Greenhouse Bioassays Research Articles

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), is a severe pest of golf course turf in eastern North America. The development of pyrethroid- and multiple-resistant populations has created a dire need for novel tactics to control adults. We examined the insecticidal properties of a petroleum-derived spray oil (PDSO; Civitas Turf Defense™.) and an organosilicone, nonionic soil surfactant (Silwet L-77®) in laboratory and greenhouse bioassays. Civitas and Silwet killed > 75% of ABW adults in multiple assays. The level of control was positively affected by increased rate, spray application volume, and soil moisture levels. Dissections of weevils treated with Civitas revealed material entering the insect's hemocoel after 15-30 min, though most mortality occurred between the 3 and 24 h observation periods. Reducing rates while increasing carrier volume or soil moisture levels through irrigation applied prior to or after application also provided excellent control of adults in the same observation periods. Silwet provided comparable, yet less consistent levels of control in the laboratory studies but was excluded from further tests after treated plants demonstrated phytotoxicity in greenhouse studies. Neither Silwet nor Civitas efficacy was affected by pyrethroid resistance levels in the ABW populations tested.

Random forest analysis reveals taxa predictive of Prunus replant disease in peach root microbiomes

Successive plantings of Prunus species produce suboptimal growth and yield in many California soils due to a poorly understood soilborne disease complex, Prunus replant disease (PRD). We explored the hypothesis that PRD is mediated by microbial taxa in roots of Nemaguard peach, a rootstock for almond and other stone fruits. In a greenhouse bioassay, portions of 10 replant soils were treated with fumigation or pasteurization or left untreated as a control before being planted with peach seedlings. Ten weeks after planting, seedlings were considered PRD-affected if their top fresh weights in the control were significantly reduced, compared to the weights in pasteurization and fumigation treatments; plants with equivalent top weights in all treatments were considered to be non-affected. The roots were washed from the soil, frozen, extracted for total DNA, and used for metabarcoding of rRNA gene amplicons from bacteria, fungi, and oomycetes. High-throughput amplicon sequencing revealed that root microbial community shifts resulted from preplant treatments, and specific taxa were associated with PRD induction among controls. Random forest (RF) analysis discriminated effectively between PRD-affected and non-affected root communities. Among the 30 RF top-ranked amplicon sequence variant (ASV) predictors, 26 were bacteria, two were oomycetes, and two were fungi. Among them, only Streptomyces scabiei, Steroidobacter denitrificans, Streptomyces bobili, and Pythium mamillatum had root abundances ≥5% that were either associated positively (former two ASVs) or negatively (latter two) with PRD. Thus, our findings were consistent with microbial mediation of PRD in roots and suggested taxa that may be involved in the mediation.

Toxicity of Bacillus thuringiensis Strains to Six Lepidopteran Pests of Brazilian Agricultural Landscape.

The first step for biological insecticide production is the evaluating of the pathogenicity and strains virulence of entomopathogens against the target pests. Bacillus thuringiensis (Bt) is widespread in nature, lethal pathogen of a range of orders and the most widely used entomopathogenic biological control agent. Therefore, our objective was to study the susceptibility of six important lepidopteran pests in Brazilian agricultural production systems, Anticarsia gemmatalis(Hübner),Chrysodeixis includens(Walker)Helicoverpa armigera(Hübner), Spodoptera cosmioides(Walker), S. eridania(Cramer), and S. frugiperda(Smith), to Bt strains. In vitro bioassays were conducted with neonate larvae exposed to two Bt strains, 1680A and 775E, in seven concentrations of spores and protein crystals. After 7days, the mortality was evaluated and indicated that lethal concentration (LC50) for 775E strain ranged from 7.72 × 104 to 2.45 × 106 spores mL-1 and for 1608A strain from 5.63 × 103 to 1.21 × 106 spores mL-1. The strain 1608A was more toxic for A. gemmatalis and H. armigera than 775E strain, and then was further evaluated in greenhouse bioassays with maize and soybean plants infested separately with target insects. The strain 1608A showed an efficient control for most insect species studied in the greenhouse bioassays, promoting considerable reduction in leaf injury and demonstrating a high potential in biological control of important lepidopteran species in crop production systems in Brazil.

