LT50 Values Research Articles

Amino acids promote the rejuvenation of degenerated Metarhizium anisopliae

Metarhizium anisopliae, an entomopathogenic fungus widely employed in agricultural and forestry pest control, faces challenges related to colony growth degradation and sporulation decline during industrial production and germplasm preservation. In this study, liquid chromatography-mass spectrometry (LC-MS) was used to detect the metabolomics of the normal strain and degenerated strain, enabling a comparison and analysis of their metabolic profiles. The results revealed significant differences in metabolic phenotypes among different strains of M.anisopliae, with amino acids playing a crucial role in spore production. Through single factor and response surface tests, optimal amino acid concentrations for sporulation media were determined as follows: lysine at 25.00 mg/L, β-alanine at 140.00 mg/L, arginine at 22.5 mg/L, glutamic acid at 155.00 mg/L. Cultivating degenerated M.anisopliae using this optimized amino acid medium resulted in approximately fivefold increase in sporulation without significantly affecting LT50 values; thus indicating that the formulation promotes M.anisopliae’s sporulation without compromising its virulence.

Cold Tolerance Assay Reveals Evidence of Climate Adaptation Among American Elm (Ulmus americana L.) Genotypes

T he American elm (Ulmus americana L.), once a dominant species in North American floodplain forests, has suffered significant population declines due to Dutch elm disease (DED). Despite this, some elms persist, potentially exhibiting disease resistance and climate-adaptive traits that could facilitate restoration. Understanding these traits is crucial for selecting genotypes suited to current and future climatic conditions, particularly in colder regions. This study evaluated the mid-winter cold tolerance of American elm genotypes across a climatic gradient to ascertain evidence of local climate adaptation. We used relative electrolyte leakage (REL) to assess mid-winter cold tolerance of current-year shoots on eleven survivor genotypes from New England and one susceptible, control genotype from Ohio. The lethal temperature, at which 50% of cellular leakage occurs (LT50), was determined and compared with 30-year climate data to identify potential climate adaptation. Genotypes from colder regions exhibited greater cold hardiness, indicating local adaptation to climate. Observed mid-winter LT50 values (−42.8 °C to −37.7 °C) were in excess of the 30-year minimum air temperature, even at the coldest source location. This calls into question whether mid-winter cold tolerance is the critical period for injury to American elm and more attention should be given to environmental conditions that cause de-acclimation to cold. By understanding the adaptive capacity of American elm, managers can better select mother trees for regional seed orchards, ensuring the long-term success of restoration initiatives.

Entomopathogenic potential of indigenous Simplicillium subtropicum (Hypocreales: Cordycipitaceae) isolates from Tamil Nadu, India, against the cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae)

BackgroundAphis gossypii Glover (Hemiptera: Aphididae) is an economically important polyphagous pest species infesting many agricultural and horticultural crops causing severe yield losses. In order to develop biopesticides for the management of aphids in an environmentally safe manner, 6 indigenous entomopathogenic fungi Simplicillium subtropicum were isolated from soils of Tamil Nadu and their pathogenicity was tested against A. gossypii under laboratory conditions after characterization.ResultsPhenotypic and molecular characterization was performed for all the isolates for species identification. Results of the pathogenicity test showed that the isolate S6 (PP446637) performed well among other isolates causing 58.33% mortality on 7 days after treatment (DAT) @ 1 × 108 spores/ml. The LC50 and LT50 values were found to be 2.36 × 107 spores/ml at 7 DAT and 160.20 h @ 1 × 108 spores/ml, respectively. SEM images of A. gossypii treated with the isolate S6 (PP446637) revealed that initial phase of infection, i.e., adhesion, formation of germ tube and appressoria starts within 24 h post-infection (hpi), hyphal development and penetration of cuticle occurred within 48 hpi and extrusion of mycelium and conidiogenesis occurred within 72 hpi.ConclusionThis study reveals the entomopathogenic potential of indigenous S. subtropicum isolates against A. gossypii and suggests their use for the eco-friendly management of aphids.

