Promising Biological Control Research Articles

In vitro screening of antagonistic activity of microorganisms against anthracnose disease

Anthracnose disease can be successfully controlled by chemical pesticides in conventional fruit growing. However, in organic farming, in order to maintain environmental safety and fulfill consumer demand for pesticide-free food, the control of this disease is a major problem. The use of biocontrol agents with the antagonistic mechanism of control of many phytopathogens is an innovative alternative for cost-effective and eco-friendly production. The antagonistic activities of Trichoderma viride and Bacillus subtilis were tested in vitro against Colletotrichum acutatum, one of major plant pathogens responsible for anthracnose. The microbial antagonists inhibited mycelial growth in the dual culture. T. viride exhibited strong antagonism against C. acutatum isolates (80%). The B. subtilis isolate also had a strong effect on inhibiting the development of C. acutatum (37.5%). The results of this study identified T. viride and B. subtilis as promising biological control agents for further testing against anthracnose disease in fruits.

Predatory Potential of Canthecona furcellata (Pentatomidae: Hemiptera) Against Key Defoliator Pests of Teak in Nursery and Chik Pea under Field Conditions

Canthecona furcellata (Wolff.) (Hemiptera: Pentatomidae) is important biological control agents of many Lepidopteron, Coleopteran and Heteropteran insects. This predatory behavior of the species, this is a promising biological control agent for insect pests of agriculture and forest ecosystem. The nursery and field experiments were conducted to find out the predation potential of E. furcellata. The results revealed that maximum 93.66% predation was recorded on larvae of E. macheralis followed by 89.0 and 84.39% on larvae of H.puera and H. armigera respectively. Therefore, E. furcellata could be utilised effectively against E. machaeralis under field conditions, moreover, H. puera and H. armigera could be employed as laboratory hosts for mass rearing of E. furcellata.

Effect of Quorum Sensing Inducers and Inhibitors on Cytoplasmic Incompatibility Induced by Wolbachia (Rickettsiales: Anaplasmataceae) in American Serpentine Leafminer (Diptera: Agromyzidae): Potential Tool for the Incompatible Insect Technique.

Agricultural crops around the world are attacked by approximately 3,000–10,000 species of pest insect. There is increasing interest in resolving this problem using environmentally friendly approaches. Wolbachia (Hertig), an insect endosymbiont, can modulate host reproduction and offspring sex through cytoplasmic incompatibility (CI). The incompatible insect technique (IIT) based on CI-Wolbachia is a promising biological control method. Previous studies have reported an association between CI and Wolbachia density, which may involve a quorum sensing (QS) mechanism. In this study, we investigated the effect of manipulating QS in Wolbachia using several chemicals including 3O-C12-HSL; C2HSL; spermidine (QS inducers), 4-phenylbutanoyl; and 4-NPO (QS inhibitors) on American serpentine leafminer (Liriomyza trifolii [Burgess]), an agricultural pest. The results showed that inducing QS with 3O-C12-HSL decreased the proportion of hatched eggs and increased Wolbachia density, whereas QS inhibition with 4-phenylbutanoyl had the opposite effects. Thus, manipulating QS in Wolbachia can alter cell density and the proportion of hatched eggs in the host L. trifolii, thereby reducing the number of insect progeny. These findings provide evidence supporting the potential efficacy of the IIT based on CI-Wolbachia for the environmentally friendly control of insect pest populations.

Risk Assessment of Insecticides Used in Tomato to Control Whitefly on the Predator Macrolophus basicornis (Hemiptera: Miridae).

