2nd Instar Larvae Research Articles

Effect of entomopathogenic fungi against invasive pest Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) in maize

Ten indigenous entomofungal strains of Beauveria bassiana, Metarhizium anisopliae, and M. rileyi were evaluated against 2nd instar larvae of the maize fall armyworm (FAW) Spodptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) in a laboratory bioassay. Among the ten strains tested, M. anisopliae ICAR-NBAIR Ma-35 caused 67.8% mortality, followed by B. bassiana ICAR-NBAIR Bb-45 with 64.3%, and ICAR-NBAIR Bb-11 with 57.1% mortality. Rest of the isolates showed 10.7–28.6% mortality. ICAR-NBAIR Ma-35 showed LC50 of 1.1 × 107 spores/ml and LT50 at 1 × 108 spores/ml is 86.04 h and ICAR-NBAIR Bb-45 showed LC50 of 1.9 × 107 spores/ml and LT50 at 1 × 108 spores/ml is 88.30 h. Field evaluation with these two promising strains were conducted against maize fall armyworm for 2 years (2018 and 2019) at ICAR-National Bureau of Agricultural Insect Resources experimental farm, Bengaluru, Karnataka, India. Field trial results indicated 68 and 69% reduction of FAW infestation and 55 and 62% increase in yield in the plots treated with M. anisopliae ICAR-NBAIR Ma-35/B. bassiana ICAR-NBAIR Bb-45, respectively, during 2018. In 2019, 70 and 76% reduction of FAW infestation and 44 and 55% increase in yield were observed in the plots treated with these two entomofungal pathogens, respectively.

Evaluation of Larvicidal Efficacy of Ricinus communis (Castor) Plant Extract and Synthesized Green Silver Nanoparticles against Aedes albopictus.

Background:Aedes mosquitoes are the most important group of vectors having ability of transmitting pathogens including arboviruses that can cause serious diseases like Chikungunya fever, Dengue fever and Zika virus in human. Biosynthesis and the use of green silver nanoparticles (AgNPs) is an important step in the search of reliable and ecofriendly control of these vectors.Methods:In this study an aqueous leaves extract of Ricinus communis (castor) and silver nanoparticles (AgNPs) synthesized from this extract were evaluated as larvicidal agent for 2nd and 3rd instar larvae of the Aedes albopictus. Different concentrations (50, 100, 150, 200 and 250ppm) of plant extract and synthesized nanoparticles were prepared and applied on second and third instar larvae. The percent mortality was noted after 6, 12, 18, 24, 30, 36, 42 and 48H of exposure and subjected to probit analysis to calculate LC50 and LC90.Results:Synthesized Ag+ nanoparticles were characterized by UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and energy-dispersive X-ray spectroscopy (XRD). The nanoparticles were more toxic against larvae of Ae. albopictus with LC50 value (49.43ppm) and LC90 value (93.65ppm) for 2nd instar larvae and LC50 (84.98ppm) and LC90 (163.89ppm) for 3rd instar larvae as compared to the plant extract (149.58ppm, 268.93ppm) and (155.58ppm, 279.93ppm) for 2nd and 3rd instar larvae of Ae. albopictus respectively after 48H.Conclusion:Our results suggest the extract of R. communis and synthesized nanoparticles as excellent replacement of chemical pesticides to control the vector mosquitoes.

Insecticidal effects of some essential oils against box tree moth (Cydalima perspectalis Walker (Lepidoptera: Crambidae))

