Use Of Selective Insecticides Research Articles

Benefits and Perspectives of Adopting Soybean-IPM: The Success of a Brazilian Programme

Abstract Soybean, Glycine max (Fabaceae), is considered one of the world’s most important crops. Planted on millions of hectares worldwide, the management of soybean pests usually requires large amounts of chemicals. Currently, integrated pest management (IPM) is one way to protect crops through the integration of different pest control tools based on plant tolerance, adoption of economic thresholds (ETs), scouting procedures, use of selective insecticides, biological control, and other sustainable pest management tools, which helps to maintain environmental quality in an ecological and economical manner. This soybean-IPM case study in Brazil is an example of how it is possible to manage soybean fields sustainably, preserving or even increasing productivity and reducing production costs, consequently, maximizing profits. In this case, we discuss the advantages and benefits as well as possible challenges for soybean-IPM adoption. We provide examples of how to reinforce the importance of IPM by focusing on experiences from Brazil, one of the major soybean producers and exporters in the world. We analyse IPM case studies to illustrate the importance for farmers to have easy and fast access to information on medium- and long-term benefits of IPM. Overall, this case highlights both the successful achievements of the Parana State in Brazil and how important IPM is for soybean sustainability. Information © The Authors 2023

Lethal, sublethal and transgenerational effects of insecticides labeled for cotton on immature Trichogramma pretiosum

The parasitoid Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) is often released to manage lepidopteran pests in cotton crops. However, growers rely on multiple insecticide applications to manage cotton pests. A harmonious integration of control tactics is required for proper pest management, and the use of selective insecticides (i.e., those promoting effective pest control while causing little impact on natural enemies) fits within this scope. This study aimed to assess the lethal, sublethal and transgenerational effects of insecticides from varying chemical groups on T. pretiosum. The insecticides were sprayed on parasitized host [Ephestia kuehniella (Zeller), Lepidoptera: Pyralidae] eggs with developing T. pretiosum stages (egg-larva, prepupa, and pupa), and biological traits were assessed following adult emergence. Overall, pupae were more susceptible to insecticides. We found thiodicarb and chlorfenapyr to reduce F0 adult emergence in rates comparable to the positive control (methomyl). Adult F0 deformation was the highest on flupyradifurone-treated organisms, and both the F0 parasitism rate and female survival were reduced by the insecticides (except for teflubenzuron). The sex ratio (proportion female) was affected by thiodicarb and flupyradifurone. Transgenerational effects occurred on adult emergence, which was reduced on the offspring (F1) of thiodicarb, chlorfenapyr, and flupyradifurone treated T. pretiosum. In addition, thiodicarb decreased the F1 sex ratio (≤ 0.33) compared to the other compounds (sex ratio ≥ 0.45). These results indicate that teflubenzuron is the safest insecticide; the other insecticides are non-selective to T. pretiosum. Field and semifield studies are required to confirm the harmfulness of chlorfenapyr, flupyradifurone and thiodicarb toward T. pretiosum.

Effect of three pest-control management systems on abundance, species richness, and selected traits of spiders (Araneae) assemblage in apple orchard

There are various modern pest-control management systems used in the current apple production, such as integrated pest management (IPM) or organic systems. All aims to support occurrence of natural enemies that should help to reduce populations of pests. Here we investigated the effect of fungicide-treated and fungicide-free (resistant tree varieties) treatment combined with biological, IPM, and conventional systems on spiders, as the major group of natural enemies occurring on foliage of apple trees. The biological treatment was based on the use of biopesticides; IPM system was based on the use of selective insecticides, conventional included the use of broad-spectrum insecticides. Abandoned plot served as a control. The study was done for three consecutive years. Spiders were sampled from canopies by beating at weekly intervals during season. We found that fungicide-treated plots had lower abundance of spiders for two years but not species richness than fungicide-free plots. Among the three pest-control management systems, IPM and conventional supported greater spider abundance but not species richness than the biological treatment. Comparison of spider abundance before and after insecticide applications revealed that only very few pesticides, particularly the broad-spectrum ones, reduced spider numbers. In addition, we focused on the comparison of three traits (body size, maturity, fecundity) among treatments. Of six species, only Philodromus cespitum showed a smaller body size on biological than the other treatments. There were three species in which adults occurred earlier on conventional treatment than on the other treatments. Neither clutch size of Phylloneta impressa nor egg size was different among treatments. The small though significant differences in abundance, richness, and selected traits, found among IPM, conventional, and biological treatments and the control show that these pest-control management systems had similar effect on spiders. Use of IPM system combined with scab resistant apple varieties is recommended. Supplemental data for this article is available online at https://doi.org/10.1080/09670874.2021.1969471 .

