Leaf-dip Bioassay Research Articles

Baseline susceptibility to afidopyropen of soybean aphid (Hemiptera: Aphididae) from the north central United States

Afidopyropen, a novel Group 9D insecticide, has proven effective for management of soybean aphid, Aphis glycines (Hemiptera: Aphididae). However, to ensure continued efficacy of this insecticide, insecticide resistance management programs are needed. The goal of this study was to evaluate baseline susceptibility of several populations of soybean aphid to afidopyropen using leaf-dip bioassays in 2017 and 2018. Overall, mortality of adult soybean aphid varied among populations. Lethal concentrations necessary to kill 50% of a population (LC50) for adults ranged from 0.0013 to 0.40 mg a.i. per liter of afidopyropen. Lethal concentrations necessary to kill 70% of a population (LC70) of adults ranged from 0.136 to 13.1 mg a.i. per liter of afidopyropen. Afidopyropen was effective against populations resistant to pyrethroid insecticides, suggesting a lack of cross-resistance between afidopyropen and pyrethroids. Furthermore, afidopyropen was effective against nymphs of soybean aphid with concentrations ranging from 0.0285 to 54.45 mg a.i. per liter of afidopyropen causing 100% mortality by 6 days after exposure. The results reported here can be used for establishment of programs to monitor for development of resistance to this insecticide by soybean aphid.

Insecticide resistance and fitness cost in Bemisia tabaci (Hemiptera: Aleyrodidae) invasive and resident species in La Réunion Island.

Global and intensive use of insecticides has led to the emergence and rapid evolution of resistance in the major pest Bemisia tabaci (Gennadius). In La Réunion, an island of the South West Indian Ocean, three whitefly species coexist, two of which are predominant, the indigenous Indian Ocean (IO) and the invasive Middle East Asia Minor 1 (MEAM1) species. To assess the resistance level of both of these species to acetamiprid and pymetrozine, whitefly populations were sampled at 15 collection sites located all over the island in agroecosystems and natural areas, and tested using leaf-dip bioassays. We also investigated the potential cost of resistance to acetamiprid by measuring six fitness-related traits for MEAM1 populations that displayed different resistance levels. IO was mainly found in natural areas and was susceptible to both acetamiprid and pymetrozine. MEAM1 populations displayed evidence of high resistance to pymetrozine, whereas resistance to acetamiprid was more variable. No fitness-related costs were associated with this resistance in MEAM1 populations. This is the first assessment of the susceptibility to insecticides for B. tabaci IO species. For the time being, no resistance to the tested insecticides has evolved in this species despite (i) its presence in agroecosystems and their surroundings, and (ii) its close proximity to, and possible hybridization with, the MEAM1 species. In contrast, with continuous selection pressure of insecticide treatments and in the absence of fitness cost to resistance, the invasive exotic species MEAM1 will continue to threaten agriculture in La Réunion. © 2019 Society of Chemical Industry.

Evaluation of toxicological responses of Helicoverpa armigera (Hübner) against some insecticides by using probit analysis in laboratory

The present study was designed to determine the LC50 of some insecticides commonly used against Helicoverpa armigera and their comparative efficacy against the insect pest. The second instar larvae of H. armigera reared in the laboratory were selected for leaf dip bioassay. Two types of insecticides viz. conventional (deltamethrin and bifenthrin) and new chemistry (spinosad and indoxacarb) were assessed in the present studies. The results revealed that bifenthrin was more toxic to the second instar larvae of H. armigera at all the doses with lower LC50 value of 120.007 ppm as compared to deltamethrin with the highest LC50 value of 292.404 ppm. Among the new chemistry insecticides, indoxacarb proved to be more toxic than spinosad with LC50 of 5.592 ppm. LC50 of spinosad was 8.201 ppm showing 1.46 times less toxicity than indoxacarb.

Silencing of the Chitin Synthase Gene Is Lethal to the Asian Citrus Psyllid, Diaphorina citri.

