Nymphal Mortality Research Articles

Virulence of Five Isolates of The Entomopathogenic Fungus, Metarhizium anisopliae, Against Brown Planthopper (Nilaparvata lugens)

The brown planthopper (Nilaparvata lugens) is one of the main pests of rice plants. This pest attack can cause crop failure or puso. Biological control of this pest can be carried out using the entomopathogenic fungus, Metarhizium anisopliae. The ability of this fungus to control pests is influenced by the source of the isolate. The purpose of this study was to obtain isolates of M. anisopliae, which is virulent to N. lugens. This study used an experimental method with a completely randomized design (CRD) in six treatments and five replications. There were five isolates of M. anisopliae used and one control. M. anisopliae was applied to nymphs and adults of N. lugens with a concentration of 108 conidia/mL. The research revealed that all M. anisopliae isolates tested were virulent against N. lugens nymphs and adults. The most virulent isolate for the two stages of BPH was Met3B, which was collected from the leek rhizosphere. The isolate caused an adult mortality rate of 52%, nymph mortality of 60% in 10 days after application, and adults formed after application was only 37.33%.

Isolation, identification and pathogenicity of local entomopathogenic bacteria as biological control agents against the wild cochineal Dactylopius opuntiae (Cockerell) on cactus pear in Morocco

The Opuntia ficus-indica (L.) cactus, a crucial crop in Morocco, is threatened by the wild cochineal, Dactylopius opuntiae (Cockerell). The aim of this research was to investigate the efficacy of nine bacterial strains against both D. opuntiae nymphs and adults females applied individually or after black soap in the laboratory, greenhouse, and field conditions. Using the partial 16S ribosomal DNA, the bacterial isolates were identified as Pseudomonas koreensis, Pseudomonas sp., Burkholderia sp. and Bacillus sp. Under laboratory conditions, the insecticidal activity of P. koreensis strain 66Ms.04 showed the level mortality (88%) of adult females’ at 108 CFU/mL, 7 days after application. At a concentration of 108 CFU/mL, P. koreensis strain 66Ms.04 and Pseudomonas sp. (strains 37 and 5) caused 100% nymphs mortality rate three days after application. Under greenhouse conditions, the use of P. koreensis strain 66Ms.04 at 108 CFU/mL following the application of black soap (60 g/L) demonstrated the maximum levels of females and nymphs’ mortalities with 80 and 91.25%, respectively, after 8 days of treatment. In field conditions, the combined application of the P. koreensis strain 66Ms.04 at 108 CFU/mL with black soap at 60 g/L, for an interval of 7 days, significantly increased the mortality of adult females to 93.33% at 7 days after the second application. These findings showed that the combined treatment of P. koreensis strain 66Ms.04 with black soap can be a potent and eco-friendly pesticide against D. opuntiae.

Insecticidal potential of Streptomyces sp. dichloromethane extracts against the cactus cochineal Dactylopius opuntiae (Cockerell)

Destructive damages caused by Dactylopius opuntiae (Cockerell) to cactus worldwide require an ecofriendly IPM approach. Streptomyces sp. produce wide range of biologically active secondary metabolites that can be an interesting alternative to chemical insecticides for pest control, as they are less toxic and easily biodegradable. The efficacy of dichloromethane extracts of four Moroccan Streptomyces sp. strains: Streptomyces bellus- E23-2, Streptomyces galilaeus- E23-9, Streptomyces africanus- E23-3, and Streptomyces bellus- E25-12 (applied at 11, 13, 15, 17 and 20 mg mL-1) against D. opuntiae nymphs and adult females was evaluated under laboratory and greenhouse conditions. Results showed that Streptomyces bellus- E23-2 and Streptomyces galilaeus- E23-9 dichloromethane extracts applied at 20 mg mL-1 were more effective, causing higher mortality against nymphs (92% and 91%, respectively) and adult females (90% and 95%, respectively) after 8 days of exposure, resulting in an LT50 value of 3.0 days (nymph), and 3.0 and 6.0 days (adult female), respectively. Streptomyces bellus- E25-12 extract had the lowest mortalities [88% (nymph) and 68% (adult female)]. In greenhouse experiment, the highest first instar nymph mortality was achieved by Streptomyces bellus- E23-2 (55.5%) and Streptomyces galilaeus- E23-9 (50.5%) dichloromethane extracts at 20 mg mL-1. The metabolites found in dichloromethane extracts of Streptomyces bellus- E23-2 and Streptomyces galilaeus- E23-9 show considerable potential to be used in the development of new biopesticide formulations for use in integrated pest management programs against D. opuntiae.

