Interaction between host plant resistance and biological activity of Bacillus thuringiensis in managing the pod borer Helicoverpa armigera in chickpea

The legume pod borer Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) has developed high levels of resistance to conventional insecticides, and therefore, efforts are being made to develop transgenic chickpea expressing toxin genes from the bacterium Bacillus thuringiensis (Bt) for controlling this pest. However, there is an apprehension that acid exudates in chickpea might interfere with the biological activity of Bt. Therefore, we studied the biological activity of Bt (Biolep^R) on four chickpea genotypes with different levels of resistance to H. armigera under field conditions, and by incorporating lyophilized leaf and pod tissue into the artificial diet with and without Bt. The pH of the acid exudates varied from 2.1 to 2.9, and malic and oxalic acids were the major components of the acid exudates in different chickpea genotypes. There was no survival of H. armigera larvae in chickpea plants sprayed with 0.1, 0.2 and 0.5% Bt. There was a significant reduction in larval survival, larval and pupal weights and fecundity, and prolongation of larval and pupal periods in chickpea plots sprayed with Bt (0.05%) as compared to the unsprayed plots. Biological activity of Bt was lower on artificial diets with leaf or pod powder of chickpea genotypes, which might be because of a low intake of Bt toxins due to the antifeedant effects of acid exudates in the chickpea or reduction in biological activity of Bt due to the interaction of biochemical constituents in chickpea with the Bt toxins. Larval survival, larval and pupal weights, pupation and adult emergence were significantly lower on diets with leaf or pod powder of the H. armigera-resistant genotypes than on the susceptible check. Chickpea genotypes with resistance to H. armigera acted in concert with Bt to cause adverse effects on the survival and development of this insect. The results suggested that development of transgenic chickpeas expressing toxin genes form Bt will be quite effective for controlling of the pod borer, H. armigera.     

Monitoring resistance of Helicoverpa armigera to different insecticides used in cotton in Spain

Helicoverpa armigera is the key pest of cotton in Spain, resulting in many insecticide treatments against it. The resistance status of H. armigera to different insecticides currently used in cotton was evaluated in Spain in two different seasons, 1999 and 2004. Four populations were tested in total, two in each season. Toxicological bioassays were conducted in the laboratory, and performed on third instar larvae by topical application of the insecticides. LD₅₀'s were estimated by probit analysis and resistance factors (RF) were calculated at the LD₅₀ level. Four insecticides were evaluated, but only endosulfan reached a moderate resistance level (RF = 11.4), and the others (methomyl, chlorpyrifos and lambda-cyhalothrin) showed low resistance (RF between 1.9 and 6.0). Such results indicate the generally low resistance of H. armigera to most of the insecticides used against this pest in cotton in Spain. Possible explanations for this situation are discussed.     

Acute toxicity and sublethal effects of methoxyfenozide and thiodicarb on survival,development and reproduction of Helicoverpa armigera (Lepidoptera: Noctuidae)

The cotton bollworm Helicoverpa armigera (Hubner) is one of the most destructive pest insects in Iran and many other countries. In this study, lethal and sublethal effects of methoxyfenozide, and thiodicarb were evaluated against H. armigera larvae that fed on insecticide-treated artificial diet. The effects of methoxyfenozide and thiodicarb were assessed in 3rd instars. Methoxyfenozide and thiodicarb showed LC₅₀ values of 4 and 639 mg a.i./ml, respectively, in H. armigera larvae. Sublethal effects on development, adult longevity, and reproduction were observed in H. armigera larvae that survived exposure to an LC₃₀ of the insecticides. Larvae that were exposed to an LC₃₀ concentration of methoxyfenozide exhibited lower pupal weight and increased larval and pupal developmental times compared with thiodicarb treated larvae or control larvae. Adults that were exposed as larvae to an LC₃₀ concentration of methoxyfenozide or thiodicarb showed reduced fecundity (35% and 30%, respectively) compared to control adults. The tested insecticides significantly reduced adult longevity. The longevity of adult females that as larvae were treated with an LC₃₀ concentration of methoxyfenozide or thiodicarb was reduced by 28% and 23%, respectively, in comparison to control females. We predict that the combination of lethal and sublethal effects of the insecticides, especially methoxyfenozide, will induce significant effects on field population dynamics of H. armigera.     