Chitin synthase is a critical enzyme that catalyzes N-acetylglucosamine to form chitin, which plays an important role in the growth and development of insects. In this study, we identified a chitin synthase gene (CHS) with a complete open reading frame (ORF) of 3180 bp from the genome database of Diaphorina citri, encoding a protein of 1059 amino acid residues with the appropriate signature motifs (EDR and QRRRW). Reverse transcription-quantitative PCR (RT-qPCR) analysis suggested that D. citri CHS (DcCHS) was expressed throughout all developmental stages and all tissues. DcCHS had the highest expression level in the integument and fifth-instar nymph stage. Furthermore, the effects of diflubenzuron (DFB) on D. citri mortality and DcCHS expression level were investigated using fifth-instar nymph through leaf dip bioassay, and the results revealed that the nymph exposed to DFB had the highest mortality compared with control group (Triton-100). Silencing of DcCHS by RNA interference resulted in malformed phenotypes and increased mortality with decreased molting rate. In addition, transmission electron microscopy (TEM) and fluorescence in situ hybridization (FISH) also revealed corresponding ultrastructural defects. Our results suggest that DcCHS might play an important role in the development of D. citri and can be used as a potential target for psyllid control.

Screening and partial characterization of d-endotoxins from some local Bacillus thuringiensis isolates for insecticidal activity against the spotted stem borer

Abstract. Kimani PG, Nyambaka H, Kasina M. 2018. Screening and partial characterization of d-endotoxins from some local Bacillus thuringiensis isolates for insecticidal activity against the spotted stem borer. Biofarmasi J Nat Prod Biochem 17: 21-38. Prolonged use of synthetic chemical pesticides is environmentally undesirable, causing the rapid development of resistance among insect pests. Kenya has unexplored potential in controlling lepidopteran pests by using proteinous delta-endotoxins sourced from local isolates of a naturally occurring bacterium, Bacillus thuringiensis Berliner (Bt). This study attempted to identify the insecticidal proteins in some Kenyan Bt isolates, characteristic of Cry1 and/or Cry2 proteins. It also aimed to test their efficacy as affected by different temperatures and their specificity on an invasive and prevalent lepidopteran stem borer, Chilo partellus (Swinhoe). Delta-endotoxin crystals were isolated and purified from cultures of twenty unidentified local Bt isolates using froth floatation and centrifugation. Total protein in the resulting suspensions was quantified using the Bradford assay method, and the approximate protein yield was 3.14 ±0.084 mg/mL of nutrient broth culture with a purity level of 54.8 % ±15.3 %. Leaf-dip bioassays used for testing the efficacy of the d-endotoxins against C. partellus. Among the isolates evaluated, Bt 44 and Bt 48 had the most potent d-endotoxin crystals towards the 1st instar larvae, leading to mortality of 62.6 % and 64.8 % respectively after 72 h. The effect of the d-endotoxins' concentration and temperature on larval mortality was examined for 72 hours at temperatures of 24°C, 27°C and 31°C and levels of 0.01 mg/mL, 0.1 mg/mL and 1.0 mg/mL. The resulting LC50 was 52.3 µg/mL and 42.0 µg/mL, while LT50 values were 76.7h and 60.9h for Bt 44 and Bt 48, respectively. Higher efficacy found at 24°C and 31°C than at 27°C, an indication that these d-endotoxins are tolerable for local conditions where temperatures are higher than in temperate regions. The relationship between concentration and temperature was significant for d-endotoxins of Bt 48 but not those of Bt 44. A major protein component of the d-endotoxins had a molecular weight Mr ~ 130 kDa, which generates a trypsin-resistant core of Mr ~ 70 kDa. Cry protein analysis detected more Cry1 in Bt 44 than Bt 48 ?-endotoxins and no Cry2 in either. However, cry gene analysis using PCR detected the presence of both cry1 and cry2 genes in the DNA of Bt 44 but none in Bt 51, a negative control from toxicity tests against the pest. The chromatographic analysis revealed some differences in the elution profiles of d-endotoxins of both Bt 44 and Bt 48, an indication that there may be different types and amounts of the Cry toxins in the crystals or even novel proteins. These findings indicate that the two local Bt isolates expressed Cry1, and probably Cry2 proteins can control C. partellus and may, therefore, become promising sources for ?-endotoxins for biopesticide development for controlling the pest.