Enhanced top-down control of herbivore population growth on plants with impaired defences.

Herbivore densities can be regulated by bottom-up and top-down forces such as plant defences and natural enemies, respectively. These forces can interact with each other to increase plant protection against herbivores; however, how much complementarity exists between bottom-up and top-down forces still remains to be fully elucidated. Particularly, because plant defences can hinder natural enemies, how these interactions affect herbivore performance and dynamics remains elusive.To address this topic, we performed laboratory and greenhouse bioassays with herbivorous mite pests and predatory mites on mutant tomato plants that lack defensive hairs on stems and leaves. Particularly, we investigated the behaviour and population dynamics of different phytophagous mite species in the absence and presence of predatory mites.We show that predatory mites do not only perform better on tomatoes lacking defensive hairs but also that they can suppress herbivore densities better and faster on these hairless plants. Hence, top-down control of herbivores by natural enemies more than compensated the reduced bottom-up herbivore control by plant defences.Our results lead to the counter-intuitive insight that removing, instead of introducing, plant defence traits can result in superior protection against important pests through biological control. Read the free Plain Language Summary for this article on the Journal blog.

Entomopathogenic fungi as biological control agents of Dactylopius opuntiae (Hemiptera: Dactylopiidae) under laboratory and greenhouse conditions

The cactus Opuntia ficus-indica L. is widly cultivated in Morocco and has a very an important economic role as a source of food, livestock feed and not forgetting that it is considered to be an income for people in rural communities. This crop is subject to the attack of a serious insect pest, the Dactylopius opuntiae (Cockerell), which sucks the sap from the plant causing huge production losses since its introduction to the country in 2014. The present study investigated the entomopathogenic effect of six fungal isolates {Beauveria bassiana [HASS; RFSL10; SPT 011(a)]; Akanthomyces lecanii [RFSLV; SPT R 215] and Cordyceps farinosa [SPSBI4]} for controlling of both nymphs and adult females of D. opuntiae in laboratory and greenhouse bioassays. Under laboratory conditions, the highest mortality of female D. opuntiae was registered by B. bassiana strain HASS at 108 conidia ml−1 with 100%, followed by B. bassiana strain RFSL10, A. lecanii RFSLV, and C. farinosa SPSBI4 isolates with 98%, respectively, 10 days after treatments. Similarly, the highest level of nymph mortality (100%) was recorded by B. bassiana RFSL10 and HASS isolates at 108 conidia ml1, respectively, 4 and 5 days after application. Under greenhouse conditions, B. bassiana (HASS and RFSL10) and A. lecanii (RFSLV) isolates sprayed alone expressed a higher toxicity on nymphs with 75, 68.5 and 58%, respectively, 12 days after treatments. However, no significant difference was observed in adult female's mortality between different fungal isolates, where B. bassiana (HASS) at 108 conidia ml−1 presented a moderate mortality rate with 55%, 12 days after application. In fact, the combination of black soap (60 g/L) with B. bassiana HASS and RFSL10 and A. lecanii (RFSLV) isolates at 108 conidia ml−1 caused the highest toxic activity on D. opuntiae adult females, with 70.5, 68.75 and 67.65%, respectively. These findings showed that entomopathogenic fungi are promising for developing a biopesticide formulation for the management of D. opuntiae as an adequate and safe alternative to chemical pesticides.

Biocontrol potential of Trichoderma harzianum against Botrytis cinerea in tomato plants

Trichoderma harzianum (TM) is a soil-borne beneficial fungus that positively affects plant growth and defense. TM shows antagonism against multiple plant pathogens; however, the TM as a biocontrol agent against Botrytis cinerea (BC) and underlying mechanisms remain unclear. Herein we studied the effects of TM on BC by dual-culture assay and greenhouse bioassay in tomato plants. In vitro experiments showed that TM rapidly occupied most of the nutrient space and eventually covered BC on potato dextrose agar (PDA) medium. The TM inhibition rate against BC was 62.05% on the sixth day of culture. The inhibitory effect of TM spore suspension on gray mold inoculated with spore suspension and solid inoculants was 33.66% and 69.44%, respectively in tomato plants. Notably, TM decreased the leaf concentrations of BC-induced hydrogen peroxide and malondialdehyde but improved the redox state. TM inoculation caused biphasic peaks in the expression of secondary metabolism and defense-related genes and increased the concentrations of flavonoids, phenols and lignin in tomato leaves. Moreover, TM alleviated stomatal closure and enhanced the net photosynthesis rate and the activity of RuBisCO and FBPase compared with only BC inoculation. Our results suggest that TM spore suspension improves tomato resistance to gray mold disease by stimulating cellular redox, secondary metabolites and stomatal movement.

