Laboratory Bioassays Research Articles

Does apple replant disease affect the soil patch selection behaviour and population growth of Collembolans?

AbstractApple replant disease (ARD) is common to all major apple‐growing regions in the world. It occurs when new apple trees are replanted on sites where previously the same or closely related crop species were grown. Biotic (fungi, bacteria and nematodes) and abiotic soil factors (poor soil structure, nutrition) contribute to the development and severity of ARD. However, the aetiology of ARD and effects on higher trophic levels are still unknown. In that sense, Collembola might play an important role, since they are one of the dominant mesofauna groups in many soils. They act as decomposer, fungivores and predators, representing different trophic levels in soil food webs. Therefore, any effect of ARD on the occurrence of Collembola could have ecological impacts on the soil quality and health. Here, we examined the colonization behaviour of two Collembolan species,Folsomia candidaandSinella curviseta, in choice tests and population growth tests using Apple Replant Diseased soil (ARD) and non‐ARD soil samples from different field sites and standardized laboratory bioassays. Additionally, Collembola behaviour was quantified by continuous video observations to investigate short‐term behavioural changes. Results showed that both Collembolan species significantly preferred colonization of the non‐ARD soils compared with ARD soils, independent of the origin of the soil samples or specific disinfection treatments. Moreover, the detailed video analysis of the foraging behaviour indicates rapid colonization of soil samples and low dispersal rates. Most likely, volatile compounds and to a lesser extent feeding stimulants play a vital role for the colonization process for both Collembolan species. Finally, results showed negative effects of ARD on population growth of both Collembolan species already after an 8‐week period, implying strong nutritional deficiencies in ARD affected soils. The hypothesis that ARD causing microorganisms directly affected orientation, colonization and population development of Collembola is discussed.

Practical resistance to Cry toxins and efficacy of Vip3Aa in Bt cotton against Helicoverpa zea.

Crops genetically engineered to make insect-killing proteins from Bacillus thuringiensis (Bt) have revolutionized management of some pests. However, the benefits of such transgenic crops are reduced when pests evolve resistance to Bt toxins. We evaluated resistance to Bt toxins and Bt cotton plants using laboratory bioassays and complementary field trials focusing on Helicoverpa zea, one of the most economically important pests of cotton and other crops in the United States. The data from 235 laboratory bioassays demonstrate resistance to Cry1Ac, Cry1Fa, and Cry2Ab occurred in most of the 95 strains of H. zea derived from Arkansas, Louisiana, Mississippi, Tennessee, and Texas during 2016 to 2021. Complementary field data show efficacy decreased for Bt cotton producing Cry1Ac + Cry1Fa or Cry1Ac + Cry2Ab, but not Cry1Ac + Cry1Fa + Vip3Aa. Moreover, analysis of data paired by field site and year shows higher survival in bioassays was generally associated with lower efficacy of Bt cotton. The results confirm and extend previous evidence showing widespread practical resistance of H. zea in the United States to the Cry toxins produced by Bt cotton and corn, but not to Vip3Aa. Despite deployment in combination with Cry toxins in Bt crops, Vip3Aa effectively acts as a single toxin against H. zea larvae that are highly resistant to Cry toxins. Furthermore, Vip3Aa adoption is increasing and previous work provided an early warning of field-evolved resistance. Thus, rigorous resistance management measures are needed to preserve the efficacy of Vip3Aa against this highly adaptable pest. © 2022 Society of Chemical Industry.

Compatibility of the bacterial entomopathogen Pseudomonas protegens with the natural predator Chrysoperla carnea (Neuroptera: Chrysopidae)

The susceptibility of the green lacewing Chrysoperla carnea to the soil-dwelling bacterial entomopathogen Pseudomonas protegens CHA0 was investigated in this study. Laboratory bioassays were conducted on larval instars exposed to different bacterial concentrations by both direct feeding and indirectly by offering a pre-treated insect prey. Potential toxicity was assessed through dose-response bioassays, while possible sublethal effects were evaluated on immature development time and the reproductive performance (fecundity) of adults emerging from treated juveniles. As a result, no significant effects were observed on larval survival and development in a comparison between treated and untreated (control) groups. No significant impact on adult emergence and no detrimental effects on female fecundity were detected. Everything considered, the use of P. protegens in the agroecosystem appears to be compatible with chrysopids.