Biological control of Dactylopius opuntiae (Cockerell) using entomopathogenic fungi in Morocco

ABSTRACT In Morocco and many other Mediterranean countries, cultivation of Opuntia spp. has been severely impacted by infestations of Dactylopius opuntiae (Cockerell) (Hemiptera: Dactylopiidae). Several control approaches have been adopted worldwide to address the spread of this pest, including biological control. Many entomopathogenic fungal isolates (EPFs) have been described as promising agents for this purpose worldwide. The efficacy of three EPFs: Alternaria murispora (PP264308), Alternaria destruens (PP264311), and Macrophomina tecta (PP264310) against D. opuntiae young females and nymphs was assessed in laboratory and field settings. Under laboratory conditions, A. murispora and A. destruens at 108 conidia mL−1, and D-limonene (the positive control) applied at 2.5 cc. L−1, were the most effective, which resulted in significant mortality rates in adult females and nymphs (97%, 86%, and 93% respectively (adult females) and 100%, 98%, and 99% respectively (nymphs)) after 6 days of exposure, leading to LT50 values of 3.0, 6.0 and 3.0 days, respectively (young female) and 3.0 (nymph). Under field conditions, A. murispora at 108 (88.9% mortality (nymphs) and 71.6% mortality (females)) and 107 conidia mL−1 (84.2% mortality (nymphs) and 64.2% mortality (females)), and D-limonene at 2.5 cc/L (88.8% mortality (nymphs) and 65.9% mortality (females)) showed the highest effectiveness in controlling D. opuntiae. We also observed that infected scale pests showed signs of mycosis, spore formation and discharge, which will contribute to the spread of the EPFs tested as biological control agents. Hence, alongside D-limonene, A. murispora, and A. destruens could be incorporated into an IPM strategy to control D. opuntiae.

Transgenerational stability of a high temperature-adapted strain of Neoseiulus barkeri Hughes (Acari: Phytoseiidae) and differential expression of antioxidant genes in response to heat stress

High temperature-adapted natural enemies may exhibit improved biocontrol effiicacy in hot weather, but transgenerational stability of the trait may affect practical applications. Neoseiulus barkeri is a commercially produced biocontrol agent, and a high temperature-adapted strain (HTAS) has been developed. Thermotolerance and the activity of antioxidant enzymes were evaluated in HTAS progeny under non-selective conditions to determine transgenerational stability of the selected adaptation. Results showed that survival of HTAS offspring decreased slightly after heat stress compared to HTAS parents, but remained significantly higher than that of the conventional strain (CS). LT50 and LT95 values of HTAS progeny were similar to HTAS parents and were approximately 2.5 and 4 h greater than CS, respectively. Similarly, predation behavior of HTAS offspring decreased somewhat compared to HTAS parents after short-term heat stress, but remained significantly higher than that of CS mites. Searching rate (a) of HTAS progeny was similar to HTAS parents and noticeably higher than CS, whereas handling time (Th) was lower than CS mites. Activities of both superoxide dismutase (SOD) and glutathione S-transferase (GST), along with malondialdehyde (MDA) content and total antioxidant capacity (T-AOC), were lower in HTAS offspring compared to HTAS parents and the CS, whereas peroxidase (POD) and catalase (CAT) activities were higher. The expression levels of ten antioxidant genes in HTAS offspring were significantly lower than in HTAS parents or CS mites before heat stress, but reached or surpassed parental levels after heat stress. Correlation analysis found both positive and negative associations between antioxidant indices and antioxidant genes. These results suggest that thermotolerance in the HTAS is relatively stably across generations in the absence of selective pressure, and is associated with changes in expression of antioxidant genes.