Simple SummaryThe whitefly Bemisia tabaci is a problem in tomato crops worldwide. The use of chemicals is one method to control this pest. Predators from the family Miridae have been used in Europe as biological control agents. We tested the insecticides most often used to control B. tabaci in tomato fields in Brazil for compatibility with the native Brazilian mirid Macrolophus basicornis. The results showed that regarding lethality, buprofezin, cyantraniliprole and spiromesifen were reduced-risk insecticides. Acetamiprid, bifenthrin, etofenprox + acetamiprid and pyriproxyfen + acetamiprid were considered broad-spectrum insecticides. The insecticides were also tested to be classified ecologically and were found to be safe, except for acetamiprid that was moderately toxic. Overall, our findings indicated that it is possible to use M. basicornis as a biological agent to control B. tabaci in tomato crops by means of pest management strategies that are compatible with agrochemicals in current use.The generalist mirid predator Macrolophus basicornis may contribute to Integrated Pest Management (IPM) of Bemisia tabaci in tomato crops. It is important to know the compatibility of the chemicals used to control this pest with this promising biological control agent. Seven insecticides were tested to investigate their toxicity to the predator. For four of the products, the LC50 for adults were determined. Buprofezin, cyantraniliprole and spiromesifen did not cause lethality and were classified as harmless. Acetamiprid, bifenthrin, etofenprox + acetamiprid and pyriproxyfen + acetamiprid caused acute toxicity and were classified as harmful. LT50 for all harmful insecticides were relatively low, ranging from 1.8 to 3.2 days. Moreover, these four insecticides have low LC50, with acetamiprid (0.26 mg a.i. L−1) as the lowest, followed by bifenthrin (0.38 mg a.i. L−1), etofenprox + acetamiprid (4.80 mg a.i. L−1) and pyriproxyfen + acetamiprid (8.71 mg a.i. L−1). However, the calculated risk quotient (RQ) values demonstrated that these insecticides were mostly ecologically safe for this predator, except for acetamiprid, classified as slightly to moderately toxic. The present study can contribute to the use of M. basicornis as a biological control agent on tomato crops and to compatible use with the insecticides tested, according to IPM strategies.

Screening and evaluation of acaropathogenic fungi against the bulb mite Rhizoglyphus robini

• Fungal isolates effective in controlling bulb mites ( Rhizoglyphus robini ) were screened. • The selected fungal isolates have high virulence and thermotolerance. • Three Metarhizium anisopliae were determined to be the most suitable for bulb mite control. Bulb mites ( Rhizoglyphus robini ) damage the bulbs, corns, and tubers of garlic, shallots, and onions. Bulb mites have recently become a serious problem because of the continuous use of acaricides, which has resulted in resistance among bulb mite populations. Thus, there is a need to find alternative control methods to suppress bulb mite populations. Here, we report the results of screening pathogenic fungi for the control of R. robini . The initial screen was performed using 342 isolates of entomopathogenic fungi from soils from South Korea. As a result, 57 isolates of putative acaropathogenic fungi were selected from cadavers of bulb mites supporting fungal sporulation. However, 11 isolates were finally selected for further study through a re-evaluation of the pathogenicity of the isolates. These isolates were identified as two isolates of Metarhizium pemphigi , two isolates of Metarhizium pingshaense , and seven isolates of Metarhizium anisopliae by a microscopic examination and sequence analysis of the ITS region and EF-1α gene. The virulence, thermotolerance and UV-B tolerance of the 11 isolates were further evaluated and compared. Eight isolates showed more than 80% mortality and three isolates showed 100% mortality at 7 days after treatment. The thermotolerance of conidia showed a large difference depending on the fungal isolate, and five isolates showed a conidial germination rate of approximately 60% or more even after 2 h of heat treatment. On the other hand, the UV-B tolerance was very low in all the isolates, and only one isolate showed more than approximately 80% tolerance to 0.1 J cm −2 , but the other isolates showed a conidial germination rate of less than 30%. Based on all of the above results, three isolates, M. anisopliae 4–3-2, 4–8-1, and 4–31-2, were the most effective isolates in controlling bulb mites and could be considered promising biological control agents against bulb mites.

