Topical LD50 Research Articles

Comparative toxicity of two neonicotinoid insecticides at environmentally relevant concentrations to telecoprid dung beetles

Dung beetles (Coleoptera: Scarabaeinae) frequently traverse agricultural matrices in search of ephemeral dung resources and spend extended periods of time burrowing in soil. Neonicotinoids are among the most heavily applied and widely detected insecticides used in conventional agriculture with formulated products designed for row crop and livestock pest suppression. Here, we determined the comparative toxicity of two neonicotinoids (imidacloprid and thiamethoxam) on dung beetles, Canthon spp., under two exposure profiles: direct topical application (acute) and sustained contact with treated-soil (chronic). Imidacloprid was significantly more toxic than thiamethoxam under each exposure scenario. Topical application LD50 values (95% CI) for imidacloprid and thiamethoxam were 19.1 (14.5–25.3) and 378.9 (200.3–716.5) ng/beetle, respectively. After the 10-day soil exposure, the measured percent mortality in the 3 and 9 µg/kg nominal imidacloprid treatments was 35 ± 7% and 39 ± 6%, respectively. Observed mortality in the 9 µg/kg imidacloprid treatment was significantly greater than the control (p = 0.04); however, the 3 µg/kg imidacloprid dose response may be biologically relevant (p = 0.07). Thiamethoxam treatments had similar mortality as the controls (p > 0.8). Environmentally relevant concentrations of imidacloprid measured in airborne particulate matter and non-target soils pose a potential risk to coprophagous scarabs.

Toxicological analysis of stilbenes against the fall armyworm, Spodoptera frugiperda

The fall armyworm (FAW), Spodoptera frugiperda, is a global pest of multiple economically important row crops and the development of resistance to commercially available insecticidal classes has inhibited FAW control. Thus, there is a need to identify chemical scaffolds that can provide inspiration for the development of novel insecticides for FAW management. This study aimed to assess the sensitivity of central neurons and susceptibility of FAW to chloride channel modulators to establish a platform for repurposing existing insecticides or designing new chemicals capable of controlling FAW. Potency of select chloride channel modulators were initially studied against FAW central neuron firing rate and rank order of potency was determined to be fipronil > lindane >Z-stilbene > DIDS > GABA >E-stilbene. Toxicity bioassays identified fipronil and lindane as the two most toxic modulators studied with topical LD50's of 41 and 75 ng/mg of caterpillar, respectively. Interestingly, Z-stilbene was toxic at 300 ng/mg of caterpillar, but no toxicity was observed with DIDS or E-stilbene. The significant shift in potency between stilbene isomers indicates structure-activity relationships between stilbene chemistry and the binding site in FAW may exist. The data presented in this study defines the potency of select chloride channel modulators to FAW neural activity and survivorship to establish a platform for development of novel chemical agents to control FAW populations. Although stilbenes may hold promise for insecticide development, the low toxicity of the scaffolds tested in this study dampen enthusiasm for their development into FAW specific insecticides.

Baseline Susceptibility of Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) to Commonly Used Insecticides in the Columbia Basin.

Colorado potato beetle (CPB), Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), is one of the most challenging pests of potato, Solanum tuberosum L., largely due to its propensity to develop insecticide resistance. Historically, L. decemlineata has rapidly evolved resistance to all major classes of synthetic insecticides, particularly in the eastern United States. However, in the U.S. Pacific Northwest, there have thus far been no confirmed reports of insecticide resistance despite anecdotal accounts of control failure. Hence, the objective of this study was to develop baseline data on the susceptibility of L. decemlineata in the Columbia Basin to abamectin, imidacloprid, and spinetoram, three insecticides commonly used to manage this insect. In 2018 and 2019, baseline susceptibility of four L. decemlineata populations, three from the Columbia Basin and one from Wisconsin (used as a resistant reference), was examined using topical LD50 bioassays. In general, L. decemlineata populations in the Columbia Basin exhibited relatively high sensitivity to imidacloprid, but variable sensitivity to abamectin and spinetoram among sites and years. Although small sample sizes hindered estimation of statistically significant LD50 values, results suggest that L. decemlineata in the Columbia Basin are beginning to develop levels of insensitivity to spinetoram, and possibly abamectin that are comparable to insecticide-resistant populations in Wisconsin. This preliminary examination of geographic variation in sensitivity to commonly used insecticides reinforces the value of rotating insecticide modes of action and suggests the need for continued monitoring for the development of insecticide resistance throughout the U.S. Pacific Northwest.