The box tree moth Cydalima perspectalis (Walker) (Lepidoptera: Crambidae) is one of the most alien insects found in the Buxus areas of Georgia and World. Many methods have been used to control this pest up to now. But, the problem is still going on. In this study, insecticidal effects of the essential oils obtained from plants Artemisia absinthium L., Seriphidium santonicum (L.) Sojak, Seriphidium spicigerum (K.Koch) Poljakov, Cuminum cyminum L., Mentha pulegium L., Origanum majorana L., Origanum onites L., Origanum syriacum L., Origanum vulgare L., and Satureja hortensis L. on C.perspectalis were tested in laboratory conditions. In this context, larvae of the 2nd and 5th instars of C.perspectalis were exposed to essential oils at doses of 10, 15 and 20 μl/petri for 24, 48, 72 and 96 h. All of the essential oils used in the study caused mortality at different rates; the highest effect on 2nd and 5th instar larvae of C.perspectalis was obtained with the essential oil from O.onites with a mortality rate of 80.0–71.6%. The oils from O. onites (73.3–65.0%), O.syriacum (73.3–63.3%), O.majorana (71.6–66.6%), A.absinthium (68.3–61.6%), S.santonicum (68.3–60.0%), S.spicigerum (66.6–60.0%), S.hortensis (66.6–61.1%), C.cyminum (58.3–53.3%) and M.pulegium (51.6–45.0%) followed this in this order. As a results of the dose effect tests conducted in the second part of the study, the most toxic plant essential oils were determined to be from O.vulgare and the lowest toxic effect from M.pulegium based on LD50 and LD90. The results obtained show that the essential oils from O.vulgare can be used in the control against C.perspectalis.

Biological characteristics and efficacy of Bacillus thuringiensis var. thuringiensis against the cotton leaf roller, Syllepte derogata (Fabricius, 1775) (Lepidoptera: Crambidae)

Cotton (Gossypium hirsutum L.) is an important fiber crop cultivated in > 50 countries of the world. The cotton leaf roller Syllepte derogata (Fabricius, 1775) (Lepidoptera: Crambidae) is considered as an invasive and widespread species in many geographic regions of the world and pose significant damages to cotton crop. This study reported the first record of S. derogata and its biological characteristics in Azerbaijan. The results indicated that S. derogata was only observed on cotton crop from the Absheron region of the country. The larvae only attacked on cotton leaves and did not damage the reproductive organs (i.e., bolls). S. derogata completed one generation in 31–42 days in the Absheron region. Larvicidal efficacy of Bacillus thuringiensis var. thuringiensis (Btt) against S. derogata was also tested under laboratory and field conditions. Three different Btt concentrations (0.3, 0.4, 0.5 g/l) were tested against 2nd and 4th larval instars of S. derogata. The 0.5 g/l concentration of Btt caused 72.88% larval mortality under field conditions. However, under laboratory conditions, 0.3, 0.4, and 0.5 g/l concentrations caused 50, 66.67, and 100% mortality of the 2nd instar larvae on the 7th day, respectively. The 0.5 g/l suspension of Btt proved the most effective against S. derogata; therefore, it can be recommended for the management of S. derogata in the infested region of the country. This study further warns that S. derogata could spread to the other cotton-producing regions of the country; thus, an effective early warning and rapid response system must be developed for the pest in the country.

Toxicological, biological and biochemical effects of two nanocomposites on cotton leaf worm, Spodoptera littoralis (Boisduval, 1833)

Cotton leaf worm, Spodoptera littoralis (Boisduval, 1833), is one of the most dangerous pests in Egypt, causing economically significant losses of different crops. The present study was aimed to evaluate toxicological, biological and biochemical effects of two nanocomposites, Silver (Ag) and graphene oxide (GO) nanomaterials over magnesium chlorophillin (Mg-Chl/Ag and Mg-Chl/GO) at three concentrations (1, 10, 100 ml/L) against 2nd instar larvae of S. littoralis. The results showed that larval mortality rate was positively correlated with the increase of concentrations of the tested nanocomposites and time after exposure. The mortality rate in nanographene oxide composite were higher than nano silver. LC50 (lethal concentration of 50% of a group of test larvae) values were 10.27 and 16.14 mg/L at Mg-Chl/Ag and Mg-Chl/GO compound at 2 h exposure to light. Some biological aspects of S. littoralis resulted from the treated 2nd instars larvae with two nanocomposites were recorded. Larval, pupal durations, pupation, adult emergence rate and pupal weight were significantly lower in all concentrations compared to untreated larvae. All tested samples showed decrease in total carbohydrates, total proteins and total lipids. Obtained results suggest that using silver and graphene oxide nanomaterials over the magnesium chlorophillin would be a useful component for controlling S. littoralis.