Evaluation of biocontrol potential of Achromobacter xylosoxidans strain CTA8689 against common bean root rot

The purpose of this research was to explore the control of common bean root rot disease caused by Fusarium solani by the bacterial strain CTA8689 under in vitro and greenhouse conditions. The strain CTA8689 was isolated from common bean root and identified as Achromobacter xylosoxidans using 16S rDNA sequence, morphological and physiological characteristics. The strain CTA8689 suppressed the mycelial growth of F. solani in dual-culture (58.67%) and culture filtrates (41.87%) methods. The volatile compounds (VOCs) produced by CTA8689 inhibited mycelial growth and conidial germination of F. solani by 42.26% and 59.12%, respectively. Also, this strain produced biofilm, lytic enzymes such as chitinase, protease and pectinase, siderophore, IAA and gibberellin, and it was able to phosphate solubilization. Furthermore, the disease severity of common bean root rot was reduced using soil and seed treatment by 83.89% and 87.60%, respectively, 60 days after inoculation. Additionally, the strain improved the plant growth parameters in common bean under greenhouse conditions. The VOCs produced by the strain CTA8689 were analyzed by Gas chromatography-mass spectroscopy (GC-MS). Out of 23 identified VOCs, 1,3-Dimethylbenzene (21.613%), Benzene, 1,3-bis (1,1-dimethylethyl)- (13.823%%), Ethylbenzene (8.636%), Dodecane, 4,6-dimethyl- (8.145%) and Decane (5.905%), were the major bioactive components. The mode of action of the strain CTA8689 on the F. solani was through the production of antifungal compounds (antibiosis) and lytic enzymes, which suppressed mycelial growth and conidial germination of the pathogen in vitro and greenhouse conditions. Overall, our results showed that A. xylosoxidans strain CTA8689 could be a promising biological control agent (BCAs) for common bean root rot.

Bactericidal Effect of Pseudomonas oryziphila sp. nov., a Novel Pseudomonas Species Against Xanthomonas oryzae Reduces Disease Severity of Bacterial Leaf Streak of Rice.

Pseudomonas is a diverse genus of Gammaproteobacteria with increasing novel species exhibiting versatile trains including antimicrobial and insecticidal activity, as well as plant growth–promoting, which make them well suited as biocontrol agents of some pathogens. Here we isolated strain 1257 that exhibited strong antagonistic activity against two pathovars of Xanthomonas oryzae, especially X. oryzae pv. oryzicola (Xoc) responsible for the bacterial leaf streak (BLS) in rice. The phylogenetic, genomic, physiological, and biochemical characteristics support that strain 1257 is a representative of a novel Pseudomonas species that is most closely related to the entomopathogenic bacterium Pseudomonas entomophila. We propose to name it Pseudomonas oryziphila sp. nov. Comparative genomics analyses showed that P. oryziphila 1257 possesses most of the central metabolic genes of two closely related strains P. entomophila L48 and Pseudomonas mosselii CFML 90-83, as well as a set of genes encoding the type IV pilus system, suggesting its versatile metabolism and motility properties. Some features, such as insecticidal toxins, phosphate solubilization, indole-3-acetic acid, and phenylacetic acid degradation, were disclosed. Genome-wide random mutagenesis revealed that the non-ribosomal peptide catalyzed by LgrD may be a major active compound of P. oryziphila 1257 against Xoc RS105, as well as the critical role of the carbamoyl phosphate and the pentose phosphate pathway that control the biosynthesis of this target compound. Our findings demonstrate that 1257 could effectively inhibit the growth and migration of Xoc in rice tissue to prevent the BLS disease. To our knowledge, this is the first report of a novel Pseudomonas species that displays a strong antibacterial activity against Xoc. The results suggest that the P. oryziphila strain could be a promising biological control agent for BLS.

