Sub-lethal influences of different insecticides on oviposition preference of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) on cotton in relation to altered plant morphology

We investigated the sub-lethal influences of spinosad, chlorpyriphos, endosulfan, acephate and cypermethrin on the oviposition responses of Helicoverpa armigera (Hübner) to cotton plants, under cage and laboratory conditions. The rank order of toxicity (LC₅₀ values as a per cent) of test insecticides against third instar larvae using the leaf disc method was: spinosad > chlorpyriphos > endosulfan > acephate > cypermethrin. On whole plants, females laid more eggs on acephate LC₅₀-, acephate LC₃₀- and cypermethrin LC₅₀-treated cotton plants than on the control. The chlorpyriphos-treated plants were least preferred for oviposition. When excised cotton leaves from different treatments were used in a multiple-choice test, cypermethrin LC₅₀- and endosulfan LC₃₀-treated leaves received more eggs than the control. The repeated application of sub-lethal concentrations of different insecticides reduced plant height in the case of acephate LC₃₀ and cypermethrin LC₅₀, while plant spread and upper canopy leaf area were reduced in both treatments of acephate and cypermethrin. Reduced plant spread, upper canopy leaf area followed by plant height were found associated with oviposition preference by H. armigera females.     

Biochemical and physiological changes on Bacillus thuringiensis cotton after imidacloprid foliar spray

Bacillus thuringiensis cotton is a variety of cotton genetically modified to contain a gene derived from B. thuringiensis bacteria; which results in expression of toxin protein that confers resistance to bollworm complex (the most destructive pest of cotton). Introduction of Bt cotton lowered the need of insecticides, but still a number of insecticides are used for other insects like jassids, whitefly, aphids and tobacco caterpillar to which Bt gene does not provide effective control. Imidacloprid (tradename Imidacel 17.8 SL) is an insecticide designed for control of these major sucking/piercing insects that affect cotton. So in the present work we studied the post effect of imidacloprid insecticide on plant health of three Bt cotton hybrids (RCH-134, JKCH-1947, NCEH-6R) as there are reports of this insecticide causing growth and yield enhancements in absence of insect pests. Imidacloprid was first sprayed at recommended concentration (40 ml/acre) on 3 months old plants sown in randomly designed plots with three replications of each hybrid. The spray was repeated three times at 10 days interval. The level of B. thuringiensis gene expression, peroxidase activity and total phenols was measured on third day after every spray in leaves along with growth and yield of plants. The insecticide has shown to increase the level of B. thuringiensis protein, peroxidase enzyme activity, total phenols, height, number of bolls retained on plants and yield. These observations suggested that the imidacloprid treated plants showed better growth and development, thereby imidacloprid has growth enhancing effect on Bt cotton plants in addition to its insecticidal properties.     

Effectiveness of thiamethoxam and imidacloprid seed treatments against Bemisia tabaci (Hemiptera: Aleyrodidae) on cotton

BACKGROUND: Bemisia tabaci (Gennadius) biotype B is one of the most important pests on cotton around the world. Laboratory, greenhouse and field experiments were conducted to determine the efficacy of thiamethoxam and imidacloprid seed treatments against B. tabaci on cotton. RESULTS: Under laboratory conditions, the two treatments caused whitefly adult mortality, reduced oviposition and increased mortality of nymphs at 10, 20, 30 and 40 days after germination (DAG). The longer the adults fed on plants from treated seeds, the higher the mortality. The two treatments did not have any effect on eggs. The efficacy of the treated seeds against B. tabaci gradually decreased from 10 to 40 DAG, being the lowest at 40 DAG. In laboratory experiments, the efficacies between the two treatments were similar. In greenhouse experiments, the two treatments were equally effective with lower numbers of whiteflies than untreated controls. With both treatments the concentrations of the active ingredient were gradually reduced with aging of the plants and from the bottom to the top leaves of the plants. Numbers of live whiteflies were well correlated with the dosage of active ingredients. Under field conditions, the seeds treated with both insecticides exhibited similar efficacy against B. tabaci for up to ～2 months. CONCLUSION: Cotton seeds treated with imidacloprid and thiamethoxam were effective against B. tabaci for up to 45 days under laboratory and greenhouse conditions, and up to ～2 months under field conditions. Use of imidacloprid‐ and thiamethoxam‐treated seeds can be an important alternative for management of whiteflies on cotton. Copyright © 2010 Society of Chemical Industry     