Green Synthesis of Silver Nanoparticles by Cardaria draba and Evaluation of its Insecticidal Effect on Schizaphis graminum

Schizaphis graminum one of the main pests of the wheat crop, causing direct and indirect damage to the growth and yield of the crop. The biosynthesis of nanoparticles using plant extracts is the most recent and workable application for pest control. This study was conducted to know the potential activity of insecticidal of synthesized silver nanoparticles (AgNPs) using plant leaf extracts of Cardaria draba. Synthesis was confirmed firstly by visual observation and then by UV-Vis spectrophotometer where The peak was recorded at 428 nm, The results of XRD technique of the colloidal solution confirmed the crystalline nature of the silver nanoparticles. FTIR analysis spectrum showed different types of functional groups which played crucial role in the biosynthesis of AgNPs. FESEM analysis determined the size and shape of AgNPs where average size was 85nm with roughly circular or spherical in shape. Different concentrations of AgNPs were prepared and tested on mortality of the stages of S. graminum, The highest mortality of adults and nymphs recorded 52.99 and 57.13% respectively at the high concentration 100 ppm compared with 4.79 and 5.87% respectively in the control treatment after 3 days from exposure time. In addition to statistically significant differences was in adult and nymph mortality between concentrations. The results suggested that using green biosynthesis of silver nanoparticles can be used as an effective way in the control S. graminum on wheat crops.

Efficacy of Sesame Oil and mustard Oil Formulations against Red Spider Mite of Tea

Crude formulations of sesame and mustard oil at 0.5%, 0.75% and 1% concentration with or without the addition of cow urine were assessed against red spider mite, Oligonychus coffeae (Nietner) in the laboratory. Efficacy tests on oviposition rate, egg hatchability, mortality of nymph and adult mites proved that sesame oil 1%, with or without the addition of cow urine was found to be effective in reducing the rate oviposition and egg hatchability of mites and was at par with the formulation prepared from commercial neem (1 : 1500). Formulations of sesame oil at the rate of 0.75% and 1% with or without cow urine were found to be highly effective for mortality of nymphs and adults of red spider mite respectively which were at par with the formulation prepared from commercial neem.

Leaf‐roll gall formation in Reynoutria × bohemica and its implications for biological control with Aphalara itadori

AbstractThe psyllid Aphalara itadori Shinji (Hemiptera: Psyllidae) is a biocontrol agent against invasive knotweed species (Polygonaceae) in Europe and North America. Despite an extensive release program, successful establishment of the agent has never been confirmed. The slow establishment of A. itadori in its introduced range appears to be predominantly the result of nymphal mortality, either through desiccation, predation, or the adaptation of captive populations to low‐stress environments. In 2016, CABI UK collected a new line of psyllids from Murakami, Niigata Prefecture, in Japan, where it was observed causing severe leaf‐roll galling on one of the many varieties of native knotweeds. The induction of leaf‐roll galls by Murakami psyllids on invasive Bohemian knotweed, Reynoutria × bohemica, has the potential to alleviate some or all of the observed nymphal mortality factors. We conducted a series of growth chamber experiments to explore the psyllid behaviors that initiate leaf‐roll galls, and the ways in which the galls might benefit the psyllids and inhibit invasive knotweed. Reynoutria × bohemica exposed to A. itadori for 4 weeks suffered reduced stem elongation and leaf area compared to control plants. Artificial leaf‐roll galls were consistently utilized by developing A. itadori nymphs, and contributed to their survival. Leaf‐roll galling in R. × bohemica was predominantly initiated by early instar nymphs of A. itadori, and only occurred when leaves were attacked at a very early stage in their development. Our results can inform the knotweed biocontrol program in several key ways. Releases of A. itadori should be timed so that developing nymphs have access to newly emerging leaves. Monitoring efforts at release sites should focus on the growing tips of R. × bohemica, where the highly mobile nymphs appear to migrate. Finally, our results provide motivation to seek additional lines of A. itadori that may affect other invasive knotweed species in similar ways.