Combining ability and heritability analysis of sweetpotato weevil resistance, root yield, and dry matter content in sweetpotato

Efficient breeding and selection of superior genotypes requires a comprehensive understanding of the genetics of traits. This study was aimed at establishing the general combining ability (GCA), specific combining ability (SCA), and heritability of sweetpotato weevil (Cylas spp.) resistance, storage root yield, and dry matter content in a sweetpotato multi-parental breeding population. A population of 1,896 F1 clones obtained from an 8 × 8 North Carolina II design cross was evaluated with its parents in the field at two sweetpotato weevil hotspots in Uganda, using an augmented row-column design. Clone roots were further evaluated in three rounds of a no-choice feeding laboratory bioassay. Significant GCA effects for parents and SCA effects for families were observed for most traits and all variance components were highly significant (p ≤ 0.001). Narrow-sense heritability estimates for weevil severity, storage root yield, and dry matter content were 0.35, 0.36, and 0.45, respectively. Parental genotypes with superior GCA for weevil resistance included “Mugande,” NASPOT 5, “Dimbuka-bukulula,” and “Wagabolige.” On the other hand, families that displayed the highest levels of resistance to weevils included “Wagabolige” × NASPOT 10 O, NASPOT 5 × “Dimbuka-bukulula,” “Mugande” × “Dimbuka-bukulula,” and NASPOT 11 × NASPOT 7. The moderate levels of narrow-sense heritability observed for the traits, coupled with the significant GCA and SCA effects, suggest that there is potential for their improvement through conventional breeding via hybridization and progeny selection and advancement. Although selection for weevil resistance may, to some extent, be challenging for breeders, efforts could be boosted through applying genomics-assisted breeding. Superior parents and families identified through this study could be deployed in further research involving the genetic improvement of these traits.

Determination of Silicon Accumulation in Non-Bt Cotton (Gossypium hirsutum) Plants and Its Impact on Fecundity and Biology of Whitefly (Bemisia tabaci) under Controlled Conditions

Considering the resistance development-potential of whitefly (Bemisia tabaci) against control tactics with limited action mechanisms, the present study investigated the accumulation of two different silicon (Si) sources (SiO2 and K2SiO3) in cotton plants. The tested dose rates (0, 200, and 400 mg/L) of both Si sources were applied directly to the soil or through foliar application on cotton leaves. Moreover, a laboratory bioassay was also conducted to evaluate the performance of applied Si sources against the oviposition preference and biology of B. tabaci. A significantly higher Si accumulation, reduction in oviposition preference, and prolonged developmental period of all nymphs and total life cycle of B. tabaci was observed in the case of foliar-applied silicon. Similarly, among Si sources, a significant decline in the number of oviposited eggs and delay in the developmental period of B. tabaci was observed in the case of SiO2, followed by K2SiO3. Moreover, cotton plants subjected to SiO2 treatments possessed higher Si contents in their leaves than K2SiO3 treated plants. The results further revealed that both Si sources showed promising results at their higher concentrations regarding the tested parameters of Si accumulation, fecundity, and developmental period of B. tabaci. Our results strongly suggest that among emerging pest control strategies in cotton plants lies the use of foliar application of Si, which can also be incorporated in different integrated pest management programs due to its safety for humans and beneficial insect fauna.

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.

Detoxification enzyme activity, reproductive and developmental fitness of abamectin-resistant Bryobia praetiosa (Acari:Tetranychidae)