Insecticide activity of botanical compounds against Spodoptera frugiperda and selectivity to the predatory bug Podisus nigrispinus

Pest control based exclusively on the use of organosynthetic insecticides can cause several problems including the reduction of populations of natural enemies. Thus, the use of selective insecticides is essential for efficient pest control. In this study, we evaluated the lethal effects of the essential oil of Lippia sidoides and its major compound thymol on the fall armyworm, Spodoptera frugiperda, as well as the selectivity and behavioral effects of these compounds on Podisus nigrispinus, an important predator of defoliating caterpillars. The botanical compounds were more selective to the predator than the insecticide deltamethrin, which was about 2.7 times more toxic to P. nigrispinus than to S. frugiperda. The insecticide deltamethrin caused rapid mortality to nymphs of P. nigrispinus with LT50 = 0.36 h. Additionally, the mortality of individuals exposed to this treatment reached 100% in less than 3 h. The essential oil (LT50 = 119 h) and the thymol (LT50 = 93 h) acted more slowly on the predator. On the contrary, for the pest, the botanical compounds acted faster than the synthetic insecticide. Nymphs exposed to deltamethrin and thymol showed behavioral changes, as there was an increase and decrease in speed and distance covered, respectively. All insects stayed longer on the untreated side of the arenas. The present study reveals the potential of the essential oil and thymol for the control of the S. frugiperda pest and, at the same time, the selectivity of these compounds over P. nigrispinus.

Do Ready-Mix Insecticides Cause Lethal and Sublethal Effects on Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) Pupa?

The use of selective insecticides aids farmers in maintaining pest populations below the economic threshold level. The integrated use of biological and chemical control is only possible if the effects of insecticides on natural enemies are studied. Although the IOBC/WPRS standards allow us to compare these studies worldwide, the methods used are sometimes inconsistent. This study determined the effects of ready-mix insecticides applied on pupae of Trichogramma pretiosum (Riley, 1879) (Hymenoptera: Trichogrammatidae) and compared the effects on emergence of two different methods of exposing T. pretiosum pupae to insecticides: immersed or sprayed using a Potter tower. Both methods gave the same results, indicating that they can be compared. Moreover, it is important to go beyond IOBC/WPRS classification and study the effects of pesticides on different biological parameters of natural enemies. This additional step may increase the likelihood of successful integration of biological and chemical control. Based on the emergence reduction, Chlorantraniliprole + lambda-cyhalothrin, abamectin + chlorantraniliprole, and alpha-cypermethrin + teflubenzuron were classified as innocuous (class 1). Cypermethrin + profenofos and cyproconazole + thiamethoxam were classified as slightly harmful (class 2). Methanol + methomyl and lufenuron + profenofos were classified as harmful (class 4). Abamectin + chlorantraniliprole, although classified as innocuous, reduced the parasitism, longevity, and flight capability of the adult parasitoids. None of these insecticides altered the emergence and sex ratio of the second generation.