Prospects for Biological Control of Macadamia Felted Coccid in Hawaii with Metaphycus macadamiae Polaszek & Noyes, a New Encyrtid Wasp Native to New South Wales, Australia.

Macadamia felted coccid (MFC), Acanthococcus ironsidei (Williams) (Hemiptera: Eriococcidae), was first discovered in 2005 on the Island of Hawaii. Host plants are restricted to Macadamia species, with Macadamia integrifolia Maiden & Betche (Proteaceae) being grown in Hawaii for nut production. Approximately 6839 hectares macadamia nuts are harvested in Hawaii with an estimated farm value of USD 48.8 million (2019-2020 records). Exploration in Australia started in November 2013 for the evaluation of potential parasitoids being host specific for introduction into Hawaii. A dominant solitary endoparasitoid of MFC from New South Wales was discovered and described as Metaphycus macadamiae Polaszek & Noyes sp. n (Hymenoptera: Encyrtidae: Encyrtinae). Biology and host specificity testing were conducted at the Hawaii Department of Agriculture, Insect Containment Facility, on nine hemipteran and three lepidopteran eggs. Results indicated that M. macadamiae is host specific to MFC. There has been no evidence of parasitism or host feeding on any of the non-target insect hosts that were tested. Parasitoid emergence from the control (MFC) averaged 30.2% compared to 0% on non-target hosts. A low rate of parasitoid emergence in the laboratory (average 30.2%) and an increased rate of MFC nymphal mortality was due to adult feeding. Field parasitism reached up to 32.7% emergence in Alstonville, New South Wales, Australia. We report on the parasitoid performance in native Australia, rearing biology, host specificity testing, and the extant natural enemies associated with MFC in Hawaii. A petition to release this parasitoid for the biocontrol of MFC in Hawaii is pending. Once permitted for release, the colony will be shared with South African Mac Nut Association for their biocontrol program of this invasive pest. They will conduct their own testing before approval for release.

Double-stranded RNA mediated knockdown of sucrase gene induced mortality and reduced offspring production in Aphis gossypii.

The importance of gut sucrase in maintaining osmotic equilibrium and utilizing phloem contents as a carbon source has been widely investigated and proven in sap-sucking insects. In the present study, silencing of Aphis gossypii sucrase1 (Agsuc1) was carried out by double-stranded RNA (dsRNA), which would be lethal to it due to disruption of osmotic balance. The dsRNA corresponding to Agsuc1 was synthesized by two methods, i.e., in vitro synthesis using T7/SP6 RNA polymerase and in vivo synthesis by bacterial expression, i.e., Escherichia coli strain HT115 transformed with the L4440 vector system. Oral delivery of double-stranded Agsuc1 synthesized in vitro (dsAgsuc1) and in vivo (HT115Agsuc1) induced around 50% mortality in nymphs of A. gossypii. Moreover, the number of offspring produced by the survived aphids decreased by 39-43%. Parthenogenetic reproduction of the aphids is the critical factor for their fast population build-up, leading to yield losses of economic significance. Thus, the present study demonstrated that the silencing of the Agsuc1 gene reduced the aphid population by killing it and inhibited the population buildup by reducing the number of offspring produced by the survived aphids, likely to result in a significant reduction in crop damage. The production of dsRNA by bacterial expression is a cost-effective method. It has the potential to be used as a biopesticide. The sucrase gene is an excellent putative target gene for RNAi against A. gossypii. It could be used to develop a transgenic plant that produces dsAgsuc1 to keep A. gossypii populations below the economic threshold level.

