Insecticidal Activity of a Petroleum-Derived Spray Oil and an Organosilicone Surfactant on Listronotus maculicollis (Kirby) Adults in Laboratory and Greenhouse Bioassays

The annual bluegrass weevil (ABW), Listronotus maculicollis Kirby (Coleoptera: Curculionidae), is the most damaging golf course insect pest in eastern North America. Heavy reliance on synthetic insecticides against this pest has led to widespread problems in controlling ABW with pyrethroid resistance already reported from populations in southern New England. This study evaluated the degree and scope of ABW resistance, determined existing cross-resistance patterns, and confirmed laboratory findings under greenhouse conditions. The susceptibility of 10 ABW populations to insecticides of different chemical classes was assessed in topical, feeding, and greenhouse assays. The level of susceptibility to pyrethroids varied significantly among populations (LD50s ranging 2.4-819.1 ng per insect for bifenthrin and 1.1-362.7 ng for λ-cyhalothrin in the topical assay). Three populations were relatively susceptible to pyrethroids, and seven populations had moderate to high resistance levels (RR50 for bifenthrin ranging 30.5-343.1). The toxicity of chlorpyrifos (RR50s ranging 3.3-15.3), spinosad (RR50s 2.4-7.7), clothianidin (RR50s 4.2-9.7), and indoxacarb (RR50s 2.8-9.7) was decreased for the pyrethroid-resistant populations. Toxicity data for bifenthrin and chlorpyrifos obtained under more realistic greenhouse conditions confirmed laboratory observations, indicating that the topical assay is an accurate method of detection and measurement of resistance level. The current study expanded the previously known geographic range of ABW pyrethroid resistance to include the New York metropolitan area, New Jersey, and eastern Pennsylvania and provided clear evidence of cross-resistance not only within the pyrethroid class but also to several other chemical classes.

The annual bluegrass weevil (ABW), Listronotus maculicollis Kirby, is arguably the most destructive turfgrass insect pest of golf courses and tennis courts in eastern North America, threatening high-value playing surfaces. The ABW was first detected on golf courses in Long Island, New York, in the late 1950s, and has since spread throughout the northeastern United States and eastern Canada. Its accelerated spread over the past 30 yr is likely related to the transport of infested sod, leading to its establishment in the southeastern and midwestern United States. Concomitantly, it has increasingly infested less favorable hosts, such as creeping bentgrass, especially in regions where its preferred host, Poa annua L., is scarce. With few viable alternatives for ABW management, insecticides remain integral to maintaining the aesthetic and functional characteristics of managed turfgrass playing surfaces. Insecticide applications are often made sequentially throughout the season due to the relatively small size of ABW, its cryptic life stages, and the potential for damage to high-value turf. This overreliance on chemical control has fueled widespread resistance to pyrethroids, with some highly resistant populations exhibiting decreased sensitivity to unrelated compounds (i.e., multiple resistance), disrupting ABW control and threatening the long-term sustainability of management programs. Understanding ABW ecology and targeting key vulnerabilities can help design management programs that disrupt its life cycle and minimize turfgrass damage. Here, we review over 50 yr of research on ABW ecology, biology, and management, highlighting key discoveries, persistent and emerging challenges, and potential opportunities for more sustainable control strategies.

Variable effect of larval stage on the efficacy of insecticides against Listronotus maculicollis (Coleoptera: Curculionidae) populations with different levels of pyrethroid resistance

The annual bluegrass weevil (ABW), Listronotus maculicollis Kirby (Coleoptera: Curculionidae), is a serious and expanding pest of short‐cut turfgrass on golf courses in eastern North America. Increasing problems with the development of insecticide resistance in this pest highlights the need for more sustainable management approaches. Plant resistance is one of the most promising alternative strategies. Bentgrasses are the dominant grass species on golf course fairways, tees, and putting greens in the areas affected by ABW. But Poa annua L. (Poaceae), a highly invasive weed, often constitutes a large percentage of turf stands in short‐mown golf courses and is thought to be particularly susceptible to ABW. We studied resistance to ABW in four cultivars of creeping bentgrass, Agrostis stolonifera L., and two cultivars each of colonial bentgrass, Agrostis capillaris L., and velvet bentgrass, Agrostis canina L. (Poaceae), in comparison with P. annua by addressing the three major components of resistance: antixenosis (adult ovipositional and feeding preferences), antibiosis (larval survival and growth), and grass tolerance (grass damage). Our findings suggest that antixenosis/non‐preference is at least partially involved in bentgrass resistance to ABW. Even though oviposition was observed in all tested grasses, females laid significantly fewer eggs in Agrostis spp. than in P. annua. Compared to P. annua, Agrostis spp. were also less suitable for larval development with lower numbers of ABW immatures recovered and larvae weighing less and being less advanced in development. Resistance levels to ABW larvae varied significantly among Agrostis spp. and cultivars. Agrostis canina was least preferred by females for oviposition and A. stolonifera was the least suitable for larval survival and development. Agrostis spp., especially A. stolonifera, were more tolerant to ABW feeding than P. annua. Our findings suggest that reduction in P. annua and replacement with Agrostis spp., especially A. stolonifera, wherever feasible should be integral to more sustainable approaches to ABW management.

