Compatibility of Entomopathogenic Nematodes with Chemical Insecticides for the Control of Drosophila suzukii (Diptera: Drosophilidae)

The spotted-wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), is a pest that reduces the productivity of small fruits. Entomopathogenic nematodes (EPNs) and chemical insecticides can suppress this pest, but the compatibility of the two approaches together requires further examination. This laboratory study evaluated the compatibility of Steinernema brazilense IBCBn 06, S. carpocapsae IBCBn 02, Heterorhabditis amazonensis IBCBn 24, and H. bacteriophora HB with ten chemical insecticides registered for managing D. suzukii pupae. In the first study, most insecticides at the recommended rate did not reduce the viability (% of living infective juveniles (IJs)) of S. braziliense and both Heterorhabditis species. The viability of S. carpocapsae was lowered by exposure to spinetoram, malathion, abamectin, azadirachtin, deltamethrin, lambda-cyhalothrin, malathion, and spinetoram after 48 h. During infectivity bioassays, phosmet was compatible with all the EPNs, causing minimal changes in infectivity (% pupal mortality) and efficiency relative to EPN-only controls, whereas lambda-cyhalothrin generally reduced infectivity of EPNs on D. suzukii pupae the most, with a 53, 75, 57, and 13% reduction in infectivity efficiency among H. bacteriophora, H. amazonensis, S. carpocapsae, and S. brazilense, respectively. The second study compared pupal mortality caused by the two most compatible nematode species and five insecticides in various combinations. Both Heterorhabditis species caused 78-79% mortality among D. suzukii pupae when used alone, and were tested in combination with spinetoram, malathion, azadirachtin, phosmet, or novaluron at a one-quarter rate. Notably, H. bacteriophora caused 79% mortality on D. suzukii pupae when used alone, and 89% mortality when combined with spinetoram, showing an additive effect. Novaluron drastically reduced the number of progeny IJs when combined with H. amazonensis by 270 IJs and H. bacteriophora by 218. Any adult flies that emerged from EPN-insecticide-treated pupae had a shorter lifespan than from untreated pupae. The combined use of Heterorhabditis and compatible chemical insecticides was promising, except for novaluron.

Pathogenicity and Virulence of Different Concentrations of Brazilian Isolates of Entomopathogenic Nematodes Against Drosophila suzukii

The invasive pest Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) was recently recorded in Brazil and constitutes a threat to fruit growing, mainly for small, soft fruits. Recent advances in research on ways of controlling D. suzukii involve the use of entomopathogenic nematodes (EPNs). In this context, the objective of this study was to evaluate the pathogenicity and virulence of four isolates in different concentrations against D. suzukii pupae. The EPN isolates used in trials were Steinernema brazilense IBCBn 06, S. carpocapsae IBCBn 02, Heterorhabditis bacteriophora HB, and H. amazonensis IBCBn 24. Both H. amazonensis IBCBn 24 and H. bacteriophora HB were effective in controlling D. suzukii as they caused a mortality rate of 86.25% and 80.0%, and virulence of 549.75 IJs/pupae and 787.75 IJs/pupae in the concentrations of 1800 IJs/ml and 5400 IJs/ml, respectively. The lowest lethal concentrations (LC50) of juveniles were found in host pupae with 771.63 IJs/ml of H. bacteriophora HB and 1115.49 IJs/ml of H. amazonensis IBCBn 24. Results showed that both EPNs, H. amazonensis IBCBn 24 and H. bacteriophora HB, could be promising eco-friendly biological agents to control D. suzukii.

Disease caused by Neofusicoccum parvum in pruning wounds of grapevine shoots and its control by Trichoderma spp. and Xenorhabdus szentirmaii

Neofusicoccum parvum, is a fungal pathogen and one of the etiological agents of dieback disease in grapevines. The fungus causes deterioration of vines due to vascular colonization and/or production of toxins. We report herein the inhibitory effects of Trichoderma spp. isolates and the antifungal effects of cell-free supernatants (CFS) from Xenorhabdus and Photorhabdus bacteria against N. parvum in agar plates. We also evaluated the effects of the most effective fungi and bacteria against the pathogen in pruning wounds of vine shoots. All isolates of Trichoderma exhibited antifungal activity ranging between 82 and 97.5% at 14 days of post-treatment. All Xenorhabdus and Photorhabdus CFS at 10 and 33% concentrations inhibited mycelial growth with X. szentirmaii PAM 11 and PAM 25 causing the highest inhibition (>74%). In the shoot experiments, T. asperellum IB 01/13 and T. asperellum Quality®, X. szentirmaii PAM 11 (undiluted growth culture and CFS) suppressed the fungus by ≥ 93%. Our study highlights the potential of Trichoderma and X. szentirmaii PAM 11 for use as biofungicides in the management of N. parvum in grapevines. Further studies should be conducted to develop formulations of Trichoderma and Xenorhabdus that enhance stability in shelf-life and increase the efficacy of N. parvum control in grapevines under field conditions.