Chitinase of Trichoderma longibrachiatum for control of Aphis gossypii in cotton plants

Chitinase-producing fungi have now engrossed attention as one of the potential agents for the control of insect pests. Entomopathogenic fungi are used in different regions of the world to control economically important insects. However, the role of fungal chitinases are not well studied in their infection mechanism to insects. In this study, Chitinase of entomopathogenic fungi Trichoderma longibrachiatum was evaluated to control Aphis gossypii. For this purpose, fungal chitinase (Chit1) gene from the genomic DNA of T. longibrachiatum were isolated, amplified and characterised. Genomic analysis of the amplified Chit1 showed that this gene has homology to family 18 of glycosyl hydrolyses. Further, Chit1 was expressed in the cotton plant for transient expression through the Geminivirus-mediated gene silencing vector derived from Cotton Leaf Crumple Virus (CLCrV). Transformed cotton plants showed greater chitinase activity than control, and they were resistant against nymphs and adults of A. gossypii. About 38.75% and 21.67% mortality of both nymphs and adults, respectively, were observed by using Chit1 of T. longibrachiatum. It is concluded that T. longibrachiatum showed promising results in controlling aphids by producing fungal chitinase in cotton plants and could be used as an effective method in the future.

Efficiency of some Jasmonic Acid Concentrations on Mortality of Two-Spotted Spider Mite Tetranychus urticae Koch on Eggplant

The efficiency of Jasmonic acid concentrations 0, 5, 50 and 100μM was examined mortality of adult female and nymphs of the two-spotted spider mite Tetranychus urticae fed on leaves of over four time intervals of 12, 24, 36 and 48 hours. The results showed the significant effect of the treatments on the corrected mortality ratios for both stages, as well as for the interaction of the treatments of variety, concentration and time. In general, the results indicated the increase of mortality with the increase of the time period. It was observed that the concentration of 100μM during the time periods and all varieties and the concentration of 50μM after the time periods 24, 36 and 48 hours on the Barcelona variety and the concentration of 5μM during the last two time periods on the Bowie variety had the highest corrected mortality ratio, which was 100%, while the lowest mortality ratio was 0% at the concentration 5μM with 12 hours after treatment on adult females fed on the leaves of Jawaher variety. Regarding the effect of treatment on nymphal stage, In general, the results of the triple interaction between treatments indicated that the concentration of 5 μM had a synergistic effect along with Bowie variety and at all time periods in obtaining of the highest mortality ratio of individuals of nymphal stage (100%) and with significant differences from the other treatment while the same concentration after 12 hours of treatment achieved lowest mortality ratio of the nymph fed on the leaves of the variety Jawaher which amounted 0%.

Biocontrol potential of some entomopathogenic fungi against the Cotton Aphid, Aphis gossypii Glover (Hemiptera: Aphididae)

