Tarnished Plant Bug Populations Research Articles

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 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.

Toxicity Assessment of Four Formulated Pyrethroid-Containing Binary Insecticides in Two Resistant Adult Tarnished Plant Bug (Lygus lineolaris) Populations.

Over the past several decades, the extensive use of pyrethroids has led to the development of resistance in many insect populations, including the economically damaging pest tarnished plant bug (TPB), Lygus lineolaris, on cotton. To manage TPB resistance, several commercially formulated pyrethroid-containing binary mixtures, in combination with neonicotinoids or avermectin are recommended for TPB control and resistance management in the mid-South USA. This study aimed to evaluate the toxicity and resistance risks of four formulated pyrethroid-containing binary mixtures (Endigo, Leverage, Athena, and Hero) on one susceptible and two resistant TPB populations, which were field-collected in July (Field-R1) and October (Field-R2), respectively. Based on LC50 values, both resistant TPB populations displayed variable tolerance to the four binary mixtures, with Hero showing the highest resistance and Athena the lowest. Notably, the Field-R2 exhibited 1.5-3-fold higher resistance compared to the Field-R1 for all four binary insecticides. Moreover, both resistant TPB populations demonstrated significantly higher resistance ratios towards Hero and Leverage compared to their corresponding individual pyrethroid, while Endigo and Athena showed similar or lower resistance. This study also utilized the calculated additive index (AI) and co-toxicity coefficient (CTC) analysis, which revealed that the two individual components in Leverage exhibited antagonist effects against the two resistant TPB populations. In contrast, the two individual components in Endigo, Hero, and Athena displayed synergistic interactions. Considering that Hero is a mixture of two pyrethroids that can enhance the development of TPB resistance, our findings suggest that Endigo and Athena are likely superior products for slowing down resistance development in TPB populations. This study provides valuable insight for selecting the most effective mixtures to achieve better TPB control through synergistic toxicity analysis, while simultaneously reducing economic and environmental risks associated with resistance development in the insect pest.

Evaluating Efficacy and Chemical Concentrations of Commonly Used Insecticides Targeting Tarnished Plant Bug in Mid-South Cotton

Studies were conducted from 2017 to 2021 at nine locations across Arkansas, Louisiana, Mississippi, and Tennessee to evaluate efficacy, residual control, and effective chemical concentrations of commonly used insecticides targeting tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), nymphs in Mid-South cotton. Foliar applications of imidacloprid, flonicamid, thiamethoxam, oxamyl, dicrotophos, acephate, novaluron, and sulfoxaflor were applied at locally recommended rates. Plots were sampled for nymphs at 4, 7, and 10 d after treatments (DAT), and leaves were analyzed for concentration of active ingredients from plots located in one site in 2021 at 4, 7, 10, and 14 DAT. Across all sampling dates, insecticide treatments reduced nymph infestations compared to untreated control, except for imidacloprid at 10 DAT. All insecticide treatments resulted in higher lint yields compared to untreated control. Overall, sulfoxaflor, novaluron, and acephate offered the best control of nymphs and provided the greatest yield protection among treatments. Moderate control was achieved with thiamethoxam, oxamyl, and dicrotophos. Imidacloprid and flonicamid resulted in less control. Concentrations of flonicamid, thiamethoxam, dicrotophos, acephate, and novaluron persisted up to 14 DAT in leaves. Imidacloprid and oxamyl were not detected at 7, 10, or 14 DAT, and sulfoxaflor was not detected at 14 DAT in leaves. In these studies, control of tarnished plant bug nymphs never exceeded 75% regardless of insecticide or sampling date. The moderate efficacy and short residual control shown in these studies explain why multiple insecticide applications within short intervals are needed to manage heavy tarnished plant bug populations

Residual Effects of Novaluron and Efficacy of Subsequent Applications to Control Mid-South Tarnished Plant Bug (Hemiptera: Miridae) Populations

Novaluron is often used in the early-square development period of cotton in the midsouthern U.S. to manage immature Lygus populations. Preventing field populations of tarnished plant bug from reaching economically damaging levels is vital when protecting cotton yield. Field experiments were conducted in 2019 and 2020 to better understand impacts of initial novaluron applications, efficacy of subsequent insecticides, and residual activity of novaluron. Tarnished plant bug populations had less impact on cotton yield when an insecticide with adult activity was applied with novaluron at the third week of squaring.

A Dynamic Threshold Approach for Tarnished Plant Bug (Hemiptera: Miridae) Management in the Midsouthern U.S. Cotton.