Mechanisms of resistance in cotton to whitefly (<Emphasis Type="Italic">Bemisia tabaci</Emphasis>): antixenosis

Screenhouse experiments were conducted under free-choice conditions to determine the mechanism of resistance operating in cotton against whitefly, Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae). Twelve cotton genotypes belonging to Gossypium hirsutum and G. arboreum were assessed for oviposition preference by whitefly. The trichome density and length, distance from lower leaf surface to nearest vascular bundles, leaf lamina thickness and compactness of vascular bundles were estimated for each genotype and correlations with number of eggs laid were determined. The genotypes RS2098, CNH911, and PA183 were non-preferred for oviposition and exhibited an antixenosis mechanism of resistance. NHH44, LK861, Supriya, RS2013 and LD694 were categorized as moderately resistant while IS-376/4/1/20/72 and F846 were categorized as susceptible. Greater leaf lamina thickness and more compact vascular bundles were correlated with egg laying by whitefly.     

Effect of Cotton leaf curl virus infected plants on the biology of the whitefly,Bemisia tabaci (Hemiptera: Aleyrodidae): Vector–virus mutualism

Cotton leaf curl virus (CLCuV) (Geminiviridae : Begomovirus), the causative agent of leaf curl disease in cotton plants (Gossypium hirsutum), is exclusively transmitted by whitefly species Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). CLCuV transmission occurs in Sriganganagar (Rajasthan), an area endemic with cotton leaf curl disease. The relationships between plant viruses, their herbivore vectors and host plants can be beneficial, neutral, or antagonistic, depending on the species involved. To further understand these relationships, fecundity and life history parameters of an indigenous non- b (Asia II genetic group) biotype whitefly, B. tabaci, were compared on 10, 25, and 40 days post-inoculation (DPI), in CLCuV-infected and healthy cotton plants to determine the effect of virus on its vector. The development time of the immature stages of whiteflies was significantly reduced on CLCuV-infected plants. The development time of the immature stages did not change with severity of symptoms at 25 and 40 DPI (45- and 60-d-old plants). Cotton leaf curl virus infection increased percent egg viability of B. tabaci. Whiteflies deposited significantly fewer eggs on virus-infected plants than on healthy plants. Whiteflies had better egg viability on younger plants than older plants, whereas plant age did not affect the fecundity. Male and female whiteflies had shorter longevity on CLCuV-infected plants than on healthy plants.     

烟粉虱成虫对不同寄主植物的选择性

选用棉花、烟草、番茄、甘蓝进行非选择性和选择性试验研究 ,探讨烟粉虱成虫对 4种寄主植物的嗜食性。结果表明 ,在 4种寄主作物共同存在时 ,烟粉虱成虫喜欢取食烟草 ,排列顺序为 :烟草 >番茄 >棉花、甘蓝 ;产卵量排列顺序为 :烟草、番茄 >甘蓝、棉花。当只有番茄和烟草两种寄主植物时 ,烟粉虱成虫趋向于取食烟草 ,但在番茄上产卵 ;只有烟草和甘蓝时 ,烟粉虱倾向于取食烟草并产卵 ;只有棉花和番茄时 ,烟粉虱对两种寄主没有明显的趋向 ;只有棉花和烟草时 ,烟粉虱显著的喜好在烟草上产卵 ;只有棉花和甘蓝时 ,烟粉虱趋向在棉花上取食产卵 ,但没有达到显著水平 ;同样只有番茄和甘蓝时 ,烟粉虱喜好在番茄上取食产卵 ,但没有达到显著水平。     

Effects of petroleum spray oils on oviposition behaviour and larval survival of Helicoverpa armigera Hubner (Lepidoptera: Noctuidae) and Ostrinia nubilalis Hubner (Lepidoptera: Pyralidae)