Abamectin is an important and environmentally friendly antibiotic pesticide, and its resistance has become an area of intense research. In this study, we employed laboratory bioassays, biochemical analyses, and life history analyses to systematically evaluate abamectin resistance, the underlying biochemical mechanisms of resistance, and the reproductive and developmental characteristics of the arthropod pest Bryobia praetiosa. An abamectin-resistant B. praetiosa strain (RR) was obtained by intensive selection of an abamectin-susceptible strain (SS) using abamectin exposure in the laboratory for 24 generations, yielding a resistance index (RI) of 30.11. Comparison of detoxification enzymes suggested that the specific activities of carboxylesterases (CarEs), glutathione S-transferases (GSTs), and mixed-function oxidases (MFOs) in the RR strain were higher than those of the SS strain by 1.13-, 1.75-, and 4.02-fold, respectively. GST and MFOS protein concentrations were also significantly different between RR and SS strains. Further analysis of life history parameters demonstrated that the developmental duration and lifespan of RR strain in addition to egg numbers were markedly decreased relative to SS strain. The net reproductive rate (R0), finite rate of increase (λ), and population doubling time (Dt) of RR strain were significantly lower than those of SS strain. The results indicated that the RR strain was more disadvantageous in developmental and reproductive characteristics than the SS strain. In addition, the relative fitness value of the resistant strain is about half (Rf = 0.49) that of the susceptible strain. In conclusion, increased abamectin resistance in B. praetiosa was associated with a rapid increase in MFOs activity, while GSTs also played a role in abamectin resistance development and RR strain exhibited reproductive disadvantages.

Batkoa major infecting the invasive planthopper Lycorma delicatula

The entomopathogenic fungi Batkoa major and Beauveria bassiana caused co-epizootics in populations of invasive spotted lanternflies, Lycorma delicatula, in 2018 in northeastern North America. Although first described from North America in 1888, the biology and ecology of Batkoa major had not been studied since that time. This entomophthoralean fungus found infecting L. delicatula in 2018 produces conidia and rhizoids similar in appearance to the original description. We conducted laboratory bioassays to investigate infection of different ages and sexes of these planthoppers, inoculating via showered conidia. All nymphs, and male and female adults were susceptible, dying in 4.3-6.7 days. Adult males died more quickly than adult females or fourth instars. Batkoa major grew out of cadavers of adult males more frequently than adult females or fourth instar nymphs. Rhizoids that provide attachment of cadavers to substrates were produced from adult cadavers more frequently than conidia. Resting spores were not observed in vivo or in vitro in the lab, or in the field.

Bumble Bee Breeding on Artificial Pollen Substitutes.

Bumble bees are important pollinators for many temperate crops. Because of the growing demand for food from entomophilous crops, bumble bee colonies are commercially reared and placed in fields or greenhouses to guarantee sufficient pollination services. Besides, commercial colonies are increasingly used in laboratories for various bioassays under controlled conditions. For both usages, bumble bee colonies are commonly provided with sugar solution and honey bee-collected pollen pellets. However, the latter display several disadvantages since they may contain pollutants, pathogens, or toxic phytochemicals. Consequently, companies have developed pollen-free artificial diets to sustain colonies. Such diets are designed to boost worker health in the field, in complement of floral pollen collected by workers outside the colonies, but their suitability in 'closed' systems without access to floral pollen, such as in laboratory bioassays, is arguable. Here, we used microcolonies of the commercially important bumble bee Bombus terrestris L. (Hymenoptera: Apidae) to assess the suitability of five artificial pollen substitutes and three mixed diets. We also assessed the evaporation rate of the different diets as it could impact their suitability. At the end of the bioassays, microcolonies fed the artificial diets showed a reduced offspring development when compared to microcolonies fed natural pollen, which was partly offset by mixing these diets with natural pollen. By contrast, the artificial diets did not have deleterious effects on worker's health. We discuss the potential nutritional and physical causes of artificial diets unsuitability for offspring development and encourage further research to accordingly establish appropriate pollen-free diets for bumble bee breeding.

Pneumatic spray delivery-based solid set canopy delivery system for oblique banded leaf roller and codling moth control in a high-density modern apple orchard.