Acute toxicity of Neonicotinoids and Carbamete on Honey Bee Apis mellifera L

Background and Objectives: The current study represents the first part of a Ph.D. research projectconducted at The University of Guelph, Ontario, Canada in co-operation with the University of Babylon,Hilla – Iraq. The main objective of this part was to estimate the acute toxicity (LD 50) of clothianidin,imidacloprid (neonicotinoids), and carbaryl (Crabmeat) to honey bees. Method: The Three insecticides havebeen blamed for the colony collapse disorder (CCD) crisis, newly emerged adult bees were challenged orallyand topically with a serial of doses of the three insecticides. Determination of the LD50 of each insecticiderevealed that clothianidin was the most toxic insecticide to bees in oral and topical applications comparedto the other two insecticides. The findings: The oral LD50 values were 0.004, 0.15, and 0.36 forclothianidin, imidacloprid, and carbaryl respectively. The topical LD50 values were 0.034, 0.085, and 0.24for the three insecticides respectively Data were statistically analyzed by probit analysis using theUS Environmental protection Agency statistical program (version 1-5).

Assessing the acute toxicity of insecticides to the buff-tailed bumblebee (Bombus terrestris audax)

The buff-tailed bumblebee, Bombus terrestris audax is an important pollinator within both landscape ecosystems and agricultural crops. During their lifetime bumblebees are regularly challenged by various environmental stressors including insecticides. Historically the honey bee (Apis mellifera spp.) has been used as an ‘indicator’ species for ‘standard’ ecotoxicological testing, but it has been suggested that it is not always a good proxy for other eusocial or solitary bees. To investigate this, the susceptibility of B. terrestris to selected pesticides within the neonicotinoid, pyrethroid and organophosphate classes was examined using acute insecticide bioassays. Acute oral and topical LD50 values for B. terrestris against these insecticides were broadly consistent with published results for A. mellifera. For the neonicotinoids, imidacloprid was highly toxic, but thiacloprid and acetamiprid were practically non-toxic. For pyrethroids, deltamethrin was highly toxic, but tau-fluvalinate only slightly toxic. For the organophosphates, chlorpyrifos was highly toxic, but coumaphos practically non-toxic. Bioassays using insecticides with common synergists enhanced the sensitivity of B. terrestris to several insecticides, suggesting detoxification enzymes may provide a level of protection against these compounds.The sensitivity of B. terrestris to compounds within three different insecticide classes is similar to that reported for honey bees, with marked variation in sensitivity to different insecticides within the same insecticide class observed in both species. This finding highlights the need to consider each compound within an insecticide class in isolation rather than extrapolating between different insecticides in the same class or sharing the same mode of action.

The Mixture of Topical Anesthetic and Chlorhexidine at the Delivery Site in Microbial Reduction Efficiency

Background:Antimicrobial properties of some anesthetic agents have been reported which may be useful for infection control. Topical lidociane (10%) showed some extent of antimicrobial activity on oral microflora.Objective:This study aimed to determine whether the antimicrobial efficiency of topical lidocaine can be enhanced by adding chlorhexidine.Methods:The Lidocaine-Chlorhexidine (LD-CHX) preparation was prepared by mixing 2.0% CHX and 10% LD with various ratios. The anesthetic efficiency was tested on the oral mucosa of 26 volunteers by Pin Prick Test. Pain scores were recorded using the Numerical Rating Scale (NRS). Antimicrobial effects of 10% LD, 0.2% CHX, and LD-CHX preparations were evaluated.In vitrostudy was conducted against seven standard bacterial strains. Forin vivostudy, oral biofilms of 26 volunteers were collected by imprint technique using filter papers. Bacterial growth from the samples after applying the test solutions was compared to the control. Antimicrobial efficiency was expressed as microbial reduction scores from 4-0 (highest to lowest).Results:The LD-CHX preparations that had comparable anesthetic efficiency to 10% LD were those containing 9% and 8% LD. These LD-CHX preparations showed microbial reduction scores of 3 and 4 on seven bacterial strains and oral biofilms.Conclusion:This study showed the antimicrobial and anesthetic effectiveness of new lidocaine-chlorhexidine preparations bothin vitroandin vivo.We also confirmed the effectiveness of infection control protocol in oral surgery using CHX mouthwash prior to topical LD.