New insights on entomopathogenic bacteria isolated from soil of citrus crops to combat the polyphagus aphid pest Hyalopterus pruni (Geoffroy 1762) (Hemiptera, Aphididae)

BackgroundThe employment of entomopathogenic microorganisms is a promising approach for ensuring optimal phytosanitary protection in the framework of biological management of insect crop pests. Among these microbes, entomopathogenic soil-borne bacteria are preferred over pesticides because they help successfully in the natural regulation of arthropod populations, as soil has a favorable ecology for the availability and richness of many beneficial bacterial species. In this study, it was focused on the isolation, identification and characterization of entomopathogenic bacteria isolated from cultivated citrus soils and on the evaluation of their insecticidal potential in the laboratory against the mealy plum aphid, Hyalopterus pruni (Geoffroy 1762) (Hemiptera: Aphididae), a polyphagous and major pest attacking and virus-transmitting of several Prunus crops.ResultsIsolation results gave 11 bacterial isolates, which were more than 50% effective in selection tests on H. pruni aphids at 1 × 108 CFU/ml. A total of seven isolates generated significant insecticidal potential at different concentrations, and their molecular identification based on 16S rRNA genome sequencing yielded the following results: Lysinibacillus fusiformis (B4), Bacillus thuringiensis (B13), B. thuringiensis (B22), B. thuringiensis (B23), B. thuringiensis (B24), Pseudomonas sp. (P2) and Enterococcus gallinarum (P4). The most pathogenic potential of these strains was for E. gallinarum (P4), which induced 100% H. pruni mortality after 72 h of treatment at the concentration (C3 = 1 × 106 CFU/ml), followed by B. thuringiensis (B23), (B22), (B4), (P2), (B13) and (B24) isolates, which caused 96, 91, 85, 83, 65 and 50% mortality rates, respectively, at the lowest concentration (C4 = 1 × 105 CFU/ml). The LC50 and LT50 values were calculated for the entomopathogenic isolates of (P2), (P4), (B23) and (B24). A lowest LC50 value was 1.08 × 102 CFU/ml for (P4) E. gallinarum after 72 h of treatment, whereas (P2) Pseudomonas sp. presented the shortest LT50 of 33.6 h at concentration (C4 = 1 × 105 CFU/ml).ConclusionsThe present study's outcomes have confirmed the existence, abundance, and variety of entomopathogenic bacteria at the soil level in citrus groves. Interestingly, these bacteria could be useful for aphids’ population control on a wide scale through the utilization of their toxins and enzymes, even against insect pests of a broad order.

Genetics and ontogeny are key factors influencing thermal resilience in a culturally and economically important bivalve

Increasing seawater temperatures coupled with more intense and frequent heatwaves pose an increasing threat to marine species. In this study, the New Zealand green-lipped mussel, Perna canaliculus, was used to investigate the effect of genetics and ontogeny on thermal resilience. The culturally and economically significant mussel P. canaliculus (Gmelin, 1971) has been selectively-bred in New Zealand for two decades, making it a unique biological resource to investigate genetic interactions in a temperate bivalve species. Six selectively-bred full sibling families and four different ages, from early juveniles (6, 8, 10 weeks post-fertilisation) to sub-adults (52 weeks post-fertilisation), were used for experimentation. At each age, each family was exposed to a three-hour heat challenge, followed by recovery, and survival assessments. The shell lengths of live and dead juvenile mussels were also measured. Gill tissue samples from sub-adults were collected after the thermal challenge to quantify the 70 kDa heat shock protein gene (hsp70). Results showed that genetics, ontogeny and size influence thermal resilience in P. canaliculus, with LT50 values ranging between 31.3 and 34.4 °C for all studied families and ages. Juveniles showed greater thermotolerance compared to sub-adults, while the largest individuals within each family/age class tended to be more heat sensitive than their siblings. Sub-adults differentially upregulated hsp70 in a pattern that correlated with net family survival following heat challenge, reinforcing the perceived role of inducible HSP70 protein in molluscs. This study provides insights into the complex interactions of age and genotype in determining heat tolerance of a key mussel species. As marine temperatures increase, equally complex selection pressure responses may therefore occur. Future research should focus on transcriptomic and genomic approaches for key species such as P. canaliculus to further understand and predict the effect of genetic variation and ontogeny on their survival in the context of climate change.

