Sampling Optimization and Crop Interface Effects on Lygus lineolaris Populations in Southeastern USA Cotton

Tarnished plant bug, Lygus lineolaris (Hemiptera: Miridae), is an economically damaging pest in cotton production systems across the southern United States. We systematically scouted 120 commercial cotton fields across five southeastern states during susceptible growth stages in 2019 and 2020 to investigate sampling optimization and the effect of interface crop and landscape composition on L. lineolaris abundance. Variance component analysis determined field and within-field spatial scales, compared with agricultural district and state, accounted for more variation in L. lineolaris density using sweep net and drop cloth sampling. This result highlights the importance of field-level scouting efforts. Using within-field samples, a fixed-precision sampling plan determined 8 and 23 sampling units were needed to determine L. lineolaris population estimates with 0.25 precision for sweep net (100 sweeps per unit) and drop cloth (1.5 row-m per unit) sampling, respectively. A spatial Bayesian hierarchical model was developed to determine local landscape (<0.5 km from field edges) effects on L. lineolaris in cotton. The proportion of agricultural area and double-crop wheat and soybeans were positively associated with L. lineolaris density, and fields with more contiguous cotton areas negatively predicted L. lineolaris populations. These results will improve L. lineolaris monitoring programs and treatment management decisions in southeastern USA cotton.

Tarnished Plant Bug (Heteroptera: Miridae) Behavioral Responses to Chemical Insecticides

The tarnished plant bug (Lygus lineolaris Palisot de Beauvois) is the dominant insect pest of cotton (Gossypium hirsutum L.) in the Mid-South Cotton Belt. This is partly due to the fact that this pest has developed resistance to most insecticides used for control. Laboratory experiments were conducted during 2014 and 2015 to study the behavioral response of tarnished plant bug nymphs to several classes of insecticides. Twenty third-instar nymphs were placed in individual dishes divided into four quadrants with five green bean pieces in each quadrant (10 treated and 10 untreated green beans in each dish). Dishes were checked at 1, 4, 8, and 24 h. Tarnished plant bug nymphs appeared to avoid green beans treated with IGR, pyrethroid, organophosphate, or carbamate insecticides, while there appeared to be an attraction to green bean pieces treated with sulfoxamine and pyridine carboxamide insecticides. No relationship was observed with neonicotinoid insecticides within 24 h.

Palmer Amaranth (Amaranthaceae) and At-Plant Insecticide Impacts on Tarnished Plant Bug (Hemiptera: Miridae) and Injury to Seedling Cotton Terminals

The direct effect of Palmer amaranth, Amaranthus palmeri Watson, on cotton growth and development is well documented, but its indirect effect through harboring feeding insects is less understood. Palmer amaranth emerged with cotton and remaining in the field for 30 days increased tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), populations compared with a weed-free system. Weedy systems noted up to 49% more damaged terminals than weed-free systems, with cotton yield decreasing as damaged terminals increased at one of two locations. Thrips (Thysanoptera: Thripidae) populations were effectively controlled with Aeris® (Bayer, St. Louis, MO) seed treatment (imidacloprid + thiodicarb at 0.375 mg active ingredient per seed), but there was no correlation between thrips infestations and increasing damaged cotton terminals. However, Aeris seed treatment significantly reduced the occurrence of damaged cotton terminals. In a second experiment, Palmer amaranth infesting an area adjacent to a weed-free cotton field had maximum damaged terminals of 51% on the cotton row proximal to the weedy area, with the distal cotton row (44 m away) having 8% terminal damage. Cotton yield significantly decreased as damaged terminals increased. A final bioassay experiment further evaluated the influence of seed treatment on tarnished plant bug feeding impacting cotton seedlings. With Aeris seed treatment, tarnished plant bug mortality was 97%, compared with 37% for nontreated seed. Results suggest tarnished plant bug infestations increased where Palmer amaranth was present in cotton fields. Additionally, greater Palmer amaranth infestations led to an increase in damaged cotton terminals and lower yields.

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

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.

Molecular Identification of a Novel Iflavirus in Brown-Spotted Pitvipers (Protobothrops Mucrosquamatus)

Background: Iflaviridae is a family of small non-enveloped viruses with monopartite, positive-stranded RNA genomes, which are identified in arthropod hosts, primarily infecting insect species. Herein, we firstly identify the sequence of an iflavirus (YB-PMP20) found in brown-spotted pitvipers in China. Results: The sequence of YB-PMP20 showed high identity to the sequences of Hubei picorna-like virus (HUPV) (99.2% in nt), Vespa velutina-associated iflavirus like virus (VVAIV) (58.6% in nt) and Lygus lineolaris virus (LyIV-1) (46.6% in nt) in nucleotides encoding polyproteins. It contained a single large ORF (304–9291 nt) encoding 2996 amino acids. The deduced amino acid sequences were compared with those of iflavirus. Helicase, protease and the RdRp domain were found to be located at the 3´ end, and structural genes (VP1, VP2 and VP3) were found to be located at the 5´ end. Phylogenetic analysis indicated that YB-PMP20 belongs to the iflavirus cluster, and is similar to HUPV, LyIV-1 and VVAIV. Conclusion: The present study described the genetic characterization of a PmIFV strain in brown-spotted pitvipers. Our genomic data extend knowledge of the diversity of viruses in snakes.

Fusarium Hardlock Associated With Lygus lineolaris (Hemiptera: Miridae) Injury in Southeastern Cotton

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is an important insect pest in cotton that feeds on reproductive fruit, contributing to yield loss. Economically damaging infestations of L. lineolaris have doubled in Virginia since 2013. Escalation of L. lineolaris abundance may increase Fusarium hardlock disease observed in this region, compounding economic losses. Research has linked Fusarium hardlock with fungal species Fusarium verticillioides and F. proliferatum. Field and greenhouse experiments were performed to investigate (i) Fusarium hardlock occurrence in field plots managed and unmanaged for L. lineolaris, (ii) severity of F. verticillioides infection of cotton bolls with and without the presence of L. lineolaris feeding in a greenhouse setting, and (iii) Fusarium species composition and prevalence within field-collected L. lineolaris and cotton lint with and without insect feeding injury and hardlock symptoms present. Nearly twice the amount of hardlock (i.e., proportion of hardlocked locules) occurred in field-collected bolls with L. lineolaris feeding symptoms (0.40 ± 0.02) compared with bolls without (0.21 ± 0.01). Based on real-time quantitative PCR, cotton bolls exposed to F. verticillioides inoculum and caged with L. lineolaris adults had greater levels of F. verticillioides DNA compared with untreated bolls. F. proliferatum, F. verticillioides, and F. fujikuroi were isolated from field-collected L. lineolaris and hardlocked cotton lint at harvest. These findings suggest that the presence of L. lineolaris is associated with an increased risk of Fusarium hardlock in Southeastern cotton, and both should be carefully managed using timely insecticide applications and cultural control practices to minimize yield loss.