Traits and tradeoffs among non-native ectomycorrhizal fungal symbionts affect pine seedling establishment in a Hawaiian coinvasion landscape.

Pine invasions lead to losses of native biodiversity and ecosystem function, but pine invasion success is often linked to coinvading non-native ectomycorrhizal (EM) fungi. How the community composition, traits, and distributions of these fungi vary over the landscape and how this affects pine success is understudied. A greenhouse bioassay experiment was performed to test the effects of changes in EM fungal community structure from a pine plantation, to an invasion front to currently pine-free areas on percent root colonization and seedling biomass. Soils were also analysed by qPCR to determine changes in inoculum and spore density over distance for a common coinvading EM fungus, Suillus pungens. Percent colonization increased with distance from the plantation, which corresponded with an increase in seedling biomass and stark changes in EM fungal community membership where Suillus spp. dominated currently pine-free areas. However, there was a negative relationship between S.pungens inoculum potential versus root colonization over distance. We conclude that the success of pine invasions is facilitated by specific traits of Suillus spp., but that the success of Suillus is contingent on a lack of competition with other ectomycorrhizal fungi.

Cover crop usage for the sustainable management of soilborne diseases in woody ornamental nursery production system

Cover crops represent a potential tool for suppression of soil borne diseases in woody ornamental nursery production, which can cause significant economic losses. Field experiments were conducted in 2019 and 2020 to explore the effects of a cover crop and the timing of cover crop disturbance on soilborne disease suppression. Soils from red maple (Acer rubrum ‘October Glory’) plantations grown with or without a cover crop [crimson clover (Trifolium incarnatum)] were sampled following senescence of the cover crop. Greenhouse bioassays were conducted using red maple cuttings on inoculated (with Rhizoctonia solani, Phytopythium vexans or Phytophthora nicotianae) and non-inoculated field soils. Plant height, total and root fresh weight were measured, and the roots were assessed for disease severity on a 0 to 100% root damage scale. Pathogen recovery was assessed by culturing root pieces (~1 cm length) on oomycetes or Rhizoctonia semi-selective media. Soil samples were analyzed for organic matter, nitrogen, phosphorus, potassium, pH and Pseudomonad population count. A minimal effect of cover crop disturbance timing (late fall or early spring) was found on disease suppression. Cover crop usage reduced disease severity and pathogen recovery in red maple field soils. Plants grown in cover cropped soil had greater total, root and aboveground fresh weight compared with those from non-cover cropped soil, but plant height was not affected. Cover crops increased soil organic matter and total nitrogen in 2020. Pseudomonad populations were higher when cover crops were used. The results suggest that cover crops can reduce soilborne disease in woody ornamentals.

Characterization of soils conducive and non-conducive to Prunus replant disease.

Successive orchard plantings of almond and other Prunus species exhibit reduced growth and yield in many California soils. This phenomenon, known as Prunus replant disease (PRD), can be prevented by preplant soil fumigation or anaerobic soil disinfestation, but its etiology is poorly understood and its incidence and severity are hard to predict. We report here on relationships among physicochemical variables, microbial community structure, and PRD induction in 25 diverse replant soils from California. In a greenhouse bioassay, soil was considered to be “PRD-inducing” when growth of peach seedlings in it was significantly increased by preplant fumigation and pasteurization, compared to an untreated control. PRD was induced in 18 of the 25 soils, and PRD severity correlated positively with soil exchangeable-K, pH, %clay, total %N, and electrical conductivity. The structure of bacterial, fungal, and oomycete communities differed significantly between the PRD-inducing and non-inducing soils, based on PERMANOVA of Bray Curtis dissimilarities. Bacterial class MB-A2-108 of phylum Actinobacteria had high relative abundances among PRD-inducing soils, while Bacteroidia were relatively abundant among non-inducing soils. Among fungi, many ASVs classified only to kingdom level were relatively abundant among PRD-inducing soils whereas ASVs of Trichoderma were relatively abundant among non-inducing soils. Random forest classification effectively discriminated between PRD-inducing and non-inducing soils, revealing many bacterial ASVs with high explanatory values. Random forest regression effectively accounted for PRD severity, with soil exchangeable-K and pH having high predictive value. Our work revealed several biotic and abiotic variables worthy of further examination in PRD etiology.

