Toxicity of Insecticides Targeting Rice Planthoppers to Adult and Immature Stages of Trichogramma chilonis (Hymenoptera: Trichogrammatidae)

Sublethal effects of nitenpyram on the development of silkworm

The utilization of nitenpyram for aphid and whitefly control may induce environmental contamination and negative repercussions on non-target organisms. Formerly, we found that nitenpyram would pollute the peripheral and sub-peripheral areas of the adjacent mulberry orchard. Under acute toxicity conditions, nitenpyram induced oxidative damage in silkworms, affected biological metabolism, synthesis, immunity, and signal transduction. Considering the impact of nitenpyram mist drift on mulberry leaves, we investigated the effects of low concentrations of nitenpyram on silkworms. The results showed that silkworms exposed to 0.17 mg/L, 0.35 mg/L and 0.70 mg/L of nitenpyram (1/40 LC50, 1/20 LC50 and 1/10 LC50) showed obvious poisoning symptoms. The cocoon weight and cocoon shell weight decreased gradually with increases in the concentration, and these decreases prolonged the growth and development time of silkworms and induced the detoxification enzymes carboxylesterase (CarE) and glutathione-S-transferase (GST) to cope with the stress damage caused by nitenpyram. Exposure to low concentrations of nitenpyram downregulates genes involved in the drug metabolism-other enzymes and peroxisome pathway in silkworms. Additionally, through injection of miRNA mimics and inhibitors, we discovered that detoxifying enzyme pathway genes are influenced by bmo-miR-3382-3P, bmo-miR-3213-5P and bmo-miR-133, regulating the immune response of silkworms. This study provides an overall view of the toxicity and detoxification metabolism of nitenpyram in silkworm, and provides a reference for environmental assessment.

Impact of Chemical Insecticide Application on Beneficial Insects in Maize

The European corn borer (ECB) (Ostrinia nubilalis Hübner) and to a lesser extent the western corn rootworm (Diabrotica virgifera virgifera LeConte) are a threat to maize in the Po Valley (Northern Italy), and their control can require insecticide applications. The results of a study to evaluate the effects of insecticide sprays on the beneficial insect Trichogramma brassicae (Hymenoptera: Trichogrammatidae) and aphid predators are reported. A three-year research project was carried out in two Study Areas, in Lombardy. In area 1, crop rotation was a common practice, while in area 2 repeated maize crop was practiced. The natural trend of ECB egg masses attacked by T. brassicae was affected and parasitism rates were reduced as a result of insecticide exposure (chlorpyriphos methyl, cypermethrin, alphacypermethrine). Repeated maize crop and insecticides spraying increased the abundance of the aphid population and negatively affected the aphid predator community, which mainly included ladybirds, hoverflies, true bugs and lacewings. The predator community was dominated by hoverflies in sprayed fields managed according to repeated maize crop protocols, whereas ladybirds and Orius spp. dominated in maize fields managed according to crop rotation protocols. Crop rotation protocols help to prevent ECB outbreaks; when the risk of exceeding the economic threshold limit is high, and this may be the case when maize is cultivated for seeds or for horticultural crops such as sweet corn, inundative release of T. brassicae and/or microbial control (i.e., use of Bacillus thuringiensis preparations) can integrate natural biocontrol, and provide a valuable alternative to chemical insecticides.

Efficacy and toxicity of different plant extracts over the period of time in Bracon hebetor (Say) (Hymenoptera: Braconidae)

Bracon hebetor (Say) is an important parasitoid and played a suitable model role for bio control programs. Pest management through biocontrol approaches such as plant extracts is an ecologically responsive and enthusiastic means of reducing insect pests. The main objective of the present research was to discover the efficiency and susceptibility periods of plant extracts for the assessment of parasitoids. The toxicity of five plants (Cymbopogon nardus, Azadirachta indica, Syzygium aromaticum, Datura stramonium and Parthenium hysterophorus) extracts were evaluated against B. hebetor to detect the possible way forward to controlling insect pests along with the adverse effects on beneficial insects. The data was recorded regarding mortality of B. hebetor, after calculated time periods with different intervals of up to 2 days. Datasets were followed by a statistical probe which exhibited significant results. The extracts of C. nardus, A. indica, S. aromaticum and D. stramonium exhibited non-toxic effects, whereas P. hysterophorus indicated low toxicity annotations against investigated parasitoid. These investigations suggested that four plants examined are not hazardous to the parasitoids whereas P. hysterophorus somehow has detrimental effects at low toxicity levels. Further development of insecticide resistance mechanisms in the parasitoid favors the enhancement of parasitoid efficacy with plant extracts. The possible selective use of these plant extracts and their effects on the safety period of parasitoids for integration with other approaches in sustainable pest management programs is discussed.