Control of Filth Flies, Cochliomyia macellaria (Diptera: Calliphoridae), Musca domestica (Diptera: Muscidae), and Sarcophaga bullata (Diptera: Sarcophagidae), Using Novel Plant-Derived Methyl Ketones.

Filth flies live in close proximity to humans and livestock and transmit pathogens. Current control relies on chemical insecticides, and flies can develop resistance to these insecticides. The public is also interested in natural and safer insecticides. Therefore, alternative pesticides compatible with the synanthropic nature of flies are needed. Four plant aliphatic methyl ketones were evaluated for control of adult house flies, Musca domestica L., blow flies, Cochliomyia macellaria (F.), and gray flesh flies, Sarcophaga bullata (Parker). In sealed petri dish assays, 2-heptanone, 2-octanone, 2-nonanone, and 2-undecanone exhibited fumigant activity against house flies with 24-h LC50s of 6.9, 7.5, 8.0, and 9.2 µg/cm3, respectively. Further research focused on undecanone (a U.S. EPA-registered biopesticide). When tested in larger enclosures at 1.7, 2.3, and 2.8 µg/cm3, undecanone provided 60.4, 82.2, and 94.4% house fly mortality; 56.9, 75.6, and 92.5% flesh fly mortality; and 62.1, 84.5, and 97.9% blow fly mortality, respectively, after a 2-h exposure. In a two-choice behavioral assay with 194.6 µg/cm2 of the test compound on the treatment versus an untreated surface of the same area, the overall mean repellencies for blow flies were 84.7% for undecanone versus 87.6% for N,N-diethyl-meta-toluamide (DEET). For house flies, mean repellencies were 80.7% for undecanone and 84.9% for DEET. The house fly topical LD50 for undecanone was 58.1 µg per fly. Undecanone was far less expensive for filth fly control than the gold standard for insect fumigation, methyl bromide.

Susceptibility of Asian citrus psyllid, Diaphorina citri (Hemiptera: Liviidae), to the insecticide afidopyropen: a new and potent modulator of insect transient receptor potential channels

A relatively new insecticide chemistry for controlling sucking insects, afidopyropen, was investigated for toxicity against Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae). We evaluated the mortality of D. citri eggs, nymphs, and adults treated with afidopyropen using both laboratory-reared and field populations. We also quantified the effects of sublethal doses of afidopyropen on D. citri feeding, host choice selection, and fecundity. For laboratory susceptible adults, the contact LC50, topical application LD50, and leaf dip LC50 were 2.13, 2.00, and 3.08 ng/µL, respectively. For adults collected from a commercially managed citrus grove in Florida, the contact LC50, topical application LD50, and leaf dip LC50 were 1.37, 1.92, and 4.89 ng/µL, respectively. Egg hatch was significantly reduced following exposure to afidopyropen at 100 ng/µL. Furthermore, afidopyropen reduced D. citri nymph survival and adult emergence at concentrations ranging between 0.01 and 100 ng/µL. Diaphorina citri adult feeding decreased on citrus leaves treated with afidopyropen in a concentration-dependent manner as measured indirectly by honeydew excretion, and appeared almost completely inhibited after treatment with 10 and 100 ng/µL solutions of afidopyropen. In choice tests, significantly fewer D. citri adults settled on afidopyropen-treated plants than on control plants at 24, 48, and 72 h after release, with no differences in settling between males and females. Afidopyropen reduced the fecundity of D. citri in a concentration-dependent manner. Collectively, the results suggest that afidopyropen could contribute to the integrated management of D. citri and may therefore be useful in rotational programs to improve resistance management.

A Comparison of Resistance to Imidacloprid in Colorado Potato Beetle (Leptinotarsa decemlineata Say) Populations Collected in the Northwest and Midwest U.S.