Endophytic colonization of tomato plants by the entomopathogenic fungus Beauveria bassiana for controlling the South American tomato pinworm, Tuta absoluta

BackgroundThe deployment of entomopathogenic fungi (EPF) for the control of crop pests is an important alternative to synthetic pesticides. Despite recent advances in EPF formulations and application techniques, their efficacy is still limited by abiotic and biotic factors. Entomopathogenic fungi naturally colonize plant tissues or they can be artificially inoculated, protecting the plants from insect attack. Beauveria bassiana is the most widely used fungal biological control agent and has potential as an endophyte to protect a range of crops. Although B. bassiana is known to be pathogenic to the South American tomato pinworm, Tuta absoluta (Meyrick), this fungus could be more efficient when deployed as an endophyte to protect tomato plants from attack.MethodsThree B. bassiana isolates were screened for virulence against T. absoluta larvae by application of conidia to leaf surfaces. Following confirmation of virulence, tomato plants were then exposed to conidial suspensions using a forced uptake technique. Only one isolate, LPP139, colonized the leaves. Seedlings were then inoculated with LPP139 and the presence of the fungus in different plant tissues was monitored over 30 days. Possible effects of B. bassiana endophytic colonization on plant development were also evaluated. Following confirmation of endophytic colonization of leaf tissues, T. absoluta 2nd or 3rd instar larvae were offered leaves and survival was monitored over a 7-day period.ResultsAll three B. bassiana isolates were virulent to T. absoluta, with approximately 90% mortality over 10 days when conidia had been applied to leaf surfaces. Various plant inoculation techniques were tested but only seedling inoculation was successful. LPP139 successfully colonized all of the plant tissues. High percentages of colonization were observed in roots, stems and leaves up to 30 days after inoculation, with no negative effects on plant growth. When T. absoluta larvae were exposed to B. bassiana colonized leaves, survival was reduced to zero over a 7-day period.ConclusionsThe endophytic colonization of tomato plants with EPF is a promising method of controlling the South American tomato pinworm. The fungus was detectable for up to 30 days, longer than has been previously observed for tomato plants. Seedling inoculation could be a viable commercial option for marketing pre-colonized tomato plants.

Lethal and sub-lethal effects of bio-and chemical insecticides on the tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

The tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is a destructive pest affecting the tomato crop causing a loss of 60–100% of the tomato crop production. In the present study, the lethal and sub-lethal effects of Bacillus thuringiensis (Bt), spinosad, and emamectin benzoate as bio-insecticides comparing with 2 synthetic insecticides: chlorpyrifos and indoxacarb against T. absoluta under laboratory conditions were evaluated. Take in consideration, life tables and reproductive parameters of treated larvae with LC30 for each pesticide (bio- and chemical insecticides) by using leaf dipping technique were calculated. The results showed that Lepinox formulation of Bt was the most effective one against the early 2nd instar larvae with 0.01 × 10−2 mg/l (ppm), followed by spinosad with 0.07 × 10−2 ppm comparing to indoxacarb and chlorpyrifos (0.01 and 11.44 μg/ml, respectively). Sub-lethal effect of the Bt formulations significantly increased pupal mortality by 29.77, 33.30, and 26.94% for Lepinox, Dipel 2×, and Protecto, respectively. In addition to their efficiency, Bt formulations and emamectin benzoate increased larval developmental period and reduced adult emergency percentage to 70.28, 66.70, 73.06, and 75.55% for Lepinox, Dipel 2×, Protecto, and emamectin benzoate, respectively. All bio-insecticides including Bt, spinosad, and emamectin benzoate caused abnormalities in different life stages. The results suggest these bio-insecticides are promising alternatives to synthetic insecticides for T. absoluta management.