One of the most economically important pests of cotton, Gossypium hirsutum L., in the midsouth region of the United States is the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois, Hemiptera: Miridae). Tarnished plant bug populations across the region have exhibited widespread resistance to numerous insecticide classes. To minimize late season resistance development, reducing unwarranted applications during the late flowering period can aid in resistance management and potentially reduce input costs. Trials were conducted during 2019 and 2020 to evaluate the impacts of tarnished plant bug populations in the later flowering period of cotton by modifying or terminating threshold regimes during the later weeks of bloom. Results showed that dynamic thresholds altered at the fourth week of bloom or later can reduce the number of late season applications made with no penalty to yield. Additionally, when utilizing a week of bloom termination approach, no significant yield losses were seen when terminating applications after the fourth week of bloom. These data may offer an alternative method to managing tarnished plant bug populations during the later flowering period of midsouth cotton.

Impact of Irrigation Timing on Tarnished Plant Bug Populations and Yield of Cotton

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.

Impact of Nitrogen Application Rate on Tarnished Plant Bug (Heteroptera: Miridae) Populations and Management in Cotton

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.

Patterns of Tarnished Plant Bug (Hemiptera: Miridae) Resistance to Pyrethroid Insecticides in the Lower Mississippi Delta for 2008-2015: Linkage to Pyrethroid Use and Cotton Insect Management.

Populations of tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae), from the Lower Mississippi Delta regions of Arkansas, Louisiana, and Mississippi were evaluated from 2008 through 2015 for susceptibility to pyrethroid insecticides using a diagnostic-dose assay with permethrin. Resulting data add to the compilation of pyrethroid susceptibility data carefully tracked in this pest since 1994 and provide continuing evidence of high frequencies of pyrethroid resistance in field populations of the tarnished plant bug. Resistance levels are variable, and some populations remain susceptible suggesting practical value in the continued use of the diagnostic-dose assays prior to pyrethroid treatments. Recent studies with dose–response models suggest that levels of pyrethroid resistance in some populations may still be evolving, with some populations requiring higher doses to reach levels of control comparable to those observed 10 yr ago. Concerns for frequent use of multiple classes of insecticides and possible selection for tarnished plant bugs with metabolic resistance mechanisms capable of detoxifying available insecticide chemistries warrant continued efforts to manage resistance in this important crop pest. Associations among measured pyrethroid resistance levels, published data on annual use of pyrethroid insecticides, and annual estimates of cotton insect losses and control costs were explored and summarized for the 8 yr of this investigation. Mortality of tarnished plant bugs at the diagnostic-dose of permethrin was negatively correlated with kilograms of pyrethroids applied per acre of harvested cropland.

Temporal and Spatial Genetic Variability Among Tarnished Plant Bug (Hemiptera: Miridae) Populations in a Small Geographic Area

ABSTRACT The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is an important pest of cotton that also feeds on other crops and many wild hosts. In the mid-South, where tarnished plant bugs in cotton are controlled exclusively with synthetic insecticides, infestations resulted in >29% of all yield loss attributed to insect damage and the control costs exceeded US$10 per acre in 2013. They have developed resistance to the most commonly used insecticides. Estimations of gene flow and migration are important to understand the spread of resistance in tarnished plant bug populations. Here, we analyzed tarnished plant bugs collected from July to September, 2006, to estimate population genetic parameters using 13 microsatellite markers. Our data indicated that tarnished plant bug populations in the study area had undergone a population bottleneck and all loci deviated from Hardy—Weinberg equilibrium in one or more collections. Bayesian simulations and factorial correspondence analysis indicated the p...

A Biological Comparison of Tarnished Plant Bug (Hemiptera: Miridae) Populations From Mississippi's Major Agricultural Regions

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.

Pollen analyses of tarnished plant bugs

Wild host plants are important for tarnished plant bug (TPB – Lygus lineolaris) populations, especially when cultivated crops are not flowering. Knowledge of native habitats is important for managing this insect pest. Although pollen has been used to characterize dispersal and food sources of many insects, it has not been used for TPB. The purpose of this study was to determine if pollen analyses could be used as a tool to determine the non-crop plants associated with TPB. Thirty-eight TPB were collected from light traps set up at two sites near the USDA-ARS research farm at Stoneville, Mississippi on 27 June 2011. Overall, 1183 pollen grains from 79 plant taxa were found in the samples. The pollen recovered was identified to 29 families, 33 genera, and 24 species. Many of the taxa of pollen found, such as Saururus cernuus C. Linnaeus (lizard's tail), Sagittaria, Echinodorus and Carya aquatic (water hickory), occur in wet habitats. From the assemblage of identified pollen grains, TBP from both sites utilized plants from disturbed and/or wet habitats.