Pneumatic spray delivery (PSD)-based solid set canopy delivery systems (SSCDS) have demonstrated comparable spray deposition and reduced off-target drift compared with axial-fan airblast sprayers in high-density apple orchards. An important next step is to quantify whether PSD-based SSCDS can provide effective pest management. This study evaluated the biological efficacy of this fixed spray system variant and compared it with that of an axial-fan airblast sprayer. Partial field trials were conducted in a commercial apple orchard (cv. Jazz) trained in tall spindle architecture. Insecticides were applied at a rate of 935 L ha-1 (100 gallons per acre) for both application systems. Twenty-four hours after spraying, leaves and fruits were collected to prepare the laboratory bioassays enabling evaluation of efficacy against obliquebanded leafroller (OBLR) and codling moth (CM). OBLR mortality for SSCDS, airblast sprayer and untreated control treatments after 24 h of larval exposure was 91%, 98% and 4%, respectively and increased to 98%, 100% and 19% after 48 h. First-instar CM leaf bioassay mortality was 100% for SSCDS and airblast sprayer treatment, and 13% for the untreated control at 24 h post exposure. Larval CM mortality on fruit was 100% for SSCDS and airblast sprayer treatments, and 33% on the untreated control. Insecticides applied using SSCDS and an airblast sprayer had comparable larval mortality in all three assays, significantly higher than the untreated controls. These results suggest that PSD-based SSCDS may provide a viable alternative to axial-fan airblast sprayers in high-density apple orchards. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Efficacy of Spinetoram for the Control of Bean Weevil, Acanthoscelides obtectus (Say.) (Coleoptera: Chrysomelidae) on Different Surfaces.

Simple SummaryContact toxicity of spinetoram on three different surfaces, concrete, ceramic floor tile and laminate flooring, against Acanthocelides obtectus (Say.) was evaluated in laboratory bioassays. Our results provide data on the insecticidal effect of spinetoram for the control of A. obtectus on various surfaces; however, its efficacy varies according to the surface type, exposure time and concentration. In conclusion, our laboratory tests indicated that spinetoram at 0.025 and 0.05 mg active ingredient (AI)/cm2 achieved satisfactory control at relatively short exposures by contact action of A. obtectus adults on three surfaces, commonly encountered in legume storage facilities and warehouses.In this study, the contact toxicity of spinetoram on three different surfaces, concrete, ceramic floor tile and laminate flooring, against Acanthocelides obtectus (Say.) (Coleoptera: Chrysomelidae) was evaluated in laboratory bioassays. Different concentrations were evaluated ranging from 0.0025 to 0.05 mg AI/cm2, against adults of A. obtectus. Adult mortality was measured after 1-, 3-, 5- and 7-day exposure. After 1-day exposure, the mortality was low on all surfaces, ranging from 0 to 27.2%. After 5- and 7-day exposure, spinetoram at concentrations of 0.01 mg/cm2 and above achieved 100% or close mortality on concrete and laminate flooring surface, whereas low concentrations (0.0025, 0.005 and 0.0075 mg AI/cm2) resulted in significantly lower mortality levels, ranging from 1.6 to 30.8%, than high concentrations. In the case of ceramic floor tile surface, spinetoram treatments at all tested concentrations did not result in 100% mortality. Significant differences were recorded among the surfaces, depending on concentrations and exposure intervals. After 3-, 5- and 7-day exposure, mortality levels on ceramic floor tile surface were generally higher at low concentrations than those on the concrete and laminate flooring surfaces, whereas those on concrete and laminate flooring surfaces were significantly higher at high concentrations than ceramic floor tile surface. These results indicate that spinetoram at 0.025 and 0.05 mg AI/cm2 achieve satisfactory control at relatively short exposures on common types of surfaces and thus can be used as an effective insecticide against A. obtectus.

Evaluation of the Toxicity of Chemical and Biogenic Insecticides to Three Outbreaking Insects in Desert Steppes of Northern China.