Pest-damage relationships for Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) on vegetative soybean

The response of vegetative soybean (Glycine max) to Helicoverpa armigera feeding was studied in irrigated field cages over three years in eastern Australia to determine the relationship between larval density and yield loss, and to develop economic injury levels. Rather than using artificial defoliation techniques, plants were infested with either eggs or larvae of H. armigera, and larvae allowed to feed until death or pupation. Larvae were counted and sized regularly and infestation intensity was calculated in Helicoverpa injury equivalent (HIE) units, where 1 HIE was the consumption of one larva from the start of the infestation period to pupation. In the two experiments where yield loss occurred, the upper threshold for zero yield loss was 7.51 ± 0.21 HIEs and 6.43 ± 1.08 HIEs respectively. In the third experiment, infestation intensity was lower and no loss of seed yield was detected up to 7.0 HIEs. The rate of yield loss/HIE beyond the zero yield loss threshold varied between Experiments 1 and 2 (−9.44 ± 0.80 g and −23.17 ± 3.18 g, respectively). H. armigera infestation also affected plant height and various yield components (including pod and seed numbers and seeds/pod) but did not affect seed size in any experiment. Leaf area loss of plants averaged 841 and 1025 cm²/larva in the two experiments compared to 214 and 302 cm²/larva for cohort larvae feeding on detached leaves at the same time, making clear that artificial defoliation techniques are unsuitable for determining H. armigera economic injury levels on vegetative soybean. Analysis of canopy leaf area and pod profiles indicated that leaf and pod loss occurred from the top of the plant downwards. However, there was an increase in pod numbers closer to the ground at higher pest densities as the plant attempted to compensate for damage. Defoliation at the damage threshold was 18.6 and 28.0% in Experiments 1 and 2, indicating that yield loss from H. armigera feeding occurred at much lower levels of defoliation than previously indicated by artificial defoliation studies. Based on these results, the economic injury level for H. armigera on vegetative soybean is approximately 7.3 HIEs/row-metre in 91 cm rows or 8.0 HIEs/m².     

Practical yield loss models for infestation of cocoa with cocoa pod borer moth,Conopomorpha cramerella (Snellen)

The cocoa pod borer, Conopomorpha cramerella (Snellen) (Gracillariidae: Gracillariinae), is an important pest of cocoa in Southeast Asia and Oceania, with devastating effects on yields. Using data on cocoa pod borer (CPB) infestation and cocoa yield from mixed-variety plantations in South Sulawesi, Indonesia, we developed models for estimating yield and yield loss under CPB attack. For six yield variables, two types of models were constructed: non-linear regressions based upon the presence or absence of infestation of pods (PI model), and multiple linear regressions for a four-point graded system of infestation severity (IS model). The IS models performed markedly better than PI models, in terms of percentage of variance explained, for all variables, also supported by Corrected Akaike Information Criterion values. But the explanatory power of the best-fit models was still poor for some variables. The fits were strongest for arguably the two most important variables in the industry, dry weight/pod and pod value (the number of pods required to achieve 1 kg of dry cocoa), with 62% and 69% of the variance accounted for, respectively. Validation of the dry weight/pod and pod value models against an independent dataset from South Sulawesi indicated that the models slightly under-estimated both yield indicators that increase concomitantly with the degree of yield loss. We propose the IS models, particularly that for pod value, as useful tools for industry, and argue that they will have broad utility given that they are based on mixed-cultivar plantations. Not only are these the first CPB yield-loss models to be based on commercial mixed plantings, they also represent the first attempt to employ a gradation of infestation severity based on simple visual assessment, which proved to be an important advance.     

Crop hosts and genotypic resistance influence the biological activity of Bacillus thuringiensis towards Helicoverpa armigera