The annual bluegrass weevil (ABW), Listronotus maculicollis Kirby, is an economically important pest of short-cut turfgrass in Eastern North America. Wide spread insecticide resistance warrants the development of alternative management strategies for this pest. ABW damage typically occurs in areas with a high percentage of annual bluegrass, Poa annua L., the preferred ABW host. Damage to bentgrasses, Agrostis spp., is much rarer and usually less severe. To aid the implementation of host plant resistance as an alternative ABW management strategy we investigated the tolerance of three bentgrass species to ABW feeding. Responses of P. annua, creeping bentgrass, Agrostis stolonifera L., colonial bentgrass, Agrostis capillaris L., and velvet bentgrass, Agrostis canina L., to adult and larval feeding were compared in greenhouse experiments. Grass responses were measured as visual damage, dry weight of the grass stems and leaves, color, density and overall grass quality. To determine possible mechanisms of grass tolerance constitutive fiber and silicon content were also determined. The three bentgrass species tolerated 2-3 times higher numbers of ABW adults and larvae than P. annua before displaying any significant quality decrease. Creeping bentgrass had the lowest damage ratings. ABW infestation caused higher plant yield reduction in P. annua (up to 42%) than in bentgrasses. Observed differences among the grass species in fiber and silicon content in the plant tissue are unlikely to play a role in the resistance of bentgrasses to ABW. Our findings clearly show that A. stolonifera is the best grass species for the implementation of host plant resistance in ABW management.

The development of pyrethroid resistance within annual bluegrass weevil (ABW), Listronotus maculicollis (Kirby), a severe pest of golf course turfgrass in eastern North America, has created a dire need for alternatives to conventional insecticides. This study assessed the efficacy of novaluron, a recently registered benzoylphenyl urea insect growth regulator which inhibits chitin synthesis in developing larvae, as an alternative to conventional neurotoxic insecticides. Field trial treatments were designed to assess the effect of application timing in relation to population development stages, including peak overwintering adult emergence and early‐instar (stem‐boring) and late‐instar (soil‐dwelling) larvae. Novaluron was effective at all timings, even when larvae were not yet present (overwintering adult peak). In laboratory assays, novaluron topically applied to adults reduced the recovery of first‐instar larvae by 91%–98% and 0%–43% in 2020 and 2021, respectively. Significant ovicidal activity was also observed with reductions of 67%–85% and 35%–68% in 2020 and 2021 trials, respectively. Females treated with 9.3 L ha−1 novaluron experienced reduced fecundity over 8 weeks (52%), though weekly reductions were only significantly different from controls in the first week after exposure. Novaluron‐treated adults resumed oviposition after being transferred to untreated turf, suggesting potential recovery from exposure. These studies demonstrate novaluron's effectiveness against a wide range of larval instars which should facilitate flexible application timing in field settings. However, the transient effects observed on adults in laboratory studies may reduce novaluron's reliability as an adulticide.

For insects that develop on few hosts and/or have immobile immature stages, optimal oviposition theory suggests that females should seek high-quality hosts that maximize larval development and reduce competition from conspecifics. However, there is a growing amount of evidence that suggests female choice may often be at odds with their offspring's development. Listronotus maculicollis (Kirby) (Coleoptera: Curculionidae) is a serious pest of golf course turfgrass in eastern North America. The weevil develops on few hosts and demonstrates improved fitness traits when developing on Poa annua L. (Poaceae). However, previous population studies observed either weak or no correlations between the spatial dispersion of larval populations and P. annua in the field. In this study, populations on three golf course fairways were monitored over a 4-year period (2009–2012) to determine whether the lack of spatial associations between preferred hosts and immatures was a result of spatial scale or the density and distribution of conspecifics. Spatial Analysis by Distance IndicEs (SADIE) was used to characterize the spatial dispersion of populations of individual stages (larvae and pupae), P. annua, and turfgrass damage. Life stages were aggregated in each observation, independent of population density or the spatial dispersion of hosts. The distribution of consecutive and non-consecutive immature stages was found to be correlated in all years, suggesting that females do not avoid patches already occupied by conspecific eggs. Surprisingly, significant spatial associations were not found between larvae and P. annua when the host plant was relatively abundant. Hence, multiple mechanisms may drive L. maculicollis oviposition site-selection behavior, and a flexible strategy may allow the weevil to persist in areas where P. annua is not the dominant species. Future studies are required to determine what other factors (e.g., natural enemy-free space, egg or time limitations) influence oviposition behavior.