Thiamethoxam toxicity on the stingless bee Friesiomelitta varia: LC50, survival time, and enzymatic biomarkers assessment

Bees play a crucial role as pollinating insects in both natural and cultivated areas. However, the use of pesticides, such as thiamethoxam, has been identified as a contributing factor compromising bee health. The current risk assessment primarily relies on the model species Apis mellifera, raising concerns about the applicability of these assessments to other bee groups, including stingless bees. In this study, we investigated the acute toxicity of thiamethoxam on the stingless bee Frieseomelitta varia by determining the average lethal concentration (LC50) and mean lethal time (LT50). Additionally, we evaluated the enzymatic profile of Acetylcholinesterase (AChE), Carboxylesterase-3 (CaE-3), and Glutathione S-Transferase (GST), in the heads and abdomens of F. varia after exposure to thiamethoxam (LC50/10). The LC50 of thiamethoxam was determined to be 0.68 ng ai/μL, and the LT50 values were 37 days for the control group, 25 days at LC50/10, and 27 days at LC50/100. The thiamethoxam significantly decreased the survival time of F. varia. Furthermore, the enzymatic profile exhibited differences in CaE3 activity within one day in the heads and ten days in the abdomen. GST activity showed differences in the abdomen after one and five days of thiamethoxam exposure. These findings suggests that the abdomen is more affected than the head after oral exposure to thiamethoxam. Our study provides evidence of the toxicity of thiamethoxam at both the cellular and organismal levels, reinforcing the need to include non-Apis species in pollinator risk assessments.and provide solid arguments for bee protection.

Effect of Methanolic Extracts of Clove (Syzygium aromaticum L.) Leaves and Galangal (Alpinia galanga L.) Rhizome for the Management of Rice Brown Plant Hopper, Nilaparvata lugens (Stal.)

The utilization of plant-based extracts derived from clove leaves and galangal rhizome represents a potential alternative for pest control, offering relative environmental safety, particularly in the case of Nilaparvata lugens (Stal.) infestations in rice plants. The objective of this study was to determine the optimal formulation of clove leaves and galangal rhizome extracts for effective management of N. lugens on rice plants. The research was conducted at the Green House of the Pest and Plant Disease Department, Faculty of Agriculture, Sam Ratulangi University, Manado. Six different concentrations of clove leaves and galangal rhizome extracts were used, each with four replications. These concentrations were 2 ml/L, 4 ml/L, 6 ml/L, 8 ml/L, 10 ml/L and a control group. Application of the extracts employed three methods: insect spraying, plant spraying and insect-on-plant spraying. The results indicated that insect spraying with clove leaves extract resulted in a mortality rate of 43.3% to 93.3%, while galangal rhizome extract caused a mortality rate of 13.3% to 80%. Plant spraying with clove leaf extract led to a mortality rate of 6.7% to 46.7% and galangal extract resulted in a mortality rate of 6.7% to 40.0%. Insect-on-plant spraying caused mortality rates of 46.7% to 86.7% for clove leaves extract and 50% to 76.7% for galangal extract at 12 to 72 hours after application. The highest efficacy in terms of the quickest insect mortality occurred at a concentration of 10% using the insect spraying and insect-on-plant spraying methods, with mortality observed at 12 hours after application. The slowest response was observed at a concentration of 10% using the plant spraying method, with mortality occurring at 48 hours after application. The LT50 values for 10% clove leaves and galangal rhizome extracts application were determined as 18.2 hours and 24.6 hours, respectively. Therefore, clove leaves and galangal extracts can serve as viable alternatives to synthetic pesticides for the management of N. lugens, a pest of rice plants.

Morphological, Biological, and Molecular Characterization of Type I Granuloviruses of Spodoptera frugiperda.

