Effects of insecticides on sex pheromone communication and mating behavior in <Emphasis Type="Italic">Trichogramma chilonis</Emphasis>

Trichogramma chilonis Ishii is an important natural enemy of several lepidopterous pests on crops. The effects of two common insecticides on sex pheromone communication and mating behavior in T. chilonis were evaluated in the laboratory. When only males were exposed to insecticide, beta-cypermethrin LC₂₀ exposure induced significant decrease in sex pheromone perception by males and significant increase in males’ courtship and copulation frequency; beta-cypermethrin LC₁ exposure caused significant decrease in males’ courtship and copulation frequency. Males exposed to spinosad LC₂₀ exhibited significantly slower initiated courtship and significantly shorter total copulation duration, and the males exposed to spinosad LC₁ exhibited significantly increased sex pheromone perception, compared with control. When both males and females were exposed to insecticide, significantly more courtship and copulation were conducted by treated pairs that survived insecticide (beta-cypermethrin or spinosad) LC₂₀ than control pairs. Our study suggests that even the LC₁ and LC₂₀ of tested insecticides could affect the sex pheromone communication and mating behavior in T. chilonis.     

Lethal and sublethal effects of cycloxaprid,a novel cis-nitromethylene neonicotinoid insecticide,on the mirid bug Apolygus lucorum

Recently, Apolygus lucorum (Hemiptera: Miridae) has become an important insect pest of Bt cotton and fruit trees in China. At present, the application of chemical insecticides is the main control option for this pest. We investigated the lethal effect of seven neonicotinoid insecticides on A. lucorum adults, including six commercialized neonicotinoids and a novel one, cycloxaprid, which is developed in China. In addition, we assessed the sublethal physiological (longevity, fecundity) and behavioral (pre-oviposition and oviposition periods) effects of LD₁₀ (low lethal dose) and LD₄₀ (moderate lethal dose) of cycloxaprid on the mirid bug. Lethal effect of the insecticides was determined using a topical exposure method; contact toxicity against the adults was ranked as follows: cycloxaprid, nitenpyram > clothianidin > acetamiprid, imidacloprid > thiamethoxam > dinotefuran. Among these insecticides, the toxicity of cycloxaprid against the adults was the highest; its LD₅₀ value was 2.54 ng a.i. (active ingredient)/adult. Both LD₁₀ (0.74 ng a.i./adult) and LD₄₀ (1.98 ng a.i./adult) of cycloxaprid induced sublethal effects in the adults; we observed a reduced longevity in males and the LD₄₀ also shortened the longevity of females. In addition, the LD₄₀ prolonged the pre-oviposition period and shortened the oviposition period of females, and it decreased their fecundity. The hatching rate of eggs laid by the females exposed to LD₁₀ and LD₄₀ greatly decreased (two-fold lower when exposed to LD₄₀). Our results demonstrate that cycloxaprid is among the best candidate insecticides for controlling A. lucorum, and it showed significant lethal and sublethal effects on this mirid bug.     

Effect of botanical insecticide Nimbecidine<Superscript>®</Superscript> on food consumption and egg hatchability of the terrestrial snail <Emphasis Type="Italic">Monacha obstructa</Emphasis>

In the laboratory, a commercial neem-based insecticide—Nimbecidine^®—was evaluated as a potential pest management tool for the terrestrial snail, Monacha obstructa (Pfeiffer, 1842) (Hygromiidae). Effects of different concentrations of the botanical insecticide on food consumption and egg hatchability of the terrestrial snail were studied. Generally, food consumption of immature and adult snails decreased as the concentrations of Nimbecidine^® increased. At the highest concentration (10 ml/l), the snails avoided contacting with food completely. The food intake of immature individuals was significantly (p < 0.05) more affected by the Nimbecidine^® treatment (at 1.25 ml/l) than that of adults. LC₅₀ of Nimbecidine^® for the treated eggs was 2.18 ml/l, and eggs failed to hatch at concentration of 10 ml/l. Nimbecidine^® showed sufficient biological activity against the food consumption and eggs viability of M. obstructa, thus the preparation has a potential to protect field crops from this pest snails.     