In this study, the effectiveness of entomopathogenic fungal (EPF) species isolated from soil and infected aphid samples taken from different districts of Antalya between 2018-2020 was investigated against the cotton aphid, Aphis gossypii. For this purpose, 19 entomopathogenic fungal isolates were tested against the nymphs and adults of A. gossypii in 9 cm diameter Petri dishes at a concentration of 1x107 spores/mL. Among the fungal species tested, Beauveria bassiana was the most pathogenic species. In pathogenicity tests, 10 days after incubation, B. bassiana caused 63.3%-100%, Cunninghamella echinulata 43.3%, Clonostachys rosea 40-70%, Isaria farinosa 43.3%-63.3%, and Purpureocillium lilacinum 73.3%-83.3% mortality of A. gossypii adults. The TaAl-1 isolate of Trichoderma atroviride used in biological control caused a mortality of 33.3%, and the ThAk-1 isolate of T. harzianum caused 50.0% mortality. Of the 3 commercial fungal preparations tested at doses of 250 mL/1lt water for comparison with indigenous fungal isolates, Nibortem (a.i.: Verticillium lecanii) caused 70% and 56.7% mortalities in nymphs and adults, respectively, 10 days after treatment, while Nostalgist (a.i.: B. bassiana) and Priority (a.i.: Paecilomyces fumosoroseus) caused 56.7% and 50% nymphal mortality, and 53.3% and 56.7% adult mortality, respectively.

Entomopathogenic fungi associated with cultivated honeybush, Cyclopia spp., in South Africa and their pathogenicity towards a leafhopper pest, Molopopterus sp. (Hemiptera: Cicadellidae)

The southern and eastern parts of the African Fynbos region favour the production of honeybush tea. Honeybush biomass and extracts are used to prepare a beverage both locally and internationally, mainly as herbal tea with health benefits. Honeybush tea is mostly grown organically requiring natural control measures for pests and diseases. The leafhopper, Molopopterus sp., is one of the most important pests of cultivated honeybush in South Africa, as its feeding compromises the quality and quantity of the yield through leaf discolouration and reduction of the photosynthetic area. Local entomopathogenic fungi (EPF) can provide a pool of potential biocontrol agents for this pest. Therefore, a total of 98 soil samples were collected from organically grown honeybush fields and vegetation surrounding the honeybush fields in the Western Cape province of South Africa. Entomopathogenic fungi were isolated using the insect bait method and were characterised using molecular techniques. Twenty fungal isolates of Metarhizium anisopliae and Fusarium oxysporum were recovered from soil samples, of which 70% were from honeybush fields and 30% were from surrounding vegetation. Fusarium oxysporum isolates comprised 20% of the recovered isolates; M. anisopliae the remainder. Laboratory bioassays of the recovered isolates against adults and nymphs of the leafhopper, showed that F. oxysporum isolates caused 10–45% mortality and M. anisopliae isolates 30–80% mortality. Metarhizium anisopliae isolates J S1, KF S3, KF S11, KF S13, LS1 and LS2 were the most virulent and induced over 60% mortality in both nymphs and adults at a concentration of 1 × 107 conidia/ml.

20E biosynthesis gene CYP306A1 confers resistance to imidacloprid in the nymph stage of Bemisia tabaci by detoxification metabolism.

Difference in physiology level between the immature and mature stages of insects likely contribute to different mechanisms of insecticide resistance. It is well acknowledged that insect 20-hydroxyecdysone (20E) plays an important role in many biological processes in the immature stage, whether 20E confers insecticide resistance at this specific stage is still poorly understood. By gene cloning, reverse transcription quantitative real-time PCR, RNA interference (RNAi) and in vitro metabolism experiments, this study aimed to investigate the potential role of 20E-related genes in conferring imidacloprid (IMD) resistance in the immature stage of the whitefly Bemisia tabaci Mediterranean. After identification of low to moderate IMD resistance in the whitefly, we found CYP306A1 of the six 20E-related genes was overexpressed in the nymph stage of the three resistant strains compared to a laboratory reference susceptible strain, but not in the adult stage. Further exposure to IMD resulted in an increase in CYP306A1 expression in the nymph stage. These results together imply that CYP306A1 may be implicated in IMD resistance in the nymph stage of the whitefly. RNAi knockdown of CYP306A1 increased the mortality of nymphs after treatment with IMD in bioassay, suggesting a pivotal role of CYP306A1 in conferring IMD resistance in the nymph stage. Additionally, our metabolism experiments in vivo showed that the content of IMD reduced by 20% along with cytochrome P450 reductase and heterologously expressed CYP306A1, which provides additional evidence for the important function of CYP306A1 in metabolizing IMD that leads to the resistance. This study uncovers a novel function of the 20E biosynthesis gene CYP306A1 in metabolizing imidacloprid, thus contributing to such resistance in the immature stage of the insect. These findings not only advance our understanding of 20E-mediated insecticide resistance, but also provide a new target for sustainable pest control of global insect pests such as whitefly. © 2023 Society of Chemical Industry.