Transgenerational hormetic effects of sublethal dose of flupyradifurone on the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae).

Both inhibitory and stimulatory (known as hormesis) effects of the sublethal flupyradifurone, a butenolide insecticide, on Myzus persicae Sulzer (Hemiptera: Aphididae) were investigated for incorporating it into integrated pest management (IPM). A leaf-dip bioassay showed that flupyradifurone was very toxic against adult M. persicae with a 48 h LC50 of 8.491 mg/L. Using the age-stage two-sex life table approach, we assessed the effects of LC25 of flupyradifurone on adult M. persicae and its progeny (F1 and F2). On the one hand, aphids exposed to flupyradifurone had significantly negative effects on the life history traits acrossing the generations, such as reduced the adult longevity and fecundity of F0, shortened the duration of third instar and fourth instar nymphs, preadult period and the pre-reproductive period of F1, and decreased the reproductive days and adult longevity of F2. On the other hand, stimulatory effects on the duration of pre-adult, adult reproductive days, and reproduction of F1 were observed in the flupyradifurone-treated aphids. Consistently with the stimulation on individual traits, a higher net reproductive rate (R0) of F1 and a shorter mean generation time (T) of F2 were observed in the flupyradifurone-treated aphids, although the other population parameters including the intrinsic rate of increase (r), finite rate of increase (λ) and T of F1 and R0, r and λ of F2 were not significantly affected. These results revealed that adult M. persicae exposed to sublethal concentration of flupyradifurone can induce hormetic effects on F1, and also cause negative effects on F2. Our results would be useful for assessing the overall effects of flupyradifurone on M. persicae and the hormetic effects should take into consideration when use flupyradifurone for control M. persicae.

Resistance and Synergism of Novel Insecticides in Field Populations of Cotton Bollworm Helicoverpa armigera (Lepidoptera: Noctuidae) in Pakistan.

The cotton bollworm Helicoverpa armigera (Hübner) is still a serious pest of non-Bt crops in Asia and Africa. It has been a notorious pest in developing resistance to all the insecticide classes applied for its control. Response of field populations of H. armigera to new chemistries having novel modes of action was monitored during 2003-2016 using a leaf-dip bioassay. No or very low level of resistance was found to newer insecticides, such as spinetoram, chlorantraniliprole, and flubendiamide during 2008-2016. There was also no or very low resistance to chlorfenapyr from 2003 to 2016. Resistance to spinosad, abamectin, and emamectin benzoate was none or very low as well during 2003-2013 and then it rose to a low level for spinosad and to a high level for avermectins by the year 2016. Methoxyfenozide resistance was very low during 2003-2010, low during 2011-2013, and moderate during 2014-2016. Resistance to thiocyclam was very low to low during 2009-2011, but it increased to moderate to high levels during 2012-2016. Resistance to indoxacarb was moderate during 2003-2006, which then decreased to low level during 2007-2010, very low level during 2011-2014, and no resistance during 2015 and 2016 corresponding to the reduced use of indoxacarb in the Pakistani agriculture. Piperonyl butoxide and tribufos exhibited a good synergism with indoxacarb and chlorfenapyr but not with spinosad in H. armigera populations. Rotation of new insecticides, having no, very low, and low resistance along with other IPM practices, is recommended to manage resistance to insecticides in H. armigera.