Studies on the influence of genotypic resistance on biological activity of a commercial formulation of Bacillus thuringiensis (Bt) and pure Bt toxin Cry1Ac were carried out to develop appropriate strategies for pod borer, Helicoverpa armigera management in chickpea, sorghum, pigeonpea and cotton. The interaction effects of host plant resistance and biological activity of commercial Bt/Cry1Ac were studied by incorporating the lyophilized tissues of chickpea leaves, milk stage sorghum grain, pigeonpea pods and cotton squares into the artificial diet with and without Bt formulation or Cry1Ac. The H. armigera larval weights were significantly lower in insects reared on diets with square powder of the insect - resistant Bt-cotton RCH 2 + Bt/Cry1Ac and pod powder of insect - resistant pigeonpea genotype, ICPL 332WR + Bt/Cry1Ac as compared to the larvae reared on diets with leaf powder of H. armigera susceptible chickpea genotype, ICCC 37 and the standard artificial diet. Pupation and adult emergence were significantly lower in insects reared on diets with tissues of pod borer-resistant genotypes + Bt/Cry1Ac as compared to insects reared on diets with tissues of the insect susceptible genotypes + Bt/Cry1Ac. Insects reared on diets containing insect-resistant and -susceptible genotypes of sorghum, pigeonpea and cotton and pod borer-resistant genotype of chickpea (ICC 506EB) + Bt/Cry1Ac did not lay any eggs. However, eggs were laid by the insects reared on diets containing pod borer-susceptible genotype of chickpea, ICCC 37 and on the standard artificial diet + Bt/Cry1Ac. The insects reared on diets with sorghum genotype, ICSV 745, and Bt-cotton, RCH 2 without Bt/Cry1Ac also did not lay eggs. The results suggested that Bt/Cry1Ac is more effective for management of H. armigera when deployed in combination with insect-resistant genotypes of cotton, chickpea, pigeonpea and sorghum.     

Pest-damage relationships for Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) on soybean (Glycine max) and dry bean (Phaseolus vulgaris) during pod-fill

The response of soybean (Glycine max) and dry bean (Phaseolus vulgaris) to feeding by Helicoverpa armigera during the pod-fill stage was studied in irrigated field cages over three seasons to determine the relationship between larval density and yield loss, and to develop economic injury levels. H. armigera intensity was calculated in Helicoverpa injury equivalent (HIE) units, where 1 HIE was the consumption of one larva from the start of the infestation period to pupation. In the dry bean experiment, yield loss occurred at a rate 6.00 ± 1.29 g/HIE while the rates of loss in the three soybean experiments were 4.39 ± 0.96 g/HIE, 3.70 ± 1.21 g/HIE and 2.12 ± 0.71 g/HIE. These three slopes were not statistically different (P > 0.05) and the pooled estimate of the rate of yield loss was 3.21 ± 0.55 g/HIE. The first soybean experiment also showed a split-line form of damage curve with a rate of yield loss of 26.27 ± 2.92 g/HIE beyond 8.0 HIE and a rapid decline to zero yield. In dry bean, H. armigera feeding reduced total and undamaged pod numbers by 4.10 ± 1.18 pods/HIE and 12.88 ± 1.57 pods/HIE respectively, while undamaged seed numbers were reduced by 35.64 ± 7.25 seeds/HIE. In soybean, total pod numbers were not affected by H. armigera infestation (out to 8.23 HIE in Experiment 1) but seed numbers (in Experiments 1 and 2) and the number of seeds/pod (in all experiments) were adversely affected. Seed size increased with increases in H. armigera density in two of the three soybean experiments, indicating plant compensatory responses to H. armigera feeding. Analysis of canopy pod profiles indicated that loss of pods occurred from the top of the plant downwards, but with an increase in pod numbers close to the ground at higher pest densities as the plant attempted to compensate for damage. Based on these results, the economic injury levels for H. armigera on dry bean and soybean are approximately 0.74 HIE and 2.31 HIE/m², respectively (0.67 and 2.1 HIE/row-m for 91 cm rows).     

Artificial neural network analysis of lipase-catalyzed synthesis of sugar alcohol ester

Artificial neural network (ANN) analysis of immobilized Candida antarctica lipase B-catalyzed esterification of palmitic acid with xylitol was carried out. Temperature, time, amount of enzyme, amount of molecular sieve, substrate molar ratio and volume of solvent were the six important parameters used as the inputs of the network trained by Levenberg-Marquardt (LM) algorithm. After evaluating different ANN configurations, the best network was found to be consisted of two hidden layers with six and seven neurons in the first and second layers respectively, using a hyperbolic tangent sigmoid transfer function. The coefficient of determination (R²) and mean square error (MSE) values between the actual and predicted responses were 1 and 1.5025e−24 for the training and 0.97239 and 0.03259 for the testing datasets. The results indicate the good generalization performance of the neural network model and its capability to predict the conversion of the substrates.     