Exposure to flupyradifurone affect health of biocontrol parasitoid Binodoxys communis (Hymenoptera: Braconidae) via disrupting detoxification metabolism and lipid synthesis

Assessing the potential effects of insecticides on beneficial biological control agents is key to facilitating the success of integrated pest management (IPM) approaches. Flupyradifurone (FPF) is a novel neonicotinoid insecticide that is replacing traditional neonicotinoids over a large geographical range to control pests. Binodoxys communis, is the dominant parasitic natural enemy of aphids. To date, no reports have addressed sublethal effects of FPF on B. communis. In this study, the lethal and sublethal effects of FPF on B. communis were investigated by indirect exposure to larvae and direct exposure to adults. Results showed that the sublethal LC₁₀ and LC₂₅ of FPF had negative effects on the biological parameters of B. communis, including significantly reducing survival rate, adult longevity, parasitism rate, and emergence rate, and significantly prolonging the developmental stages from egg to cocoons. In addition, we observed a transgenerational effect of FPF on the next generation (F1). RNA-Seq transcriptomic analysis identified a total of 1429 differentially expressed genes (DEGs) that were significantly changed between FPF-treated and control groups. These DEGs are mainly enriched in metabolic pathways such as peroxisomes, glutamate metabolism, carbon metabolism, fatty acid metabolism, and amino acid metabolism. This report is the first comprehensive evaluation of how FPF effects B. communis, which adds to the methods of assessing pesticide exposure in parasitic natural enemies. We speculate that the significant changes in pathways, especially those related to lipid synthesis, may be the reason for weakened parasitoid biocontrol ability. The present study provides new evidence for the toxic effects and environmental residue risk of FPF.

Toxicity of nitenpyram to silkworm (Bombyx mori L.) and its potential mechanisms

Silkworm (Bombyx mori L.), as an economic insect, occupies a certain position in the development of China's economy. The neonicotinoid insecticide nitenpyram is commonly used in farmland to control planthoppers and aphids. In China, mulberry orchards are often planted adjacent to fields or commercial crops, and mist drifts occur during application, which may affect the production safety of Bombyx mori. In this study, a risk assessment of nitenpyram was carried out, and the results showed that there were risks in spraying nitenpyram around the periphery and subperipheries of mulberry fields. However, few studies have reported the mechanism underlying nitenpyram's toxic effect on silkworms. Here, we validated 25 differentially expressed (DE) miRNAs in the nitenpyram treatment group of silkworms, and the significantly enriched mTOR signaling pathway, oxidative phosphorylation and FoxO signaling pathway were verified. Among them, bmo-miR-2766-5P was up-regulated by 2.122-fold, and the expression of its regulated target gene 101,741,287 was up-regulated. After the injection of bmo-miR-2766-5P inhibitor, the Log₂FC value of 101,741,287 was changed from 1.26 to -2.19. Bmo-miR-3326, bmo-miR-3378-5P and bmo-miR-2761-3P were down-regulated by 2.386-fold, 1.158-fold and 2.359-fold, respectively. After injecting miRNA mimics into silkworms, the Log₂FC values of the target genes 100,302,609, 101,740,730 and 101,746,319 were changed from 1.24 to -11.94, -1.12 changed to 2.84 and 1.93 changed to -0.37, respectively. In addition, nitenpyram induced oxidative damage in silkworms, and the degree of DNA damage increased with the increase of concentration and time. Meanwhile Imd was significantly up-regulated in IMD-related pathways (38.7-fold, p < 0.01). The results indicated that nitenpyram could affect the growth and development process of silkworms, and these DE-miRNAs may have an important impact on the stress response of silkworms to nitenpyram.