Resistance to acaricides in Tetranychus truncatus ehara on vegetables

A study was undertaken at the College of Horticulture, Vellanikkara, KAU to investigate the status of acaricide resistance in Tetranychus truncates Ehara (Prostigmata: Tetranychidae), the predominant species of spider mite infesting vegetable crops of Thrissur district, Kerala. Susceptibility of three field strains of T. truncatus collected from okra (VkOk1), amaranthus (VkAm3) and pumpkin (VkPm3) to three commonly used acaricides, viz., spiromesifen 240 SC, fenazaquin 10EC and diafenthiuron 50WP was evaluated in the laboratory following leaf dip bioassay in comparison with a laboratory maintained susceptible strain (SS). Bioassay study revealed that the level of resistance varied among the strains for the acaricides evaluated. The strain VkOk1 recorded highest LC50 value and has developed 8 (1794.293 ppm), 13 (852.394 ppm) and 10 (1968.496 ppm) fold resistance to spiromesifen, fenazaquin and diafenthiuron, while VkAm3 recorded 7.0 (1571.021 ppm), and 5.53 (362.789 ppm) resistance to spiromesifen and fenazaquin, respectively. The strain VkPm3 showed susceptibility on par with the SS to all the acaricides evaluated. The study reports acaricide resistance in T. truncatus for the first time in India.

Efficacy of tolfenpyrad against red pumpkin beetle Aulacophora Foveicollis lucas in Cucumber

A field experiment was conducted at the Central Research Station, Orissa University of Agriculture Technology, Bhubaneswar in RBD with nine treatments replicated thrice during kharif, 2016 and rabi, 2016–17 to evaluate the efficacy of eight pesticides viz., tolfenpyrad 15% EC @ 150 g a.i./ha, fipronil 5% SC @ 50 g a.i./ha, indoxacarb 14.5% SC @ 72.5 g a.i./ha, flubendiamide 480 SC @ 78.70 g a.i./ha, chlorantraniliprole 18.5% SC @ 30.83 g a.i./ha, spinosad 45% SC @ 75 g a.i./ha, cartap hydrochloride 50% SP@ 375 g a.i./ha and acephate 75% SP @ 375 g a.i./ha against the red pumpkin beetle Aulacophora foveicollis Lucas on cucumber cv. “Machaar”. All the insecticides evaluated were at par and significantly suppressed adult red pumpkin beetle (RPB) population up to 15 days after spraying to the extent of 77.11 to 81.59% and 75.46 to 82.59% over control during kharif, 2016 and rabi, 2016–17, respectively. The leaf-dip bioassay of tolfenpyrad against RPB revealed LC50 of 32.88 ppm with a fiducial limit of 25.41 to 42.56 ppm.

Resistance in field populations of Amrasca devastans (Hemiptera: Cicadellidae) to new insecticides in Southern Punjab, Pakistan

Cotton jassid, Amrasca devastans (Distant), is an economically important pest of various crops (i.e. cotton, okra, brinjal) and has the potential to become resistant against insecticides due to the intense use of insecticides in the region which entails high selection pressure. To monitor the resistance levels against recently used new chemistry insecticides (nitenpyram, spirotetramat, chlorfenapyr, fipronil, emamectin benzoate, sulfoxaflor, and flonicamid), four field populations of A. devastans collected from Khanewal, Multan, Muzaffargarh and Lodhran districts were examined by leaf dip bioassays. The results revealed the 32.95–136.47 fold resistance to nitenpyram, 23.03–56.74 fold to spirotetramat, 10.84–31.33 fold to chlorfenapyr, 1.20–9.43 fold to fipronil, 3.27–43.77 fold to emamectin benzoate, 0.66–2.81 fold to sulfoxaflor and 0.59–1.25 fold to flonicamid in different field populations, compared to the susceptible strain. Based on present study findings, it may be suggested to discontinue the use of nitenpyram, spirotetramat, chlorfenapyr and emamectin benzoate for which the populations were resistant and the rotational use of fipronil, sulfoxaflor and flonicamid for which the populations were susceptible. Proactive resistance management approaches such as judicious use of insecticides with proper dose selection, time of spray on early stages and correct method of application are necessary to prevent the development of resistance.

Reduced Susceptibility of Homalodisca vitripennis (Hemiptera: Cicadellidae) to Commonly Applied Insecticides.