Effectiveness of Steinernema rarum PAM 25 (Rhabditida: Steinernematidae) Against Drosophila suzukii (Diptera: Drosophilidae)

Drosophila suzukii (Matsumura 1931) represents one of the main pests of small fruits. The use of biological agents is very promising for insect control. In the present study, the nematode Steinernema rarum PAM 25 was evaluated for the control of D. suzukii pupae, this species has not been evaluated previously. First, we evaluated the pathogenicity of S. rarum PAM 25 at the concentration of 1,000 infective juveniles (IJs) inoculated into D. suzukii pupae. In the second bioassay, we evaluated the influence of 1,500; 2,000; 2,500; 3,000; 4,000 IJs/ml nematode concentration and temperature on D. suzukii mortality. In the third bioassay, we evaluated the influence of the isolate S. rarum PAM 25 on D. suzukii adult lifespan following pupal infection, using the concentrations with the highest mortality rate of pupae at each temperature as determined in the second experiment. The S. rarum PAM 25 isolate is pathogenic to D. suzukii. The most effective temperature for S. rarum PAM 25 activity was 14°C at a concentration of 4,000 IJs/ml. Adults infected with S. rarum PAM 25 showed a significant reduction in longevity. The results confirmed the potential of S. rarum PAM 25 for the control of D. suzukii.

Virulence of entomopathogenic nematodes and their symbiotic bacteria, under laboratory conditions, aiming controlling Saccharicoccus sacchari (Cockerell, 1895) (Hemiptera: Pseudococcidae) on sugarcane

Sugarcane crops Saccharum spp. (Poales: Poaceae) produces different derivatives to the world: sugar, ethanol and bioenergy. Despite the application of pesticides, insect pests still cause economic losses, among these the pink sugarcane mealybug Saccharicoccus sacchari (Cockerell, 1895) (Hemiptera: Pseudococcidae) causing direct and indirect damage to the plant. This study assess the virulence of three entomopathogenic nematodes (EPNs) species and their symbiont bacteria against the pink sugarcane mealybug, under laboratory conditions. Fourteen treatments represented by control (distilled water), Heterorhabditis bacteriophora Poinar, 1976 (HB EN01) (Rhabditida: Heterorhabditidae), Steinernema rarum (Doucet, 1986) (PAM25) and Steinernema carpocapsae Weiser, 1955 (All) (Rhabditida: Steinermatidae) at concentrations of 25, 50, 75 and 100 infective juveniles (IJs)/insect, and the standard chemical product, thiamethoxam, were assayed. In a second experiment, the bacteria Photorhabdus luminescens (Thomas and Poinar, 1979), Xenorhabdus szentirmaii Lengyel, 2005 and Xenorhabdus nematophila (Poinar and Thomas, 1965) (Enterobacterales: Morganellaceae) at 3.0 x 109 cells/ml were assessed for each treatment. Ten replications were stablished, each one counting ten females/mealybugs inside a 10 cm Petri dish, amounting 100 individuals/treatment. All treatments were kept under stable conditions (25±1 ºC, H 70±10%, in the dark). All nematodes species infected S. sacchari. Steinerma rarum (PAM25) provided the highest mortality against the pink sugarcane mealybug (79.25%), followed by H. bacteriophora (HB EN01) (58.25%) and S. carpocapsae (All) (42.50%) (P<0.001). The mortality rate caused by X. szentirmaii, P. luminescens and X. nematophila were 40, 45 and 20%, respectively. Steinerma rarum (PAM25) has conditions to be a potential agent to be incorporate into the integrated pest management in sugarcane.

Culture media to detect and criteria to evaluate and report the activity of extracellular enzymes produced by phytopathogenic fungi

ABSTRACT: Extracellular enzymes are involved in the fungal pathogenesis in plants. Currently, culture media, data analyses, and data report related to extracellular enzymes produced in vitro conditions are different and therefore, lack standardization. This work aimed to compare the culture media cited on the literature (normal) with the potato-dextrose-agar (PDA) medium combined with a specific compound to produce extracellular enzymes through three soilborne phytopathogenic fungi (F. solani f. sp. passiflorae, S. rolfsii, and R. solani AG-4 HGI), as well as to analyze and report enzyme data based on five different criteria. The assay was randomized, with three factors (culture media, isolates, and enzymes) and six repetitions. The studied enzymes were amylase (AM), carboxymethylcellulase (CMCase), lipase (LP), laccase (LC), catalase (CT), and gelatinase (GT). The normal media detected more enzymes and was more precise compared to the PDA medium plus specific compound. The criteria that calculated the area of the circular crown of AM, CMCase, LP, and LC and measured the intensity (0 = absence, up to 4 = intense) of CT and GT adopting note scale were the best to evaluate and report the results of the enzymes. We suggest the normal media culture to study enzyme production, as well as the criteria mentioned to assess and report the data related to enzyme activities.