The locusts Oedales asiaticus (Bey-Bienko) and Myrmeleotettix palpalis (Zubovski) (Orthoptera Acrididae) and the leaf beetle Galeruca daurica (Joannis) (Coleoptera, Chrysomelidae) are economically devastating insect species in the desert steppes of Northern China. Control is mainly and frequently dependent on highly toxic chemicals. To date, there have been no complete and comprehensive reports of insecticide applications to these key pests. In this study, laboratory bioassays were carried out to determine and compare the toxicity of twelve insecticides to three outbreaking insects, O. asiaticus, M. palpalis, and G. daurica, from three typical desert steppe regions, SZWQ, XHQ and WLTQQ, respectively. The responses of the two locust species and the leaf beetle were evaluated by topical application and leaf dip bioassay techniques across a range of concentrations to develop dosage–mortality regressions. The insecticides tested included six chemical insecticides (β-cypermethrin, imidacloprid, phoxim, λ-cyhalothrin, methomyl, chlorantraniliprole) and six biogenic insecticides (spinosad, avermectin, rotenone, matrine, azadiracthin, and methoxyfenozide). The results showed that phoxim, λ-cyhalothrin, β-cypermethrin and spinosad showed highly toxic activity to O.asiaticus, M. palpalis, and G. daurica, while methonyl, chlorantraniliprole, and rotenone were moderately toxic to both locust species and the leaf beetle. The LC50 values of matrine, azadiractin, and avermectin were more than 1 μg a.i./adult for O. asiaticus and M. palpalis, the LC50 values of which were higher 2 g/L for G. daurica. Our findings complement information from previous similar studies and will inform future studies relating to the control of outbreaking insects, such as O.asiaticus, M. palpalis, and G. daurica in desert steppes of northern China. This study is also expected to provide basic data on the use of chemical and biogenic insecticides for application in desert steppes.

Cropping and livestock impacts on surface waters in the Pampas region (Argentina)

The rivers and streams of the cropping and livestock regions of Buenos Aires province (Argentina) contain variable concentrations of pollutants and high concentrations of nutrients that simultaneously affect aquatic ecosystem communities. In the present study, we evaluated the water quality of the Burgos stream and El Tala river (San Pedro, Buenos Aires province) by analyzing chemical contaminants (As, Cu, Pb, Zn, and glyphosate), nutrients (ammonium, nitrate, and phosphate), and algal toxicity bioassays. Surface water was collected at six sampling stations in three months (April and September 2019, and February 2020). By taking into account the percentages of algal growth inhibition (%I), the standard species Raphidocelis subcapitata and a species isolated from the study area, Scendesmus acutus, showed different sensitivities to the water samples, with a maximum %I of 70.64% and 34.62%, respectively. Moreover, algal growth stimulation was observed due to the high nutrient concentrations. A risk quotient (RQ) was applied to evaluate the environmental hazards of the chemical contaminants Cu, Pb, Zn, and glyphosate on the algal populations. According to the RQ values obtained for Pb (1.20 and 3.30) and Zn (1.17 and 2.12), the growth of algal populations could be at risk due to the maximum environmental concentrations measured of Pb (132 µg L-1) and Zn 106 µg L-1). The present study showed the first approach of an environmental risk analysis based on simultaneous determinations of chemical contaminants and laboratory bioassays with algae, using a strain of alga isolated from the aquatic ecosystems studied.

Host‐marking pheromone of the South American fruit fly Anastrepha fraterculus and cross‐recognition by the Mediterranean fruit fly Ceratitis capitata (Diptera: Tephritidae)

AbstractFollowing oviposition, females of many fruit flies deposit on the fruit surface a host‐marking pheromone (HMP) that can deter oviposition by conspecifics and heterospecifics, thereby minimizing overexploitation of hosts. We describe the oviposition behaviour of two economically important fruit flies (Anastrepha fraterculus and Ceratitis capitata) in agar spheres marked with methanolic and aqueous faeces extracts that contain the HMP. Laboratory bioassays revealed that A. fraterculus mated female produces an HMP that can be extracted from faeces, and causes a significant reduction in fruit infestation by both conspecifics and heterospecifics (cross‐recognition). Furthermore, mated female faeces extract contains higher amounts of methyl (9E)‐hexadecenoate, methyl hexadecanoate, methyl linoleate and methyl (9Z)‐octadecenoate than male faeces extract. Our results provide evidence for the potential use of this ovipositional deterrent in crop protection and pest management programmes for A. fraterculus and C. capitata.