Rice Resistance Buffers against the Induced Enhancement of Brown Planthopper Fitness by Some Insecticides

The brown planthopper, Nilaparvata lugens (Stål)[BPH], is a damaging pest of rice in Asia. Insecticides and rice varietal resistance are widely implemented BPH management practices. However, outbreaks of BPH have been linked to excessive insecticide use—challenging the compatibility of these two management practices. IR62 is a variety with resistance against BPH, the whitebacked planthopper, Sogatella furcifera Horváth [WBPH], and the green leafhopper, Nephotettix virescens (Distant)[GLH]. We compared BPH responses to IR62 and to the susceptible variety IR64 treated with buprofezin, carbofuran, cartap hydrochloride, cypermethrin, deltamethrin, fipronil, or thiamethoxam + chlorantraniliprole. In greenhouse bioassays, cypermethrin, fipronil and thiamethoxam + chlorantraniliprole reduced egg laying on both varieties, and, together with buprofezin, reduced nymph survival to zero. Buprofezin, carbofuran, and cartap hydrochloride stimulated egg laying, and carbofuran increased nymph biomass, but these effects were reduced on IR62. Planthopper populations were ten times higher on deltamethrin-treated rice than untreated rice in a screenhouse experiment. Host resistance failed to buffer against this insecticide-induced resurgence in BPH and WBPH. However, IR62 reduced the effect in GLH. Rice treated with cypermethrin and fipronil had reduced yields compared to untreated controls, suggesting possible phytotoxic effects. We found little evidence of synergies between the two management practices; but host resistance did buffer against the undesirable effects of some insecticides.

Virus Yellows in sugar beet – possibilities to achieve virus resistance

Virus yellows in sugar beet is caused by different virus species. Monitoring has shown that Beet yellows virus (BYV), Beet mild yellowing virus (BMYV), Beet chlorosis virus (BChV) are common and widespread, while Beet mosaic virus (BtMV) is less prevalent. The green peach aphid (Myzus persicae) is considered the main vector of these viruses. Sugar beet varieties with resistance or tolerance traits are currently not available to practical growers, therefore it is imperative to support breeding efforts with improved strategies to achieve virus resistance. For this purpose, a field test was established in which yield differences between susceptible and tolerant varieties can be generated by a 3% inoculation with BMYV-carrying aphids. A greenhouse bioassay has also been developed to distinguish susceptible and tolerant genotypes following BYV infection. Both assays pave the way for future use of natural resources such as wild forms and other breeding material to screen for virus resistance. In addition, molecular biology approaches are used to identify plant susceptibility factors of the plant-virus interaction, which will be knocked out via modern precision breeding methods to generate recessive virus resistance. Consequently, genotypes with naturally occurring mutations in the appropriate factors can be used for crossbreeding processes into elite breeding material.

Effects of geographic variation in host plant resources for a specialist herbivore's contemporary and future distribution