Development of Temporal Modeling for Forecasting and Prediction of the Incidence of Lychee,Tessaratoma papillosa (Hemiptera: Tessaratomidae), Using Time-Series (ARIMA) Analysis

The most destructive enemy of the lychee, Litchi chinensis Sonn. (Sapindales: Sapindaceae), in India is a stink bug, Tessaratoma papillosa (Drury) (Hemiptera: Tessaratomidae). The population of T. papillosa on lychee trees varied from 1.43 ± 0.501 to 9.85 ± 3.924 insects per branch in this study. An increase in the temperature and a decrease in the relative humidity during summer months (April to July) favor the population buildup of T. papillosa. A forecasting model to predict T. papillosa incidences in lychee orchards was developed using the autoregressive integrated moving average (ARIMA) model of time-series analysis. The best-fit model for the T. papillosa incidence was ARIMA (1,1), where the P-value was significant at 0.01. The highest T. papillosa incidences were predicted for April in 2010, January in 2011, May in 2012, and February in 2013. A model based on time series offers longer-term forecasting. The forecasting model, ARIMA (1,1), developed in this study will predict T. papillosa incidences in advance, thus providing functional guidelines for effective planning of timely prevention and control measures.     

Frequency of Bt resistance alleles in Helicoverpa armigera in 2007-2009 in the Henan cotton growing region of China

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is a key insect pest of cotton in the Henan cotton growing region of China. In this region, cotton is grown on small acreages in rich agricultural landscapes, contrary to cropping systems in the United States or Australia. Under such cropping regimes, naturally occurring refuges (with non-Bt plants) may be sufficient to prevent H. armigera resistance development to Bt toxins. In order to gain a timely understanding of the evolution of resistance of H. armigera to Bt toxin after continuous cultivation of Bt cotton for c. 10 years, we assessed the frequency of alleles conferring resistance to Cry1Ac toxin in field populations of H. armigera sampled from Xinxiang County in Henan province during 2007-2009. Screening F₁ and F₂ generations from isofemale lines, derived from female moths trapped in the field, were used with a discriminating dose of Cry1Ac diet to estimate the frequency of resistance alleles. Totals of 625, 516 and 488 isofemale lines were screened for the F₁ generation in 2007, 2008 and 2009, respectively. Resistance gene frequency in Xinxiang fluctuated between 0.0000 and 0.0005, and it did not increase significantly from 2007 to 2009. Based on the relative average development rates (RADR) of H. armigera larvae in F₁ tests, no substantial increase in Cry1Ac tolerance was found in the Xinxiang region over the 3-yr period.     

Field assessment of novaluron for sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), management in Louisiana sugarcane

On-farm field experiments were conducted in 2004 and 2007 to assess the suitability of novaluron, a chitin synthesis inhibitor, for sugarcane borer, Diatraea saccharalis (F.), management in Louisiana sugarcane (Saccharum spp. hybrids). Aerial insecticide applications reproducing commercial production practices were made when D. saccharalis infestation levels exceeded a recommended action threshold. In addition to decreased D. saccharalis infestations, 6.3 – 14.5-fold reductions in end of season injury, expressed as the percentage of bored sugarcane internodes, were observed in plots treated with novaluron. D. saccharalis control in novaluron plots was equivalent to (P > 0.05) or better (P < 0.05) than that achieved with tebufenozide, an ecdysone agonist that has been extensively used for over a decade on sugarcane. With a numerical trend of a 3.1-fold decrease in percent bored internodes, the pyrethroid gamma-cyhalothrin seemed less effective than the biorational insecticides in protecting sugarcane against D. saccharalis. Using continuous pitfall trap sampling, no measurable (P > 0.05) decreases in predaceous and non-predaceous soil-dwelling non-target arthropods were associated with insecticides. However, numerical trends for decreases in immature crickets associated with novaluron and gamma-cyhalothrin were recorded in 2007. Our data suggest that novaluron will fit well in Louisiana sugarcane integrated pest management.     

Threshold-based interventions for cotton pest control in West Africa: What's up 10 years later?