Life history responses of the small brown planthopper Laodelphax striatellus to temperature change

Temperature is a key environmental factor in ectotherms and influences many life history traits. In the present study, the nymphal development time, sex ratio and wing dimorphism of the small brown planthopper Laodelphax striatellus were examined under the conditions of constant temperatures, naturally varying temperatures (or different generations), and different temperatures combined with different photoperiod. The results showed that from 18 to 28 °C, the developmental time of nymphs was gradually shortened with the increase of temperature, whereas the high temperatures of 30 and 32 °C in the third to fifth instar nymphal stages and high summer temperature of 28.8 and 29.7 °C significantly delayed developmental time and resulted in higher mortality of nymphs. In all treatments, the developmental time was longer in females than males. The nymphs took significantly longer time to develop in the short daylength of 12 h than in longer daylengths of 13, 14, 15 and 16. Differences in developmental time were also found between wing morph, with long-winged individuals being significantly longer than the short-winged individuals at lower temperatures and significantly shorter than the short-winged individuals at higher temperatures. In all treatments, the sex ratio was stable, approaching 1:1, without being affected by temperature, generations and photoperiod. Photoperiod and temperature had significantly influence on the wing dimorphism. Long daylength combined with different temperatures resulted in significantly higher proportions of long-winged morph, whereas the low temperatures combined with the short daylengths in autumn and winter resulted in significantly high proportion of short-winged morph.This study broadens our understanding of the life-history traits of this planthopper and provides basic data for analyzing the effects of climate change on the planthopper reproduction.

Technique to deliver dsRNA in Bemisia tabaci nymphs and its validation through silencing of juvenile hormone esterase gene

AbstractRNA interference (RNAi) is a technique employed to investigate the functions of various genes in whitefly and other insects. The effectiveness of the RNAi technique depends upon the delivery of dsRNA into the insects and it has been achieved through microinjection, oral feeding, egg soaking, transfection, topical application, spraying with nanoparticles, leaf‐mediated dsRNA feeding or plant‐mediated/ transgenic plants. In Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae), most of the studies on RNAi were conducted on the adult through either injection or oral feeding. There is a need to develop a system to deliver dsRNA in whitefly nymphs because the first instar nymphs after hatching find a suitable place on the leaf and feed on the same place till adult emergence. So, we evaluated nine different techniques using different sponges, tubes, and, Petri plates for feeding nymphs. The detached leaf survived for maximum number of days (8.25 days) with minimum nymphal mortality (12.01%) in the Whitefly Nymphal Feeding System‐1 (WNFS‐1) treatment; therefore, WNFS‐1 was selected for the delivery of dsRNA to B. tabaci nymphs. In WNFS‐1, blue food dye was used to confirm that nymphs were being fed, and the results were evidenced by blue‐coloured bodies. The juvenile hormone esterase (jhe) gene was silenced in order to successfully deliver dsRNA to nymphs using WNFS‐1 and resulting in much higher nymphal mortality (68.36%). Therefore, WNFS‐1 is a reliable method of delivering dsRNA for the purpose of silencing the genes in the nymphal stages of whiteflies. The WNFS system may also be used extensively to evaluate any chemistry (insecticides, hormones, biopesticides, etc.) in nymphs of whitefly.

