Genetic variation in zoophagy and dietary shift in the phytozoophagous tarnished plant bug, Lygus lineolaris

ABSTRACTThe polyphagous tarnished plant bug (TPB), Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae), inflicts substantial damage to strawberries and to several other valuable crops, impacting both yield quantity and quality. Effective control strategies are crucial to mitigate these losses. This study aimed to elucidate TPB host preferences and reproductive behaviours under various integrated pest management approaches. Experimental arenas with strawberry plants included treatments involving the predator Nabis americoferus (Carayon) (Hemiptera: Nabidae) and trap crops. In each arena, 30 adult TPBs were exposed to different configurations: (i) three strawberry plants, (ii) three strawberry plants with predators, (iii) one strawberry plant alongside two trap crop plants (buckwheat and canola), and (iv) one strawberry plant with the two trap crops and predators. TPB distribution among the arena, plant species and plant sites (flower, stem and adaxial and abaxial leaves) were monitored over 72 h. One week later, adults were removed and the number of emerged first instar nymphs (L1) was recorded three times postexperiment. The results indicate a preference shift in TPB behaviour influenced by plant diversity and predator presence. TPBs exhibited a reduced presence on strawberries when trap crops were introduced, with canola as a preferred plant. This preference for canola was supported by higher TPB offspring counts. Conversely, buckwheat, although less preferred, contributed to diluting TPB populations across plant species. The introduction of N. americoferus showed dual effects: While reducing TPB oviposition on canola, it increased TPB presence on strawberries, highlighting the importance of nonconsumptive effects (NCEs) of predators in agroecosystems. Nonetheless, the combination of canola as a trap crop and N. americoferus as a predator effectively reduces TPB presence on strawberry flowers, essential for fruit development. This approach shows promise when integrated with other strategies, such as vacuuming and pheromone‐enhanced coloured traps.

A laboratory experiment was performed to compare fitness parameters of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), populations collected from the Hills and Delta regions of Mississippi. Each population was split into two cohorts to be reared on cotton or artificial diet to make comparisons of food source and region of collection. Each population was maintained separately and allowed to mate. Nymphal survivorship from the F1 generation of each population from each region and food source was compared. Parameters measured included development times to fourth instar, fifth instar and adult, total nymphal survivorship, fecundity, and fertility. Populations collected from the Delta region and reared on cotton developed significantly faster at all life stages than other populations. Tarnished plant bugs from the Hills reared on cotton developed significantly slower than other populations, except those from the Hills reared on artificial diet. Populations reared on diet had significantly higher survivorship than those reared on cotton. Tarnished plant bug populations from the Delta region laid significantly more eggs per female per day than those from the Hills region. Populations reared on cotton also laid significantly more eggs per female per day than those reared on diet. Populations collected in the Delta region laid significantly more viable eggs per female per day than those from the Hills region. Tarnished plant bugs reared on cotton produced significantly more nymphs per female per day than those reared on diet. These data indicate there are differences in several fitness parameters between tarnished plant bug populations from the Hills and Delta regions of Mississippi.

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is one of the most economically important pests of cotton, Gossypium hirsutum L., in the mid-southern U.S. Experiments were conducted during 2012 and 2013 to evaluate the effect of nitrogen fertilizer application rate on tarnished plant bug populations and management as well as cotton growth, development, and yield. Fertilizer (N) was applied as a 32% urea ammonium nitrate (UAN) solution at pinhead square at five different application rates: 0, 45, 90, 134, and 179 kg N ha-1. Plots were managed for tarnished plant bug with insecticides using treatment thresholds recommended by the Mississippi State University Extension Service. A corresponding set of plots for each N fertilizer application rate were not treated with insecticides fto determine tarnished plant bug infestation level and subsequent damage. The interaction of N fertilizer application rate and tarnished plant bug management level (treated or not treated) was significant for total number of plant bugs observed during the growing season. Fertilizer N application rate and tarnished plant bug management each had a significant impact on the mean number of plant bugs observed on a weekly basis and cotton lint yield. Fertilizer N application rate had a significant impact on the number of applications required to manage tarnished plant bug populations. This research demonstrated that there was an optimal level of N availability to balance yield and insecticide applications for tarnished plant bug, thus maximizing profits.