AbstractSpecies distributions are driven by abiotic and biotic factors, but the importance of variation in the availability and quality of critical resources is poorly understood. Disentangling the relative importance of these factors—abiotic environment, availability of critical resources, and resource quality—will be important to modeling species current distributions and responses to projected climate change. We address these questions using species distribution models (SDMs) for the western monarch butterfly population (Danaus plexippus), whose larvae feed exclusively on Asclepias species known for their heterogeneous distribution and variation in host quality. We modeled the distribution of 24 Asclepias species to compare three monarch distribution models with increasing levels of complexity: (1) a null model using only environmental factors (climate envelope model), (2) a model using environmental factors and Asclepias availability estimated as species richness, (3) and a model using environmental factors and Asclepias’ availability weighted by host plant quality as assessed through a greenhouse bioassay of larval performance. Asclepias models predicted that half of the Asclepias species will expand their ranges and shift toward higher latitudes, while half will contract. These patterns were uncorrelated with host plant quality. Among the three monarch models, the climate envelope model was the poorest performing. Models accounting for host plant availability performed best, while accounting for host plant quality did not improve model performance. The climate envelope model estimated more restrictive contemporary and future monarch ranges compared to both host plant models. Although all three models predicted future monarch range expansions, the projected future distributions varied among models. The climate envelope model predicted range expansions along the Pacific coast and contractions inland. In contrast, the host plant availability and quality models predicted range expansions in both of these regions and, as a result, 14% and 19% increases in distribution (respectively) relative to the climate envelope model. These models do not include other factors affecting monarch persistence. Nevertheless, our findings suggest that accounting for information on host plant availability and response to climate change is necessary to predict future species distributions, but that variation in the quality of those critical resources may be of secondary importance.

Effect of an adjuvant, Jijian, on isoproturon to control fenoxaprop-P-ethyl-resistant Beckmannia syzigachne

Continuous and exclusive use of fenoxaprop-P-ethyl has resulted in serious resistance in Beckmannia syzigachne. Isoproturon, a photosystem II inhibitor, is very frequently used in wheat fields, and there are currently few reports about isoproturon resistance in B. syzigachne. However, excessive use of isoproturon is detrimental to the ecological environment. Therefore, adding additives is a good choice to enhance the effect of isoproturon and reduce its usage. Jijian is a non-ionic and polyhydric alcohol surfactant. Greenhouse whole-plant bioassay results showed that 0.05% (v/v) of Jijian + 600 g ai ha−1 of isoproturon achieved the best synergistic effect on controlling fenoxaprop-P-ethyl-resistant B. syzigachne. Jijian significantly reduced the surface tension and contact angle of the isoproturon solution by 15.8 mN m−1 and 33.2°, respectively, and significantly increased the expanded diameter and maximum retention by 0.92 mm and 8.39 mg cm−2 respectively. In conclusion, Jijian had a synergistic effect on isoproturon in the control of fenoxaprop-P-ethyl-resistant B. syzigachne and Jijian may achieve the synergistic effect by changing the physical properties of isoproturon solution on weeds.

Exploiting the Innate Potential of Sorghum/Sorghum-Sudangrass Cover Crops to Improve Soil Microbial Profile That Can Lead to Suppression of Plant-Parasitic Nematodes.

Sorghum/sorghum–sudangrass hybrids (SSgH) have been used as a cover crop to improve soil health by adding soil organic matter, enhancing microbial activities, and suppressing soil-borne pathogens in various cropping systems. A series of SSgH were screened for (1) allelopathic suppression and (2) improvement of soil edaphic factors and soil microbial profile against plant-parasitic nematode (PPNs). The allelopathic potential of SSgH against PPNs is hypothesized to vary by variety and age. In two greenhouse bioassays, ‘NX-D-61′ sorghum and the ‘Latte’ SSgH amendment provided the most suppressive allelopathic effect against the female formation of Meloidogyne incognita on mustard green seedlings when using 1-, 2-, or 3-month-old SSgH tissue, though most varieties showed a decrease in allelopathic effect as SSgH mature. A field trial was conducted where seven SSgH varieties were grown for 2.5 months and terminated using a flail mower, and eggplant was planted in a no-till system. Multivariate analysis of measured parameters revealed that increase in soil moisture, microbial biomass, respiration rate, nematode enrichment index, and sorghum biomass were negatively related to the initial abundance of PPNs and the root-gall index at 5 months after planting eggplant in a no-till system. These results suggested that improvement of soil health by SSgH could lead to suppression of PPN infection.