An in vitro generated variant of Tephrosia villosa defensin (α-TvD1) enhances biotic stress tolerance in transgenic tobacco

Plant defensins are small, cationic, cysteine-rich peptides with well conserved four disulphide bridges between an α-helix and three anti-parallel β-strands, produced by plants as a first line of innate immunity against the invading fungal pathogens. Some of the plant defensins exhibit strong antibacterial and anti-insect activities in vitro as well as in vivo. TvD1, a defensin from Tephrosia villosa was characterized in our previous studies with demonstrated inhibitory effect against many plant pathogenic fungi and some insects. To further enhance its activity, α-TvD1, a peptide variant of TvD1, was generated through site directed mutagenesis. It showed enhanced antifungal and Tenebrio molitor α-amylase inhibitory activity under in vitro condition. In the present study, we compared the antifungal and anti-insect activities of α-TvD1 with the native TvD1 in transgenic tobacco plants. α-TvD1 transgenic plants showed enhanced tolerance against the oomycetes pathogen Phytophthora parasitica var. nicotianae and the fungal pathogens Alternaria alternata and Rhizoctonia solani. Also, it showed enhanced anti-insect activity against the 1st and 2nd instar larvae of the generalist herbivore, Spodoptera litura. These results demonstrated that α-TvD1 appears to be a potent antimicrobial gene that can be used for generating superior transgenic crops with enhanced resistance against many phytopathogens and insect pests.

Glyphosate-based herbicide has soil-mediated effects on potato glycoalkaloids and oxidative status of a potato pest

Glyphosate is the most used herbicide worldwide, targeting physiological pathways in plants. Recent studies have shown that glyphosate can also cause toxic effects in animals. We investigated the glyphosate-based herbicide (GBH)-induced changes in potato (Solanum tuberosum) plant chemistry and the effects of a GBH on the survival rate and oxidative status of the Colorado potato beetle (Leptinotarsa decemlineata). The beetles were reared on potato plants grown in pots containing soil treated with a GBH (Roundup Gold, 450 g/l) or untreated soil (water control). The 2nd instar larvae were introduced to the potato plants and then collected in 2 phases: as 4th instar larvae and as adults. The main glycoalkaloids of the potato plants, α-solanine and α-chaconine, were measured twice during the experiment. The α-solanine was reduced in potato plants grown in GBH-treated soil, which can be detrimental to plant defenses against herbivores. GBH treatment had no effect on the survival rate or body mass of the larvae or the adult beetles. In the larvae, total glutathione (tGSH) concentration and the enzyme activity of catalase (CAT), superoxide dismutase, and glutathione-S-transferase were increased in the GBH treatment group. In the adult beetles, CAT activity and tGSH levels were affected by the interactive effect of GBH treatment and the body mass. To conclude, environmentally relevant concentrations of a GBH can affect the potato plant’s glycoalkaloid concentrations, but are not likely to directly affect the survival rate of the Colorado potato beetle, but instead, modify the antioxidant defense of the beetles via diet.

Toxicity of Some Essential Plant Oils Against Cotton Leaf Worm, Spodoptera littoralis (BOISD.)

The study aims to evaluate the bioactivity of plant essential oils (neem oil, garlic oil, marjoram oil, and menthol oil) on 2nd instar larvae of the cotton leafworm, Spodoptera littoralis in the laboratory. Also, LC50 of each treatment was established against 2nd instar larvae of S. littoralis under semi-field conditions. The obtained results reveal that neem oil was more effective than the other oils followed by, marjoram oil then garlic oil and then, menthol oil.LC50 was3022.50, 3803.41, 4630.13and5323.38ppm for neem oil, marjoram oil, garlic oil, and menthol oil, respectively, for 2nd instar larvae. While, when LC50of these oils applied on the 2nd instar larvae in the semi-field, the results indicated that, garlic oil was the most effective essential oil followed by, menthol oil, marjoram oil, and neem oil.