Grain amaranth, Amaranthus cruentus L., is a potential, alternative crop for midwestern farmers. The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is a potentially serious pest of amaranth, feeding on grain amaranth and causing developing seed to shrivel and discolor. Field tests were conducted during 1987 and 1988, at Ames, Iowa, to determine the effect of L. lineolaris on amaranth seed weight. The treatments included artificially (by hand) infesting heads with selected numbers of tarnished plant bugs and determining the effect of tarnished plant bug density, the effect of a naturally occurring tarnished plant bug population, and the effect of tarnished plant bug feeding duration. In 1987, when 50 tarnished plant bugs were caged on developing heads for 8 wk, seed weight decreased by 82%. When 10 bugs were caged on developing heads, there was no significant decrease in seed weight. In 1988, when 12 bugs were caged on developing heads for 8 wk, seed weight decreased by 80%. In 1987, when tarnished plant bugs were caged on developing heads for 2, 4, 6, or 8 wk, seed weight significantly decreased by 39.5% between the second and fourth week of feeding. In 1988, tarnished plant bugs feeding on the developing heads for 5 wk reduced seed weight by 57.6%. During 1987, naturally occurring tarnished plant bugs feeding continuously on the terminal heads significantly reduced seed weight by 28.2% between the third and fifth week of feeding.

Tarnished plant bugs (TPB), Lygus lineolaris (Palisot de Beauvois), were collected from wild host plants growing in weed fields undistrubed by agricultural practices, and from the same plant species found in disturbed areas adjacent to cotton fields in Washington County, MS during 1984 and 1985. Euphorine parasitism of TPB adults and nymphs collected in these 2 types of habitats was determined by dissection. For each year of the study period, parasitism of TPB collected from all host plant species sampled in weed fields peaked at 8 and 32% on 28 June 1984, and at 6 and 12% on 30 May 1985 for nymphs and adults, respectively. On these 2 dates parasitism of adult TPB found on all host plant species sampled in the weed fields was significantly higher (P ≤ 0.01) than parasitism of those TPB collected from the same plant species in areas adjacent to cotton fields. Parasitism of TPB in the undisturbed areas may have been sufficient to locally reduce TPB populations. However, undisturbed areas are uncommon in Washington County and the parasitoids are probably univoltine. Consequently, the impact of euphorine parasitoids on area-wide TPB populations was probably small.

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is one of the most yield- limiting insect pests attacking cotton in the Mid-Southern region of the U.S. This pest is almost exclusively managed with chemical control strategies. The organophosphate insecticide, acephate, has been one of the most important insecticides recommended to control tarnished plant bugs. In recent years, reports of unsatisfactory acephate performance have become common and actual field rates have been increased to improve control. The objective of this study was to survey acephate susceptibility in Louisiana populations of tarnished plant bug using laboratory bioassays and evaluate acephate efficacy in field trials. Insecticide residual on glass (vial tests) bioassays were used to estimate acephate dose mortality responses (LC50’s) for five, nine, and six populations during 2007, 2008, and 2009, respectively. The LC50‘s for these collections ranged from 1.63-32.36 µg/vial. Resistance ratios (RR) were calculated relative to a susceptible standard population (LC50 = 3.1 µg/vial) and ranged from 0.52-10.44 among populations. Field control failures with acephate are likely when RR’s >3.0 and when persistent infestations exceed the action threshold for foliar sprays. Twenty field trials were conducted during 2007-2009 to determine acephate performance against native infestations. Five treatments (0[control], and acephate at 0.54, 0.82, 1.1, 1.34 kg AI/ha) were arranged in a Latin square design and were placed in commercial production fields and on LSU AgCenter Research Stations. Acephate efficacy was collected five to seven days after treatment using a one meter black shake sheet. The lowest acephate rate (0.54 kg AI/ha) significantly reduced tarnished plant bugs compared to that in the non-treated plots at 17 locations. However, this rate only reduced numbers below the action threshold in the 2007 trials. During 2008 and 2009, acephate rates of 0.82-1.34 kg AI/ha were needed to adequately control infestations. These results indicate that acephate susceptibility in Louisiana populations of tarnished plant bug is shifting and field performance is decreasing.

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is the most significant insect pest of cotton, Gossypium hirsutum (L.), in the mid-southern United States (Arkansas, Louisiana, Mississippi, Missouri, and Tennessee). Past research has shown the impact that planting date, nitrogen rate, and variety selection has on tarnished plant bug populations, but a paucity of data exists on the effect irrigation timing has on tarnished plant bug. Experiments were conducted at the Mississippi State University Delta Research and Extension Center in Stoneville, MS to determine if insecticide applications targeting the tarnished plant bug could be reduced in response to irrigation timings. Treatments were in a strip-block arrangement, with the main plot factor being irrigations initiated at squaring, first flower, peak flower, and a non-irrigated control. The sub-plot factor was tarnished plant bug management that consisted of insecticide applications made weekly, at threshold, and a non-treated control. Overall, insecticide applications for tarnished plant bug increase yield. Irrigation initiated at squaring resulted in tarnished plant bugs exceeding the recommended treatment threshold significantly more than when irrigations were initiated later in the growing season. Also, when irrigation was postponed until peak flower, no yield loss or delay in maturity was observed. These results indicate that irrigation timing could be a potential cultural control practice that reduces the number of insecticide applications targeting tarnished plant bug populations in Mid-South cotton.

Tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is the major insect pest of cotton, Gossypium hirsutum L., in the mid-South. This pest moves into cotton fields from non-cotton hosts during late spring and early summer. Stable carbon isotope (SCI) analysis was used to characterize plant hosts of tarnished plant bugs, as well as adult tarnished plant bugs that had developed as immatures on the plants. Plants of two host types (C3 versus C4) were identified using the SCI analysis, and tarnished plant bug adults reared as immatures on the plants retained a carbon isotopic signature similar to the host plant. Thus, carbon isotope ratios of tarnished plant bugs reared on C3 plants differed from those reared on C4 plants. Carbon and nitrogen isotope ratios were analyzed jointly using cluster and discriminant analyses to discriminate between adults that developed as immatures on two primary C4 hosts (maize, Zea mays L., and pigweed, Amaranthus spp.). These analyses distinguished tarnished plant bugs that developed as nymphs on maize from those that developed on pigweed. To evaluate the impact on the carbon isotopic signature of immature tarnished plant bugs moving from one host type to another, nymphs were reared for the first three instars on broccoli, Brassica oleracea L. var. italica, (a C3 plant) and transferred to maize (a C4 plant) for the final two instars. The reverse was also done, and isotope ratios of these insects were compared to those that completed all instars on either broccoli or maize. The isotopic signature of the host plant was primarily obtained by tarnished plant bugs during the last two instars. Results from this study demonstrated the utility of carbon and nitrogen isotope ratio determination for evaluating the ecology of host plants of tarnished plant bugs in the mid-South. Knowledge of the primary hosts of tarnished plant bugs could allow for population management/reduction of these insects before moving into cotton.

A field experiment was conducted in Stoneville, MS, during 2010 and 2011 to investigate the impact of varietal maturity, planting date, and insecticide application on tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), populations and damage in cotton. Four planting dates were selected to encompass the cotton-planting period in Mississippi. An early and late maturing variety were planted at each planting date, and each variety and planting date combination was either sprayed or unsprayed for tarnished plant bugs. Plots were sampled weekly from first square until physiological maturity. Plots were harvested at the end of the season. Early planting dates had lower densities of tarnished plant bug and required fewer insecticide applications than the later planting dates. Mid-April to early May planting dates sustained less yield loss from tarnished plant bug than mid-May to late-May planting dates. Tarnished plant bug had less impact on yield of the early maturing variety than on the late maturing variety. The sprayed plots yielded more than unsprayed plots. These data demonstrate that later plantings of cotton in the Mississippi Delta are likely to experience yield losses from tarnished plant bug and need to be sprayed more compared with early cotton plantings. As a result, growers should manage their crop for earliness through planting date and varietal selection.

Reduced insecticide use in cotton, Gossypium hirsutum L., as a consequence of the Boll Weevil Eradication Program and the broad adoption of Bt cotton, have helped make the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), a consistent pest of cotton each year in the mid-south. Maize, Zea mays L., has been implicated as having a role in the season-long dynamics of tarnished plant bug infestations in cotton. To date, no published information exists describing the quality of maize as a host for tarnished plant bug. No-choice field studies indicated that adult tarnished plant bug females oviposited into maize leaves, tassels, and ears. Laboratory studies showed that first-instar tarnished plant bugs could successfully develop to the adult stage when fed maize silks at the R1 growth stage, tassels before (VT) and during (R1) pollen shed, and milk stage (R3) kernels from the tip and base of the ear. The proportion of nymphs surviving to the adult stage on these tissues was often similar to that of broccoli, Brassica oleracea L. Nymphs did not develop to adults when fed V5 or R1 maize leaves. However, survival of first instars to the adult stage was improved when nymphs fed on tassels with pollen for 6 d and then moved to silks or leaves. Another field study showed that tarnished plant bugs reproduced in maize mainly during the tassel (VE and VT) and the R1-R3 ear growth stages, and a single new generation was produced in maize during these stages. The highest population recorded during the study (24 June 2005) consisted mostly of nymphs and was estimated to be 29,600/ha (12,000/acre). These studies showed that maize is a suitable host for tarnished plant bug reproduction and development, and its production plays a significant role in the population dynamics of the tarnished plant bug in the mid-south.