Susceptibility of Cydalima perspectalis (Lepidoptera: Crambidae) larvae to some reduced-risk insecticides in laboratory bioassays

Box tree moth (BTM) Cydalima perspectalis (Walker, 1859) is the most harmful pest of different boxwood species in Europe and Asia including Caspian boxwood Buxus hyrcana in the Hyrcanian forests of Iran. Accessible and effective eco-friendly insecticides are required for the pest control. Thus, susceptibility of 2<sup>nd</sup> and 4<sup>th</sup> instar larvae of BTM to commercial formulation of Bacillus thuringiensis (Bt), two plant extract formulations, Bio1<sup>®</sup> and Matrine<sup>®</sup>, and three insect growth regulator (IGR) insecticides, chlorfluazuron, chromafenozide and diflubenzuron were investigated in laboratory bioassay. Except for diflubenzuron, significant mortality of both instar larvae was observed. At the endpoint of the experiments (96 h), 75.2–90% of second and 80–85% of fourth instar larvae had already died, as a result of feeding on leaves treated with the highest concentration of the insecticides. Furthermore, based on Probit analysis, Matrine<sup>®</sup> exhibited the highest efficiency (lethal concentration LC<sub>50</sub> = 2.87 μL·L<sup>–1</sup>) on 2<sup>nd</sup> instar larvae and followed by Bio1<sup>®</sup> (8.07 μL·L<sup>–1</sup>), chlorfluazuron (173.3 μL·L<sup>–1</sup>) and Bt (326.3 mg·L<sup>–1</sup>). The LC<sub>50</sub> of Matrine<sup>®</sup> and Bt for 4<sup>th</sup> instar larvae were 1.75 μL·L<sup>–1</sup> and 335.8 mg·L<sup>–1</sup>, respectively. Our study revealed that Matrine<sup>®</sup> and chromafenozide could be alternatively used against BTM in situations where there is a permission and need to use insecticides.

Comparison of Current Peanut Fungicides Against Athelia rolfsii Through a Laboratory Bioassay of Detached Plant Tissues.

Southern stem rot of peanut, caused by Athelia rolfsii, is an important fungal disease that impacts peanut production worldwide. Foliar-applied fungicides are used to manage the disease, and several fungicides have been recently registered for southern stem rot control in peanuts. This study compared fungicidal, residual, and potential systemic activity of current fungicides against A. rolfsii using a laboratory bioassay. Peanut plants grown in the field were treated with eight fungicides approximately 90 days after planting, and plants were collected for the laboratory bioassay weekly for 5 weeks following application. Peanut plants were separated into the newest fully mature leaf present at sample collection, the second newest fully mature leaf present at the time of fungicide application, the upper stem, and the crown tissues. Each plant tissue was inoculated with A. rolfsii then incubated at 30°C for 2 days. Lesion length was measured, and percent inhibition of fungal growth by each fungicide relative to the control was calculated. All fungicides provided the greatest inhibition of A. rolfsii on leaf tissues that were present at the time of fungicide application, followed by the newly grown leaf and upper stem. Little inhibition occurred on the crown. Fungal inhibition decreased at similar rates over time for all fungicides tested. Succinate dehydrogenase inhibitors provided less basipetal protection of upper stems than quinone outside inhibitor or demethylation inhibitor fungicides. Properties of the fungicides characterized in this study, including several newly registered products, are useful for developing fungicide application recommendations to maximize their efficacy in controlling both foliar and soilborne peanut diseases.

Association of voltage-gated sodium channel mutations with field-evolved pyrethroid resistant phenotypes in soybean aphid and genetic markers for their detection

The frequent use of insecticides to manage soybean aphids, Aphis glycines (Hemiptera: Aphididae), in the United States has contributed to field-evolved resistance. Pyrethroid-resistant aphids have nonsynonymous mutations in the voltage-gated sodium channel (vgsc). We identified a leucine to phenylalanine mutation at position 1014 (L1014F) and a methionine to isoleucine mutation (M918I) of the A. glycines vgsc, both suspected of conferring knockdown resistance (kdr) to lambda-cyhalothrin. We developed molecular markers to identify these mutations in insecticide-resistant aphids. We determined that A. glycines which survived exposure to a diagnostic concentration of lambda-cyhalothrin and bifenthrin via glass-vial bioassays had these mutations, and showed significant changes in the resistance allele frequency between samples collected before and after field application of lambda-cyhalothrin. Thus, a strong association was revealed between aphids with L1014F and M918I vgsc mutations and survival following exposure to pyrethroids. Specifically, the highest survival was observed for aphids with the kdr (L1014F) and heterozygote super-kdr (L1014F + M918I) genotypes following laboratory bioassays and in-field application of lambda-cyhalothrin. These genetic markers could be used as a diagnostic tool for detecting insecticide-resistant A. glycines and monitoring the geographic distribution of pyrethroid resistance. We discuss how generating these types of data could improve our efforts to mitigate the effects of pyrethroid resistance on crop production.