We determined the effects of petroleum spray oil (PSO) (Caltex Canopy®) on oviposition responses of Helicoverpa armigera Hubner and Ostrinia nubilalis Hubner adults, and larval survival of the pest moths on cotton and maize plants in the laboratory. Application of 2% (v/v) of the PSO deterred H. armigera oviposition. Increasing the rate from 2 to 5% (v/v) did not significantly reduce the number of eggs laid by H. armigera on the treated plants. In contrast, the minimum rate at which the oil could deter oviposition of O. nubilalis on maize plants was 5% (v/v). Increasing the rate from 5 to 10% (v/v) did not significantly reduce the number of eggs laid per plant. However, a reduction in the rate of the PSO from 5 to 3% (v/v) resulted in a 73.9% increase in oviposition activity on the maize plants. In wind tunnel bioassay tests, all mated H. armigera females tested could detect and settle on plants treated with water but with plants treated with PSO at various times, only 50% of tested females settled on the plants 4?–?5 days after treatment (DAT) and none on the plants 0?–?2 DAT. A solid phase micro-extraction (SPME) test to determine the effect of the PSO on volatiles released by the cotton plants showed that the quantity of volatiles released by the cotton plants treated with PSO was lower than for water treated plants. This indicates that the PSO sprays may be suppressing or masking the leaf surface volatiles of the cotton plants, thereby deterring oviposition of H. armigera. Larval survival data show that PSO sprays can cause direct mortality of first, second and third instar O. nubilalis larvae. PSOs may have the potential to be integrated into pest management programme targeting H. armigera and O. nubilalis on cotton and maize crops, respectively.     

Control strategy for the sweetpotato whiteflyBemisia tabaci,late in the cotton-growing season

Populations of the sweetpotato whitefly,Bemisia tabaci (Gennadius), were sampled late in the cotton-growing seasons of 1990, 1991 and 1992, in commercial ‘Acala’ cotton fields in southwestern Israel. In mid summer, when populations ofB. tabaci started to build up, cotton fields were commercially treated with a single application of an IGR (insect growth regulator). The experimental plots were then treated in September with conventional adulticides or with the novel insecticides buprofezin and pyriproxyfen (IGR), and diafenthiuron (a thiourea derivative). The effects of the insecticides onB. tabaci larval and adult populations, and the amount of damage to the cotton lint, were recorded. Untreated populations of larvae and pupae ofB. tabaci in the three end-of-season studies, had the tendency to build up toward the defoliation treatment. However, the level of theB. tabaci populations observed in the experimental fields and the short period of exposure of the open cotton bolls to the whiteflies, did not result in lint damage, probably because the whitefly numbers had been reduced considerably after the defoliation treatment. At the end of the 1991 and 1992 cotton seasons, a high level of parasitism, ranging between 50% and 80%, was recorded. The shift in chemical applications toward the novel IGRs during the season, along with the reduction in insecticide use in general, probably contributed to the propagation of parasitoids, thereby improving whitefly control.     

Influence of three diets on susceptibility of selected insecticides and activities of detoxification esterases of Helicoverpa assulta (Lepidoptera: Noctuidae)

The oriental tobacco worm, Helicoverpa assulta Guenée, is one of the most destructive pests of tobacco and peppers in China. We determined the susceptibility of H. assulta reared on an artificial diet, chili pepper and tobacco to four insecticides (fenvalerate, phoxim, methomyl, indoxacarb) under laboratory conditions associated with the activities of acetylcholinesterase (AChE), carboxylesterase (CarE) and glutathione S-transferase (GST) in its larvae. H. assulta larvae that were fed with chili pepper were more susceptible to fenvalerate, indoxacarb, and phoxim than those that were fed with tobacco and the artificial diet, but not to methomyl. The larvae that were fed with chili pepper were 3.65-, 2.49-, 1.92- and 2.44-fold more susceptible to fenvalerate, phoxim, methomyl, and indoxacarb than those fed with tobacco, respectively. The AChE activities of H. assulta larvae that were fed with chili pepper and tobacco were 2.12 and 1.07 μmol mg⁻¹ 15 min⁻¹, respectively, almost 2-fold difference. The CarE activity of H. assulta larvae that were fed with chili pepper, tobacco and the artificial diet was 4.12, 7.40 and 7.12 μmol mg⁻¹ 30 min⁻¹, respectively. Similarly, the GST activities of H. assulta larvae that were fed with chili pepper, tobacco and the artificial diet was 52.02, 79.37 and 80.02 μmol mg⁻¹ min⁻¹, respectively. H. assulta larvae that were fed with chili pepper were more resistance to the tested insecticides. The low activities of AChE and the high activities of CarE and GST lead to H. assulta become more susceptible to the tested insecticides.     