In the late 1980s, after a long period during which insecticides were sprayed at preset dates to control cotton (Gossypium hirsutum L.) pests and their damage, some French-speaking countries in sub-Saharan areas decided to disseminate a special form of crop protection approach among smallholders, i.e. targeted staggered control (LEC, for Lutte étagée ciblée). According to this approach, decisions on some insecticide applications were made on the basis of infestation levels or the extent of crop injury caused by major pests: Aphis gossypii Glover aphids, Haritalodes (=Syllepte) derogata F., leaf-eating caterpillars, and more generally Helicoverpa armigera (Hübner), Diparopsis watersi Rothschild, Earias insulana (Boisduval) and Earias biplaga (Walker) bollworms. Polyphagotarsonemus latus (Banks) mites were sometimes included on this list. Today, the calendar-based or conventional program is still widely implemented with some changes in insecticides applied due to the development of pyrethroid resistance in H. armigera. Depending on the country, protection programs based on pest monitoring have been preserved or replaced by programs still using thresholds (staggered or true). In Benin, there are two forms of LEC tailored to two regions delineated according to the extent of damage caused by of bollworms that live inside cotton bolls, i.e. Thaumatotibia (=Cryptophlebia) leucotreta (Meyrick). The logical follow-up to LEC, involving true thresholds, was developed in Mali, Cameroon and, recently, Senegal. Cameroon opted for a sequential plan for individual decision program or LOIC (for Lutte après observation individuelle des chenilles), based on control after sequential sampling of bollworms. A calendar program with additional applications of insecticides based on a particular scouting of H. armigera was developed in Togo. In Ivory Coast, the use of true thresholds is limited to the beginning of the cotton crop cycle whereas in Burkina Faso true thresholds are used after the first two calendar sprayings. The present article describes the diversity of these cotton protection programs, sampling methods and associated intervention thresholds based on pests or injury levels in addition to the advantages and constraints associated with their adoption.     

Sudanese cotton and the whitefly: a case study of the emergence of a new primary pest

In the late 1970s the whitefly Bemisia tabaci (Gennadius) became the primary cotton pest in the Sudan, superseding the American bollworm Heliothis armigera (Hübner). DDT and a DDT/dimethoate combination were used to control the bollworm and, simultaneously, jassids and whiteflies. B. tabaci, a secondary pest at first, became resistant to dimethoate by frequent selections from 1964 onwards. At the same time, fertility stimulation occurred due to DDT residues on cotton plants. Finally, resistance reached a level so that the whitefly were not controlled by dimethoate, monocrotophos or other organophosphorus insecticides, and stimulation by DDT could exert its full effect. The consequence of this was a tremendous flare-up of the whitefly by 1980/81. This train of events was concluded from laboratory and field studies of the resistance patterns, as well as the acceleration effects from DDT residues on plants to the whitefly. A current hypothesis claiming that the problems arose from the elimination of beneficial insects through insecticide applications is reviewed in the light of experimental evidence and practical experience.     

Biorational versus conventional insecticides – Comparative field study for managing red spider mite and fruit borer on tomato

Tomato, Lycopersicum esculentum L. (Solanaceae), is an important crop worldwide that is grown both outdoors and under protected structures, for fresh market consumption and for processing. In the Mariana Islands, tomato is grown as an outdoor crop throughout the year. Tomatoes are attacked by a variety of pests, including the tomato fruitworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), and, in Pacific islands, the red spider mite Tetranychus marianae McGregor. These pests cause scarring, tissue damage, and aberrations in fruit shape or color, making the tomatoes undesirable for fresh market. Also, insect bodies, excretia or parts in fruits reduce their market suitability. Field trials aimed at improving management of these pests were undertaken at two locations in Guam (Yigo and Inarajan), USA in 2012 and 2013, assessing the efficacy of different biorational and conventional insecticides against T. marianae and H. armigera on tomato. At both locations, the mean percentage of mite-infested leaves and the population density of T. marianae were higher in control than in treated plots. An integrated pest management (IPM) program comprising sprays of selective insecticides (Petroleum spray oil, Beauveria bassiana, azadirachtin, and Bacillus thuringiensis), evaluated at 15, 30, 45 and 60 days after transplantation of tomato seedlings, significantly reduced the number of T. marianae-infested leaves and the density of T. marianae over plots treated with carbaryl, malathion, six applications of B. bassiana or B. thuringiensis and over both controls at both locations. Similarly, significantly lower fruit damage by H. armigera was recorded in the plots treated with the IPM program than in plots treated with carbaryl, malathion, or the control treatments at both locations. Marketable tomato yields from the plots which received with the IPM program were significantly greater at both locations than were those in the other treatments.     