Aquatic Contamination in Lugano Lake (Lugano Lake Ecological Reserve, Buenos Aires, Argentina) Cause Negative Effects on the Reproduction and Juvenile Survival of the Native Gastropod Biomphalaria straminea.

Lugano Lake is located in an Ecological Reserve of Buenos Aires City. Biomonitoring of its water quality is essential due to its importance as a place for recreation and protection of native species. Biomphalaria straminea is a native hermaphrodite aquatic gastropod that inhabits different freshwater bodies of Argentina and was recently selected as a potential bioindicator. We propose this study as a first approach to assessing specific organisms’ use in biomonitoring of urban wild reserves, and the usefulness of reproduction assays. B. straminea survival, behavior, reproduction success and offspring survival after the exposure to water samples from Lugano Lake (L1, L2, and L3) were evaluated. Temperature, pH, conductivity and dissolved oxygen were registered in situ. Samples were transported to the laboratory and chemical analysis and bioassays were performed using 20 snails per site. A control group with tap water was added. Egg masses were separated, exposed individually and observed daily using a stereoscopic microscope. After hatching, juveniles were placed in tap water and offspring survival was registered at the first, second, third and fourth months after the beginning of the assay. High levels of conductivity, turbidity and nutrients were obtained. Ammonium and nitrite were higher than the guideline level for the protection of aquatic life. During the bioassay 20% of the snails (L2 and L3) showed abnormally protruding of the head-food region. The number of eggs and embryonated eggs per mass did not differ between treatments. Egg masses exposed to water samples from the lake presented overlapping and abnormal eggs and arrested embryos. Besides, low % of hatching (L1: 33%, L2: 42%, and L3: 16%) and juvenile survival after the first (L1:14%; L2:78%) and second month (L1: 60%) were noted. In the control group, 85% of hatching and 100%–90% of survival were observed. Our results suggests the presence of pollutant in the lake. B. straminea seems to be a sensitive local species. Biomphalaria spp. reproduction assays can provide a valuable endpoint for toxicity and risk assessments and a usefulness tool for biomonitoring water quality.

Cu@C core-shell nanoparticles modified polydimethylsiloxane -based coatings with improved static antifouling performance

PDMS-based fouling release coatings have promising applications in the fields of marine fouling control. However, development of silicone-based coatings with good antifouling / fouling-release property under relative static conditions remains challenging. In this work, a new PDMS-based nanocomposite coating consisting of PDMS matrix and nanofiller of copper@carbon core-shell nanoparticles was developed. Uniformly dispersed Cu@C core-shell in the PDMS matrix enhance the antifouling ability. The PDMS with low surface energy endows the composite coatings with hydrophobicity thus fouling release property. The introduction of Cu@C core-shell/PDMS improves both the Young's modulus, tensile strength and the elongation at break. Furthermore, laboratory bioassay against diatom adhesion and field tests indicated that the PDMS-based nanocomposite coatings with Cu@C core-shell exhibited outstanding antifouling / fouling-release property even under static conditions, showing promising application in marine antifouling.

In vitro determination of LD50 for AgriX365 on corn strain of Spodoptera frugiperda

Fall armyworm, Spodoptera frugiperda, is currently a major and invasive pest that is threatening global maize production and food security especially in sub–Saharan Africa. Its tolerance to several available synthetic pesticides has led to research into novel pest management strategies. An in vitro laboratory bioassay was conducted at Bindura University of Science Education to determine the LD50 for AgriX365, a botanical pesticide, in a complete randomised design. There was a relative dose-dependent response in mortality rates of S. frugiperda from 0.5ml/L to 2ml/L of AgriX365. The logistic function Probit, P, calculation indicated an LD50 =1.25ml/L (1250 ppm); y=0.5998x+4.2749; R2=0.9979) of the standard or recommended field rate for AgriX365. There was a high significant difference between mean per cent mortality between treated S. frugiperda larvae and the untreated ones (p