Effect of fluoride on the learning and memory ability of larvae of Zaprionus indianus

BackgroundMany pesticides contain fluoride that enters the food chain and affect the non-target organisms. Fluoride is a known neurotoxin and may cause neurobehavioral defects. A study was conducted to see the effect of fluoride on the learning and memory ability of larvae of Zaprionus indianus. The learning and memory ability of 2nd instar larvae of normal (control) and sodium fluoride (NaF)-treated Zaprionus indianus was compared.ResultsSublethal concentration of NaF for Z. indianus was found to be 0.8 ppm. Olfactory assay results showed that the larvae of normal (control) Z. indianus had better learning and memory ability in comparison to NaF-treated larvae.ConclusionsThis study indicates that the insects exposed to pesticides containing fluoride may have difficulty in locating food sources and carrying out pollination.

Compatibility of entomopathogenic fungi and Azadirachta indica extract against the cotton pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae) under controlled conditions

Compatibility of entomopathogenic fungi (EPFs) viz. Verticillium lecanii, Metarhizium anisopliae and Beauveria bassiana with Azadirachta indica extract (alone and in combinations) was evaluated against 2nd instar larvae of the cotton pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae) under controlled conditions. Results indicated that maximum mortality rate of P. gossypiella larvae was recorded at combination of the highest conidial concentrations of V. lecanii + M. anisopliae + B. bassiana along with A. indica extract, while minimum mortality rate was recorded at A. indica extract alone, 12 days post exposure interval. Maximum mycosis and sporulation from dead cadavers of P. gossypiella larvae were recorded at the highest concentration of B. bassiana, while the lowest mycosis and sporulation were recorded at the highest conidial concentrations of V. lecanii + M. anisopliae + B. bassiana along with A. indica extract. Maximum percent of pupation and adult emergence in P. gossypiella larvae was observed in the treatment, where A. indica extract was applied alone, while the minimum percent of pupation and adult emergence was observed at the treatment combination of the highest concentration of B. bassiana + V. lecanii + M. anisopliae along with A. indica extract was applied. EPFs proved their enhanced long-term protection potential for cotton crop against P. gossypiella. A. indica extract integrated with the EPFs can be a potential alternative to the chemicals and as an effective component of IPM program against P. gossypiella.

Efficacy of entomopathogenic nematodes for the control of white grub, Anomala corpulenta Motschulsky, in laboratory and field

Summary Anomala corpulenta is one of the major white grubs that cause serious damages in peanut production. To develop an environmentally friendly method to control A. corpulenta larvae, the efficacy of species of entomopathogenic nematodes (EPN), application rate and larval stage against A. corpulenta were determined. Results showed that Steinernema longicaudum X-7 and S. glaseri B-4-1 were the most virulent species, which caused 77.8 and 84.4% corrected mortalities of the 2nd instar larvae at 25°C 14 days after treatments. Corrected mortalities of A. corpulenta caused by EPN were significantly affected by EPN application rate. A decrease but no significant difference in susceptibility from the 2nd to the 3rd instar was observed for the test EPN species S. longicaudum, S. glaseri and Heterorhabditis bacteriophora. The field experiments indicated that S. longicaudum and S. glaseri applied at a relatively high rate (⩾5.0 × 103 infective juveniles (IJ) plant−1, i.e., 7.5 × 108 IJ ha−1) were able to provide not only control efficacy against A. corpulenta with ⩾92.7% reduction of larvae and ⩽5.06% of damaged pods, and the peanut yield increase was as good as phoxim, but also gave better control persistency compared to phoxim. Our findings indicated that EPN could be an effective strategy for the management of A. corpulenta in peanut fields.

Cold Responses of the Mediterranean Fruit Fly Ceratitis capitata Wiedemann (Diptera: Tephritidae) in Blueberry.