The Colorado potato beetle, Leptinotarsa decemlineata Say, is a serious pest of potato, Solanum tuberosum L., worldwide. Leptinotarsa decemlineata has a history of repeated adaptation to insecticides, and exhibits a geographic pattern of decreasing insecticide resistance from east to west in the USA. Imidacloprid is one of the most widely used insecticide in western states. In this study, we measured imidacloprid resistance among larval and adult L. decemlineata from ten locations in the Columbia Basin (southeastern Washington and northeastern Oregon) using topical LD50 bioassays, and compared them to estimates from ten locations in Minnesota and Wisconsin. Larval and adult imidacloprid LD50’s and mean percent mortality were generally lowest in Washington and Oregon, but some sites exhibited reductions in mortality comparable to those observed at some Wisconsin sites. Adult LD50’s suggest L. decemlineata in the Columbia Basin may be evolving in response to selection by neonicotinoid insecticides, but larval data suggest high susceptibility to imidacloprid remains in most populations. Future work should expand resistance monitoring efforts to include more regions in the West and other insecticide modes of action.

Toxicity evaluation of two insecticides on Tetragonisca angustula and Scaptotrigona xanthotricha (Hymenoptera: Apidae)

Stingless bees (Hymenoptera: Apidae, Meliponini) have crucial roles in the ecosystem, offering pollination service and contributing to genetic diversity of species, and also providing honey and wax to humankind. Tetragonisca angustula and Scaptotrigona xanthotricha are species that have been used since ancient times for beekeeping. Currently these and other species have been exposed to agronomic practices, among which the use of synthetic pesticides used for crop protection stands out. The aim of this study was to evaluate the toxicity of the insecticides thiamethoxam and fipronil, which are used in agriculture in several countries in the tropical and subtropical belt in order to establish the risk that these products represent to the survival of these two species. The oral and topical LD50 was obtained by Probit analysis. Comparisons with the LD50s of other stingless bees and Apis mellifera were realized. Although further studies are required to calculate the real risk of the two compounds, the results showed an evident susceptibility of both species. We concluded that it is essential to use tools and practices that reduce the risk, and perform toxicological evaluations of new and existing pesticides on stingless bees.

Efecto letal agudo de los insecticidas en formulación comercial Imidacloprid, Spinosad y Thiocyclam hidrogenoxalato en obreras de Bombus atratus (Hymenoptera: Apidae)

The effect of insecticides on bees has gained great attention, however, there are few studies that explore this issue on Neotropical bees. Bombus atratus is a neotropical species broadly distributed in Colombia and is considered an important pollinator of both Andean ecosystems and agroecosystems. However, as for many wild bees species, the effect of insecticides on B. atratus is unknow. In this study we determined the acute median lethal dose (LD50) of commercial formulations of insecticides Imidacloprid, Spinosad and Thiocyclam hydrogen oxalate, widely used in Colombia to control several pests of important crops. The LD50 was carried out by oral and contact routes, following and modifying the EPPO and OECD guidelines to perform LD50 on A. mellifera. We evaluated five doses for each route and insecticide, in a total of 25 medium-size workers for each dose by duplicate. Mortality was registered at 24, 48 and 72 hours after the experiment; and data were analyzed with the Probit regression model. For Imidacloprid, contacts and oral LD50 were 0.048 µg/bee and 0.010 µg/bee, respectively. For Thiocyclam hydrogen oxalate, topical and oral LD50 were 0.244 µg/bee and 0.056 µg/bee, respectively. For Spinosad, the oral LD50 corresponded to 0.28 µg/bee; it was not possible to establish the LD50 for the contact route. The Hazard Quotient (HQ) and Index of Relative Toxicity indicated that all three active ingredients are highly toxic. We discussed the risk of the insecticides use on B. atratus, considering their chemical nature.