The annual bluegrass weevil, Listronotus maculicollis Kirby (Coleoptera: Curculionidae), has emerged as a serious pest of Poa annua L. (Poales: Poaceae) (annual bluegrass), in the Northeastern US. In 2007, topical application bioassays of bifenthrin and λ-cyhalothrin conducted on field-collected populations of L. maculicollis Kirby from eight southern New England golf courses resulted in LD50 ranges of 1.80-244.67 ng/insect and 0.52-159.53 ng/insect for bifenthrin and λ-cyhalothrin respectively. These results revealed low to high levels of resistance to bifenthrin (6.1-135.9 fold) and λ-cyhalothrin (28.7-306.8 fold), possibly due to insecticide overuse. In 2008, topical application bioassays with bifenthrin and bifenthrin plus synergists affecting three detoxification systems were conducted on four field-collected adult populations of L. maculicollis to determine if resistance was metabolically mediated. In the population with the lowest resistance only detoxification by cytochrome P450 monooxgenases (P450s) was significant. Detoxification in the population with the second highest level of resistance involved both P450s and glutathione S-transferases (GSTs), and detoxification in the population with the highest level of resistance involved P450s, GSTs and carboxyl-esterases (COEs). Since P450s are inhibited by demethylation inhibitor fungicides (DMI-Fs) and gibberellin inhibitor plant growth regulators (GI-PGRs), both of which are commonly used on golf courses, we tested these compounds using topical application bioassays and simulated field trials for synergistic activity with bifenthin against a pyrethroid resistant population of L. maculicollis . The LD50 for bifenthrin (120 ng/insect) was significantly higher than the LD50s for bifenthrin plus the fungicides fenarimol, fenpropimorph, prochloraz, propiconazole, pyrifenox and plus the plant growth regulators, flurprimidol, paclobutrazol and trinexapac-ethyl (range of 8-36 ng/insect). The means of mortality for Talstar® (bifenthrin) in combination with each of the following, BannerMAXX® (propiconizole), Rubigan® (fenarimol), Cutless® (flurprimidol) and PrimoMAXX® (trinexapac-ethyl) ranged from 9.8 to 14 and were significantly higher than an untreated control (0.3) and Talstar ® (5.0) alone. We also studied the effects of liquid and granular formulations of Metarhizium anisopliae (Metschnikoff) Sorokin strain F52 against L. maculicollis larvae under field conditions. The liquid formulation provided 31-46% control of L. maculicollis larvae, but the granular formulation provided no control.

The annual bluegrass weevil (Listronotus maculicollis), is the most destructive insect pest of fine turf found on golf courses in eastern North America. Although considerable densities of adults may be found on putting greens in spring following emergence from overwintering, larval damage in these areas is rare. Annual bluegrass (Poa annua L.) putting surfaces are frequently treated with nitrogen and plant growth regulators during this time. We assessed whether these inputs alone and in combination influenced L. maculicollis oviposition site selection, larval fitness, or survival. Significantly more females were found in high‐nitrogen (39 kg N ha–1 mo–1) treatments in laboratory preference assays, though significantly more eggs were found in the moderate concentration treatments (19.5 kg N ha–1 mo–1). Choice and no‐choice assays demonstrated an ovipositional preference for the moderate nitrogen rate as well, though no fitness advantage was observed. Given that most P. annua greens management programs include plant growth regulation, field experiments were conducted to assess ovipositional preference in P annua treated with various nitrogen concentrations (4.88, 19.5 and 39 kg N ha–1 mo–1) in combination with a gibberellic acid inhibitor (trinexapac‐ethyl) and/or a seedhead suppressor (ethephon). Significantly fewer larvae were found in trinexapac‐ethyl treatments in two of the three years of study, with significantly higher counts in the other year. No differences were detected in larval survival or fitness related to nitrogen in any year. Taken together, these findings suggest that fertility regimes are not likely to influence L. maculicollis development, though further studies are needed to assess the effects of trinexapac‐ethyl.