Toxicity of chemical pesticides commonly used in maize to Trichogramma ostriniae (Hymenoptera: Trichogrammatidae), an egg parasitoid of Asian corn borer

Chemical pesticides are largely applied worldwide for the control of agricultural pests, and often cause lethal and sublethal side effects on natural enemies. To determine the compatibility of chemical pesticides, commonly used by maize growers, with Trichogramma ostriniae, the toxicities of four herbicides (pendimethalin, topramezone, glyphosate, and atrazine), three insecticides (imidacloprid, emamectin benzoate, and ethiofencarb), and three fungicides (propiconazole, benzoyl cyclazole, and difenoconazole) were tested under laboratory conditions, measuring residual toxicity to T. ostriniae adults, their lethal effects on the parasitoid's eggs inside the host egg, and on the reproduction of the parasitoid's female offspring. Three tested pesticides including ethiofencarb, glyphosate, and benzoyl cyclazole were slightly harmful to T. ostriniae adults, whereas the other seven pesticides were moderately harmful. The pesticide residues of ethiofencarb, and emamectin benzoate, showed slightly persistence of toxicity to T. ostriniae adults, in contrast to the remaining pesticides. Glyphosate, emamectin benzoate, imidacloprid, ethiofencarb, and propiconazole were classified as harmless, causing < 30% reduction in emergence rate of wasps from host eggs, while atrazine, pendimethalin, topramezone, benzoyl cyclazole, and difenoconazole were classified as slightly harmful, causing 31-52% reduction in parasitoid emergence rates. Furthermore, the number of eggs subsequently laid by T. ostriniae females that had emerged from parasitized host eggs treated with atrazine was significantly reduced compared to which of untreated parasitized host eggs. No negative effects were observed with atrazine treatment on the emergence rates of F₁ wasps, their wing deformity rates and sex ratios. The data presented here indicate that the safety interval between pesticide applications and releases of T. ostriniae wasps is 2-3 weeks, which provide valuable information in designing a sound maize integrated pest management program that combines chemical pesticide applications with augmentative releases of T. ostriniae wasps.

The Mechanism of Chlorantraniliprole Resistance and Detoxification in Trichogramma chilonis (Hymenoptera: Trichogrammatidae)

Parasitic Trichogramma chilonis Ishii, an egg parasitoid of Grapholita molesta, is a critical agent for biological control of insect pests in crop plants. However, the efficiency of T. chilonis is influenced by its resistance to the common pesticide chlorantraniliprole. To elucidate the chlorantraniliprole detoxification mechanism, differentially expressed genes (DEGs) related to chlorantraniliprole resistance were studied at different developmental stages of the wasp. Individuals of T. chilonis were grouped and treated with chlorantraniliprole at different developmental stages. Untreated wasps were used as controls. Transcriptomic analysis identified the DEGs associated with chlorantraniliprole resistance and detoxification in T. chilonis. A total of 1,483 DEGs were associated with chlorantraniliprole resistance at all developmental stages. DEGs that correlated with chlorantraniliprole sensitivity of T. chilonis at different developmental stages were distinct and had various functions. The newly identified DEGs are involved in cytochrome P450- and glutathione metabolism-related pathways, which were predicted to contribute to chlorantraniliprole detoxification. Chlorantraniliprole detoxification by T. chilonis was associated with cytochrome P450- and glutathione-related pathways. Our findings may be useful for balancing chemical and biological control practices aimed to optimize agricultural production.

Resistance of Lepidopteran Egg Parasitoids, Trichogramma japonicum and Trichogramma chilonis, to Insecticides Used for Control of Rice Planthoppers

Trichogramma wasps are commonly used as biocontrol agents to manage lepidopteran rice pests in rice fields. However, lepidopteran pests synergistically occur with rice planthoppers which are not targeted by Trichogramma. The use of Trichogramma parasitoids in field-based pest control efforts is greatly affected by the application of insecticides targeting planthoppers. As such, insecticide-resistant strains of Trichogramma are urgently needed for the incorporation of these beneficial natural enemies into integrated pest management programs in rice agroecosystems. In the present study, Trichogramma japonicum Ahmead (Hymenoptera: Trichogrammitidae) and Trichogramma chilonis Ishii (Hymenoptera: Trichogrammitidae) were treated with sublethal doses of four insecticides which target rice planthoppers, to generate tolerant strains in the laboratory. The resistance rate of T. japonicum to imidacloprid was the highest (17.8-folds) after 10 successive treatments and experienced 2.5, 4.72, and 7.41-fold increases in tolerance to thiamethoxam, buprofezin, and nitenpyram, respectively. Tolerance of T. chilonis to imidacloprid, thiamethoxam, buprofezin, and nitenpyram were 8.8, 6.9, 4.43, and 5.67-fold greater, respectively. The emergence and deformity (without spreading wings or short wings) rates of T. japonicum and T. chilonis gradually recovered with an increased exposure time of treatments. The fecundity of T. japonicum treated with thiamethoxam was significantly higher than that of the control and T. chilonis treated with thiamethoxam and nitenpyra. Our results demonstrate that screening for insecticide-tolerant/resistant Trichogramma strains was feasible, especially in the pairing of T. japonicum and imidacloprid, which could provide a valuable biological control tool that can be combined with traditional chemical control strategies for use in IPM of rice agroecosystems.