In this study, the effects of cold treatment at 1.0 ± 0.2 °C were investigated on the eggs of the 1st, 2nd, and 3rd instar larvae of Ceratitis capitata in two Australian blueberry cultivars C99-42 and C00-09. Pupariation, emerged adults, and sex ratios were examined on C. capitata after the treatment. The results showed that exposure time at low temperatures was a key factor to affect pupariation and adult emergence. Eleven days of exposure to cold treatment at 1.0 ± 0.2 °C were enough to eradicate all four immature stages in both cultivars. Cold tolerance of the four C. capitata stages was not affected when reared on two different blueberry cultivars. The third instar larva is the most tolerant stage for cold treatment in two blueberry cultivars. There were no significant differences in sex ratios from surviving C. capitata among different stages after treatment. This study improves understanding of C. capitata responses to cold treatment in blueberries, which may contribute to phytosanitary required quarantine treatment of this destructive horticulture pest species.

Biological activity and safety profile of monoterpenes against Plutella xylostella L. (Lepidoptera: Plutellidae).

Plutella xylostella L. is a cosmopolitan pest of wild and cultivated crucifer vegetables worldwide. It has developed resistance to almost all commercial chemicals, making them one of the most problematic field pests in China. The natural plant extracts and essential oils (EOs) could be a safe alternative for agricultural pests. The development and production of EOs decrease the negative effects of synthetic chemicals. In the present study, the fumigation activity of 8 pure monoterpenes against P. xylostella was evaluated. Results from fumigation tests revealed that 8 tested compounds exhibited various degrees of toxicity against adults of the diamondback moth. Cuminaldehyde was the most toxic compound based on the 12-h LC50 (0.17mg/L) and 24-h LC50 (0.12mg/L) values, respectively. Also for larvae and eggs, cuminaldehyde was the most toxic compound. The 12-h LC50 value for cuminaldehyde to 1st, 2nd, and 3rd instar larvae was 0.10mg/L, 0.12mg/L, and 0.55mg/L, respectively. The 24-h LC50 value for the different instar larvae was 0.07mg/L, 0.09mg/L, and 0.35mg/L, respectively. The 24-h LC50 value for eggs (endpoint hatching rate) was 1.95mg/L for cuminaldehyde, followed by carvacrol and eugenol (2.05mg/L and 2.31mg/L, respectively). Cuminaldehyde was very friendly to the larvae and adults of Harmonia axyridis and did not cause any mortality. Our results indicated that cuminaldehyde had potential insecticidal activity against P. xylostella and could be utilized in the novel biological pesticide development.

Biochemical and Toxicological Studies of Some Pesticides on Cotton leafworm ( Spodoptera littoralis)

The present study is to through light on role of some insecticides (chemical insecticides (a.i.chlorphyrifos) Dursban® 48% EC, spinosyns group (a.i.spinosad) Tracer® 24% SC and insect growth regulator (a.i.lufenuron) Match® 5% EC) against insect attacking cotton cultivation Spodoptera littoralis under Egyptian conditions. The toxicological effects and biochemical analysis carried out against laboratory strain of target insects after 24 and 72 hours. Toxicity of the three insecticides chlorphyrifos, spinosad and lufenuron were tested against the 2nd instar larvae of the cotton leafworm, spodoptera littoralis. The results showed that lufenuron was more effective on the 2nd instar larvae than chlorphyrifos and spinosad. The LC25 values for lufenuron, chlorphyrifos and spinosad were 0.0005, 2.21 and 8.1 ppm, respectively. The biochemical study used for tested insecticides at LC25 on some biocomponents namely acetylcholinesterase (AchE), glutathione-s-transferase (GST), chitinase, phenoloxidase, aspartate (AST) and alanine (ALT) aminotransferases, α-esterase (α-EST), total protein and protein gel electrophoresis for laboratory strain were investigated. The tested chlorphyrifos and lufenuron were significantly increased (AchE). Spinosad was significantly decreased (GST) and phenoloxidase. Spinosad and lufenuron significantly increased (α-EST) and (chitinase) (ALT). Chlorphyrifos caused significantly decreased on α-esterase and total protein and (AST). Lufenuron significantly decreased total protein and phenoloxidase. Spinosad showed insignificant increase in (AchE) and total protein (levels). Chlorphyrifos decreased both of phenoloxidase and (ALT) levels insignificantly and increased the levels of (GST) and chitinase, while lufenuron, recorded insignificant decrease in GST levels. The total body proteins of 2nd instar larval of S. littoralis treated with LC25 of insecticides performed by SDS-PAGE. Control and different treatments were separated into 56 different bands according to their relative frequencies (Rf values), and molecular weights (MW). Samples of electrophoresis were carried out for three different insecticides namely chlorphyrifos, spinosad and lufenuron which used to treat insects. The treatment with insecticides on protein gel electrophoresis led to detection of new bands, and disappeared some bands in comparison to control. It is concluded that treatment with insecticides have strong efficacy on the soluble protein in the body of insects.