Selective insecticides secure natural enemies action in cotton pest management

Cotton hosts a variety of arthropod pests requiring intensive control mostly with insecticides, which in turn may impact beneficial insects and the environment. Therefore, insect control in cotton fields preconizes the use of selective insecticides that offer pest control but conserve natural enemies. In this work, we measured the impact of recommended insecticides on the abundance of predatory insects and predation upon sentinel preys in the field. Further, the survival of four key selected predatory insects of cotton ecosystem, representing chewing and sucking feeding habits and different pest species attacked [Chrysoperla externa Hagen, Eriopis connexa (Germar), Podisus nigrispinus (Dallas) and Orius insidiosus (Say)], were assessed when exposed to the dried residues of the tested insecticides. Mortality of sentinel prey caused by natural enemies was higher in areas treated with selective insecticides relative to the non-selective ones, and most of time similar to the untreated areas. Furthermore, areas treated with non-selective insecticides experienced prolonged impact between sprays depending on the insecticide applied. Seasonal abundance of predatory insects was 2× greater in fields under selective and untreated fields compared to those under non-selective recommendation. Survival of predators exposed to the dried residues of the selective insecticides pymetrozine, chlorantraniliprole, pyriproxyfen, and cyantraniliprole were greater than when exposed to the non-selective lambda-cyhalothrin, malathion, dimethoate, and thiamethoxam. Among the non-selective insecticides, malathion and dimethoate exhibited shorter residual time compared to the thiamethoxam and lambda-cyhalothrin + thiamethoxam. Therefore, the recommendation of selective insecticides provides benefits for cotton pest management by maintaining the action of the natural enemies present in the field.

Reduction of sooty mold damage through biocontrol of the greenhouse whitefly Trialeurodes vaporariorum (Hemiptera: Aleyrodidae) using selective insecticides in tomato cultivation greenhouses

The proliferation of sooty mold on tomato fruit, Solanum lycopersicum L.—as caused by the secretion of honeydew on the fruit by greenhouse whitefly, Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae)—has recently become a serious problem in estivo-autumnal greenhouse tomato cultivation in Japan. It is becoming increasingly difficult to control T. vaporariorum using insecticides because whiteflies have developed resistance to a variety of insecticides. As the first step towards integrated pest management, we examined whether the use of selective insecticides could prompt a cascade process in which an increase in parasitoids is followed by a decrease in whitefly occurrence and then a reduction in sooty mold damage. We compared greenhouses in which nonselective insecticides effective against T. vaporariorum and its parasitoids were used (hereafter denoted “nonselective insecticide greenhouses”) with greenhouses in which selective insecticides for T. vaporariorum were used (hereafter denoted “selective insecticide greenhouses”) in terms of the density and level of parasitism of T. vaporariorum as well as the degree of damage from sooty mold. The number of parasitized whiteflies increased with the number of whiteflies in the selective insecticide greenhouses, whereas it remained at low levels regardless of the number of whiteflies in the nonselective insecticide greenhouses. Furthermore, the selective insecticide greenhouses showed significantly higher parasitism levels, fewer whiteflies, and reduced sooty mold damage compared to the nonselective insecticide greenhouses. These results suggest that the use of selective insecticides causes an increase in parasitism, which in turn suppresses the number of greenhouse whiteflies and, eventually, sooty mold.

Life-stage-dependent side effects of selected insecticides on Trichogramma cacoeciae (Marchal) (hymenoptera: Trichogrammatidae) under laboratory conditions

Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is classified as one of the most harmful pest of tomato crops. Many species of predators and parasitoids including Trichogramma cacoeciae (Marchal) (Hymenoptera: Trichogrammatidae) are noted as potential candidates used for biological control of this pest. Therefore, the use of selective insecticides is critical to conserve and protect natural enemies in the field. This study assessed the side effects of insecticides on different development stages of T. cacoeciae under laboratory conditions. For this, eleven pesticides such as: Indoxacarb, spiromesifen, cyromazin, chlorfenapyr, cypermethrin, diafenthiuron, chlorantraniliprole, spinosad, azadirachtin, Bacillus thuringiensis (Bt) and virus HaNPV were tested. This study shows that indoxacarb, spiromesifen, chlorfenapyr, cypermethrin, diafenthiuron and spinosad had a negative effect on immature stages of Trichogramma. All insecticides residues on tomato leaves were found to be toxic to Trichogramma adults except azadirachtin, Bt and virus HaNPV. Therefore, the use of the tested natural products (azadirachtin, Bt and HaNPV) at the recommended doses is viable, having no negative impact on T. cacoeciae in tomato crops.