Translaminar activity of different insecticides against Bemisia tabaci

One of the main mechanisms of action for many insecticides is translaminar redistribution or local systemic. The present study was carried out at Chaudhary Charan Singh Haryana Agricultural University, Hisar, Haryana during 2019 and 2020 to investigate the translaminar activity of different insecticides having different doses and sprays on treated brinjal plant having Bemisia tabaci (Gennadius) nymphs. Different treatments, i.e. diafenthiuron 50% WP (150, 210, and 300 g a.i./ha), fenpropathrin 30% EC (50, 70, and 100 g a.i./ha), thiamethoxam 25% WG (25, 35, and 50 g a.i./ha), and deltamethrin 2.8% EC (7.5, 10.5 and 15 g a.i./ha) were frequently sprayed on brinjal plants (var. Hisar Shyamal) growing in pots. Insecticides effectiveness was measured through nymphal mortality of B. tabaci (whitefly). Similar study was conducted in 2020 to ensure reliability of results. The results revealed that, almost similar trendswere obtained during 2019 and 2020, hence proving reliability. Among all tested insecticides, maximum translaminar effect was observed in thiamethoxam 25% WG treated plant at 50 g a.i./ha (50.72% nymphal mortality). Whereas, deltamethrin 2.8% EC treated plant at 15 g a.i./ha showed minimum translaminar effect (0.63% nymphal mortality) as compared to other treatments. Translaminar effect of leaves treated with diafenthiuron 50% WP and fenpropathrin 30% EC was found at par with each other. Nymphal mortality is low in sub-lethal doses of insecticides as compared to lethal doses. It can be concluded that resistance may develop due to sub-lethal doses of insecticides. Farmers and agricultural experts would benefit from this study's findings.

Morphological and biological characteristics of the Korean population of Leptoglossus occidentalis Heidemann (Heteroptera: Coreidae), an invasive insect pest of conifer cones

In this study, we investigated the morphological and biological characteristics of a serious insect pest of conifer cones, the western conifer seed bug (WCSB), Leptoglossus occidentalis Heidemann (Heteroptera: Coreidae), in Korea. WCSB adults shared external morphology with overseas populations, including zig-zag fascia on the coria, dilation of the hind tibiae, and color pattern on the abdominal dorsum. The average body length and width of WCSB adults were 17.20 and 4.85 mm, respectively, in males and 19.05 and 5.55 mm in females. The average body weights were 111.27 and 169.89 mg in adult males and females, respectively. On average, eggs were 2.12 mm long and 1.17 mm wide. The average body lengths of the first- to fifth-instar nymphs were 3.07, 4.76, 8.77, 13.56, and 15.53 mm, respectively. For biological characteristics, developmental durations of the egg and five nymphal instar stages were 8.6, 3.7, 7.6, 5.8, 5.8, and 9.1 days, respectively, in laboratory conditions. Nymphal mortality was 47.5% in total. The average life expectancy of WCSB adults was 58.2 and 63.9 days in males and females, respectively. Oviposition of the adult females started 23.4 days after emergence, and the total number of eggs laid by a single adult female was 68.6 on average. The results of this study offer basic morphological and biological information that can be used to design an effective control strategy to manage the WCSB population in Korea.

Chemical profiling of Artemisia herba-alba, Cuminum cyminum, Cinnamomum camphora, and Salvia rosmarinus essential oils and assessment of their insecticidal potential to control the wild cochineal Dactylopius opuntiae (Cockerell)