Identification of Lygus hesperus by DNA barcoding reveals insignificant levels of genetic structure among distant and habitat diverse populations.

BackgroundThe western tarnished plant bug Lygus hesperus is an economically important pest that belongs to a complex of morphologically similar species that makes identification problematic. The present study provides evidence for the use of DNA barcodes from populations of L. hesperus from the western United States of America for accurate identification.Methodology/Principal FindingsThis study reports DNA barcodes for 134 individuals of the western tarnished plant bug from alfalfa and strawberry agricultural fields in the western United States of America. Sequence divergence estimates of <3% reveal that morphologically variable individuals presumed to be L. hesperus were accurately identified. Paired estimates of Fst and subsequent estimates of gene flow show that geographically distinct populations of L. hesperus are genetically similar. Therefore, our results support and reinforce the relatively recent (<100 years) migration of the western tarnished plant bug into agricultural habitats across the western United States.Conclusions/SignificanceThis study reveals that despite wide host plant usage and phenotypically plastic morphological traits, the commonly recognized western tarnished plant bug belongs to a single species, Lygus hesperus. In addition, no significant genetic structure was found for the geographically diverse populations of western tarnished plant bug used in this study.

Bioassay for Determining Resistance Levels in Tarnished Plant Bug1Populations to Neonicotinoid Insecticides

A laboratory bioassay was developed and used to test field populations of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), for development of resistance to the neonicotinoid insecticides imidacloprid (Trimax®) and thiamethoxam (Centric®). The bioassay determined LC50 values by feeding adult tarnished plant bugs known doses of the insecticides in a 10% solution (by weight) of honey in water. Field populations from 19 (imidacloprid) and nine (thiamethoxam) locations in the mid-South were tested in 2006 and their LC50s were compared to LC50 values determined in tarnished plant bug populations at the same locations in 2007. The LC50 values were also compared to LC50 values determined using imidacloprid and thiamethoxam on a susceptible population from Crossett, AR. Results of the comparisons showed that no resistance to thiamethoxam had developed in the nine populations tested. Some resistance to imidacloprid was found in most of the test populations, because their LC50 values were significantly greater than the LC50 value for the susceptible population from Crossett. Resistance to imidacloprid did not increase in populations at 10 locations from 2006 to 2007, and the LC50 values were not significantly different between the two years. The LC50 for imidacloprid in 2007 was significantly greater than the LC50 in 2006 in populations at only four of the 19 test locations. These results showed that while some resistance to imidacloprid was present, the overall tendency was for the resistance to remain the same or decrease during the two years it was studied. The bioassay developed and used in the study is the only rapid method available for monitoring resistance in tarnished plant bug populations to neonicotinoid insecticides. The baseline data for both imidicloprid and thiamethoxam provide a basis for comparison to determine changes in resistance in future monitoring studies.

Tarnished Plant Bug (Heteroptera: Miridae) Populations near Fields After Early Season Herbicide Treatment

A single herbicide (Trimec® or Strike 3™) application in early season (March or April) was made to marginal areas around fields in 23-km2 test sites of the Mississippi Delta in 1999, 2000, and 2001. The herbicide was used to kill broadleaf weeds in the marginal areas that served as hosts for tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois). The herbicide treatment caused a significant reduction in wild host densities in the treated test sites in all 3 yr. Tarnished plant bug populations in treated test sites did not increase significantly in the treated marginal areas during April and May after treatment of the margins in the first 2 wk of March in 2000 and 2001. The herbicide application was made in the first 2 wk of April 1999, and plant bug populations increased in treated marginal areas in this year. The increase was thought to be caused by plant bugs moving to Italian ryegrass, Lolium multiflorum Lamarck, a previously unreported plant bug host, which was not affected by the herbicide. Laboratory tests showed that plant bugs would oviposit in flowering or nonflowering ryegrass when caged on ryegrass for a 6-d period. Newly emerged nymphs developed into adults (56%) when reared on floral spikelets of ryegrass, but no adults were obtained when they were reared on ryegrass stems and leaves. Rearing on floral spikelets beginning with third-instar nymphs resulted in 92% adults, whereas third-instar nymphs reared on stems and leaves produced no adults. These results showed that ryegrass could serve as a reproductive host for plant bugs when it flowered during late April and May. Application of the herbicide in March, when ryegrass was not in flower, resulted in no significant increases in plant bug populations on wild hosts (mainly ryegrass) during April and May in 2 yr of the field study.