Conidiobolus lunulus, a newly discovered entomophthoralean species, pathogenic and specific to leaf-cutter ants

Conidiobolus lunulus is a recently described entomophthoralean species isolated from leaf-cutter ants. This fungus discharges not only primary but also secondary conidia and microconidia of different shapes. Because nothing was known about the biology of the fungus, and its interactions with hosts, we first evaluated if its pathogenicity against leaf-cutter ants changes with the fungal age (time grown in vitro), and if it is related to the conidial structures produced. Afterwards, we tested its virulence at three combinations of temperature and relative humidity. In addition, we noted all visible causes of death by recovering different microorganisms from the dead, non-sterilized, ants to evaluate C. lunulus virulence when pathogens carried naturally by the ants were present. Finally, we used the conditions that lead to the highest mortality to evaluate fungal virulence to other host species, including non-leaf-cutter ants. Results indicated that C. lunulus was pathogenic from a culture age of 1 to 5 days, with a peak at 2-days-old, from which we registered median lethal times of 1–2 days and 85% of the cadavers with fungal conidiation. Our results suggest that primary conidia and moon-shaped microconidia were infective. Evaluations of mortality using 2-days-old cultures on several leaf-cutter ant colonies showed 1) significantly faster mortality of C. lunulus inoculated ants in comparison to controls, 2) significantly greater and faster mortality at 23.7 °C than at 21.2 °C, 3) significantly higher and faster mortality at 88% than at 57% RH, and 4) a significant reduction of other pathogens in C. lunulus inoculated ants in comparison to controls. C. lunulus was highly specific to leaf-cutter ants, as hardly any increase in mortality was observed on inoculated ants, and no conidia were recorded on cadavers of the other three non-leaf-cutter ant species tested. Our results highlight that C. lunulus is a very promising biological control agent against leaf-cutter ants.

Sequencial passages of the multiple nucleopolyhedrovirus of Anagrapha falcifera(Kirby) (Lepidoptera: Noctuidae) (AfMNPV) in Spodoptera cosmioides (Walker) (Lepidoptera, Noctuidae)

The aim of this work was to evaluate the effects of Anagrapha falcifera (AfMNPV) multiple nucleopolyhedrovirus passages in the S. cosmioides caterpillar’s biology at different times of infection and histological changes that the virus could cause in the caterpillar midgut, seeking correlate histopathologic effects to the effectiveness of this virus as a potential biological control of this pest. Larvae were infected with seven days of development, by using three different passages of AfMNPV on S. cosmioides (F1, F4 and F7, which is the first, fourth and seventh passages, respectively) and the control treatment. Compared biology assays with the same treatments for analyzing behavior and mortality of caterpillars were performed concomitantly. The midgut morphology was compared between infected and uninfected larvae. The digestive tubes were collected at 24, 72 and 144 hours of infection (20 tubes/treatment/time of infection). After collection, the digestive tubes were fixed in Karnovsky, processed, stained with Hematoxylin-Eosin, and examined under a light microscope. The biology results of F4 and F7treatments, showed a drastic reduction in locomotion and feeding from the fourth day after infection and higher cumulative mortality rate compared to the control and F1. All treatments caused morphological changes in the midgut of S. cosmioides, in the three times of infection, with the greatest changes occurring at the epithelium. The AfMNPV, in the three passages tested in S. cosmioides, caused behavioral and morphological changes in the midgut, indicating that it can be a promising agent for biological control of this pest.

Diagnosis and bioefficacy of endospheric trichoderma strains of selected medicinal plant on pepper root rot and vascular wilt in Cameroon

We attempted to detect and assess the pathogenic potentials of the mycoflora causing wilt and root rot in pepper and to screen the antagonistic potentials of two medicinal plant-derived Trichoderma species (Trichoderma atroviride T32 and Trichoderma sp. N97) against the more pathogenic fungal pathogens. The taxonomic characterization revealed that the Fusarium spp. (56.9%), constituted of F. oxysporium f. sp. capsici (47.1%) and F. solani (9.7%) was the most distributed. Axenic soil infestation with the recovered pathogens successfully induced root rot, leaves chlorosis and root rot, resulting in 52% and 68.92% root stunting in sweet and hot pepper, respectively. The bioagents produced up to 64% inhibition of pathogens’ mycelia growth in confrontation assay, presumably by antibiosis. The ethyl acetate-based extracts from the Trichoderma spp. (10 mg/ml) completely lysed the Fusarium conidia and chlamidospores. The tested bioagents are no doubt promising biological control candidates against pepper wilt and root rot pathogens.