Determination of acute lethal doses (LD50 and LC50) of imidacloprid for the native bee Melipona scutellaris Latreille, 1811 (Hymenoptera: Apidae)

The bee species Melipona scutellaris (L.) is native to Brazil, stingless and belongs to the Apidae family. In Brazil, stingless bees are responsible for 40 % to 90% of tree species pollination, depending on the considered ecosystem. However, their survival has been threatened since the country has been standing out as the biggest pesticides consumer in the world. Many of the pesticides used are considered toxic to bees, including imidacloprid (all existing studies were conducted with the Apis mellifera (L.) species). Although the bees are not the target of these substances, they are highly vulnerable to contamination. Thereby, the objective of this study was to establish the mean lethal dose (LD 50 ) and the mean lethal concentration (LC 50 ) of imidacloprid in the M. scutellaris fodder. In order to carry out this experiment, bees were collected and the test was performed according to OECD's protocol (1998a, 1998b), developed for A. mellifera . For the determination of LD 50 and LC 50 , data was analyzed through the Probit method, using the BioStat software. The topical LD 50 established in this study was 2.41 ng/bee for 24 hours and 1.29 ng/bee for 48 hours. The oral LC 50 was 2.01 ng i.a./μL for 24 hours and 0.81 ng i.a./μL for 48 hours. This data showed that native bees of M. scutellaris species are more sensitive to this pesticide than A. mellifera. Thus, it is important to establish management methods which take this higher susceptibility into account to protect native species.

Toxicity and biochemical changes in the honey bee Apis mellifera exposed to four insecticides under laboratory conditions

The toxicity and biochemical changes in honey bees (Apis mellifera) treated with four insecticides—acetamiprid, dinotefuran, pymetrozine, and pyridalyl—were evaluated under controlled laboratory conditions. Foraging bees were exposed to different dosages of tested insecticides by oral feeding at different dosages recommended by the manufacturers for agricultural crops in Egypt (0.01-, 0.02-, 0.04-, 0.1-, and onefold). Moreover, the acute toxicity of these insecticides was evaluated by topical application on the thorax of foragers to calculate the LD50 values. The specific activities of acetylcholinesterase (AChE), carboxylesterase, glutathione S-transferase (GST), and polyphenol oxidase (PPO) were measured in different tissues of surviving foragers after 24 h of treatment to explore the possible mode of action of insecticides and honey bees' strategies for detoxification and tolerance. The results indicated that regardless of how the bees were exposed to insecticides, dinotefuran was extremely toxic to adult A. mellifera (topical LD50 = 0.0006 μg/bee and oral feeding LC50 = 1.29 mg/L). Pyridalyl showed moderate toxicity compared to dinotefuran at the recommended application rate; however, acetamiprid and pymetrozine were relatively less toxic to bees (<25 % mortality at the recommended application rates). Data showed that tested insecticides varied in their influence on AChE, carboxylesterase, GST, and PPO activities that were highly correlated to their toxicity against A. mellifera. The biochemical analysis of carboxylesterase and GST showed that these enzymes detoxified the low doses of acetamiprid, pymetrozine, and pyridalyl, but not dinotefuran. Overall, our results are valuable not only in evaluating the toxicity of common insecticides onto honey bees, but also in highlighting the validity of enzymes activities as proper indicators for exposure to agrochemicals.

Defensive chemicals of tawny crazy ants, Nylanderia fulva (Hymenoptera: Formicidae) and their toxicity to red imported fire ants, Solenopsis invicta (Hymenoptera: Formicidae)

Nylanderia fulva (Mayr) has been reported as being able to displace Solenopsis invicta Buren, one of the most aggressive invasive ants in the world. Like S. invicta, N. fulva use chemical secretions in their defense/offense, which may contribute to their observed superior competition ability. In this study, the defensive chemicals of N. fulva workers and their toxicity against S. invicta workers were investigated. Like other formicine ants, N. fulva workers produce formic acid in their poison glands and 2-ketones and alkanes in Dufour glands. Of these, undecane and 2-tridecanone are two principal compounds in the Dufour gland. Topical LD50 values of 2-tridecanone and undecane against S. invicta workers ranged from 18.51 to 24.67 μg/ant and 40.39 to 84.82 μg/ant, respectively. Undecane and 2-tridecanone had significantly higher contact toxicity than formic acid, whereas formic acid had significantly higher fumigation toxicity than undecane and 2-tridecanone. The combination of 2-tridecanone as a contact toxin and formic acid as a fumigant significantly decreased KT50 values when compared to those of individual compounds. N. fulva does not seem unique in terms of the chemistry of its defensive secretion as compared to other formicine ants. However, this ant contained more than two orders of magnitude of formic acid (wt/wt) than other formicine ants and one order of magnitude of 2-tridecanone than the common crazy ant, Paratrechina longicornis (Latreille). The quantity, rather than quality, of the chemical secretion may contribute to the superior competition ability of N. fulva.