Colonization of vines by Petri disease fungi, susceptibility of rootstocks to Phaeomoniella chlamydospora and their disinfection

ABSTRACT: Petri disease is complex, attacks young vine plants and it is difficult to be controlled. The fungus Phaeomoniella chlamydospora (Phc) has been identified as the main causative agent of this disease. This study aimed to evaluate the prevalent colonization of the Petri disease fungi in different portions of vine plants; to assess the susceptibility of grapevine rootstocks to the fungus P. chlamydospora; to assess the effect of solarization and biofumigation, followed by hot-water treatment (HWT), on the disinfection of cuttings of the rootstock IAC 766 infected with P. chlamydospora, and assess the effect of solarization and biofumigation, followed by HWT, on the rooting of cuttings of the rootstock IAC 766. For the prevalent colonization test, the fungus species detected and identified in ‘Niagara Rosada’ grafted on two rootstocks different were Phc and Phialemoniopsis ocularis. This is the first report of P. ocularis in a young vineyard in Brazil. Both fungi, in particular Phc, colonized only the plant’s basal part, drawing attention to the rootstock as target for control measures. Measurement of the dark streaks in the vascular system revealed that Golia was the least susceptible rootstock, and IAC 572 was the most susceptible to Phc. Moreover, biofumigation or temperature of 37°C applied for 7 and 14 days, both followed by HWT, suppressed Phc in cuttings of the rootstock IAC 766 without hampering their rooting. Meanwhile, new studies are needed to validate the efficiency of these disinfection techniques.

Mortality of Conotrachelus humeropictus in response to combined application of the nematode Steinernema brazilense and the fungus Beauveria bassiana

ABSTRACT: The fruit borer Conotrachelus humeropictus is one of the most important pests of the cupuaçu crop, and can promote yield losses of around 50%. The present study involved the selection of Beauveria bassiana isolates on Conotrachelus psidii larvae, which was used as test insect due to its taxonomic closeness to C. humeropictus. In order to assess their interaction using combined application, we studied the ability of the nematode to carry conidia of B. bassiana and Metarhizium anisopliae to soil layers. This study also aimed to establish a biological control method for cupuaçu borer with the use of the fungus B. bassiana at 10 kg/ha and the entomopathogenic nematode Steinernema brazilense at 1, 3, 9, and 27 IJ/cm2, applied as single and combined treatments. In the selection of B. bassiana strains for C. psidii, the IBCB 276 and IBCB 165 isolates were the most promising ones, causing 86 and 84% mortality, respectively. The IBCB 276 strain was applied in the field to control C. humeropictus. In the study of carriage of conidia in soil, the nematode S. brazilense was found to be capable of carrying conidia of B. bassiana to deep 7 to 10 cm soil layers. This was not observed with M. anisopliae, found only in the topsoil. In field trials against C. humeropictus larvae, B. bassiana promoted 15.6% mortality. The nematode promoted 60.0% mortality at the highest concentration used, and their combined use with B. bassiana (10 kg/ha) increased mortality to 65.6%, with an additive interaction observed between the two entomopathogens.

Two methods for isolation of endophytic and edaphic Bacillus spp. from sugarcane fields

ABSTRACT: Bacillus has been widely studied and used for the control of pests and diseases. The adapted protocol proposed by POLANCZYK (2004) proved to be more efficient than the one by the World Health Organization (WHO, 1985) to isolate edaphic strains of Bacillus. However, it has not been assessed for isolation of endophytic strains, which are much less abundant in the nature and more difficult to be isolated. This study aimed to compare two methodological procedures for isolation of Bacillus, established by the WHO (1985) and by POLANCZYK (2004), regarding their efficiency for isolation of endophytics and edaphics Bacillus strains from inside the root tissue of sugarcane, as well as from the associated soil sample, collected from 11 locations; and to compare the density of bacteria in both environments. Endophytic and edaphic strains of Bacillus were isolated by both procedures. However, the isolation protocol performed by POLANCZYK (2004) made more efficient by having a greater number of colony forming units (CFU) per gram of soil and root indicating that this procedure is more useful, especially for isolation of endophytic strains of Bacillus, which are much less abundant in the nature than edaphic strains, being therefore more difficult to be isolated. Using the Polanczyk protocol (2004), Bacillus strains were recovered from all roots (endophytic) and soil (edaphic) samples of all the 11 fields, suggesting that the plant root may be another important source for isolation of Bacillus besides the soil. Higher densities of Bacillus were isolated from the edaphic environment compared with the endophytic environment, with significant differences when isolated by Polanczyk method (2004).