Susceptibility of Helicoverpa armigera from different host plants in northern China to Bacillus thuringiensis toxin Cry1Ac

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is a serious pest of cotton and many other crops in northern China. To evaluate the contribution of alternative hosts as an effective refuge for transgenic cotton expressing the Bacillus thuringiensis (Bt) Cry1Ac toxin, the susceptibility to this toxin was measured in progeny derived from field-collected H. armigera larvae and pupae from different hosts in the Xiajin’s region of the Shandong Province in northern China. During 2008-2010, progeny from a total of 258,56,184 and 160 single-pair crosses derived from wheat (first-generation), Bt cotton (second-generation), Bt cotton (third-generation), and corn (third-generation) were screened on Cry1Ac diets, respectively. Based on relative average development rates (RADR) of H. armigera larvae in these F₁ tests, the second and third-generation moths emerging from Bt cotton fields were more tolerant to the Bt toxin than the first and third-generation moths emerging from wheat and corn each year. These results suggest that there is significant variation in susceptibility to Bt toxins among H. armigera populations derived from different host crops. Alternate crops, such as corn, that maintain Bt susceptible populations of H. armigera could be used as refugia to minimize the evolution of resistance to Bt cotton.     

Use of fluorescence to determine reduction in Bemisia tabaci (Hemiptera: Aleyrodidae) nymph feeding when exposed to cyantraniliprole and imidacloprid through systemic applications

The Bemisia tabaci whitefly is an important pest of many agricultural crops. Direct feeding by this pest can cause physiological plant symptoms including irregular ripening in tomatoes and silverleaf disorder in squash. In addition, B. tabaci can transmit more than 100 plant viruses that cause severe diseases that affect crop yield and quality. Insecticides are often applied to control this pest and they may be applied to the foliage and/or to the soil. Insecticides that kill quickly or cause feeding cessation reduce the damage caused by B. tabaci on the host plant most effectively. In this study fluorescence was used to assess B. tabaci feeding and to determine the effect of systemically applied insecticides on feeding by the pest. Cyantraniliprole (Verimark™) and imidacloprid (AdmirePro^®) produced a rapid reduction in B. tabaci feeding. At 24 h after a systemic application, the percentage of whitefly nymphs still feeding in plants treated with cyantraniliprole (anthranilic diamide) and imidacloprid (neonicotinoid) were 19% and 33%, respectively. Both products showed a good reduction in insect feeding and since they have different modes of action they should be considered as rotational partners for B. tabaci control in areas where there is no resistance to neonicotinoid insecticides. While the fluorescein sodium salt cannot be used to trace the uptake of insecticides, it has been shown to reliably demonstrate feeding cessation of whitefly nymphs after foliar and systemic applications of insecticides.     

An artificial neural network approach to prediction of the colorimetric values of the stripped cotton fabrics

This paper presents an artificial neural network (ANN) modeling by Levenberg-Marquardt (LM) algorithm for predicting the colorimetric values of the stripped cotton fabrics dyed using commercial reactive dyes. Achieving the expected efficiency in the application of stripping process is a very important aspect for the success of the reproduction. In the study, the predictions of L* and ΔE colorimetric values of stripped cotton samples for different stripping applications by artificial neural network are reported. We set up different network structures with different number of nodes in the hidden layer, the number of inputs and MSE of results as stopping criteria in order to get the best fitting model. According to the result of the best neural network models predicting L* and ΔE, we achieved 97 % of R for both of them. We are able to predict the L* value of the stripped samples using some working parameters as inputs with only 1.2 % error. We think that our results are very promising and the predictions of L* and ΔE values of stripped samples before applying any process are possible using the ANN model set up in the study, especially for L*.     