Granuloviruses (GVs) Betabaculovirus associated with the fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), especially those of the type I, have scarcely been studied. These GVs might be an effective alternative for the biocontrol of this insect. In this study, the native GVs SfGV-CH13 and SfGV-CH28 were isolated from FAW larvae and characterized for morphology, molecular traits, and insecticidal activity. The elapsed time between symptomatic infection of larvae and stop feeding as well as the weight of larvae before death or prior to pupation were also evaluated. Both GVs had ovoid shape and a length of 0.4 µm. They had the same DNA restriction profiles and their genome sizes were about 126 kb. The symptomatic infection with the tested GVs mainly caused flaccidity of larva body and discoloration of integument. The integument lysis was only observed in 8% of infected larvae. Infected larvae gradually stopped feeding. Overall, these symptoms are characteristic of infections caused by type I GVs, which are known as monoorganotropic or slow-killing GVs. The median lethal dose (LD50) values for SfGV-CH13 and SfGV-CH28 isolates were 5.4 × 102 and 1.1 × 103 OBs/larva, respectively. The median lethal time (LT50) ranged from 17 to 24 days. LT50 values decreased as the viral dose was increased. The elapsed time from symptomatic infection until pupation and body weight of larvae (third instar) were higher with SfGV-CH28 than SfGV-CH13. Both granulovirus isolates were able to kill the FAW larvae from the 12th day.

Physiological Response to Low-Temperature Stress and Cold Resistance Evaluation of Ziziphus jujuba var. spinosa Clones from Different Provenances

To investigate the low-temperature adaptability of different provenances of Ziziphus jujuba var. spinosa, we used 21 clones from seven provenances as experimental materials and observed the changes in physiological and biochemical indicators and the characteristics of anatomical structures under low-temperature stress. A comprehensive evaluation of their cold resistance was conducted using the membership function method. As the temperature decreased, the relative electrical conductivity (REC) of clone 89 became stable and had the lowest LT50 value (−44.04 °C). The cold-resistant Z. jujuba var. spinosa had a higher bound water/free water (BW/FW) ratio and antioxidant enzyme activity and accumulated large quantities of osmotic regulatory substances. Higher xylem, phloem, and xylem–cortex ratios and greater conduit density enhanced the cold resistance of Z. jujuba var. spinosa. The membership function values of clones 89, 90, 91, 604, and 612 were greater than 0.6, indicating that they could be evaluated as resources with the potential for low-temperature resistance. The cold resistance rankings for the different provenances were as follows: Kazuo, Liaoning > Jiaxian, Shaanxi > Fuxing, Heibei > Changqing, Shandong > Neiqiu, Heibei > Yanchuan, Shaanxi > Xiaxian, Shanxi. These results provide a scientific basis for the rapid and accurate identification of cold resistance in Z. jujuba var. spinosa resources and the breeding and cultivation of new cold-resistant varieties of this subspecies.

Evaluation of indigenous isolates of Beuveria bassiana (Balsamo) Vuillemin (Deuteromycotina: Hyphomycetes) against the cotton aphid Aphis gossypii Glover

AbstractThe cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is one of the most important pests and causes major damage to cultivated plants in Turkey. It has recently become a serious problem in Antalya (southwestern Turkey) due to its high resistance to insecticides used. To address this problem, the present study aimed to evaluate the pathogenicity of five indigenous Beuveria bassiana (Balsamo) Vuillemin (Deuteromycotina: Hyphomycetes) isolates (BbFn-2, BbKm-2, BbSr-2, BbDs-4, and BbDm-2) with high virulence in previous studies against the pest. All the isolates were tested at five different conidial concentrations (1 × 105, 1 × 106, 1 × 107, 1 × 108 and 1 × 109 conidia mL−1) against the nymphs and adults of A. gossypii using Petri dish and pot trials in the laboratory. The results from the bioassays showed that virulence of the isolates increased significantly with elapsed time up to 10 days after inoculation. All five B. bassiana isolates at the highest concentration (1 × 109 conidia mL−1) caused mortalities ranged from 83.3% to 100% in both nymphs and adults 10 days post-treatment. While the LT50 and LT95 values of the isolates were 1.72–2.12 days and 4.81–8.49 days, respectively, for the nymphs, they were calculated for the adults as 1.65–2.54 days and 4.66–12.93 days, respectively. Results of the phylogenetic analysis showed that these five B. bassiana isolates had high similarities (ranging from 99 to 100%) with the other B. bassiana isolates in GenBank. All the results suggest that above-mentioned five indigenous B. bassiana isolates have significant biocontrol potential against A. gossypii.