Virulence potential of two entomopathogenic nematodes, their associated bacteria, and its metabolites to larvae of Pieris brassicae L. (Lepidoptera, Pieridae) in cabbage under greenhouse and field bioassays

Virulence potential of two entomopathogenic nematodes, their associated bacteria, and its metabolites to larvae of Pieris brassicae L. (Lepidoptera, Pieridae) in cabbage under greenhouse and field bioassays

Evaluation of Agricultural Byproducts and Cover Crops as Anaerobic Soil Disinfestation Carbon Sources for Managing a Soilborne Disease Complex in High Tunnel Tomatoes

Anaerobic soil disinfestation (ASD) is a viable option for disease management in tomato production and reduces damage due to a soilborne disease complex consisting of Pyrenochaeta lycopersici, Colletotrichum coccodes, Verticillium dahliae, and Meloidogyne spp. There are plentiful options for ASD carbon sources using byproducts of Midwestern United States agriculture or cover crops, yet these carbon sources have not been evaluated for use in Midwestern settings. Low (10.1 Mg/ha) and high (20.2 Mg/ha) rates of corn gluten meal, distillers dried grains, soybean meal, wheat bran, and dry sweet whey were evaluated as ASD carbon sources in growth chamber and greenhouse bioassays. Cover crops including buckwheat, cowpea, crimson clover, mustard, oilseed radish, sorghum-sudangrass, white clover, and winter rye were evaluated in similar bioassays with one amendment rate (20.2 Mg/ha). Reducing conditions developed in soils regardless of carbon source or rate. Use of high rates of corn gluten meal, distillers dried grains, soybean meal, and wheat bran led to the lowest levels of root rot severity compared to non-treated controls. The higher rate of any byproduct carbon source was always more effective than the lower rate in reducing root rot severity. Use of both rates of soybean meal or corn gluten meal and the high rate of distillers dried grains or dry sweet whey led to significant increases in dry root and shoot biomass compared to controls. For cover crops, ASD with crimson clover, sorghum-sudangrass, white clover, or winter rye amendments reduced root rot severity relative to the aerobic control, but not relative to the anaerobic control. Use of cover crops did not significantly impact plant biomass. A subset of three ASD carbon sources [distillers dried grains, soybean meal, and wheat middlings (midds), all 20.2 Mg/ha] were evaluated in five on-farm ASD trials in high tunnels. Soil temperatures were low during the application period, limiting treatment efficacy. Reducing conditions developed in all soils during ASD treatment, and a moderate but significant reduction in root rot severity was observed following ASD with the soybean meal or wheat midds compared to ASD with distillers dried grains. Tomato yield was not significantly affected by ASD treatment.

Host finding behaviour of the egg parasitoid, Gryon pennsylvanicum (Hymenoptera: Scelionidae)

ABSTRACT The squash bug, Anasa tristis (De Geer) is a serious pest of cucurbit crops. The egg parasitoid, Gryon pennsylvanicum (Ashmead), is the primary parasitoid of the squash bug and has been considered as a biological control agent. In the present study, we conducted both laboratory and greenhouse bioassays to determine the effects of kairomones emitted by A. tristis on the host searching behaviour of G. pennsylvanicum. Chemicals were extracted from A. tristis eggs, unmated females and males, and mated females and males. The percentage of females responding to extracts was significantly higher for egg extracts than the other extracts tested. In greenhouse tests, percent parasitism of egg masses baited with extract-treated lures was significantly higher than for those treated with solvent-treated control lures for all six extracts tested: ethanol and hexane extracts of eggs, mated females and mated males. Further research on kairomones of A. tristis may result in the development of synthetic lures that could be used in squash fields to increase parasitism by G. pennsylvanicum. The promising results from this study highlights the potential application of kairomones in enhancing the efficacy and effectiveness of biological control programmes and should be of interest to growers and pest control professionals.

Evaluating efficacy of preemergence soybean herbicides using field treated soil in greenhouse bioassays