Larvicidal,molluscicidal and nematicidal activities of essential oils and compounds from <Emphasis Type="Italic">Foeniculum vulgare</Emphasis>

Plant-based products, namely essential oils (EOs), are environmentally friendly alternatives for the control of disease vectors, hosts and/or parasites. Here, we studied the general toxicity and biopesticidal potential of EOs and phenylpropanoids from Foeniculum vulgare var. vulgare (bitter fennel), a perennial plant well adapted to temperate climates. EO/compound toxicity was tested against a freshwater snail and potential intermediate host of Fasciola hepatica (Radix peregra), a mosquito and former European malaria vector (Anopheles atroparvus) and one of the most damaging plant-parasitic nematodes, the root-knot nematode (Meloidogyne javanica). Lethal concentrations (LC₅₀; LC₉₀) of EOs (infrutescences/stems with leaves) and compounds were calculated by probit analysis. All displayed noteworthy activity against R. peregra adults (LC₅₀ 21–39 µg ml^?1) and A. atroparvus larvae (LC₅₀ 16–56 µg ml^?1). trans-Anethole revealed acute nematicidal activity after 24 and 48 h (LC₅₀ 310 and 249 µg ml^?1, respectively), and estragole (1,000 µg ml^?1) showed some effectiveness against M. javanica hatching and juveniles after 15 days. Plant and EO yields were determined to evaluate the bitter fennel productivity. The chemical composition of the EOs was analyzed by gas chromatography coupled to mass spectrometry. EOs extracted from whole plants, infrutescences and stems with leaves were characterized by estragole-dominant profiles (28–65 %), considerable amounts of phellandrene (10–34 %) and fenchone (6–16 %), and minor trans-anethole contents (1–4 %). Although additional toxicological studies against nontarget organisms are required, our study demonstrates that bitter fennel is a productive source of molluscicides and larvicides, and thus a potential sustainable biological agent to control particular host species, namely freshwater snails and mosquitoes.     

Chemical composition,insecticidal and biochemical effects of essential oils of different plant species from Northern Egypt on the rice weevil,Sitophilus oryzae L.

The extensive use of synthetic insecticides and fumigants for control stored-product insects has led to the development of resistance. Essential oils from aromatic plants may provide proper alternatives to currently used insect control agents. Essential oils from 20 Egyptian plants were obtained by hydrodistillation. The chemical composition of the oils was identified by gas chromatograph/mass spectrometer. Fumigant and contact toxicities of the essential oils were evaluated against Sitophilus oryzae. The inhibitory effects of the essential oils on acetylcholinesterase and adenosine triphosphatases activities were examined. The oils were composed of monoterpene hydrocarbons (i.e., limonene, sabinene, β-pinene and γ-terpinene) and oxygenated monoterpenes (i.e., terpinen-4-ol, β–thujone, 4-terpineol, α-citral and 1,8-cineole) with the exception of the oil of Schinus terebinthifolius which was contained sesquiterpenes, and the oil of Vitex agnus-castus which contained similar amounts of monoterpenes and sesquiterpenes. In the fumigation assay, the oils of Origanum vulgare (LC₅₀ = 1.64 mg/L air), Citrus lemon (LC₅₀ = 9.89 mg/L air), Callistemon viminals (LC₅₀ = 16.17 mg/L air), Cupressus sempervirens (LC₅₀ = 17.16 mg/L air), and Citrus sinensis (LC₅₀ = 19.65 mg/L air) showed high toxicity to S. oryzae. In the contact assay, the oils of Artemisia judaica, C. viminals, and O. vulgare caused the highest toxicity to S. oryzae with LC₅₀ values of 0.08, 0.09, and 0.11 mg/cm², respectively. The oil of A. judaica (I₅₀ = 16.1 mg/L) invoked the highest inhibitory effect on AChE activity, while the oils of C. viminals and O. vulgare were the most potent inhibitors to ATPases activity with I₅₀ values of 4.69 and 6.07 mg/L, respectively. The results indicate that the essential oils of A. Judaica, O. vulgare, C. limon, C. viminals, and C. sempervirens could be applicable to the management of populations of S. oryzae.     

The effects of cold pre-treatment on the toxicity of several contact insecticides on adults of three Sitophilus granarius (L.) populations

As very little is known about the impact of cold pre-treatments on insecticidal toxicity to the surviving stored-product insects, we examined the effects of cooling (?5 °C) on the toxicity of five contact insecticides to Sitophilus granarius adults from three populations (laboratory, field and selected). We determined: (a) weevil lethal time after exposure to ?5 °C, (b) the effects of two cold pre-treatments (LT₂₀ and LT₅₀—lethal time for 20 and 50 % of exposed adults) on 24 and 72 h recovery rates of laboratory adults after exposure to five insecticides and (c) deltamethrin, dichlorvos and malathion toxicity to two weevil populations with altered insecticide susceptibility after exposure to the LT₂₀ and LT₅₀ pre-treatments. The tested S. granarius populations showed no significant differences in their susceptibility to cooling. All insecticides except dichlorvos were more toxic to the laboratory weevils after 24 h than after 72 h recovery from the LT₂₀ pre-treatment. Dichlorvos and deltamethrin were more toxic to the other two populations after 72 h of recovery. Comparing the effects of cold pre-treatment and non-treatment on the laboratory strain, no significant increase in the toxicity of insecticides was detected, while only deltamethrin was significantly more toxic to the field and selected populations recovering for 24 h (12.1 and 11.0 times, respectively) and 72 h (6.9 and 36.6 times) from the LT₂₀ pre-treatment. In conclusion, only the shorter of the two cold pre-treatments was found effective in terms of increasing the insecticidal toxicity, especially against the populations with altered susceptibility to insecticides.     