Relative toxicity of insecticides to the crucifer pests Plutella xylostella and Myzus persicae and their natural enemies

The widespread and intensive use of conventional pesticides, particularly insecticides, presents a major risk to natural enemies of target pests, as well as to the environment in general. The aim of this study was to investigate the differential intrinsic toxicity of insecticides to two key pests of crucifers, Plutella xylostella and Myzus persicae and their respective hymenopteran parasitoids, Cotesia vestalis and Aphidius colemani. Such knowledge can help inform effective integration of insecticides and biological control in IPM systems. Three insecticides generally regarded as being compatible with natural enemies (abamectin, spinosad and indoxacarb) and one compound regarded as harmful to natural enemies (lambda-cyhalothrin) were examined. A comparative measure of the intrinsic toxicity of fresh deposits of insecticides on Chinese cabbage leaf discs was determined for both pest and parasitoids species after exposure to insecticide for 24 h and 120 h, and after 24 h exposure to insecticide plus 96 h on untreated leaf discs. Differences in the susceptibility of pests and parasitoids to different insecticides were marked for P. xylostella and C. vestalis, LC₅₀ values being significantly lower for the pest species. Such differences were not observed for M. persicae and A. colemani. There was a direct relationship between dose, exposure time and toxicity for all insecticides tested. All insecticides tested showed lower toxicity to both parasitoids compared with P. xylostella, which suggests that for this pest species side-effects on parasitoids can be minimised through IPM practices that reduce exposure time to such non-target organisms.     

Lethal and sublethal effects of a novel cis-nitromethylene neonicotinoid insecticide,cycloxaprid, on Bemisia tabaci

The tobacco whitefly, Bemisia tabaci (Gennadius), is an important pest because of its potential to threaten agricultural crops worldwide. Currently, this pest is controlled by the application of chemical insecticides. In our pursuit to identify better insecticides for an effective control of this insect pest, we investigated the lethal effects of five neonicotinoid insecticides including four commercial neonicotinoids and a novel neonicotinoid (cycloxaprid) on B. tabaci MED and MEAM1 cryptic species. In addition, we assessed the sublethal effects of cycloxaprid on B. tabaci MED. Lethal effects of the insecticides were determined using the leaf-dip bioassay, and the results showed that among the tested insecticides cycloxaprid was more toxic to B. tabaci MED and MEAM1 than others, with LC₅₀ values of 0.70 mg/L and 0.59 mg/L, respectively. Cycloxaprid at LC₂₅ (0.16 mg/L) induced sublethal effects in adult MED by prolonging the developmental periods and decreasing the survival rates of all larval instars, pseudopupal and adult stages. Moreover, it significantly shortened the oviposition period of females and decreased their fecundity. Hatching rate of eggs laid by females exposed to LC₂₅ was also markedly reduced. These results indicate that cycloxaprid is a novel alternate insecticide that may effectively control B. tabaci populations.     

Efficacy of entomopathogenic nematodes (Nematoda: Rhabditida) and insecticide mixtures to control Spodoptera frugiperda (Smith, 1797) (Lepidoptera: Noctuidae) in corn crops

The main insect pest in Brazilian corn is fall armyworm, Spodoptera frugiperda (Smith, 1797) (Lepidoptera: Noctuidae). Entomopathogenic nematodes (EPNs) can be used to control this pest, and can be applied together with various insecticides. Thus, the objective of this work was to evaluate the efficacy of mixtures of EPNs and insecticides to control S. frugiperda in corn crops. In laboratory bioassays three species of EPNs were tested (Heterorhabditis indica, Steinernema carpocapsae and Steinernema glaseri) together with 18 registered insecticides to control S. frugiperda in corn. Efficacy of association between insecticides and EPNs on S. frugiperda larvae was evaluated against the insect's third instar, 2 and 4 days after applications in laboratory. Experiments in the field were performed in two consecutive years, with located application of H. indica and S. carpocapsae (250 IJs/cm²) mixed with chlorpyrifos (0.3 L/ha) and lufenuron (0.15 L/ha) on the corn husk. In laboratory, after two days exposure the interaction between chlorpyrifos and H. indica was synergistic, while interaction with cypermethrin, spinosad, methoxyfenozide and deltamethrin + triazofos was additive, as was interaction between lufenuron, chlorpyrifos and cypermethrin with S. carpocapsae. In contrast, the interaction between chlorpyrifos (Vexter™ and Lorsban™) and lufenuron with S. glaseri was synergistic. In the field, the best treatment was the mixture of H. indica with lufenuron (0.15 L/ha), with 62.5% and 57.5% larval mortality in the two evaluation years in the field, respectively.