Pest management for the glassy-winged sharpshooter, Homalodisca vitripennis Germar (Hemiptera: Cicadellidae), in Kern County, California relies on the application of insecticides. These treatments have contributed to low H. vitripennis field counts since applications were initiated in 2001. However, densities have been high in recent years despite continued management, prompting efforts to evaluate the susceptibility of current populations to insecticides. H. vitripennis adults were subjected to bioassays with five commonly applied insecticides, and the results were compared to baseline toxicities determined in 2002. Two neonicotinoids, imidacloprid and thiamethoxam, were evaluated using systemic uptake bioassays. Contact toxicities of the neonicotinoid acetamiprid and pyrethroids bifenthrin and fenpropathrin were estimated using leaf dip bioassays. Dose-mortality responses were analyzed by probit analysis. For each compound, there was no significant difference in annual LC50 values determined over 2 yr. Compared to baseline toxicities, acetamiprid and bifenthrin were found to be significantly less toxic to H. vitripennis. The LC50 values of these two compounds increased sevenfold and 152-fold, respectively. Tests with the neonicotinoids revealed a trend of decreasing susceptibility levels within each season followed by reversion back to early season LC50 estimates in the following year. In addition, data showed seasonal and site variation in susceptibility to imidacloprid, possibly due to differential applications in nearby fields.

Susceptibility of cotton whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) to diverse pesticides in Pakistan.

The cotton whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a serious pest of several summer crops in hot and dry climates. Its field populations (Asia II-1 biotype) were assessed for their susceptibility to diverse pesticides by using leaf-dip bioassay. There was no or a very low resistance to amitraz, hexythiazox, and pyridaben during 1992-2015. B. tabaci also exhibited no resistance to endosulfan during 1992-1997 and a very low resistance during 1998-2010, which then rose to a low level during 2011-2015. Chlorfenapyr resistance was very low during 1997-2008 and it reached to a high level during 2009-2011 and to a very high level in 2013 and 2015. Among avermectins, abamectin showed a very low resistance up to 2013 but a high resistance in 2015. Emamectin benzoate also demonstrated a very low resistance up to 2010, but a moderate-to-high resistance during 2011-2015. It may be concluded that the diverse chemistries, having novel modes of action and showing no, very low or low levels of resistance, can be substituted in rotation in the wake of resistance development to conventional insecticides.

Tea saponin reduces the damage of Ectropis obliqua to tea crops, and exerts reduced effects on the spiders Ebrechtella tricuspidata and Evarcha albaria compared to chemical insecticides.

BackgroundTea is one of the most economically important crops in China. However, the tea geometrid (Ectropis obliqua), a serious leaf-feeding pest, causes significant damage to tea crops and reduces tea yield and quality. Spiders are the most dominant predatory enemies in the tea plantation ecosystem, which makes them potentially useful biological control agents of E. obliqua. These highlight the need for alternative pest control measures. Our previous studies have shown that tea saponin (TS) exerts insecticidal activity against lepidopteran pests. Here, we investigate whether TS represents a potentially new alternative insecticide with no harm to spiders.MethodsWe investigated laboratory bioactivities and the field control properties of TS solution against E. obliqua. (i) A leaf-dip bioassay was used to evaluate the toxicity of TS to 3rd-instar E. obliqua larvae and effects of TS on the activities of enzymes glutathione-S-transferase (GST), acetylcholinesterase (AChE), carboxylesterase (CES) and peroxidase (POD) of 3rd-instar E. obliqua larvae in the laboratory. (ii) Topical application was used to measure the toxicity of 30% TS (w/v) and two chemical insecticides (10% bifenthrin EC and 50% diafenthiuron SC) to two species of spider, Ebrechtella tricuspidata and Evarcha albaria. (iii) Field trials were used to investigate the controlling efficacy of 30% TS against E. obliqua larvae and to classify the effect of TS to spiders in the tea plantation.ResultsThe toxicity of TS to 3rd-instar E. obliqua larvae occurred in a dose-dependent manner and the LC50 was 164.32 mg/mL. Activities of the detoxifying-related enzymes, GST and POD, increased in 3rd-instar E. obliqua larvae, whereas AChE and CES were inhibited with time by treatment with TS. Mortalities of E. tricuspidata and E. albaria after 48 h with 30% TS treatment (16.67% and 20%, respectively) were significantly lower than those with 10% bifenthrin EC (80% and 73.33%, respectively) and 50% diafenthiuron EC (43.33% and 36.67%, respectively). The highest controlling efficacy of 30% TS was 77.02% at 5 d after treatment, which showed no difference to 10% bifenthrin EC or 50% diafenthiuron SC. 30% TS was placed in the class N (harmless or slightly harmful) of IOBC (International Organization of Biological Control) categories for natural enemies, namely spiders.ConclusionsOur results indicate that TS is a botanical insecticide that has a good controlling efficacy in E. obliqua larvae, which suggests it has promise as application in the integrated pest management (IPM) envisaged for tea crops.