Larvicidal Activity of Red Betel Leaves (Piper ornatum) Ethanolic Extract Against Mosquito Larvae

Larvae are the initial carriers of dengue hemorrhagic fever (DHF) and culex, making them significant in disease transmission. Excessive chemical larvicides pose serious risks to human health, thus driving the development of biological alternatives like red betel leaf extract. This study aimed to assess the efficacy of red betel leaf extract in larval control. Using 300 larvae, concentrations of 5%, 6%, and 7% were tested with three replicates over 24 h. The bioassay involved placing the larvae into a plastic container filled with the extract. It was found that ethanol extract from Piper ornatum leaves contained alkaloids, tannins, saponins, flavonoids, and terpenoids. After 24 h, results revealed 83% mortality at 5%, 98% at 6%, and 100% at 7% of extract concentration. Consequently, the 7% concentration showed the fastest efficacy in killing mosquito larvae (100% in 50 min). The LC50 value, representing the concentration at which 50% of larvae are killed, was determined to be 0.04%. Additionally, the LT50 value, indicating the time required to kill 50% of larvae (based on the LC50 value), was found to be 3.34 hours. In conclusion, red betel leaf extract demonstrated promising larvicidal activity against mosquito larvae. Future research is anticipated to prove its safety via in vitro and in vivo test.

Evaluation of methyl salicylate, limonene, and thymol as potential biocidal against Trogoderma granarium everts larvae

The investigation of plant-based natural products, especially essential oils, as insecticide alternatives, responds to challenges as induced resistance and environmental drawbacks linked to prolonged synthetic insecticide use. Although essential oils demonstrate promising activity, their utilization faces hurdles related to standardization. In this study, contact/fumigation properties of three molecules (methyl salicylate, limonene and thymol) known for their activity against stored product beetles, were tested in laboratory bioassays toward young and old larval stages of Trogoderma granarium. The experiment revealed significant differences in their effects based on larval age and chemical concentration. Methyl salicylate exhibited concentration-dependent effects on both young and old larvae, with higher concentrations leading to accelerated mortality rates. For instance, young larvae exposed to 10 mg displayed an LT50 of 33.75 h, while old larvae showed an LT50 of 39.07 h. Similarly, at a concentration of 5 mg, young and old larvae exhibited LT50 values of 72.79 and 79.68 h, respectively, after treatment. Limonene also exhibited concentration-dependent effects, although with lower potency compared to methyl salicylate. Thymol showed efficacy only against young larvae of T. granarium. Statistical analyses confirmed the significant impact of each chemical on larval survival time, with tested chemicals displaying significant concentration-dependent variations in mortality rates. These findings suggest the potential of methyl salicylate, and to a lesser extent limonene and thymol, as effective biocidal agents against T. granarium larvae.

Patogenisitas Jamur Entomopatogen Metarhizium Anisopliae Metch. Terhadap Larva Spodoptera Litura F. Pada Tanaman Kubis (Brassicae Oleracea L.) Di Laboratorium

This study aims to analyze the pathogenicity of the entomopathogenic fungus M. anisopliae in infecting S. litura. The research was conducted over a period of 3 months, from February to May 2024. It took place at the Kalasey Biological Agents Laboratory, Balai Perlindungan dan Pengujian Mutu Tanaman Pangan dan Hortikultura (BPPMTPH) in North Sulawesi Province. The study employed a Completely Randomized Design (CRD) with 4 treatments, each replicated 4 times. The number of samples per replication was 20 larvae, resulting in a total of 80 larvae per treatment. Data were analyzed using probit analysis and ANOVA followed by Least Significance Different (LSD) test at a 5% significance level. The results indicated that the pathogenicity of the entomopathogenic fungus M. anisopliae could infect S. litura larvae as early as one day after application. The concentration of 108 conidia/ml was highly effective, achieving 100% mortality within 6 days of application. The fastest LT50 value was observed at the concentration of 108 conidia/ml, which required only 2.8 days, while the LC50 value was found at a concentration of 107.6 conidia/ml.