Efficacy of entomopathogenic nematodes against the cabbage butterfly (Pieris brassicae (L.) (Lepidoptera: Pieridae) infesting cabbage under field conditions

Experiments were conducted to test the pathogenicity of entomopathogenic nematode, Heterorhabditis pakistanensis alone and in combination with the chemical insecticides, viz., Dichlorvos and Quinalphos and Neem product, viz., Azadirachtin against the cabbage butterfly, Pieris brassicae (L.) (Lepidoptera: Pieridae) infesting cabbage plants under laboratory and field conditions. In laboratory test, inoculum level of 200 infective juveniles (IJs) was most effective causing mortality to both 3rd and 4th instars larvae at 48 h. Nematode multiplication rate in insect cadaver was inversely proportional to the size of initial inoculum level of IJs, whereas IJs yield was directly proportional to the size of larva. The 4th instar larva resulted in a highest yield of IJs, followed by 3rd, 2nd, and 1st instars larvae at all the inoculum levels used in the study. IJs were found compatible with the chemical insecticides and Neem product at lower than half of the optimum single dose. The cumulative mean survival percentage of IJs recorded the highest (77.5%) in the combination of 100 IJs + Azadirachtin (0.25%) and lowest (70.6%) in 100 IJs + Dichlorvos 76 EC (0.05%). Under field conditions, H. pakistanensis (3.0 lakh IJs/m2) + Dichlorvos 76 EC (0.025%) resulted to the highest larval mortality (79.65%), followed by H. pakistanensis (3.0 lakh IJs/m2) + Azadirachtin (0.25%), where it was 76.22%. The larval mortality was the least (61.16%) in case of H. pakistanensis (3.0 lakh IJs/m2) when applied alone. H. pakistanensis + Dichlorvos resulted to the highest increase (31.42%) in cabbage yield over untreated control.

Effects of emamectin benzoate combined with acetamiprid, eforia and hexaflumuron against Tuta absoluta (Lep.: Gelechiidae)

Tomato leafminer, Tuta absoluta Meyrick (Lepidoptera: Gelechiidae) is one of the most destructive pests of tomato in many parts of the world including Iran. The toxicity of emamectin benzoate alone and combined with acetamiprid, eforia (thiamethoxam + lambda-cyhalotrin) and hexaflumuron was evaluated against 2nd instar larvae of Tuta absoluta (Meyrick) under 25 ± 1 °C, the relative humidity of 75 ± 5% and a photoperiod of 16:8 (L:D). Also the mixtures of tested insecticides with emamectin benzoate at LC15:LC15 ratio were evaluated on the activity of general esterase enzyme and total protein content of 2nd instar larvae. After 96 hour, emamectin benzoate had the highest toxicity (LC50 = 0.52 mg A.I./L), followed by acetamiprid (LC50 = 56.39 mg A.I./L) and eforia (LC50 = 312.01 mg A.I./L). Hexaflumuron showed no toxicity against larvae. The combination of emamectin benzoate with acetamiprid at LC50:LC50 ratio produced synergistic effects and all of the other ratios showed additive effects. The emamectin benzoate combined with either eforia or hexaflumuron at all of the ratios produced additive and antagonistic effects, respectively. Esterase activity of larvae increased when emamectin benzoate was mixed with either acetamiprid or eforia, but no significant differences were seen between emamectin benzoate alone and its mixture with hexaflumuron. The combination of emamectin benzoate with tested insecticides significantly reduced the total protein content of larvae. According to the results of this study, the mixtures of acetamiprid and eforia with emamectin benzoate showed higher negative impacts against 2nd instar larvae than emamectin benzoate alone