Effect of essential oils from Callistemon viminalis and Ferula gummosa on toxicity and on the hemocyte profile of Ephestia kuehniella (Lep.: Pyralidae)

This study was carried out to evaluate toxicological and haematological effects of essential oils from Callistemon viminalis and Ferula gummosa against Ephestia kuehniella larvae through fumigant and topical exposure. The results indicated that fumigant LC10, LC30 and LC50 values were 8.42, 15.86 and 24.60 μl/l air for C. viminalis oil and 38.51, 57.75 and 76.44 μl/l air for F. gummosa, respectively. Also, topical LD values were measured to be 4.28, 9.64 and 16.91 μg insect −1 for C. viminalis oil and 1.28, 3.39 and 6.65 μg insect−1 for F. gummosa oil, respectively. Haematological observations showed that in comparison to fumigation, topical application of tested oils caused a drastic reduction in total hemocyte count of treated larvae in a dose-dependent manner at all time intervals. Also, it is shown that plasmatocytes and granulocytes were the most sensitive hemocytes of E. kuehniella larvae to the tested oils after topical application. So, it is concluded that topical application of essential oils of C. viminalis and F. gummosa provided effective control of E. kuehniella causing negative effects on its immune cells.

Recent Status of Insecticide Resistance in Asian Rice Planthoppers

Since 2005, outbreaks of rice planthoppers have occurred in East-Asian countries such as Vietnam, China and Japan. These outbreaks are closely related to the development of insecticide resistance in these regions. The susceptibilities of the brown planthopper (BPH) and the whitebacked planthopper (WBPH) to four insecticides were evaluated by a topical application method on insects collected from Japan, China, Taiwan, Vietnam, and Philippines in 2006. Species-specific changes in insecticide susceptibility were found in Asian rice planthoppers: imidacloprid resistance in BPH and fipronil resistance in WBPH. Topical LD50 values for imidacloprid in the BPH strains from East Asia (Japan, China and Taiwan) and Vietnam were significantly higher than those from the Philippines, suggesting that resistance to imidacloprid has developed in BPH in East Asia and Indochina, but not in the Philippines. Almost all the WBPH populations collected had extremely large LD50 values for fipronil, suggesting that resistance to this insecticide is widespread in WBPH populations throughout East and Southeast Asia. Possible reasons for species-specific development of insecticide resistance are identified and discussed.

Species‐specific insecticide resistance to imidacloprid and fipronil in the rice planthoppers Nilaparvata lugens and Sogatella furcifera in East and South‐east Asia

In 2003 the development of insecticide resistance against neonicotinoids in the brown planthopper (BPH), Nilaparvata lugens (Stål) (Homoptera: Delphacidae), was first observed in Thailand and has since been found in other Asian countries such as Vietnam, China and Japan. However, the LD(50) values of BPH and the whitebacked planthopper (WBPH), Sogatella furcifera (Horváth), against both neonicotinoid and phenylpyrazole insecticides have been poorly reported in many Asian countries. The topical LD(50) values for imidacloprid in the BPH populations collected from East Asia (Japan, China, Taiwan) and Vietnam in 2006 were 4.3-24.2 microg g(-1) and were significantly higher than those collected from the Philippines (0.18-0.35 microg g(-1)). The BPH populations indicated a positive cross-resistance between imidacloprid and thiamethoxam. Almost all the WBPH populations from Japan, Taiwan, China, Vietnam and the Philippines had extremely large LD(50) values (19.7-239 microg g(-1) or more) for fipronil, except for several populations from the Philippines and China. Species-specific changes in insecticide susceptibility were found in Asian rice planthoppers (i.e. BPH for imidacloprid and WBPH for fipronil). Insecticide resistance in BPH against imidacloprid occurred in East Asia and Indochina, but not in the Philippines. In contrast, insecticide resistance in WBPH against fipronil occurred widely in East and South-east Asia.

Catnip essential oil as a barrier to subterranean termites (Isoptera: Rhinotermitidae) in the laboratory.