Impact of Three Species of Aquatic Plants on Anopheles quadrimaculatus and its Effect on the Efficacy of Boric Acid Sugar Baits.

The purpose of this study was to investigate the sugar-feeding behavior of Anopheles quadrimaculatus by measuring the impact of different aquatic plants on its survival. At the same time, the potential use of boric acid in toxic sugar bait (TSB) applications to the leaves of these plants was also evaluated. Mean survival rates of mosquitoes after 120 h feeding on 3 common aquatic plant species-Thalia geniculata, Pontederia cordata, and Limnobium spongia-were 10.55%, 1.86%, and 6.21%, respectively. No significant difference in mortality between mosquitoes feeding on separate plant species was detected (P = 0.05). The TSB efficacy was evaluated by leaf dip bioassay to compare 24-h mortality of mosquitoes feeding on leaves treated with TSB formulation (1% boric acid, 10% sucrose) and leaves dipped in 10% sucrose. Mortality was significantly higher for TSB-treated leaves for T. geniculata (t = 12.5, df = 8, P < 0.0001) and P. cordata (t = 5.42, df = 8, P = 0.0006) than for L. spongia (t = 1.4003, df = 8, P = 0.199). One-way ANOVA analysis showed no significant difference in efficacy between TSB-treated leaves of the 3 plants.

Resistance to new insecticides and their synergism in Spodoptera exigua (Lepidoptera: Noctuidae) from Pakistan

The beet armyworm Spodoptera exigua (Hübner) is an important pest of field and vegetable crops in Pakistan. Due to persistent use of insecticides, it developed high levels of resistance to organophosphates and pyrethroids in the mid 2000s and farmers then switched to new chemistries. In the present study, its resistance to new chemistries such as indoxacarb, spinosad, chlorfenapyr, methoxyfenozide and avermectins was monitored from 1998 to 2017 using a leaf-dip bioassay. There was generally a very low to low resistance to these insecticides during the first 11 years of their introduction (1998-2008). Resistance to methoxyfenozide remained very low throughout the 20 years of monitoring. A moderate resistance was recorded to indoxacarb (2011-2015), spinosad (2009-2012), chlorfenapyr (2011-2017), abamectin (2016-2017) and emamectin benzoate (2010-2013). A high resistance was found to indoxacarb during 2016–2017, spinosad during 2013–2017 and emamectin benzoate during 2014–2017. A rotation of diverse chemistries, having novel modes of action, along with other integrated pest management tactics, is recommended for the management of insecticide resistance in S. exigua.