The annual bluegrass weevil (Listronotus maculicollis) is the most damaging insect pest of short-mown turfgrass on golf courses in eastern North America. Listronotus maculicollis larvae cause limited visible damage as stem-borers (L1-3), compared to the crown-feeding (L4-5) developmental instars. Prolonged larval feeding results in discoloration and formation of irregular patches of dead turf, exposing soil on high-value playing surfaces (fairways, collars, tee boxes, and putting greens). Annual bluegrass (Poa annua) is highly susceptible to L. maculicollis compared to a tolerant alternate host plant, creeping bentgrass (Agrostis stolonifera). This study explored whether defense signaling phytohormones contribute to A. stolonifera tolerance in response to L. maculicollis. Concentrations (ng/g) of salicylic acid (SA), jasmonic acid (JA), jasmonic-isoleucine (JA-Ile), 12-oxophytodienoic acid (OPDA), and abscisic acid (ABA) were extracted from turfgrass (leaf, stem, and root) tissue samples as mean larval age reached 2nd (L2), 3rd (L3), and 4th (L4) instar. Poa annua infested with L. maculicollis larvae (L2-4) possessed significantly greater SA in above-ground tissues than A. stolonifera. Levels of constitutive JA, JA-Ile, OPDA, and ABA were significantly higher within non-infested A. stolonifera aboveground tissues compared to P. annua. Inducible defense phytohormones may play a role in P. annua susceptibility to L. maculicollis but are unlikely to provide tolerance in A. stolonifera. Additional studies in turfgrass breeding, particularly focusing on cultivar selection for increased constitutive JA content, could provide a non-chemical alternative management strategy for L. maculicollis for turfgrass managers.

The annual bluegrass weevil, Listronotus maculicollis (Kirby), is a highly destructive pest of golf course turfgrass in eastern North America. Previous research has demonstrated that females prefer to oviposit within short-mown turfgrasses (<1.25 cm), and these offspring have improved fitness traits compared with larvae developing in higher-mowed turf. However, damage to putting green turf (<3.55 mm) is rarely reported. We investigated whether this phenomenon was due to adult removal through mowing or an inability of larvae to develop within a shortened plant. Greenhouse studies revealed that between 26% and 38% of adults were removed when turf was mowed at 2.54 mm (0.100 in), but the effect diminished with increasing mowing heights. The majority of adults survived mowing, indicating a potential for adults to reinvade turf stands adjacent to areas where grass clippings are discarded. Females oviposited in all mowing height treatments in laboratory and field experiments. However, behavior was influenced by plant height, as significantly fewer eggs were placed inside of the turfgrass stem at the lowest mowing height. Larval development was not affected by egg placement or turf height, and significant numbers of larvae were capable of developing to damaging stages (fourth- and fifth-instar larvae) in all treatments. Our findings suggest that L. maculicollis poses a threat to putting green-height turf, but the probability of damage occurring and need for insecticide applications may be lessened on low-mown surfaces. Future studies are needed to determine factors that influence L. maculicollis movement within the turfgrass canopy to optimize mechanical control.

The annual bluegrass weevil, Listronotus maculicollis Kirby, is a severe pest of short-mown turfgrasses in eastern North America. Previous research has demonstrated that adults can be removed from golf course putting greens during mowing. However, the impact of mechanical control on adult removal diminishes with increases in mowing height. Therefore, to optimize adult removal we sought to describe adult presence on top of the turfgrass canopy to identify periods when mowing would be most effective. Growth chamber studies using time-lapse photography revealed that greatest activity occurred between 15 and 20°C, with few weevils active on the surface when temperatures were less than 10°C. A mark-release technique combining fluorescent marks with still photography was used to assess adult movement in the field. This novel mark-recapture system confirmed laboratory findings that adult activity on top of the turfgrass canopy was greatest during the day and strongly correlated with temperature early in the season (April, May). However, adult presence on the surface in early summer was greatest briefly after sunrise, then declined during the mid-morning when temperatures exceeded 21°C. The effect of temperature on surface activity was best described by a second-order polynomial function, which predicts maximum adult surface activity between 14 and 17°C. Our findings suggest that adult surface activity is strongly associated with temperature and not photophase, and therefore, monitoring populations and scheduling mowing with the intent to remove adults need to be adjusted seasonally with changes in temperature.