Compatibility of Insecticides with Rice Resistance to Planthoppers as Influenced by the Timing and Frequency of Applications

Simple Summary

The brown planthopper, Nilaparvata lugens (Stål)(BPH) is a pest of rice in Asia. Varietal resistance is proposed as an alternative to insecticides that reduces BPH densities. However, in practice, resistance is often combined with insecticide use. We examined the effects of combining seven insecticides with resistance. We applied insecticides as one, two or three applications (experiment 1), or as early or late applications (experiment 2) to resistant (IR62) and susceptible (IR64) rice in a screenhouse environment. Carbofuran and fipronil reduced BPH biomass density. Single applications of cartap hydrochloride, cypermethrin, or buprofezin reduced BPH biomass densities on IR62, but not on IR64 (i.e., synergies); however, the effects were weak and multiple applications of all insecticides (≥2) eliminated synergies. Multiple applications of deltamethrin were antagonistic to resistance as indicated by higher densities of planthoppers on treated IR62 than on treated IR64. In non-infested plants from experiment 2, late applications reduced rice yields compared to early applications. Results suggest that early applications of some insecticides risk enhancing BPH densities, whereas late applications risk reducing rice yields. To avoid negative effects, applications should be made in compliance with Integrated Pest Management principals and multiple insecticide applications to BPH resistant rice should be avoided.

Abstract

The brown planthopper, Nilaparvata lugens (Stål)(BPH) is a pest of rice in Asia. We examined the effects of seven insecticides combined with host resistance against BPH. In a screenhouse environment, we treated BPH-infested and non-infested resistant (IR62) and susceptible (IR64) rice with buprofezin, carbofuran, cartap hydrochloride, cypermethrin, deltamethrin, fipronil, or thiamethoxam + chlorantraniliprole. In one experiment, plants received one, two or three applications. In a second experiment, plants received one early or late insecticide application. Carbofuran and fipronil reduced planthopper biomass densities but resistance did not contribute to these effects (i.e., resistance was redundant). Single applications of cartap hydrochloride (at 20 or 50 days after sowing (DAS)), cypermethrin (20 DAS), or buprofezin (50 DAS) reduced BPH biomass densities on IR62 (i.e., synergies); other insecticides and application times, and multiple applications of all insecticides did not reduce BPH biomass densities on IR62 more than on IR64 (i.e., either resistance or insecticides were redundant). Deltamethrin (three applications) was antagonistic to resistance, but host resistance tended to buffer against the negative effects of single deltamethrin applications. Yields of infested IR62 were not statistically improved by insecticide applications. Late applications reduced yields of non-infested rice. We discuss how prophylactic insecticide applications could destabilize BPH populations and reduce the productivity and profitability of resistant rice.

Genome-Wide Identification and Analysis of Nilaparvata lugens microRNAs during Challenge with the Entomopathogenic Fungus Metarhizium anisopliae

The resistance of the notorious rice pest Nilaparvata lugens to many insecticides has caused significant concerns. Our previous study demonstrated that the fungus Metarhizium anisopliae CQMa421 shows great potential for the control of this pest, but the interactions between them are still unclear. Thus, we further investigated fungal infection-related microRNAs (miRNAs) in N. lugens during M. anisopliae CQMa421 challenge using Illumina sequencing. In this study, we constructed twenty-four small RNA libraries over different time courses (i.e., 4 h, 8 h, 16 h, and 24 h). A total of 478.62 M clean reads were collected, with each sample producing more than 13.37 M reads, after the removal of low-quality reads. We identified 2324 miRNAs and their 11,076 target genes within the twenty-four libraries by bioinformatics analysis. Differentially expressed miRNAs (DEmiRNAs), including 58 (32 upregulated vs. 26 downregulated), 62 (30 upregulated vs. 32 downregulated), 126 (71 upregulated vs. 55 downregulated), and 109 (40 upregulated vs. 69 downregulated) DEmiRNAs were identified at 4 h, 8 h, 16 h, and 24 h post-infection, respectively. We further conducted Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis to predict the functions of all target genes of DEmiRNAs. These DEmiRNAs targets identified during 24 h of infection were primarily involved in energy metabolism, lysine degradation, the FoxO signaling pathway, ubiquitin-mediated proteolysis, the mRNA surveillance pathway, and the MAPK signaling pathway. Taken together, our results provide essential information for further study of the interactions between the entomopathogenic fungus M. anisopliae and N. lugens at the posttranscriptional level.