Effects of water volume rates on spray deposition and control of tarnished plant bug [Hemiptera : Miridae] in strawberry crops

Field experiments were performed on the effect of three volumes of application on spray deposition and insecticidal efficacy against the tarnished plant bug (Lygus lineolaris) in two strawberry (Fragaria ananassa) cultivars, Kent and Chambly. The rate of application of malathion was kept constant at 4.5 kg a.i. ha-1 for volumes of application of 500 and 1500 L ha-1. Plant coverage was measured using a fluorescent tracer applied at volumes of application of 500, 1000 and 1500 L ha-1. The tracer was recovered from samples taken from different plant locations and on the ground. Tarnished plant bug populations were evaluated 24 hours before and after insecticidal treatment. When coverage data were normalized for a fixed active ingredient rate, an increase in the volume of application from 500 to 1500 L ha-1 frequently had no effect on the amount of tracer recovered at the various locations. On some occasions, an increase in volume of application resulted in a decrease in the amount of tracer recovered, i.e. leaves at the top and bottom of the canopy (Kent), sepals (Kent). Tarnished plant bug population control was commercially acceptable at 500 and 1500 L ha-1.

The relationship between populations of European tarnished plant bug ( Lygus rugulipennis) and crop losses due to fruit malformation in everbearer strawberries

Field experiments in SE England in 1997–1999 were used to determine strawberry crop losses due to the European tarnished plant bug, Lygus rugulipennis. Feeding by the pest on flowers and developing fruits caused malformation of fruits at harvest. A range of pest population densities were generated by different insecticide spray programmes on replicated plots. Relative pest populations were estimated by sampling 40 plants per plot with a beating tray. This method of sampling was shown to have a similar efficiency to suction sampling. A positive correlation was found between the percentage of fruit with moderate or severe malformation and the number of adults plus nymphs of L. rugulipennis. The mean berry weight was also significantly lower in plots with high L. rugulipennis numbers at some sampling dates. A regression analysis of the percentage of moderately and severely malformed fruit against the number of L. rugulipennis was highly significant ( P< 0.001, adjusted R 2=0.34) and had a slope of 0.55, i.e. two Lygus bugs in a beat sample from 40 plants caused approximately 1% of fruits to be malformed. Based on the value of the crop, the cost of insecticide treatment and allowing a safe margin of error, a simple economic spray threshold of one L. rugulipennis per 40 plants is suggested.

Effect of ULV Malathion Use in Boll Weevil (Coleoptera: Curculionidae) Eradication on Resistance in the Tarnished Plant Bug (Heteroptera: Miridae)

Tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois), from regions 1, 2, and 3 of the boll weevil, Anthonomous grandis Boheman, eradication program in Mississippi were collected from wild hosts and tested for malathion resistance during the spring and fall of 2000 and 2001. Plant bugs were also tested in region 1 in late-July and October of 1999, just before and after multiple applications of ultra-low-volume (ULV) malathion were used for reproduction-diapause control of boll weevils in August and September. Regions 1 (north Delta), 2 (south Delta), and 3 (hills) began boll weevil eradication in 1999, 1998, and 1997, respectively. A glass-vial bioassay was used to determine resistance in plant bugs to malathion by comparing LC50 values against an LC50 value obtained for susceptible plant bugs. Comparison of the LC50 value obtained for plant bugs at a location in the spring was also made with the LC50 value obtained in the fall at the same location. After multiple applications of malathion made for reproduction-diapause boll weevil control in region 1 in August and September, malathion resistance increased by 4.9-, 6.5-, and 20.8-fold in plant bug populations from the three test locations. Results from testing bugs from all three eradication regions were similar. Malathion resistance usually increased significantly from spring to fall and then declined significantly from fall to spring of the next year. Despite reduced use of malathion in all three eradication regions for boll weevils in 2001, resistance to malathion in plant bugs still increased significantly from spring to fall at all test locations in regions 1 and 2 (the Delta). Malathion resistance did not increase significantly in plant bug populations in region 3 (the hills) in 2001 from spring to fall at three of four test locations in this year. Possible causes for the higher malathion resistance found in plant bugs in the Delta are discussed. Overall test results showed that the use of malathion in boll weevil eradication in cotton probably contributed to increases in resistance to malathion in plant bug populations in the eradication areas. However, the expression of this resistance was usually rapidly lost by spring of the following year. Boll weevil eradication did not seem to produce a permanent increase in the expression of malathion resistance in tarnished plant bug populations found in the eradication regions.