We determined the potential of the entomopathogenic fungus Metarhizium brunneum Petch (Hypocreales: Clavicipitaceae) F52 strain, and of a microsclerotial formulation, for the control of the annual bluegrass weevil, Listronotus maculicollis Kirby, which is a major pest of golf course turf in eastern North America with widespread insecticide resistance. Under laboratory conditions in Petri dishes with moist sand, the microsclerotia (23-46 kg granules/ha) caused high rates of mortality (85-100%) and infection (67-80%) in annual bluegrass weevil adults, but these levels did not occur until after 9 d at constant 26°C and 12-15 d at 14 h at 23°C and 10 h at 17°C. Production of viable conidia was marginally higher at the higher temperature regime (7.3 vs. 5.2 × 109 per gram of granules). Application of microsclerotia did not provide significant control and infection of adults in pots with grass in the greenhouse. In field trials targeting spring generation larvae, microsclerotia application (50-100 kg granules/ha) was ineffective, and coapplication of hydrogel to stabilize soil moisture did not increase larval control. A liquid M. brunneum F52 conidial formulation (4.75-9.5 × 1013 colony forming units/ha) provided up to 51% control. Combinations of M. brunneum F52 with the neonicotinoid insecticide imidacloprid provided additive control with up to 70% control with the conidial formulation. Field efficacy was probably limited by suboptimal temperatures for the fungus, and future tests need to examine whether higher control rates can be achieved in applications targeting the summer generation larvae.

The annual bluegrass weevil, Listronotus maculicollis Kirby, is the most difficult to control insect pest of short-mown golf course turf in the northeastern United States and Eastern Canada. We conducted a survey among golf course superintendents throughout the weevil's area of impact to better understand the severity of damage, prevalence of insecticide resistance, information sources, and trends in management practices. Responses were received from 293 golf courses in 14 U.S. states and 2 Canadian provinces. The average population caused damage to 6.6 fairways, 5.7 tee boxes, and 6.4 greens/collars, amounting to a total of 5.2 ha requiring protection on an 18-hole facility. On average, courses made 3.9 insecticide applications per year and spent US$9,270 on L. maculicollis management. Twenty percent of the responders reported having a pyrethroid-resistant L. maculicollis population. "Resistant" populations were located across the region, though higher-than-average incidence was reported from areas with long histories of managing L. maculicollis. "Resistant" populations caused more damage than "susceptible" populations, reported higher average insecticide budgets, and were more likely to make more than five insecticide applications per year than "susceptible" courses. Surveys indicated that, despite the reliance on chemical controls, 90% of turf managers used multiple monitoring tactics to better time and target controls. The greatest influence on management philosophy was by University personnel (43%) followed by colleagues (31%) and sales/distributors (21%). This survey highlights the need for developing alternatives to chemical insecticides to control L. maculicollis and provides insight into the costs associated with the development of pyrethroid resistance.

The annual bluegrass weevil, Listronotus maculicollis (Kirby) (Coleoptera: Curculionidae), is the most difficult to control insect pest on golf courses in eastern North America. Insecticide resistance, particularly to pyrethroids, is a serious and expanding issue in its management. Optimal diagnostic tools for resistance detection are crucial for efficient resistance monitoring and mitigation. Developed vial and Petri dish assays clearly separated different resistance levels among weevil populations. With the pyrethroid bifenthrin, susceptible, moderately resistant (resistance ratios, RR50s 12.2-95.7), and highly resistant (RR50s 258.2-1760.9) populations were distinguished. With the organophosphate chlorpyrifos, susceptible, tolerant (RR50s 2.4-6.7), and resistant (RR50s 8.8-120.7) populations were distinguished. In validation assays, several bifenthrin and chlorpyrifos concentrations were needed to separate resistance levels in Petri dish (bifenthrin: 112.2 and 336.3 or 3,362.5 mg AI/m2; chlorpyrifos: 3.4 and 33.6 mg AI/m2) and vial (bifenthrin: 112.1 or 1,120.8 mg AI/m2; chlorpyrifos: 2.2 and 11.2 mg AI/m2) assays. The Petri dish assay with formulated bifenthrin and chlorpyrifos was the best option for L. maculicollis resistance detection and monitoring. It demonstrated sufficient discriminating power, accurately reflected resistance levels, and was easier to conduct. A single diagnostic concentration sufficed to separate susceptible and resistant populations. To determine different resistance or tolerance levels, two to three concentrations were necessary.