The essential oil of catnip, Nepeta cataria (Lamiacae) was evaluated for behavioral effects on two populations of subterranean termite, Reticulitermes flavipes (Kollar) and R. virginicus (Banks) (Isoptera: Rhinotermitidae). The catnip essential oil contained approximately 36:64 E,Z-nepetalactone and Z,E-nepetalactone, respectively. The time to 50% dissipation (DT50) of the isomers in sand was dependent on dose, and ranged from 5.7 to 12.6 d for the E,Z-isomer and 7.7-18.6 d for the Z,E-isomer. For R. flavipes, the 24-h topical LD50 value was approximately 8200 microg/g termite. The 24-h fumigation LC50 value for R. flavipes was between 36 and 73 microg/ml air, and the 7-d fumigation LC50 value was between 14 and 36 microg/ml air. Exposure of R. virginicus to treated sand resulted in a 24-h LC50 value (95% F.L.) of 84 (67.6, 112) microg/cm2 and a 7-d LC50 value of 21.1 (16.4, 26.8) microg/cm2; for R. flavipes these values were 63.2 (53.7, 73.9) and 44.4 (34.6, 58.1) microg/cm2, respectively. Vertical tunneling through treated sand was eliminated at 500 ppm for R. virginicus and at 250 ppm for R. flavipes. Horizontal tunneling was stopped at 250 ppm for R. virginicus and reduced at doses above 250 ppm for R. flavipes. Although tunneling ceased in these tests, mortality was not high, indicating that the termites avoided the treated sand. Efficacy of catnip oil was equivalent to other monoterpenoids reported in the literature.

Spinosad selection of a laboratory strain of the tobacco budworm, Heliothis virescens (Lepidoptera: Noctuidae), and characterization of resistance

The potential for insect resistance to the spinosyns, a novel class of insecticide chemistry, was examined using a laboratory strain of the tobacco budworm, Heliothis virescens (F.), originally collected from tobacco at sites in North Carolina. Technical grade spinosad (spinosyns A and D), was topically applied to third instars. Initially 533 third instars were used but one to two thousand larvae were treated per generation thereafter. Initially mortality ranged from 75% to 85% with doses of 0.044–0.088μg per larva, until the fifth generation (G5) when mortality decreased. The selection dose was subsequently increased every generation from G5 to G11 in an attempt to restore mortality to >70%. After six generations of selection, the LD50 of the selected budworms was 1.68-times that of the parental generation (G1) as estimated 15d after treatment. By G14, the topical LD50 of the selected insects was 1068-fold greater than the parental generation. Four additional populations of the budworm from the southeastern US demonstrated similar LD50s to spinosad as our parental strain, suggesting that the parental budworms from North Carolina were representative of field populations elsewhere. The resistance ratio determined with spinosad (formulated as Tracer®) in heliothine diet was 314-fold at 15d after the start of exposure. Injection of spinosad into the larval hemocoel resulted in a >163-fold resistance ratio 15d after injection, indicating that resistance could not be explained simply by altered penetration alone. Mortality was delayed in the resistant relative to the parental generation regardless of whether third instars were topically treated or exposed to treated diet. Spinosad resistance was also expressed in G14 adults, indicating that an adult vial test would be feasible for monitoring resistance. A feeding disruption assay was developed to monitor larval resistance in the field.

Monitoring on Insecticide Resistance of the Brown Planthopper and the White Backed Planthopper in Asia

Annual change in insecticide susceptibility of the long-range migrating rice insects, the brown planthopper (BPH) and the white backed planthopper (WBPH), monitored by topical application was reviewed covering temperate and tropical Asia. Monitoring in Japan revealed consistent increase in topical LD 50 of BPH for various insecticides during the period between 1967 and 1983 with small peak in 1979 and abrupt increase occurred in 1984 and 1985 with the highest peak ever observed, and then recovered to the 1979 level and remain unchanged to the present. The WBPH showed no obvious change until 1984 when marked increase in LD 30, especially for the organoosphates occurred and gradual increase still continues. In the tropics, recent data on BPH obtained from Vietnam, Thailand and Malaysia shows apparent development of insecticide resistance with remarkable increase in LD 50 as compared to the late 1970's data. Present level of insecticide susceptibility is close to those in temperate Asia. WBPH from those tropical zone also showed remarkable increase in LD 50 during the last two decades.