First Detection of the Adventive Egg Parasitoid of Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) Trissolcus mitsukurii (Ashmead) (Hymenoptera: Scelionidae) in France.

Simple SummaryThe invasive brown marmorated stink bug (BMSB), Halyomorpha halys, is a polyphagous species and a serious pest worldwide. Classical biological control (CBC), i.e., the introduction of a natural enemy from the native area of the pest, is considered as the preferential solution for BMSB regulation. Adventive populations of exotic egg parasitoids of BSMB, Trissolcus japonicus and T. mitsukurii, have been reported worldwide. With the aim to characterize the French diversity of egg parasitoids associated to various stink bugs including BMSB, field surveys were conducted between 2018 and 2020. Surprisingly, morphological and molecular analyses unambiguously revealed 12 specimens of T. mitsukurii, an Asian egg parasitoid of BSMB. Although its permanent establishment has to be confirmed, this first record in France could actually facilitate CBC initiatives, T. mitsukurii being considered with T. japonicus as the two most promising biological control agents against BMSB.We report the first detection of Trissolcus mitsukurii in France. More than 1860 sentinel egg masses of Halyomorpha halys (BMSB) were exposed in the field during the 2018–2020 period, and 12 specimens of T. mitsukurii emerged from one egg mass. Their taxonomic identification was confirmed both by morphological and molecular analysis. Trissolcus mitsukurii, similar to T. japonicus, is an egg parasitoid of BMSB in its area of origin in Asia, and both species are considered to be candidates for a classical biological control strategy against BMSB. Trissolcus mitsukurii was previously recorded in Italy where it is well established and widespread, and this may be the source of the French population. Possible permanent establishment and dispersion of T. mitsukurii in France should be monitored with emphasis on its potential effect on BMSB populations.

Spatial population structure: patterns of adaptation in populations of the water hyacinth grasshopper Cornops aquaticum (Bruner 1906)

AbstractThe water hyacinth grasshopper Cornops aquaticum (Bruner 1906) constitutes an appropriate model to assess phenotypic and karyotypic variability in the context of differentiation and adaptation of insect populations because it occurs over a wide latitudinal range. This study represents a general analysis of phenotype, karyotype and molecular variation in native populations of C. aquaticum in South America. This is also relevant because this insect is considered a promising biological control agent of water hyacinth, a native South American aquatic plant but a pest in South Africa. Along Paraná and Uruguay River Basins, body size correlated negatively with latitude, and positively so with temperature and rainfall in both sexes. To test whether the chromosomal and phenotypic patterns were adaptive, we compared them with neutral microsatellite loci variation in populations from the medium and lower course of the Paraná River. Firstly, the lack of pairwise association between karyotype and phenotype distance matrixes with that of neutral loci suggested non-neutrality. Secondly, phenotypic differentiation for all morphometric traits (PST) was significantly larger than molecular differentiation (FST), indicating a prevailing divergence selection effect on the observed phenotypic patterns. Finally, the phenotypic and genotypic spatial structures – inferred from Bayesian approaches – were discordant: neutral genetic structure clustered together most populations except for the two southernmost, downstream ones, whereas phenotypic spatial structure groups together all the deltaic populations and singles out the two northernmost ones. The results suggest directional selection leading to higher centric fusion frequencies in the downstream populations and favouring morphometric optimal differences in relation to the environment.

