PCR‐based profiling of CSP transcript abundance in adult L.lineolaris tissues revealed broad expression for most of the CSPs with antenna specific expression limited to a subset of the CSPs.Comparative sequence analyses and homology modeling suggest that variations in the amino acids that comprise the Lygus CSP binding pockets affect the size and nature of the ligands accommodated.

Remote Sensing of Selected Winter and Spring Host Plants of Tarnished Plant Bug (Heteroptera: Miridae) and Herbicide Use Strategies as a Management Tactic

Remote sensing was used in a series of experiments over a three-year period to obtain spectral reflectance data for studying differences in vegetation indices between grasses, broadleaf plants, and grass/broadleaf plant mixtures. Selected non-crop winter and spring host plants of tarnished plant bug, Lygus lineolaris, were planted in field-plot experiments. Multispectral reflectance data were aerially acquired with both a Real-Time Digital Airborne Camera System (RDACS) sensor and Geospatial Systems (Duncan Tech) MS-2100 multispectral camera. The following six vegetation indices of spectral reflectance were evaluated in this study: normalized difference vegetation index, ratio vegetation index, green normalized difference vegetation index, green vegetation index, green ratio vegetation index, and Ashburn vegetation index. Vegetation indices calculated with imagery data for the grasses and broadleaves differed significantly;there appeared to be more discriminating differences between vegetation indices for grasses and broadleaf plants when the indices were based on a combination of green and near infrared or green and red spectral bands than when the indices were based on red and near infrared spectral bands. Insect data from these studies confirm that tarnished plant bug prefers broadleaf host plants, but can use Italian ryegrass for food and reproduction. The narrow temporal window of host suitability for Italian ryegrass may limit its significance. Herbicide destruction of broadleaf host plants in early spring prevented the tarnished plant bug population increases that occurred in untreated plots. Findings of this study would be useful in site-specific vegetation management decisions in programs such as the prototypical area-wide tarnished plant bug management experiment conducted in the Delta region of Mississippi.