Pyriproxyfen,a novel insect growth regulator for controlling whiteflies: Mechanisms and resistance management

Pyriproxyfen, a novel juvenile hormone mimic, is a potent suppressor of embryogenesis and adult formation of the sweetpotato whitefly, Bemisia tabaci (Gennadius), and the greenhouse whitefly, Trialeurodes vaporariorum (Westwood). Dipping of cotton or tomato seedlings infested with 0 to 1-day-old eggs in 0.1 mg litre^?1 resulted in over 90% suppression of egg hatch of both B. tabaci and T. vaporariorum. Older eggs were affected to a lesser extent. Exposure of whitefly females to cotton or tomato seedlings treated with pyriproxyfen resulted in oviposition of non-viable eggs. The LC90 values for egg viability of B. tabaci and T. vaporariorum exposed to treated plants were 0.05 and 0.2 mg litre^?1, respectively. Treatment of whitefly larvae with 0.04–5 mg litre^?1 resulted in normal development until the pupal stage; however, adult emergence was totally suppressed. Second instars of B. tabaci exposed to 5 mg litre^?1 pyriproxyfen, excreted honeydew at a level similar to the control level until the fourth instar (pupation), after which a strong reduction was observed. Inhibition of egg-hatch on the lower surface of cotton leaves was observed when their upper surface was treated with 1–25 mg litre^?1, indicating a pronounced translaminar effect. These findings indicate that pyriproxyfen is an efficient control agent of both B. tabaci and T. vaporariorum. The compound has been used successfully for controlling whiteflies in Israeli cotton fields since 1991. Adults of B. tabaci collected from a rose greenhouse and from adjacent cotton fields were monitored during 1991–1993 for their susceptibility to pyriproxyfen. A high level of resistance was recorded in whiteflies collected from a greenhouse after three successive applications of pyriproxyfen. Based on LC50 values, the resistance ratio for egg-hatch suppression was 554-fold and, for adult emergence failure, 10-fold. However, a single treatment of pyriproxyfen in cotton fields during the summer season (according to an insecticide resistance management (IRM) strategy) did not alter appreciably the susceptibility of B. tabaci to this compound. In order to prevent development of resistance, an attempt should be made to restrict its use to one treatment per crop season applied during the peak activity of the pest. Pyriproxyfen can be alternated with other novel compounds such as buprofezin and diafenthiuron for controlling whiteflies in cotton, vegetables and ornamentals as part of integrated pest management (IPM) and IRM strategies. In pyriproxyfen- or buprofezin-resistant strains of B. tabaci or T. vaporariorum, no appreciable cross-resistance was observed among pyriproxyfen, buprofezin and diafenthiuron.     

Screening insecticides against the tobacco whitefly (Bemisia tabaci) on cotton,using a leaf cage laboratory method

Over 20 insecticides were screened against the tobacco whitefly,Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), on cotton. AsB. tabaci feeds only on live plants, a suitable laboratory test method incorporating young cotton plants was developed. Both cover sprays and systemic insecticides applied to the soil were tested. Triazophos, pyridaphenthion, azinphos-methyl, bendiocarb and flucythrinate were found to be effective and persistent. The best of the systemic insecticides was aldicarb, followed by butocarboxim.     