Physiological host range of Trissolcus mitsukurii, a candidate biological control agent of Halyomorpha halys in Europe

The invasive stink bug Halyomorpha halys, native to East Asia, is a severe agricultural pest of worldwide importance, and chemical insecticides are largely sprayed for its control. Negative impact and failures of chemical pest management led to consider classical biological control as one of the most promising methods in a long-term perspective. The Asian egg parasitoid Trissolcus japonicus is the main candidate biocontrol agent of H. halys, but more recently a second species, Trissolcus mitsukurii, which shares the area of origin with H. halys, has drawn special attention after adventive populations were found in Europe. Despite its recent detection, intentional release or redistribution are bound to approval of national petitions, which requires detailed risk analyses. With the aim of providing a contribution for the future development of a risk assessment for release purposes, here we present the first study on the physiological (fundamental) host range of T. mitsukurii in Europe. Tests conducted on different hemipterans common to Southern Europe, using three different experimental designs, revealed a oligophagous host range, limited to Pentatomoidea and comparable with the host range displayed by T. japonicus under similar laboratory conditions. In addition to its coevolved host H. halys, T. mitsukurii successfully parasitized the majority of tested pentatomid species and one scutellerid, although with highly variable emergence rates. Notably high parasitization rates were detected on H. halys, Acrosternum heegeri and Dolycoris baccarum. Host egg sizes positively affected parasitoid size and female egg load. Although T. mitsukurii might be a promising biological control agent of H. halys in Europe, further studies (e.g., chemical ecology, field parasitism) are needed for assessment of non-target risks.

Functional response and egg production of a native Typhlodromus recki Wainstein, 1958 (Acari: Phytoseiidae) population to Tetranychus urticae Koch, 1836 (Acari: Tetranychidae)

In this study, which was conducted to determine predation potential of Typhlodromus recki Wainstein, 1958 (Acari: Phytoseiidae) at Ege University, Faculty of Agriculture, Department of Plant Protection in 2018-2019. Functional response and egg production of the predatory mite, T. recki fed on different biological stages (egg, larva, protonymph, deutonymph and adult male) of the two-spotted spider mite (green form), Tetranychus urticae Koch, 1836 (Acari: Tetranychidae) were studied under laboratory conditions (25±1°C, 60±10% RH and 16:8 h L:D photoperiod). In the experiments, seven prey densities (2, 4, 8, 16, 32, 64 and 128) for each biological stage of the prey were offered daily to the predatory mite. The results of logistic regression analysis indicated that T. recki had a Type II functional response on each developmental stage of its prey according to Holling’s models. The attack rate (α) and the handling time (Th) varied based on the biological stages of the prey. The highest α and the lowest Th values were determined as 1.035 and 0.001 when the predator fed on larvae and eggs of its prey, respectively. The highest average daily mean number of the eggs consumed by T. recki was 111 at 128 prey densities. The highest average daily mean number of eggs deposited by the predator were found to be 1.05 when it fed on the eight-prey density of T. urticae protonymphs. In addition, the lowest average daily mean number of eggs deposited by the predator was 0.15 when fed on the two-prey density with T. urticae adult males. The study indicates that T. recki could be effective and promising biological control agent for T. urticae .

Control of Magnaporthe oryzae and Rice Growth Promotion by Bacillus subtilis JN005

It is quite important to develop the microorganism resources with biocontrol capacity for rice blast. This study evaluated Bacillus subtilis JN005 for growth promotion and biocontrol efficacy against Magnaporthe oryzae. Results showed that rice seeds treated with 1 × 107 cfu/mL suspension of B. subtilis JN005 had 16% germination energy, 14% germination rate, 15% germination index, and 270% vigor index compared to those treated with sterile water (control). In pot experiments, the JN005 strain-treated rice plants exhibited notable increase in plant height, root length, stem circumference, and fresh weight, as well as higher concentration of chlorophyll a, chlorophyll b, and total chlorophyll in rice leaves. Rice leaves inoculated with the JN005 strain resulted in increased activities of defense-related enzymes, including peroxidase (POD), phenylalanine ammonialyase (PAL), superoxide dismutase (SOD), and catalase (CAT) compared to the water and the M. oryzae-inoculated treatments. In vitro inoculated rice leaves with 1 × 107 cfu/mL bacterial suspension compared to sterile water or control treatment exhibited lower disease incidence in the curative and preventive groups by 79% and 76%, respectively. Field experiment showed that after spraying with 1 × 107 cfu/mL bacterial suspension, efficacy rates on controlling rice blast on plants were (56.82 ± 1.12)% and (58.39 ± 3.05)% at seedling and maturity stages, respectively, and that rice production yield was (524.40 ± 17.88) g/m2. Therefore, B. subtilis JN005 could be a promising biological control agent for rice blast, thereby warranting further investigation of its efficacy.