Gamma irradiation induced thermotolerance in Metarhizium spp. enhancing biocontrol of Nilapavarta lugens (Stål)

The Brown Planthopper (BPH), Nilaparvata lugens (Stål), is a devastating pest to rice crops in Southeast Asia, primarily due to its resistance to insecticides. As a result, the fungus Metarhizium spp. is used as an alternative control for BPH. However, their efficiency is limited due to delayed infectivity and sensitivity to environmental variables. In this study, two isolates of Metarhizium spp. MLUBN038 and MNMHN031, were induced for thermotolerance and biocontrol potential against Nilapavarta lugens (Stål). A multilocus phylogeny of four protein-coding genes including Beta-tubulin, rpb1, rpb2, and tef has identified the two isolates to be Metarhizium koreanum. Seventy-nine potential thermotolerant mutants were screened from the two isolates. These mutant isolates demonstrated significant tolerance to vegetative heat at 39 °C and enhanced resistance to wet heat stress at 45 °C after exposure for 60 h, outperforming the wild-type (WT) isolates. The mutant isolates also showed increased mycelial growth, conidial germination, and spore production compared to the WT isolates. Two mutant isolates, ML038_Mt 71 and MN031_Mt 46, exhibited the highest efficacy against BPH nymphs (4th-5th instars), resulting in a maximum mortality of 88.82 % and 83.55 %, respectively, compared to the WT (54.07 % and 47.54 %) after 14 days of inoculation in the greenhouse. These two highly virulent mutant isolates presented the lowest LT50 values of 2.88 and 3.72 days at a concentration of 1 × 109 conidia/mL. RAPD analysis revealed genetic diversity between the mutant and WT isolates, indicating distinct diversity profiles and supporting the successful generation of mutant variants. These findings suggest that the use of gamma irradiation and heat stress to induce mutations is crucial for the successful production of thermotolerant mutant isolates. Our results suggest that ML031_Mt 71 and MN031_Mt 46 have potential as effective biocontrol agents.

Susceptibility Status of Several Field-Collected German Cockroaches (Blattella germanica) to a Pyrethroid Insecticide and Molecular Detection of Knockdown Resistance (kdr).

High frequency of insecticide used to control German cockroaches may lead to insecticide resistance development. We aimed to compare the level of insecticide resistance and heterogeneity in insecticide resistance of field-collected German cockroaches in eight selected zones of Mashhad City, Razavi Khorasan Province, Iran. The present study was conducted from October 2019 to May 2021. Adult and nymphs of German cockroaches were collected from infested restaurants or hotels in eight zones of Mashhad City and then colonized in an insectarium. The cockroaches were subjected to bioassay against cypermethrin insecticide. In addition, the genomic DNA of each cockroach population was analyzed in the region where the kdr mutations reside in the German cockroach. The LT50 values against cypermethrin in the susceptible strain (SS) and eight field-collected strains so varied from 17.52 to 95.36 min. The resistance ratio of the strains was also different in response to the insecticide. The similarity of multiple sequence alignments at the amino acid level was 97.5%-100%. An exon 20 transversion mutation and a nonsynonymous substitution were found. The L1014F substitution was detected in 83.4% of the cockroach samples. The field-collected strains were resistant to cypermethrin at different levels. Furthermore, the molecular study confirms the heterogeneity in the level of resistance among eight strains. Therefore, eight strains might have a different history of insecticide treatment.