Effect of fenvalerate on the reproduction and fitness costs of the brown planthopper, Nilaparvata lugens and its resistance mechanism

The brown planthopper (BPH), Nilaparvata lugens Stål, is a primary insect pest of cultivated rice, and its effective control is essential for crop production. However, in recent years, outbreaks of the brown planthopper have occurred more frequently in China. In order to determine the causes and mechanisms of insecticide-induced BPH resurgence and perform population management, we conducted the following studies. By the topical application method, our results showed that, fenvalerate acted as stimulus of fecundity from 3.50 × 10⁻³ to 2.02 × 10⁻² μg/female in the BPH. Apart from 7.00 × 10⁻³ μg/female, the number of hatched nymphs was increased gradually with an increase in application dose from 3.50 × 10⁻³ to 1.74 × 10⁻² μg/female. After continuous selection with fenvalerate for 11 generations by the rice-stem dipping method, a resistant strain was achieved with medium resistance to fenvalerate (RR 39.22). Life table study indicated that the resistant strain (G4 and G8) showed reproductive advantages, including increased female ratio, copulation rate and fecundity. But the hatchability of resistant strain was lower. The survival rate and emergence rate were significantly lower in G4 and G8 resistant strain. Resistant strains in G4 and G8 showed a fitness advantage (1.04 and 1.11), and the number of offspring in G8 generation was higher than that in G4 generation. The significant difference detected between resistant insects (G4, G5, G8 and G9) and S-strain contains not only the effect of resistant selection but also the effect of continuous rearing itself. Hence it was concluded that the BPH had the potential to develop high resistance against fenvalerate and the induction of the nymphs by sublethal doses of fenvalerate was of importance in the BPH population management, particularly in the predicting. Further studies demonstrated that triphenyl phosphate (TPP) and diethyl maleate (DEM) had no synergism on fenvalerate. However, piperonyl butoxide (PBO) displayed significant synergism in susceptible strain (1.97) and resistant strain (2.73). We concluded that esterase and glutathione S-transferase play little role in fenvalerate detoxification. The increase of the P450-monooxygenases detoxification is an important mechanism for fenvalerate resistance. Because their resistant populations had a fitness advantage, we should pay close attention to the occurrence of BPH and use other functionally different insecticides to control the BPH.     

Influence of neem on susceptibility of Beauveria bassiana and investigation of their combined efficacy against sweetpotato whitefly, Bemisia tabaci on eggplant

A study on the compatibility of the entomopathogenic fungus Beauveria bassiana with neem was conducted against sweetpotato whitefly, Bemisia tabaci, on eggplant. Initially, three concentrations of neem (0.25%, 0.5% and 1.0%) were used to investigate the physiological responses of B. bassiana. Thereafter, above three concentrations of neem along with three concentrations of B. bassiana (10⁶, 10⁷ and 10⁸ conidia/ml) were used to investigate combined deterrence index, DI under two application methods (foliar and soil) of B. tabaci. Significant differences were observed among neem concentrations on all variables- germination percentage, vegetative growth, number of conidia, amount of biomass and proteolytic activity of B. bassiana. The reduction percentage of germination, vegetative growth, sporulation, biomass production and proteolytic activity of B. bassiana were as high as 12%, 13%, 35%, 38%, and 34%, respectively, to neem. Significant differences were also observed on deterrence index, DI (adult and oviposition) of B. tabaci. The current study investigated that the highest adult DI (80.15) and oviposition DI (88.25) occurred when 1.0% neem was combined with 10⁸ conidia/ml of B. bassiana. As the results show, neem is compatible with B. bassiana; and soil application of neem along with foliar application of B. bassiana might be useful for the control of B. tabaci.     

Variation of acephate susceptibility and correlation with esterase and glutathione S-transferase activities in field populations of the tarnished plant bug, Lygus lineolaris