A modified semi-selective medium for isolation and enumeration of Pochonia chlamydosporia (Goddard) Zare & W. Gams

Pochonia chlamydosporia, is one of the most promising biological control agents for managing phytoparasitic nematodes. Isolation and enumeration of viable colonies of P. chlamydosporia from soil and other substrates without contamination is a major limitation, when commonly available nutrient media are used. Development of a suitable selective/semi-selective media by incorporating one or more inhibitors of microbial growth can facilitate isolation of the fungus. In vitro studies were carried out to test the compatibility of commonly used pesticides, namely, metalaxyl, metalaxyl-mancozeb, carbendazim, copper oxychloride, and chlorpyrifos with P. chlamydosporia. The fungus showed relatively high tolerance to higher doses of metalaxyl and carbendazim and was used in the modified medium for better suppression of other soil borne fungi. In the present study, Kerry’s semi-selective medium was modified and evaluated by counting the viable fungal propagules in different substrates (rice, farmyard manure, maize, rice bran, barley, and sorghum) and soil artificially inoculated with the fungus. The results showed that the modified Kerry’s semi-selective medium can effectively be used for isolation and quantification of P. chlamydosporia in routine studies.

Genetic variability among three Egyptian isolates of Heterorhabditis indica using a new marker technique (SCoT)

BackgroundEntomopathogenic nematodes (EPNs) are a group of nematode families, have the ability to search for their hosts, and are considered as promising biological control candidates for insect pests, providing protection to non-target organisms and the environment.ResultsThis study was conducted to isolate indigenous EPN isolates from Egyptian agricultural soils for further use in biological control programs and study their genetic polymorphism among the previously isolated isolates under accession no. MH553167 and MK300683 and the new isolate (MH496627), using the start codon targeted (SCoT) marker. One out of 15 soil samples obtained from a banana cultivated field was positive for the presence of EPNs, using the Galleria baiting method. Morphological analysis and sequencing of the internal transcribed spacer (ITS) region suggested that the isolate obtained belongs to Heterorhabditis indica. The sequence of the ITS was submitted to the National Center for Biotechnology Information (NCBI) and registered under accession no. MH496627. Ten SCoT primers were used in the study; the polymorphic bands were 68 out of 76 with 89% as polymorphism percentage. The highest numbers of bands were 10 bands generated by SCoT 1 and SCoT 18 while SCoT 48 and SCoT 60 recorded the lowest band number (5 bands).ConclusionsThe present study is considered as a preliminary study to demonstrate the effectiveness of the SCoT marker for the first time in assessing genetic relationships in EPNs.

Growth chamber and greenhouse screening of promising in vitro fungal biological control candidates for the soybean cyst nematode (Heterodera glycines)