Gut content analysis of arthropod predators of codling moth in Washington apple orchards

Codling moth, Cydia pomonella (L.), is the key pest of pome fruits in many temperate areas of North America, Eurasia, South Africa, South America and Australia. Many predatory arthropods species are found in organic apple orchards of central Washington; here we use PCR-based gut content analysis of arthropod predators to identify predators that attack codling moth. Predators were sampled from tree canopies, tree trunks and from the understory and were homogenized in a lysis buffer to provide a template for Direct PCR. PCR showed 8.9% of 2591 predators had preyed on C. pomonella. Spiders, including 25 genera from 15 families, two carabid beetle species (Pterostichus melanarius (Illiger) and Harpalus pennsylvanicus DeGeer) and the European earwig (Forficula auricularia [L.]) represented 87% of predator specimens analyzed and were 8.2%, 8.3% and 14.7% positive for C. pomonella. PCR products from 38% of predators that appeared positive for C. pomonella COI were sequenced; all showed 99% or more similarity to C. pomonella COI sequences in GenBank. Digestion rates of adult earwigs fed on mature codling moth larvae showed a detection half-life of 3.7days; half-life from the fecal pellets from the same earwigs was 3.6days. When fed mature codling moth larvae, the carabid P. melanarius showed a digestion half-life of 3.14days. Identification of the key predators of C. pomonella can guide the use of selective insecticides and the conservation of these natural enemies, enhancing biological control and supporting stable IPM programs in pome fruit orchards in the western USA.

Incidence of non-target pest species and validation of IPM strategies in Bt cotton hybrids deployed with different events of cry genes

Cotton cultivars incorporated with different events of Cry proteins were evaluated for the incidence of sucking insect pests and abundance of predators under unprotected conditions during the years, 2009 and 2010. Among the sucking pests, whitefly, leafhopper and thrip were the major pests and there was no difference in the abundance of sucking pests among different hybrids. An integrated pest management (IPM) module based on use of eco-friendly strategies was developed and evaluated for transgenic cotton cultivars carrying different events including non-Bt cotton during 2010 and 2011 and was compared with the recommended regional package of practices (RPP) involving use of selective insecticides for sucking insect pests and bollworms. Results indicated low population of leafhopper, thrips and whitefly in IPM as compared to RPP. In addition, the cotton hybrids managed by IPM practices supported higher abundance of natural enemies. The incidence of cotton leaf curl disease (CLCuD) was also less in IPM as compared to RPP module. No bollworm incidence was recorded in any of transgenic cotton hybrid in either of the modules; however IPM and RPP with non-Bt hybrid showed rosette flowers and green boll damage due to pink bollworm, which was less in IPM as compared to RPP. IPM module resulted in low cost of insecticidal sprays and increase in C: B ratio compared to RPP. Furthermore, as the hybrids carrying different events did not differ significantly for the incidence of sucking pests, the IPM module developed was found effective for all hybrids including non Bt cotton hybrid with some revision in the light of bollworm incidence.

Compatibility of flonicamid and a formulated mixture of pyrethrins and azadirachtin with predators for soybean aphid (Hemiptera: Aphididae) management

The invasive soybean aphid, Aphis glycines Matsumura, is an important pest in North American soybean production. Predators can play an important role in suppressing A. glycines. However, current A. glycines management practices rely primarily on broad-spectrum insecticides, which can adversely affect natural enemy populations. An alternative is the use of selective insecticides that control the targeted pest species, while having a reduced impact on natural enemies. In greenhouse and laboratory assays, we tested the effects of lambda-cyhalothrin, two rates of flonicamid, which is currently not registered for use in soybean, and a formulated mixture of pyrthrins and azadirachtin on A. glycines and its natural enemies, Chrysoperla rufilabris (Burmeister), Orius insidiosus (Say) and Hippodamia convergens (Guerin-Meneville). All insecticides significantly reduced A. glycines populations. Lambda-cyhalothrin was highly toxic to the natural enemies tested. Flonicamid showed the lowest toxicity to natural enemies, but the high rate did decrease survival of O. insidiosus. The mixture of pyrethrins and azadirachtin was toxic to larvae of C. rufilabris and adult O. insidiosus. Moreover, the mixture of pyrethrins and azadirachtin increased the developmental time of C. rufilabris. These results indicate potential for flonicamid and the mixture of pyrethrins and azadirachtin to increase compatibility between chemical and biological controls.