The tarnished plant bug (TPB) has increasingly become an economically important pest of cotton. Heavy dependence on insecticides, particularly organophosphates and pyrethroids, for TPB control facilitated resistance development to multiple classes of insecticides. To better understand resistance and explore ways to monitor resistance in field populations, this study examined acephate susceptibility and the activities of two major detoxification enzymes in nine field populations collected in the Delta region of Mississippi and Arkansas in 2010. Two Arkansas populations from Reed and Backgate had 3.5- and 4.3-fold resistance to acephate, as compared to a susceptible laboratory strain. Extensive planting of cotton and heavy chemical sprays is a major driving force for resistance development to acephate in Mid-south cotton growing areas. Reduced susceptibility to acephate was highly correlated with elevated esterase activities. The acephate-resistant populations from Backgate, Lula, and Reed consistently had higher (up to 5.3-fold) esterase activities than susceptible populations. Regression analysis of LC₅₀s with kinetic esterase activities revealed a significant polynomial quadratic relationship with R² up to 0.89. Glutathione S-transferase (GST) also had elevated activity in most populations, but the variations of GST activities were not significantly correlated with changes of acephate susceptibility. Finally, examination of esterase and GST inhibitors indicated that suppression rates (up to 70%) by two esterase inhibitors in 2010 were slightly lower than those detected in 2006, and ethacrynic acid (EA) inhibited GST effectively in both years. Two other GST inhibitors (sulfobromophthalein and diethyl maleate) displayed significantly lower suppression rates in 2010 than those detected in 2006, suggesting a potential genetic shift in pest populations and a necessity of continued monitoring for insecticide resistance with both bioassay and biochemical approaches. Results indicated that using major detoxification enzyme activities for resistance monitoring may provide insight into acephate resistance in field populations of TPB.     

Thiamethoxam is a neonicotinoid precursor converted to clothianidin in insects and plants

Neonicotinoid insecticides are compounds acting agonistically on insect nicotinic acetylcholine receptors (nAChR). They are especially active on hemipteran pest species such as aphids, whiteflies, and planthoppers, but also commercialized to control many coleopteran and some lepidopteran pest species. The most prominent member of this class of insecticides is imidacloprid. All neonicotinoid insecticides bind with high affinity (I₅₀-values around 1 nM) to [³H]imidacloprid binding sites on insect nAChRs. One notable ommission is the neonicotinoid thiamethoxam, showing binding affinities up to 10,000-fold less potent than the others, using housefly head membrane preparations. Electrophysiological whole cell voltage clamp studies using neurons isolated from Heliothis virescens ventral nerve cord showed no response to thiamethoxam when applied at concentrations of 0.3 mM, although the symptomology of poisoning in orally and topically treated noctuid larvae suggested strong neurotoxicity. Other neonicotinoids, such as clothianidin, exhibited high activity as agonists on isolated neurons at concentrations as low as 30 nM. There was no obvious correlation between biological efficacy of thiamethoxam against aphids and lepidopterans and receptor affinity in electrophysiological and binding assays. Pharmacokinetic studies using an LC-MS/MS approach to analyze haemolymph samples taken from lepidopteran larvae revealed that thiamethoxam orally applied to 5th instar Spodoptera frugiperda larvae was rapidly metabolized to clothianidin, an open-chain neonicotinoid. Clothianidin shows high affinity to nAChRs in both binding assays and whole cell voltage clamp studies. When applied to cotton plants, thiamethoxam was also quickly metabolized, with clothianidin being the predominant neonicotinoid in planta briefly after application, as indicated by LC-MS/MS analyses. Interestingly, the N-desmethylated derivative of thiamethoxam, N-desmethyl thiamethoxam, was not significantly produced in either lepidopteran larvae or in cotton plants, although it was often mentioned as a possible metabolite, being nearly as active as imidacloprid. In conclusion, our investigations show that thiamethoxam is likely to be a neonicotinoid precursor for clothianidin.     

B型烟粉虱对不同棉花品种的选择性及适生性

29号上最高,在泗杂3号上最低.两代B型烟粉虱在不同品种上的平均产卵量存在显著差异,第1代最多达66.5粒,最少为41.6粒;第2代最多为65.8粒,最少仅为31.8粒.生命表参数表明,B型烟粉虱在中棉所29号上的种群数量增殖速度最快,而在国抗22号上则最慢.     

Persistence on cotton foliage of insecticide residues toxic to Heliothis larvae

Control measures for Heliothis spp. on cotton are usually applied against eggs and newly hatched larvae that infest plant terminal growth. In order to investigate the rate of degradation of a range of insecticides, leaf disc samples were collected, at intervals after application, from both fully expanded cotton leaves and unfolding terminal leaves. The samples were subjected separately to bioassay with newly hatched larvae, and to chemical analysis of the surface deposits. On old leaves, larval mortality caused by two biological insecticides declined by half after field exposure for 36 h, but for the synthetic insecticides, the interval ranged from 4.5 days with endosulfan to 18 days with fenvalerate. On new leaves, the longest interval was 7 days with fenvalerate. Chemical half-life on old leaves ranged from 1 day with endosulfan to 12 days with DDT, and was also shorter on young leaves than the equivalent biological half-life. Bioassay appears to be the most reliable method of assessing insecticidal activity over time. Dosage/mortality data were integrated to give LC₅₀ and LC₉₀ values. Leaf expansion may have the greatest effect on insecticide persistence during the 6 week period of rapid growth commencing 2 months after sowing. Expansion was slower when plants were water stressed, and accelerated following irrigation. The implications of the above findings for cotton pest management are discussed.     