The soybean cyst nematode (SCN; Heterodera glycines) is the most economically consequential pathogen of soybeans worldwide. Although biological control of SCN was proposed decades ago, only a few products are available on the market. Mining for new fungal biological control organisms and evaluating their potential to enhance integrated management of SCN is crucial. In this study, we evaluated 20 candidate biological control organisms in vivo that were selected out of a culturable mycobiome of over 5000 isolates based on their performance in in vitro assays. Of these isolates, labelled A through T, we identified three isolates, one Ilyonectria sp. (D), and two Purpureocillium sp. isolates (E and T), that significantly reduced SCN reproduction on a susceptible soybean variety (Sturdy) inoculated with both high and low levels of SCN eggs, compared to an untreated control, in a growth chamber cone-tainer assay. In a greenhouse pot assay, Purpureocillium isolates E and T also controlled nematode reproduction better than an untreated control and performed on par with the commercial fungal biological control agent, MeloCon® WG, which was applied at 41-fold higher concentration. In a second greenhouse assay, with higher nematode numbers, only isolate E performed as well as MeloCon® WG. This research identified promising candidate biological control agents of SCN that are as or more effective than existing products at much lower spore inoculation levels.

Host plant and humidity effects on phytoseiid mite, Gynaeseius liturivorus (Acari: Phytoseiidae) egg hatchability.

Gynaeseius liturivorus (Ehara) (Acari: Phytoseiidae) is a promising biological control agent for tiny arthropod pests, including Thrips tabaci Lindeman (Thysanoptera: Thripidae) known as a major pest of Welsh onion. In fields during summer, G. liturivorus is observed on soybean, but not on Welsh onion, even when numerous T. tabaci are present. To elucidate G. liturivorus's occurrence on soybean and Welsh onion in relation to relative humidity (RH), we examined its egg hatching on their seedlings under low RH conditions. Then we estimated the moisture transpiration from both plants. Egg hatching occurred only on soybean plants exhibiting greater moisture transpiration. Aiming at utilizing G. liturivorus as a biological control agent for Welsh onion production in summer, evaluation of its relative tolerance and compensation potential for drought injury is necessary. Therefore, we used five phytoseiid species including G. liturivorus and Neoseiulus californicus to estimate the RH and vapor pressure deficit (VPD) at which 50% of eggs hatch (RH50 and VPD50). Furthermore, we examined G. liturivorus and N. californicus egg hatching under different RH oscillation conditions. Results show G. liturivorus as the most drought-sensitive among the five species tested, but G. liturivorus isable to compensate for lethal low-RH effects on egg hatching in part by periodic exposure to high RH conditions, as observed for N. californicus.

Pathogenicity of entomopathogenic fungus, Metarhizium anisopliae MET-GRA4 isolate on dengue vectors, Aedes albopictus and Aedes aegypti mosquito larvae (Diptera: Culicidae)

Abstract Considering the rapid transmission of the dengue virus, substantial efforts need to be conducted to ward-off the epidemics of dengue viruses. The control effort is depending on chemical insecticides and had aroused undesirable conflicts of insecticide resistance. Here, we study the entomopathogenic fungus, Metarhizium anisopliae as a promising new biological control agent for vector control. The pathogenicity effects of Metarhizium anisopliae against field and laboratory strains of Aedes albopictus and Aedes aegypti larvae were tested using the larvicidal bioassay technique. The results demonstrate that the treatments using M. anisopliae isolate MET-GRA4 were highly effective and able to kill 100% of both Ae. albopictus and Ae. aegypti mosquito larvae at a conidia concentration of 1 × 10⁶/ml within 7 days of the treatment period. The fungus displayed high larvicidal activity against laboratory and field strain of Ae. aegypti larvae with LC50 values (9.6 x 103/ml, 1.3 x 103/ml) and LC95 values (1.2 x 10⁶/ml, 5.5 x 105/ml) respectively. For Ae. albopictus, LC50 values for laboratory and field strains were (1.7 x 104/ml, 2.7 x 104/ml) and the LC95 values were (2.1 x 10⁶/ml, 7.0 x 105/ml) respectively. Interestingly, the susceptibility of field strain towards M. anisopliae was higher as compared to the laboratory strain Aedes larvae. In which, the causative agents of all the dead larvae were verified by the virulence of M. anisopliae and caused morphological deformities on larval body. The findings from this study identify this isolate could be an effective potential biocontrol agent for vector mosquitoes in Malaysia.