English

Chilo partellus (Swinhoe) is the most important destructive pest of sorghum in Africa which results in complete crop loss. Currently the management strategies rely heavily on chemical insecticides, which do not provide effective control. The uses of bio-pesticides are encouraging over chemical pesticides. The study was carried out to identify effective plant and animal products and optimum concentrations against C. partellus. 7 treatments each at 3 concentrations (2.0, 2.5 and 3.0 g and 1.0, 1.5 and 2.0 ml) were applied on 2nd and/or 3rd instars larvae. The untreated check was used for comparison. The experiment was laid out in a completely randomized design with 3 replications for each concentration. Result revealed among the treatments Milletia ferruginea Hochst seed powder and aqua extract caused the highest (100%) mortality at 3 g and 2.0 ml concentration on the 2nd day. Cow urine and the mixture (M. ferruginea+cow urine) were recorded higher efficacy mean mortality (86.7 and 93.3%) at 3.0 ml concentration within 3 days respectively. Phytolacca dodecandra L. seed powder, aqua extract and the mixture (P. dodecandra+cow urine) showed significantly lower efficacy mean mortality. In conclusion, M. ferruginea powder and aqua extract, cow urine and combination of M. ferruginea with cow urine were identified as good alternatives to chemical pesticides against C. partellus. Key words: Chilo partellus, cow urine, Milletia ferruginea, Phytolacca dodecandra, sorghum.

Profiling of RNAi sensitivity after foliar dsRNA exposure in different European populations of Colorado potato beetle reveals a robust response with minor variability

In recent years, substantial effort was spent on the exploration and implementation of RNAi technology using double-stranded RNA (dsRNA) for pest management purposes. However, only few studies investigated the geographical variation in RNAi sensitivity present in field-collected populations of the targeted insect pest. In this baseline study, 2nd instar larvae of 14 different European populations of Colorado potato beetle (CPB), Leptinotarsa decemlineata, collected from nine different countries were exposed to a foliarly applied diagnostic dose of dsactin (dsact) to test for possible variations in RNAi response. Only minor variability in RNAi sensitivity was observed between populations. However, the time necessary to trigger a dsRNA-mediated phenotypic response varied significantly among populations, indicated by significant differences in mortality figures obtained five days after treatment. An inbred German laboratory reference strain D01 and a Spanish field strain E02 showed almost 100% mortality after foliar exposure to 30 ng dsactin (equal to 0.96 g/ha), whereas another Spanish strain E01 was least responsive and showed only 30% mortality. Calculated LD50-values for foliarly applied dsact against strains D01 (most sensitive) and E01 (least sensitive) were 9.22 and 68.7 ng/leaf disc, respectively. The variability was not based on target gene sequence divergence or knock-down efficiency. Variability in expression of the core RNAi machinery genes dicer (dcr2a) and argonaute (ago2a) was observed but did not correlate with sensitivity. Interestingly, RT-qPCR data collected for all strains revealed a strong correlation between the expression level of dcr2a and ago2a (r 0.93) as well as ago2a and stauC (r 0.94), a recently described dsRNA binding protein in Coleopterans. Overall, this study demonstrates that sensitivity of CPB to sprayable RNAi slightly varies between strains but also shows that foliar RNAi as a control method works against all tested CPB populations collected across a broad geographic range in Europe. Thus, underpinning the potential of RNAi-based CPB control as a promising component in integrated pest management (IPM) and resistance management programs.