Sequence Analysis of Insecticide Action and Detoxification-Related Genes in the Insect Pest Natural Enemy Pardosa pseudoannulata.

The pond wolf spider Pardosa pseudoannulata, an important natural predatory enemy of rice planthoppers, is found widely distributed in paddy fields. However, data on the genes involved in insecticide action, detoxification, and response are very limited for P. pseudoannulata, which inhibits the development and appropriate use of selective insecticides to control insect pests on rice. We used transcriptome construction from adult spider cephalothoraxes to analyze and manually identify genes enconding metabolic enzymes and target receptors related to insecticide action and detoxification, including 90 cytochrome P450s, 14 glutathione S-transferases (GSTs), 17 acetylcholinesterases (AChEs), 17 nicotinic acetylcholine receptors (nAChRs), and 17 gamma-aminobutyric acid (GABA) receptors, as well as 12 glutamate-gated chloride channel (GluCl) unigenes. Sequence alignment and phylogenetic analysis revealed the different subclassifications of P450s and GSTs, some important sequence diversities in nAChRs and GABA receptors, polymorphism in AChEs, and high similarities in GluCls. For P450s in P. pseudoannulata, the number of unigenes belonging to the CYP2 clade was much higher than that in CYP3 and CYP4 clades. The results differed from insects in which most P450 genes were in CYP3 and CYP4 clades. For GSTs, most unigenes belonged to the delta and sigma classes, and no epsilon GST class gene was found, which differed from the findings for insects and acarina. Our results will be useful for studies on insecticide action, selectivity, and detoxification in the spider and other related animals, and the sequence differences in target genes between the spider and insects will provide important information for the design of selective insecticides.

Development of Action Thresholds for Management of Bactericera cockerelli and Zebra Chip Disease in Potatoes at Pukekohe, New Zealand

Bactericera cockerelli (tomato potato psyllid, TPP) is a serious pest of potato crops, causing feeding damage and also vectoring Candidatus Liberibacter solanacearum, the causal agent of the Zebra Chip (ZC) disease in potatoes. The results of 6 years of early and main crop potato trials at Pukekohe, New Zealand, are summarised and damage caused by TPP is reported. Results show that spring-sown (early) potato crops do not require insecticides. In main crop summer trials we tested action thresholds based on 10 and 20 TPP nymphs per 100 middle leaves but the incidence of ZC damage was commercially unacceptable, ranging from 4 to 9 %. Subsequently we tested an action threshold of >3 TPP adults per yellow sticky trap per week that led to ZC damage ranging from 0.9 to 1.6 %. We also compared monitoring of TPP using sticky trap catches with a degree day model started in mid winter (1 July) for forecasting generation times of TPP. On the basis of the field trial results, we recommend that from early summer onwards, the timing of the first foliar application of insecticide needs to be applied early enough to protect main crop potatoes from the first generation of TPP that occurs after potato tubers have emerged (at Pukekohe, this is the third TPP generation from 1 July when using degree day modelling). Three years of main crop trials indicate that an action threshold of >3 TPP per trap per week provides effective TPP/ZC management in the Pukekohe region when used in conjunction with natural enemies and an insecticide programme that features the use of selective insecticides.

Toxicity of spinosad on common green lacewing Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae) larvae via ingestion technique under laboratory conditions

The use of selective insecticides could improve conservation of natural enemies and therefore contribute to the success of integrated pest management programmes. In this study, the toxicity of one selective insecticide, spinosad to common green lacewing Chrysoperla carnea (Stephens) was evaluated. Several stages of C. carnea larvae were exposed to spinosad via ingestion technique under laboratory conditions. The used quantities of spinosad were less than the maximum recommended rate given on the product label. In ingestion bioassay tests, a direct relationship was detected between the concentration of spinosad and mortality rate of first instar larvae. So that, the applied of 250 and 2500 ppm of spinosad caused 35 and 90% mortality, respectively. Mortality rate was recorded 1–3 days of post treatment. An implementation of 250 ppm of spinosad on second and third instar larvae showed negligible mortality rate after 3 days, whereas the first instars larvae suffered 35% mortality. On the basis of collected data we could conclude that spinosad is not merited to be considered to have an environmental safety profile on C. carnea similar to well-established conventional biological insecticides.