Efficacy baselines of seven insecticides against larvae of Pandemis heparana (Lepidoptera: Tortricidae)

A diet-incorporation larval bioassay was used to evaluate the response of the leafroller Pandemis heparana (Denis and Schiffermüller) to seven insecticides: tebufenozide (Mimic 23% a.i., Bayer), methoxyfenozide (Prodigy 23% a.i., Bayer), flufenoxuron (Cascade 50 DC 4.7% a.i., BASF), lufenuron (Match 5.32% a.i., Syngenta), indoxacarb (Steward WG 30% a.i., Du Pont), abamectine (Vertimec EC 1.9% a.i., Syngenta) and spinosad (Laser 44.2% a.i., Dow Agro Science). Both neonate and 12-day-old (third to fourth instar) larvae were used in the bioassay. The obtained efficacy baselines were compared with the response of the pest exposed to leaves treated with the same insecticides. The persistence of field-aged leaf residues of the seven insecticides was bioassayed on neonate larvae. Given the obtained LC₅₀ values in the diet-incorporation bioassays larval age was not always a significant factor affecting the response of P. heparana larvae. Differences in LC₅₀ values between neonate and 12-day-old larvae were not statistically significant for abamectine, tebufenozide and methoxyfenozide. Young larvae seemed to be more susceptible than older larvae to spinosad, indoxacarb and lufenuron, while flufenoxuron was more effective against 12-day-old than neonate larvae. When the larvae were exposed to the insecticides on treated leaves, all the tested compounds were less effective on older larvae than on neonates. When applied at the recommended field rates, all seven insecticides can be considered highly effective against both neonate and 12-day-old larvae of P. heparana because their security index (SI = recommended field rate/LC₉₀) always exceeded the threshold value of 1. The high persistence of insect growth inhibitors (IGIs) and moulting accelerating compounds (MACs) in the field compensates for their relatively low SI values. For this reason and given their activity against Cydia pomonella, IGIs and MACs are the most interesting insecticides for spring treatments for the combined control of both species, P. heparana and C. pomonella.     

Impact of agricultural adjuvants on the toxicity of the diamide insecticides chlorantraniliprole and flubendiamide on different life stages of the navel orangeworm (<Emphasis Type="Italic">Amyelois transitella</Emphasis>)

The navel orangeworm (Amyelois transitella) (Walker) is a destructive pest of tree nuts in California orchards. Overall demand for these crops and acreage expansions have resulted in significant insecticide applications to reduce A. transitella damage. Despite widespread use in A. transitella insecticide applications, the potential toxicity of adjuvants applied in combination with insecticides remains uncharacterized. In these experiments, five adjuvants (Cohere^®, Dyne-Amic^®, FastStrike^®, Induce^®, Latron B-1956^®), alone and in combination with the diamide insecticides chlorantraniliprole (Altacor^®) and flubendiamide (Belt^®), were assessed for activity against the adults and eggs of A. transitella. Laboratory studies utilized a spray tower for application while field studies used orchard air-blast sprayers. Laboratory exposure of both adults and eggs demonstrated that adjuvant toxicity varied across life stages. In the laboratory, the addition of chlorantraniliprole to adjuvants increased incapacity (dead + moribund). The results for flubendiamide were variable, and only FastStrike had the same high adult toxicity for both diamides. For eggs exposed to these diamides, overall mortality was similar. In field studies, Dyne-Amic and Latron B-1956 were tested and their adult toxicity varied. In contact assays, effects of adjuvants were similar when used with Belt^® and differed when used with Altacor^®. We conclude that the adjuvants for navel orangeworm management are intrinsically toxic to A. transitella in both the laboratory and field. Further studies are needed to attain the toxicity realized in the laboratory in field applications and also to determine whether our findings of adjuvant enhancement of insecticide toxicity are applicable to other insecticide classes.     