Effect of ULV malathion use in boll weevil (Coleoptera: Curculionidae) eradication on resistance in the tarnished plant bug (Heteroptera: Miridae).

Tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois), from regions 1, 2, and 3 of the boll weevil, Anthonomous grandis Boheman, eradication program in Mississippi were collected from wild hosts and tested for malathion resistance during the spring and fall of 2000 and 2001. Plant bugs were also tested in region 1 in late-July and October of 1999, just before and after multiple applications of ultra-low-volume (ULV) malathion were used for reproduction-diapause control of boll weevils in August and September. Regions 1 (north Delta), 2 (south Delta), and 3 (hills) began boll weevil eradication in 1999, 1998, and 1997, respectively. A glass-vial bioassay was used to determine resistance in plant bugs to malathion by comparing LC50 values against an LC50 value obtained for susceptible plant bugs. Comparison of the LC50 value obtained for plant bugs at a location in the spring was also made with the LC50 value obtained in the fall at the same location. After multiple applications of malathion made for reproduction-diapause boll weevil control in region 1 in August and September, malathion resistance increased by 4.9-, 6.5-, and 20.8-fold in plant bug populations from the three test locations. Results from testing bugs from all three eradication regions were similar. Malathion resistance usually increased significantly from spring to fall and then declined significantly from fall to spring of the next year. Despite reduced use of malathion in all three eradication regions for boll weevils in 2001, resistance to malathion in plant bugs still increased significantly from spring to fall at all test locations in regions 1 and 2 (the Delta). Malathion resistance did not increase significantly in plant bug populations in region 3 (the hills) in 2001 from spring to fall at three of four test locations in this year. Possible causes for the higher malathion resistance found in plant bugs in the Delta are discussed. Overall test results showed that the use of malathion in boll weevil eradication in cotton probably contributed to increases in resistance to malathion in plant bug populations in the eradication areas. However, the expression of this resistance was usually rapidly lost by spring of the following year. Boll weevil eradication did not seem to produce a permanent increase in the expression of malathion resistance in tarnished plant bug populations found in the eradication regions.

Field Evaluation of Efficacy and Persistence of an Insect Vacuum Device Against the Tarnished Plant Bug (Hemiptera: Miridae) in a Day-Neutral Strawberry Field

The efficacy of a vacuuming device to reduce Lygus lineolaris (Palisot de Beauvois) populations was evaluated over 3 yr in a day-neutral strawberry field. Immediately after treatments, a significant reduction of population estimates (by tapping of flower clusters) was observed for adults (75% of the time) and nymphs (50% of the time). Under the same conditions, control (i.e., vacuum turbine off) treatments significantly reduced adult population estimates 25% of the time. Lygus lineolaris tapping samples taken from strawberry plants adjacent to the treated zone did not show significant variations over sampling time, suggesting that no escape behavior occurred. This was supported by adult catches on sticky traps located in zones adjacent to the treated one. Our results suggest that vacuuming had inconsistent effect on tarnished plant bug populations and that L. lineolaris mobility plays a marginal role in the use of this control method.

Circadian Activity of &lt;I&gt;Lygus lineolaris&lt;/I&gt; (Hemiptera: Miridae) and Effectiveness of Sampling Techniques in Strawberry Fields

Mobility and distribution of adult tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), was studied on a day-neutral strawberry cultivar ('Selva') in 1991 and 1992 at L'Acadie, Quebec, Canada. On cage-covered plants, individuals were located mainly on reproductive parts. Study of the flight activity with sticky posts revealed that most captures were obtained < 1 m from ground level and that the time of the day at which the maximum counts occur varied among seasons. Three pest-sampling methods (white sticky trap, tapping of flower clusters, and D-Vac) were evaluated over continuous 24-h periods. Maximum captures of adults with white sticky traps were made at midday (1000-1400 hours), whereas the two other methods proved more effective at the beginning (0600-0800 hours) or the end of the day (2000-2200 hours) or during night time. For nymphs, maximum catches were obtained during the day with tapping and D-Vac; white sticky traps were ineffective. Because the D-Vac captures individuals present on all parts of the plant, these counts were used to monitor the effectiveness of the two other sampling techniques. The data suggest that tapping flower clusters throughout the day is a very effective sampling method to estimate nymphal tarnished plant bug populations in strawberries. However, sampling of populations with a high proportion of adults should take into account the bias caused by their flight activity, and sampling should be conducted early in the morning or at the end of the day.