Mitigating the effects of insecticides on arthropod biological control at field and landscape scales

Integrated pest management (IPM) programs emphasize the combination of tactics, such as chemical and biological control, to maintain pest populations below economic thresholds. Although combining tactics may provide better long-term sustainable pest suppression than one tactic alone, in many cases, insecticides and natural enemies are incompatible. Insecticides can disrupt natural enemies through lethal and sub-lethal means causing pest resurgence or secondary pest outbreaks. Legislative actions such as the Food Quality Protection Act (US) and the Directive on Sustainable Use of Pesticides (EU) have placed greater restrictions on insecticides used in agriculture, potentially enhancing biological control. Here we focus on the effects of insecticides on biological control, and potential mitigation measures that can operate at different scales. At the farm scale, natural enemies can be conserved through the use of selective insecticides, low doses, special formulations, creation of refugia, special application methods, and targeted applications (temporal or spatial). At the landscape scale, habitat quality and composition affect the magnitude of biological control services, and the degree of mitigation against the effects of pesticides on natural enemies. Current research is teasing apart the relative importance of local and landscape effects of pesticides on natural enemies and the ecosystem services they provide, and the further development of this area will ultimately inform the decisions of policy makers and land managers in terms of how to mitigate pesticide effects through habitat manipulation.

The Importance and Management Option of Onion thrips, Thrips tabaci (L.) (Thysanoptera: Thripidae) in Ethiopia: A Review

Thrips attack a number of vegetable crops particularly onion thrips causing considerable economic damage on onion crops. Usually young leaves are preferred, but buds and flowers also get infested. Under severe infested conditions the leaves shed and hence plant growth is affected and their control is vital to the production and profitability of onion crop. Most onion fields need protection against onion thrips for two to three months depends on the varieties. If onion thrips are not controlled, damage can routinely reduce bulb yields. In addition to use integrated pest management, use of selective insecticides in rotation to be the most important tools for thrips control, but there are few labeled insecticides that registered in Ethiopia provide effective and consistent control. Therefore, the objective of this review was undertaken to evaluate previous work in the management of onion thrips.

The Response of Natural Enemies to Selective Insecticides Applied to Soybean

Natural enemies of the invasive pest Aphis glycines Matsumura can prevent its establishment and population growth. However, current A. glycines management practices include the application of broad-spectrum insecticides that affect pests and natural enemies that are present in the field at the time of application. An alternative is the use of selective insecticides that affect the targeted pest species, although having a reduced impact on the natural enemies. We tested the effects of esfenvalerate, spirotetramat, imidacloprid, and a combination of spirotetramat and imidacloprid on the natural enemies in soybean during the 2009 and 2010 field season. The natural enemy community that was tested differed significantly between 2009 and 2010 (F = 87.41; df = 1, 598; P < 0.0001). The most abundant natural enemy in 2009 was Harmonia axyridis (Pallas) (56.0%) and in 2010 was Orius insidiosus (Say) (41.0%). During 2009, the abundance of natural enemies did not vary between the broad-spectrum and selective insecticides; however, the abundance of natural enemies was reduced by all insecticide treatments when compared with the untreated control. In 2010, the selective insecticide imidacloprid had more natural enemies than the broad-spectrum insecticide. Although we did not observe a difference in the abundance of the total natural enemy community in 2009, we did observe more H. axyridis in plots treated with spirotetramat. In 2010, we observed more O. insidiosus in plots treated with imidacloprid. We suggest a couple of mechanisms to explain how the varying insecticides have different impacts on separate components of the natural enemy community.