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is a major pest of cotton in the midsouthern United States, including the states of Arkansas, Mississippi, Louisiana, western Tennessee, and southeastern Missouri. Insecticides provide the primary form of control for this pest, and numerous applications are required annually to control the tarnished plant bug. Little information exists regarding when to terminate insecticide applications targeting tarnished plant bugs in cotton. Numerous sprays are made late in the season to protect a small percentage of the overall yield. Experiments were conducted at the Mississippi State University Delta Research and Extension Center to determine the impact of tarnished plant bug infestation timings on cotton yield. Two separate planting dates were utilized to determine the weeks of flowering that tarnished plant bugs can cause significant yield losses. There was a significant planting date by treatment interaction. Overall, yields were greater in the first planting date than the second planting date. In both planting dates, the first 4 wk of flowering were the most critical for tarnished plant bug control, and this is when the greatest yield losses occurred. Also, when no insecticide applications were made after the fourth week of flowering, no significant yield loss was observed. These data demonstrate the importance of scouting and adhering to treatment thresholds during the early flowering period. These data also suggest that thresholds may be able to be modified or eliminated after the fourth week of flowering, but more research is needed to confirm this.

Replicated field trials indicated that tarnished plant bug (TPB), Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae) attained relatively-high densities on hybrid vetches, Vicia sativa L. X V. cordata Wulf cv ‘Cahaba White’ and ‘Vantage’, lower densities on crimson clover, Trifolium incarnatum L. cv ‘Dixie,’ and particularly-low densities on subterranean clover, Trifolium subterraneum L. cv ‘Mt. Barker’. Densities of TPB were also relatively low on an additional 10 types of subterranean clover, including 7 cultivars representing T. subterraneum, 1 cultivar of T. brachycalycinum Katznelson and Morley, and 3 of T. yanninicum Katznelson and Morley. Field longevity trials indicated that late-instar and adult TPB lived longer when caged on crimson clover than on hybrid vetch, which in turn supported better survival than did subterranean clover. When adult TPB were caged on hybrid vetch or subterranean clover with or without floral and fruiting structures, there was no evidence that the presence of these structures prolonged TPB survival on either crop. In laboratory choice tests with flowering and fruiting shoots of three cover crops, TPB preferred crimson clover over hybrid vetch, which in turn was more attractive than subterranean clover. When shoots were presented after reproductive structures had been excised, there was no statistically-significant preference by TPB.

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 LC50 values, the field-resistant TPBs displayed higher resistance to permethrin, esfenvalerate, and bifenthrin (approximately 30 fold) and moderate resistance to λ-cyhalothrin, β-cyfluthrin, ζ-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, λ-cyhalothrin, and bifenthrin in resistant TPBs. Furthermore, elevated esterase, GST, and P450 activities were significantly expressed in field-resistant TPBs. Additionally, GST and esterase were reduced after 48 h exposure to certain pyrethroids at LC50 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.

Nosema leptocoridis sp. n., microsporidian parasite of Leptocoris trivittatus (Say) (hemiptera)

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae), has become the primary target of foliar insecticides in cotton, Gossypium hirsutum L., throughout the Midsouth over the past several years. This prompted a reevaluation of existing action thresholds for flowering cotton under current production practices and economics. A trial was conducted at 19 locations throughout the Midsouth during 2006 and 2007. Threshold treatments ranged from a weekly automatic insecticide application to a very high threshold of 10 tarnished plant bugs per 1.5 row-m on a black drop cloth. Individually, all locations reached the lowest threshold, and eight locations had a significant yield loss from tarnished plant bugs. Across all locations, lint yield decreased 0.85 to 1.72% for each threshold increase of one tarnished plant bug per 1.5 row-m. Yield loss was most closely correlated to pest density during the latter half of the flowering period. The relationship between plant bug density or damage and yield was similar for drop cloth, sweep net, and dirty square sampling methods, but the correlations among these sampling methods were not high. Incorporating actual insecticide application data from the trial and average production and economic factors for Midsouth cotton, the economic threshold, if monitoring once per week, should be between 1.6 and 2.6 tarnished plant bugs per 1.5 row-m during the flowering period. More frequent monitoring or situations where insecticide applications are more efficacious may alter this threshold.