An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 2: impacts on organisms and ecosystems

New information on the lethal and sublethal effects of neonicotinoids and fipronil on organisms is presented in this review, complementing the previous Worldwide Integrated Assessment (WIA) in 2015. The high toxicity of these systemic insecticides to invertebrates has been confirmed and expanded to include more species and compounds. Most of the recent research has focused on bees and the sublethal and ecological impacts these insecticides have on pollinators. Toxic effects on other invertebrate taxa also covered predatory and parasitoid natural enemies and aquatic arthropods. Little new information has been gathered on soil organisms. The impact on marine and coastal ecosystems is still largely uncharted. The chronic lethality of neonicotinoids to insects and crustaceans, and the strengthened evidence that these chemicals also impair the immune system and reproduction, highlights the dangers of this particular insecticidal class (neonicotinoids and fipronil), with the potential to greatly decrease populations of arthropods in both terrestrial and aquatic environments. Sublethal effects on fish, reptiles, frogs, birds, and mammals are also reported, showing a better understanding of the mechanisms of toxicity of these insecticides in vertebrates and their deleterious impacts on growth, reproduction, and neurobehaviour of most of the species tested. This review concludes with a summary of impacts on the ecosystem services and functioning, particularly on pollination, soil biota, and aquatic invertebrate communities, thus reinforcing the previous WIA conclusions (van der Sluijs et al. 2015).

Comparative ecotoxicity of neonicotinoid insecticides to three species of Trichogramma parasitoid wasps (Hymenoptera: Trichogrammatidae)

Compatibility of neonicotinoid insecticides with the natural enemies has been concerned for decades. This study aims to evaluate and compare the acute and sublethal toxicity effects of neonicotinoid insecticides on three species of Trichogramma parasitoid wasps (i.e. Trichogramma dendrolimi, T. ostriniae and T. confusum) with broad distribution and great relevance to integrated pest management (IPM) strategies. A residual contact bioassay demonstrated that nitenpyram had the greatest intrinsic toxicity to T. dendrolimi and T. ostriniae with LC₅₀ values of 0.060 (0.056-0.065) and 0.066 (0.050-0.087) mg a.i. L^-1, respectively. But for T. confusum, the most toxic neonicotinoid insecticide is dinotefuran with a LC₅₀ value of 0.065 (0.055-0.078) mg a.i. L^-1. Furthermore, based on the risk quotient estimation, acetamiprid was considered to be the only safe neonicotinoid insecticide (Class 1, RQ＜50). A dipped egg contact bioassay showed that neonicotinoid insecticides induced significant toxic effects on the parasitism of three Trichogramma spp. at low-lethal concentrations. Additionally, emergence probability of the unexposed offspring was also significantly reduced by neonicotinoids. According to the estimated EC₅₀ values, acetamiprid possessed the least toxicity to the parasitism and emergence of T. dendrolimi and T. ostriniae, and for T. confusum, the least toxic neonicotinoid insecticide was thiacloprid. Overall, among the test neonicotinoid insecticides, acetamiprid and thiacloprid may exhibit the less ecotoxicity to the test Trichogramma species.