Side effects of selected insecticides on the Tuta absoluta (Lepidoptera: Gelechiidae) predators Macrolophus pygmaeus and Nesidiocoris tenuis (Hemiptera: Miridae)

Tuta absoluta is a pest native to South America that produces significant damage to tomato crops and was first detected in Europe in late 2006. Data obtained during 2008 from commercial tomato crops in which IPM was applied suggested that good pest control was possible through the combined action of the predatory mirid bugs Macrolophus pygmaeus and Nesidiocoris tenuis and the use of selective insecticides. The aim of our study was to evaluate the lethal and sublethal side effects of three of the insecticides most widely used to control T. absoluta on these predators: azadirachtin, spinosad and indoxacarb. Seven days after applying the treatment at the maximum recommended field rates, the mortality produced by indoxacarb ranged from 28% for nymphs of M. pygmaeus to 77% for females of N. tenuis and were significantly higher than those produced by azadirachtin, spinosad and the control (<13%). However, indoxacarb did not affect the number of descendants of females exposed to residues during the last days of their preimaginal development. In contrast, spinosad significantly reduced the offspring of M. pygmaeus and azadirachtin significantly reduced the offspring of N. tenuis females. The sublethal effects of azadirachtin and spinosad on predator reproduction should therefore not be ignored. This information could be useful when selecting the most appropriate insecticide to control T. absoluta in greenhouses and field crops in which M. pygmaeus and N. tenuis are used as biological control agents.

Susceptibility of cocooned pupae and adults of the parasitoid Microplitis mediator to selected insecticides

The braconid parasitoid Microplitis mediator (Haliday) is a key natural enemy of the cabbage moth, Mamestra brassicae (L.), in Europe. In the context of an Integrated Pest Management approach, the use of selective insecticides is essential for the conservation of naturally occurring beneficial arthropods. The present laboratory study investigated the side effects of six insecticides applied at recommended field rates on adults and cocooned pupae of M. mediator. Male and female parasitoids were paired in drum cells contaminated with dry residues of insecticides. Besides lethal effects after 24 h, parasitization capacity and longevity of the surviving parasitoids was evaluated. Lethal effects on cocooned pupae were also investigated by assessing adult emergence from treated cocoons. Pirimicarb caused 100% adult mortality after 24 h, whereas the other tested insecticides caused no direct toxic effects. However, sub-lethal effects in terms of reduced parasitization activity, percentage of parasitism or female longevity were found for flonicamid, pymetrozine, spinosad and thiacloprid. Spirotetramat shortened only male longevity. Adult emergence from treated cocoons was reduced only by flonicamid and pymetrozine.

Feeding behaviour of the greenbug Schizaphis graminum on wheat plants treated with imidacloprid and/or silicon

AbstractThe greenbug Schizaphis graminum (Rond.) (Hemiptera: Aphididae) is one of the principal pests of Triticum aestivum L. and may be responsible for the injection of toxins, the transmission of viral infections and, ultimately, plant death. The aphid can be controlled by the use of selective insecticides or with the application of silicon. The objective of the present study was to investigate the influence of imidacloprid and silicon on the feeding behaviour of S. graminum on wheat plants. Aphids collected from and reared on sorghum plants were maintained in a growth room at 25 ± 2°C; 12 h photoperiod. Seeds of the wheat cultivar EMBRAPA 22 were planted in plastic pots containing a commercially available soil substrate and thinned out 8 days after sowing to leave two vigorously growing seedlings in each pot. Four treatments (each replicated 25 times) were applied: (i) seeds were treated with imidacloprid (36 g/100 kg) 1 day prior to sowing; (ii) silicon (50 ml of 1% silicic acid; equivalent to a dose of 1000 kg of silicon/ha) was applied directly to the substrate 10 days after plant emergence; (iii) the described treatments with imidacloprid and silicon were applied jointly; and (iv) neither seeds nor substrate were treated (untreated controls). Electrical penetration graph assays were performed 15, 30 and 45 days after plant emergence. The results showed that wheat seed treatment with imidacloprid and/or the application of silicon to the substrate reduced both the feeding time of S. graminum and the percentage of insects that fed on phloem sap. Moreover, this study provides further support that the action of silicon may not be restricted to physical resistance (constitutive or induced) but may also involve induced plant chemical defence.