The wild cochineal, Dactylopius opuntiae (Hemiptera: Dactylopiidae), has become a serious pest of prickly pear Opuntia ficus-indica L. in the Mediterranean region. The present study investigated the insecticidal activity of four essential oils, namely Cuminum cyminum, Cinnamomum camphora, Artemisia herba-alba, and Salvia rosmarinus against D. opuntiae nymphs and adult females in laboratory and greenhouse bioassays. Laboratory tests showed that at a concentration of 2.5%, C. cyminum oil was the most effective (inducing 100% nymph mortality at 3 h after treatment), followed by C. camphora, A. herba-alba and S. rosmarinus oils which recorded comparable mortality rates ranging from 89.40 to 100%, while S. rosmarinus and C. cyminum oils induced the highest mortality rates on adult females (88% and 86%, respectively) 8 days after treatments. Under greenhouse conditions, the combined application of C. cyminum oil (2.5%) and black soap (10 g/L) showed the highest nymphs’ mortality (100%) at 3 days after application. Adult female mortality in the greenhouse was lower than in the laboratory bioassay for all tested oils, with S. rosmarinus inducing 47% mortality at 2.5% at 14 days after the second spray. Eucalyptol was the main constituent of S. rosmarinus (41.20%) and C. camphora (56.47%) oils, and thujon-camphor was the major chemotype of A. herba-alba (30.55%/28.16%), while cuminaldehyde was the main compound of C. cyminum oil seeds (32.53%). These findings showed that the compounds of the two essential oils S. rosmarinus and C. camphora potential sources of insecticidal compounds and warrant further investigation.

LABORATORY EVALUATION OF BIGSHOT MAXIM, REPELCARE, AND CLOVE ESSENTIAL OIL, SYZYGIUM AROMATICUM AGAINST THE LONE STAR TICK, AMBLYOMMA AMERICANUM

Synthetic acaricides have been the most used method for controlling tick populations. However, their frequent application has had negative impacts on treated animals and the environment and led to the development of resistance in tick populations. These factors generated interest and the need to find more environmentally friendly alternatives. In this study, the repellency and acaricidal effects of BigShot Maxim (AIs: cedarwood oil, cinnamon oil, thyme oil), RepelCare (AIs: turmeric oil and eucalyptus oil), and clove oil, Syzygium aromaticum L., were tested against the lone star tick, Amblyomma Americanum (Linnaeus). Despite no evidence of repellency for BigShot Maxim, RepelCare and clove oil, its disruption of the host seeking behavior after contact to the products was observed and further investigated. BigShot Maxim and clove oil were selected for mortality testing and resulted in complete mortality of male, female ticks, and nymphs with some application rates. The results from this study provide a better understanding of repellency and acaricidal effects of botanical products against the lone star tick that can be used to further improve the development of green chemistry. However, further studies are warranted before these botanical products can be implemented as effective alternatives to chemical acaricides to use in integrated vector control.

Off‐host survival of blacklegged ticks in eastern North America: A multistage, multiyear, multisite study

AbstractClimatic conditions are widely thought to govern the distribution and abundance of ectoparasites, such as the blacklegged tick (Ixodes scapularis), vector of the agents of Lyme disease and other emerging human pathogens. However, translating physiological tolerances to distributional limits or mortality is challenging. Ticks may be able to avoid or tolerate unsuitable conditions, and what is lethal to one life history stage may not extend to others. Thus, even after decades of research, there are clear gaps in our knowledge about how climatic conditions determine tick distributions or patterns of abundance. We present results from a 3‐year study combining daily hazard models and data from field experiments at three sites spanning much of I. scapularis' current latitudinal distribution. We examine three predominant hypotheses regarding how temperature and vapor pressure deficits affect stage‐specific survival and transition success and consider how these results influence population growth and distribution. We found that larvae are sensitive to temperature and vapor pressure deficits, whereas mortality of nymphs and adults is consistent with depletion of energy reserves. Consistent with prior work, we found that overwinter survival was high and successful stage transitions (e.g., fed nymphs molting to adults) were sensitive to temperature. Collectively, results from this comprehensive, multiyear, multistage field study suggest that population growth of I. scapularis is less limited by restrictive climatic conditions than has been broadly assumed, although influences on larval survival may slow tick population growth and establishment in some desiccating conditions. Further studies should integrate climate effects on stage‐specific survival to better understand these effects on population dynamics and range expansion in a changing climate.