The effect of temperature and exposure time on redroot pigweed (Amaranthus retroflexus) and yellow foxtail (Setaria pumila) seed mortality in the natural soil seedbank

Abstract Heat disinfection of soil can be used to reduce the content of the soil seedbank. However, species differ in the lethal temperature needed for seed destruction and mortality. Laboratory research was conducted on the seeds of two weed species, redroot pigweed (Amaranthus retroflexus L.) and yellow foxtail [Setaria pumila (Poir.) Roem. & Schult]. The soil samples were collected at the experimental station Šašinovečki Lug, Zagreb, Croatia (45.850289°N, 16.180465°E), and exposed to linearly increasing constant temperatures of 40, 50, 60, 80, 100, and 120 C and exposure times of 30, 60, and 90 min in a laboratory oven. Weed seeds were then extracted from the soil using the sieve separation method and survival was measured by germinating seeds on filter paper. Germination counts were converted into percentages of mortality compared with untreated seeds. The results show that both temperature and exposure time significantly affected seed mortality of both weed species. Amaranthus retroflexus shows a greater susceptibility to high temperatures than S. pumila. A fitted three-parameter sigmoid model was used to define the relationship between temperature and exposure time needed for 50% (LT50) and 90% (LT90) seed mortality. The estimated LT50 values for A. retroflexus are 58.89 to 46.08 C over the 30- to 90-min exposure times; the estimated LT90 values were 113.36 to 65.72 C for the same durations. The estimated LT50 values for S. pumila over the 30- to 90-min exposure times ranged from 91.33 to 75.15 C; the estimated LT90 ranged from 98.79 to 90.32 C over the same durations. The research results contribute to the knowledge about the thermal sensitivity of seeds. Estimating efficacy of soil-heating treatments is essential when comparing the environmental, economic, and social costs of alternatives to conventional weed control methods.

Frost hardiness of flower buds of 16 apricot cultivars during dormancy

ABSTRACT The effectiveness of apricot cultivation is greatly threatened by frost damage to flower buds during the dormancy period. One of the most important aspects of the evaluation of cultivars is therefore the determination of their frost tolerance. In this paper, the frost hardiness of flower buds of 16 apricot cultivars was investigated in three dormancy periods, applying a standardised artificial freezing test protocol and determining LT50 values. The results showed that both the genotypes and the yearly climatic conditions had a significant effect on frost tolerance. A genotype generally determines the potential maximum of its frost tolerance (‘Sweet Red’ and ‘Primaya’ were very sensitive to frost every year, while ‘Harlayne’ and ‘Rózskajszi C.1406’ could be considered as frost hardy). Flower buds can reach different levels of frost resistance each year depending on the temperature conditions during the hardening and dehardening periods. From the point of view of yield security, it is essential when planning an orchard, to take into account and harmonise the frost hardiness of the cultivars selected and the growing site conditions. Therefore, it is very important to have adequate information about the frost hardiness of different apricot cultivars, which should be included in cultivar descriptions. This paper is intended to contribute to this goal.

Interactions between Bacillus thuringiensis and selected plant extracts for sustainable management of Phthorimaea absoluta

Phthorimaea absoluta is a global constraint to tomato production and can cause up to 100% yield loss. Farmers heavily rely on synthetic pesticides to manage this pest. However, these pesticides are detrimental to human, animal, and environmental health. Therefore, exploring eco-friendly, sustainable Integrated Pest Management approaches, including biopesticides as potential alternatives, is of paramount importance. In this context, the present study (i) evaluated the efficacy of 10 Bacillus thuringiensis isolates, neem, garlic, and fenugreek; (ii) assessed the interactions between the most potent plant extracts and B. thuringiensis isolates, and (iii) evaluated the gut microbial diversity due to the treatments for the development of novel formulations against P. absoluta. Neem recorded the highest mortality of 93.79 ± 3.12% with an LT50 value of 1.21 ± 0.24 days, Bt HD263 induced 91.3 ± 3.68% mortality with LT50 of 2.63 ± 0.11 days, compared to both Bt 43 and fenugreek that caused < 50% mortality. Larval mortality was further enhanced to 99 ± 1.04% when Bt HD263 and neem were combined. Furthermore, the microbiome analyses showed that Klebsiella, Escherichia and Enterobacter had the highest abundance in all treatments with Klebsiella being the most abundant. In addition, a shift in the abundance of the bacterial genera due to the treatments was observed. Our findings showed that neem, garlic, and Bt HD263 could effectively control P. absoluta and be integrated into IPM programs after validation by field efficacy trials.