AbstractAmid widespread occurrence of herbicide-resistant weeds in the United States, the use of PRE herbicides and cover crops have resurged once again as important strategies for weed management in cropping systems. The objective of this experiment was to evaluate the length of soil residual weed control from PRE soybean herbicides and the detrimental impact of these herbicides on cover crop species using field treated soil in greenhouse bioassays. Greenhouse bioassays were conducted using soil from field experiments conducted in 2018 and 2019 in Arlington and Lancaster, WI. PRE herbicides consisted of imazethapyr, chlorimuron-ethyl, and cloransulam-methyl (acetolactate synthase [ALS] inhibitors); metribuzin (photosystem II [PS II] inhibitor); sulfentrazone, flumioxazin, and saflufenacil (protoporphyrinogen oxidase [PPO] inhibitors); acetochlor, S-metolachlor, dimethenamid-P, and pyroxasulfone (very long-chain fatty acid [VLCFA] inhibitors); and a nontreated control. Greenhouse bioassays were conducted using soil (depth, 0 to 10 cm) sampled at 0, 10, 20, 30, 40, and 50 d after treatment (DAT). Palmer amaranth and giant foxtail (weeds), and radish and cereal rye (cover crops) were used as bioindicators of herbicide levels in the soil. Bioassay results showed extended soil residual control of Palmer amaranth with sulfentrazone and pyroxasulfone; extended residual control of giant foxtail was observed with pyroxasulfone and S-metolachlor. Chlorimuron-ethyl and metribuzin were the most injurious herbicides to radish and cereal rye shortly after application, respectively, but minimal injury was observed from soil samples collected 50 DAT, indicating the use of PRE and fall-seeded cover crops in southern Wisconsin can be compatible. These results can support growers and practitioners with selection of effective PRE herbicides for Palmer amaranth and giant foxtail control and reduced impact on fall-seeded radish and cereal rye cover crops, altogether leading to more effective, diverse, and sustainable weed management programs.

Effect of broflanilide on the phytophagous mite Tetranychus urticae and the predatory mite Typhlodromips swirskii.

Two-spotted spider mite (TSSM), Tetranychus urticae Koch, is one of the most serious pests of agricultural crops. Broflanilide exhibits high lethality against various pests and has been marketed worldwide under the Vedira and Tenebenal brands in 2020. Nevertheless, little information has been reported about its effects on agricultural mites. Broflanilide displayed higher toxicity to TSSM eggs (24 h LC50 , 1.015 mg L-1 ) and adult females (24 h LC50 , 2.062 mg L-1 ) than commercial acaricides, including cyflumetofen, bifenazate, and profenofos. In contrast, the adverse effects of broflanilide on the predatory mite, Typhlodromips swirskii Athias-Henriot, was lower than those of fenpyroximate and abamectin. In the sublethal effect study, while adult females were treated with broflanilide, the number of eggs and longevity were reduced in LC10 and LC30 treatments; when eggs were treated with broflanilide, the egg duration and deutonymph duration were prolonged in LC30 treatment. A significant decrease in the total life span and duration and fecundity of adult females was observed in LC10 and LC30 treatments. Furthermore, the number of eggs per adult female was significantly reduced from 103.48 ± 3.69 in the control group to 69.42 ± 2.22 and 48.33 ± 1.75 in LC10 and LC30 treatments, respectively. In the greenhouse bioassay, broflanilide 5% suspension concentrate (MCI-8007) showed excellent acaricidal activity to TSSM, with 99.22% corrected control, compared with the MCI-8007 untreated group. Our results indicated that broflanilide has a high acaricidal activity to TSSM and significant inhibition to fecundity of adult female, and could be considered as a potential alternative for TSSM management. © 2021 Society of Chemical Industry.

Olfactory attraction to aggregation pheromone is mediated by disti-flagellum of antennal segments in Riptortus pedestris

Riptortus pedestris (Hemiptera: Alydidae) is a serious pest of soybean and sweet persimmon and uses male produced aggregation pheromone, (E)-2-hexenyl (Z)-3-hexenoate, (E)-2-hexenyl (E)-2-hexenoate, and tetradecyl isobutyrate to facilitate food location and recognition by conspecifics. Using electroantennogram (EAG) and greenhouse bioassay, we determined which antennal segment is involved in the detection of their aggregation pheromone. In the first EAG test using individual antennal segments, significant EAG responses to 1:1:1 mixture of the aggregation pheromone were observed only from the disti-flagellum segments of both male and female antennae at both pheromone doses tested (1 µg and 100 µg). In the following EAG tests using gradually removed antennal segment(s), EAG response was still maintained when the distal half of a disti-flagellum was surgically removed, while EAG response was lost when whole segment of disti-flagellum or other whole segments were gradually removed from intact antenna of both sexes. In greenhouse experiment, removing one or both segment(s) of disti-flagellum from male or female antennae resulted in significant reduction in their attraction to the aggregation pheromone. Together, these findings support that the disti-flagellum of R. pedestris houses olfactory neurons associated with attraction to their aggregation pheromone.