Synergist induced susceptibility of tobacco caterpillar, Spodoptera litura (Fabricius) from Kerala, India exposed to conventional insecticides

The present study was undertaken to assess the insecticide resistance developed in various field collected population of S. litura and to induce susceptibility by using the synergists. Third-instar larvae collected from three different locations of Kerala viz., Thiruvananthapuram (TVM), Pathanamthitta (PTA) and Alappuzha (ALP) were exposed to conventional insecticides like chlorpyriphos, quinalphos, lambda-cyhalothrin and cypermethrin by leaf dip bioassay and resistance ratios were calculated by using the baseline data generated for respective insecticides using susceptible strain. Resistance ratios recorded were 1965, 840 and 320 against chlorpyriphos, 605, 255 and 59 against quinalphos, 926, 250 and 108 against lambda-cyahlothrin and 2566, 534 and 396 against cypermethrin respectively for TVM, PTA and ALP populations. The effect of selected synergists viz., piperonyl butoxide (PBO), diethyl maleate (DEM) and triphenyl phosphate (TPP) was studied in combination with respective test insecticides against the highly resistant population of S.litura collected from TVM of Kerala. The population was tested with insecticide in combination of the above synergists at different ratios. When PBO, TPP and DEM at ratio of 1:4 were used the synergistic ratio was 8.47, 7.26 and 3.98 for chlorpyriphos, 6.09, 5.26 and 3.05 for quinalphos, 13.37, 4.53 and 7.39 for lambda cyhalothrin and 4.77, 3.36 and 3.40 for cypermethrin respectively. PBO showed highest synergistic activity against both the organophosphates tested followed by DEM and TPP. Highest synergistic activity against synthetic pyrethroids also was shown by PBO, followed by TPP and DEM. The results obtained from the present study revealed that PBO at 1:4 ratio showed higher synergism with the test insecticides against the resistant populations of S.litura and proved to be an effective molecule alternate for breaking the resistance against conventional organophosphates and synthetic pyrethroids.

Efficacy of newer and neonicotinoid insecticides against whitefly Bemisia tabaci on vegetables

Whitefly Bemisia tabaci (Gennadius) is an important sucking insect pest of vegetables, and against this pest fifteen insecticides belonging to neonicotinoid, organophosphate, synthetic pyrethroid and new green chemistries were evaluated. The evaluation was done with laboratory and field collected populations with leaf dip bioassay. Significant variations in the susceptibility of the two populations were observed, and the population collected from field was less susceptible to the neonicotinoid, organophosphate and synthetic pyrethroids. The newer insecticides like flonicamid 50WG, spirotetramate 15OD, diafenthiuron 50WP, sulfoxaflor 240SC, cyantraniliprole 10OD, flupyridifurone 200SL and spiromesifen 22.9SC proved to be the most effective against field collected population (mortality of 100, 100, 97.78, 96.30, 87.92, 78.89 and 66.03%, respectively), as compared to neonicotinoid and conventional insecticides. These newer molecules with novel mode of action could be used as an effective alternative for neonicotinoids against whitefly in vegetables crops.

Glufosinate Ammonium Suppresses Tetranychus urticae in Cotton

Twospotted spider mites, Tetranychus urticae, are an important agricultural pest of many field crops worldwide. Insecticides and acaricides play a primary role in controlling T. urticae populations on agricultural crops. Here, we used greenhouse and field applied foliar spray tests and leaf dip bioassays to examine the susceptibility of T. urticae to glufosinate ammonium in cotton. Leaf dip bioassay results indicated that T. urticae is highly susceptible to concentrations of formulated glufosinate ammonium. The LC50 value was determined to be 10.31 ppm. Field-applied glufosinate ammonium at 1.61 and 3.14 L ha−1 provided 48.9 and 80.2% control, while fenpyroximate provided 89.6% control five days after treatment in 2015. Greenhouse applications resulted in 55.4% control 14 days after treatment with 0.73 L ha−1, while 1.61 L ha−1 resulted in 72.9% control and 3.14 L ha−1 resulted in 91.9% control of T. urticae populations. Treatment with glufosinate ammonium resulted in significant phytotoxic effects to drought-stressed cotton in the 2015 field trial. These results suggest that glufosinate ammonium may be a useful tool for integrated pest management of weeds and spider mites in cotton. Due to the high cost associated with glufosinate ammonium and possibility of phytotoxic effects under certain conditions, this herbicide it is not considered a viable treatment targeting spider mites but may prove useful for managing mites when utilized for weed management.