Comparative susceptibility of thirteen selected pesticides to three different insect egg parasitoid Trichogramma species

The parasitoid Trichogramma species are indispensable natural enemies of many lepidopterans and it plays an important role in integrated pest management (IPM) programs throughout the world. Laboratory studies were conducted to compare the susceptibility of three Trichogramma egg parasitoid species to ten common insecticides and three herbicides. The adults of Trichogramma dendrolimi, T. chilonis, and T. ostriniae were exposed to the above-mentioned pesticides by a glass-vial residue method. Among the four neonicotinoids, dinotefuran and thiamethoxam exhibited extremely toxic effects on the Trichogramma dendrolimi and T. chilonis, with Risk Quotient (RQ) values ranging from 1471.2 to 5492.5. However, these two neonicotinoids have a relatively low toxicity to T. ostriniae, with RQ values 433.6 and 915.4, respectively. In addition, Imidacloprid and acetamiprid were slightly to moderately toxic to all the tested parasitic wasps and their RQ values are less than 500. For pyrethroids, all the selected compounds were slightly to moderately toxic to three Trichogramma species except that cyhalothrin was dangerously toxic to T. dendrolimi and T. chilonis, with RQ values 2567.6 and 3950.4. Among the three herbicides tested, pendimethalin, butralin and napropamid were slightly to moderately toxic to egg parasitoids, with all RQ values below 1000. For two avermectins, abamectin were slightly to moderately toxic to all three wasps with RQ values 635.6, 148.3 and 254.2, respectively. However, emamectin benzoate was found to be safe for the parasitoids. Furthermore, T. dendrolimi showed higher sensitivity than T. chilonis and T. ostriniae to the pesticides based on the comparison of LR₅₀ (application rate causing 50% mortality) values. The present results provide informative data for implementing biological and chemical control strategies in integrated pest management.

Favorable compatibility of nitenpyram with the aphid predator, Coccinella septempunctata L. (Coleoptera: Coccinellidae)

The increasing demand for lessening the chemical input in agricultural ecosystems requires an efficient combination of pesticides and biological controls. Thus, fully understanding the compatibility of pesticides and beneficial arthropod predators is helpful and essential. In this study, we evaluated the influence of nitenpyram on both larvae and adults of Coccinella septempunctata using exposure doses of 10, 25, 50, 100, and 150% of the maximum recommended field rate (MRFR) (3, 7.5, 15, 30, and 45 g a.i. ha^-1, respectively) and a blank control based on a preliminary acute 72-h toxicity experiment. In the long-term test, the LR₅₀ (application rate causing the mortality of 50% of the individuals) of nitenpyram for C. septempunctata decreased from 73.43 to 63.0 g a.i. ha^-1, while the HQ (hazard quotient) values remained below the threshold value of 2. Nitenpyram did not significantly influence the survival rate, fecundity, pupation, or adult emergence at 150% of the label rate (lowest LR₅₀ = 63.0 g a.i. ha^-1), and its demonstrated NOER (No Observed Effect application Rates) values are all above 45 g a.i. ha^-1. Likewise, the total developmental time and egg hatchability were not significantly affected at 100% of the label rate (NOER = 30 g a.i. ha^-1). The assessment of the total effect (E) suggested that nitenpyram could be classified as harmless to C. septempunctata below/at a dose of 30 g a.i. ha^-1. The lowest LR₅₀ and NOER values were both above the maximum recommended field application rate for nitenpyram (30 g a.i. ha^-1) for controlling aphids in China. All results indicated that the on-label use of nitenpyram is compatible with the natural enemy C. septempunctata in agricultural ecosystems.

Effects of Insecticides on Oviposition and Host Discrimination Behavior in Trichogramma chilonis (Hymenoptera: Trichogrammatidae)

Trichogramma chilonis Ishii is an important natural enemy of many lepidopterous pests on various crops. Effects of two conventional insecticides on oviposition and host discrimination behavior in T. chilonis were evaluated in the laboratory through video tracking. During the oviposition period, when the number of host eggs was limited (only one host egg), females exposed to beta-cypermethrin LC₁ or LC₂₀ exhibited significantly higher feeding and re-drilling rate and significantly longer post-oviposition duration than control females. Spinosad LC₂₀ treatment not only decreased the wasp oviposition rate but also significantly extended the oviposition duration. When the number of host eggs was six, similarly, females exposed to spinosad LC₂₀ exhibited a significantly lower oviposition rate (79.2%) than control ones (100%). In the host discrimination experiment, females exposed to LC₂₀ of both tested insecticides (beta-cypermethrin and spinosad) spent significantly more time on the extra-patch area. The females that survived spinosad LC₂₀ could not discriminate between unparasitized and parasitized host eggs. Our study suggests that even the LC₁ and LC₂₀ of the tested insecticides had negative effects on the oviposition and host discrimination behavior of T. chilonis Thus, the use of these two insecticides should be carefully evaluated.