Effect of short term exposure of fenvalerate on biochemical and haematological responses in Labeo rohita (Hamilton) fingerlings

Experiment was carried out to determine the median lethal concentration (LC₅₀) of fenvalerate to Labeo rohita fingerlings. After determining the LC₅₀ value of fenvalerate, a sub-lethal concentration (1/3rd of LC₅₀) of fenvalerate was exposed for 15 days. Significant alterations in SOD (P < 0.05) activity of liver and gill was observed due to fenvalerate. Catalase activity in gills of fishes was also affected significantly (P < 0.05). WBC, NBT and Hct values were reduced significantly in fenvalerate exposed fishes as compared to control group, whereas blood glucose level showed higher values in fenvalerate exposed group. Serum total protein and albumin were also reduced significantly as a result of fenvalerate exposure. Significant increase in the serum GOT, serum GPT, creatinine, triglyceride and serum ACP was noticed after 15 days of fenvalerate exposure. Results indicated that short term exposure of fenvalerate can induce biochemical and haematological alterations causing stress to L. rohita fingerlings.     

Effect of fenvalerate on oxidative stress biomarkers in the brackish water prawn Penaeus monodon

The toxicity of fenvalerate to the prawn Penaeus monodon was evaluated using biomarkers of stress. In a preliminary bioassay test, P. monodon was exposed to a series of fenvalerate concentrations, which showed 4, 6.5 and 8.5 μg L⁻¹ to be sublethal, median lethal and lethal, respectively. Sublethal effect of fenvalerate was further evaluated in hepatopancreas, muscle and gills of prawns with reference to oxidative stress biomarkers. Significant induction of lipid peroxidation and glutathione-S-transferase activity was found in hepatopancreas, muscle and gills of prawns exposed to fenvalerate when compared to control (P < 0.001, P < 0.05 and P < 0.05). On the contrary, the activities of Superoxide dismutase, catalase, glutathione peroxidase, vitamin C, vitamin E and glutathione were found to be reduced in the experimental group of prawns when compared to control. The results suggest that the animals were under oxidative stress when exposed to sublethal concentration of fenvalerate.     

Aerial electrostatic‐charged sprays for deposition and efficacy against sweet potato whitefly (Bemisia tabaci) on cotton

Background: The efficacy of aerial electrostatic‐charged sprays was evaluated for spray deposit characteristics and season‐long control of sweet potato whitefly (SWF), Bemisia tabaci Genn. biotype B (aka B. argentifolii Bellows & Perring), in an irrigated 24 ha cotton field. Treatments included electrostatic‐charged sprays at full and half active ingredient (AI) label rate, uncharged sprays and conventional sprays applied with CP nozzles at full label rate with several different insecticides. Results: Spray droplet size was significantly smaller for electrostatic‐charged sprays than for conventional sprays in top‐ and mid‐canopy locations. The seasonal mean numbers of viable eggs and live large nymphs on cotton treated with electrostatic‐charged sprays were comparable with those on cotton treated with conventional applications. Lethal concentration (LC₅₀) for adults for electrostatic‐charged sprays was comparable with that for conventional sprays. Conclusion: The amenability of electrostatic‐charged sprays to a wide array of pesticides with different chemistries should be a useful tool in combating insect resistance. Results reported here suggest that the potential exists for obtaining increased efficacy against whiteflies using an electrostatic spray charging system, and that additional research will be required to improve charge‐to‐mass (Q/M) ratio in order to increase deposition of pest control materials to the lower surfaces of cotton leaves where the whiteflies reside. Copyright © 2009 Society of Chemical Industry