Susceptibility Status of &amp;lt;i&amp;gt;Bemisia tabaci&amp;lt;/i&amp;gt; Biotypes to Pyrethroid Insecticides in North-Eastern Nigeria

A study was conducted to assess the effect of treatments with the recommended application rate of α-Cypermethrin, Permethrin, Allethrin, Tetramethrin, Cyhalothrin and Deltamethrin pesticides on Bemisia tabaci biotypes. Two localities each were selected from three States of North-eastern Nigeria for sample collections and determination of susceptibility to the insecticides. The localities include Toro and Wuro wasse in Bauchi State, College of Agric farm center (COAG) and Tudun wada in Borno State, Dadin kowa and Kwadon in Gombe State. The insecticides were applied against adult B. tabaci using a leaf-dip bioassay. Insect population that survived any of the insecticides after 24 hours post exposures were considered resistance to the insecticide and their biotypes were determined using Polymerase Chain Reaction (PCR). Overall mean mortality response was 88.89%, 91.27%, 88.09%, 96.83%, 93.65%, and 96.05 for α-Cypermethrin, Permethrin, Allethrin, Tetramethrin, Cyhallothrin and Deltamethrin respectively and all were significantly different from control (P<0.05). Populations from Kwadon showed high resistant factor to α-Cypermethrin, Tetramethrin and Cyahallothrin (RF = 221.99, 128.05 and 98.8-folds respectively). All populations displayed significant resistance to Allethrin (RF ranging from7.01-fold in Tudun wada to 78.93-fold in Kwadon. Tetramethrin resistant was followed by Dadin kowa and Tudun wada (RF = 13.43 and 13.33) respectively and Cyahallothrin resistant was followed by population from Dadin kowa (RF = 82.94-folds) while Deltamethrin resistant was found to be insignificant between almost all locations. Biotype B exhibited higher resistance for all the evaluated insecticides compared to Q in all locations.

Efficacy of some combination insecticides against Epilachna beetle, Henosepilachna vigintioctopunctata (Fabricius)

The contact toxicity of three combination insecticides was determined against 10 d old grubs (mean wt. 0.02 g/grub) of H. vigintioctopunctata by atomization method under laboratory conditions (Temp. 28°C, R.H. 78%). At 48 HAE, deltamethrin + triazophos and profenofos + cypermethrin were equitoxic (LC50 = 0.0003%) showing 1.5 times lesser toxicity than chlorpyriphos + cypermethrin (LC50 = 0.0002%); and at 72 HAE, all the three were equitoxic (LC50 = 0.0002%). In another experiment, the contact and stomach toxicity of six combination insecticides was determined against adults (mean wt. 0.021 g/adult) of H. vigintioctopunctata by leaf dip bioassay method under laboratory conditions (Temp. 28°C, R.H. 78%). At 24 HAF, beta-cyfluthrin + imidacloprid (LC50 = 0.0001%) showed 130 and 9 times higher toxicity than ethion + cypermethrin (LC50 = 0.0139) and chlorpyriphos + cypermethrin (LC50 = 0.0009%), respectively; at 48 HAF, the order of toxicity was beta-cyfluthrin + imidacloprid (LC50= 0.00004%) > chlorpyriphos + cypermethrin (LC50= 0.0005%) > deltamethrin + triazophos (LC50= 0.0009%) > ethion + cypermethrin (LC50= 0.0024%) > profenofos + cypermethrin (LC= 0.0026%) > cypermethrin + indoxacarb (LC50 = 0.0065%); and at 72 HAF, profenofos + cypermethrin and cypermethrin + indoxacarb proved equitoxic (LC50= 0.0013%) being 65, 2.60 and 1.62 times less toxic than beta-cyfluthrin + imidacloprid (LC50=0.00002%), deltamethrin + triazophos (LC50= 0.0005) and ethion + cypermethrin (LC50= 0.0008%), respectively.