Basis and monitoring of methoxyfenozide resistance in the South American tomato pinworm Tuta absoluta

The South American tomato pinworm, Tuta absoluta (Meyrick, 1917) (Lepidoptera: Gelechiidae), is heavily targeted by insecticide applications. Methoxyfenozide is highly effective against T. absoluta with reduced side effects to natural enemies. This work aimed to (1) genetically and biochemically characterize resistance of the T. absoluta GBN population to methoxyfenozide, (2) establish cross resistance profiles with other insecticide groups and (3) monitor resistance in populations with the goal of improving T. absoluta insecticide resistance management (IRM). Methoxyfenozide resistance was completely recessive, polyfactorial and autosomal. Effective dominance revealed that 10 mg methoxyfenozide/L would be enough to eliminate susceptible homozygotes and heterozygotes, thus used to diagnose resistance in field populations. The synergism of methoxyfenozide toxicity in the resistant population for PBO (SR?=?95×), DEF (SR?=?51×) and DEM (SR?=?45×), suggested monooxygenases, esterases and glutathione S-transferases as resistance mechanisms. However, only monooxygenase activity appeared to be involved in methoxyfenozide resistance. Resistance ratio for methoxyfenozide (2352-fold) after selection and cross-resistance ratios of a lab-selected GBN strain (“GBN-Sel”) were significant relative to a susceptible strain “JDR1-Sus” for tebufenozide (656-fold), cartap hydrochloride (10.68-fold), deltamethrin (4.70-fold), abamectin (2.65-fold), lufenuron (2.22-fold) and indoxacarb (1.92-fold), with negative cross-resistance to spinetoram (0.32-fold). Evidence of control failures was observed in 10 field populations of T. absoluta (mortalities between 13 and 76%), and all populations showed frequencies of resistant phenotypes (percentage survivorship ranging between 4 and 96%). A rational basis for managing resistance to bisacylhydrazines is discussed, along with details of recommended T. absoluta resistance management tactics.

     

Effects of chlorantraniliprole on development and reproduction of beet armyworm, <Emphasis Type="Italic">Spodoptera exigua</Emphasis> (Hübner)

The lethal and sublethal effects of chlorantraniliprole against Spodoptera exigua (Hübner) were evaluated under laboratory conditions by oral exposure of neonate larvae to the compound. The 72 h LC₅₀ value of this insecticide to S. exigua was found to be 12.747 μg l⁻¹. A progressive larval mortality of 24.32% for LC₃₀ treatment and 42.61% for LC₅₀ treatment was observed from 4th to 6th day after exposure, which resulted in the reduced pupation rates in exposure groups. The sublethal effects of this chemical were indicated by prolongation of larval period, the increase of pupal weight and decrease in hatch rate of egg. Chlorantraniliprole at LC₃₀ and LC₅₀ rate significantly delayed larval development; the developmental duration of surviving larvae was extended for 22.5 and 28.6%, respectively, compared with that of control group. LC₃₀ treatment increased the mean weight of pupa and induced to the production of heavier pupa (>150 mg). In LC₅₀ treatment, heavier pupa also showed up but the mean weight of pupa was not influenced. The egg hatch rate in LC₅₀ group was significant lower than that in control and LC₃₀ groups. No significant differences in pupal duration, emergence rate, sex ratio, egg number per female, and longevity of adults were observed among treatments. Chlorantraniliprole had exceptional activity against S. exigua according to concentration–response bioassay in laboratory, and the toxicities were primarily resulted from immediate lethality.     

Monitoring and efficacy of selected insecticides for European corn borer (<Emphasis Type="Italic">Ostrinia nubilalis</Emphasis> Hubn., Lepidoptera: Crambidae) control

The European corn borer (ECB), Ostrinia nubilalis (H?bner) (Lepidoptera: Crambidae), is the major arthropod pest of corn in Croatia. However, chemical control is carried out only in maize for seed production, and in sweet corn. A 3-year investigation was carried out in corn fields in northwest Croatia to establish the most attractive pheromone lure for ECB monitoring, the optimal timing of insecticide applications, and the efficacy of selected insecticides against ECB. During each of the 3 years, the pheromone lures E, Z and E/Z («Isagro») were evaluated in the field from May to July. Insecticides were sprayed 14–20 days after the maximal capture in 2002 and 2003. In 2004, three different trials were set up: one trial with one early treatment (when corn was in the R49 development stage according to the extended BBCH scale); one with one late treatment (when corn was in the R65 development stage according to the BBCH scale); and one with two treatments in both stages. In the trials studying Bacillus thuringiensis var. kurstaki (B.t.k.), insect growth regulators (IGR), spinosad and classical chemical insecticides were applied. Pheromone lure E was the most attractive for monitoring ECB flights throughout 2 years of investigation. Insecticide efficacy depended on application timing. The insecticides most suitable for integrated pest management (IPM) programs, including spinosad, B.t.k. and IGR, resulted in high (spinosad) to moderate (B.t.k.) efficacy. The efficacy of IGRs indicates the need for earlier application. The efficacy of chemical insecticides depended on the year and the insecticide. The organophosphate (OP) insecticides and pyrethroids gave moderate to good results; imidacloprid did not provide significant efficacy. One application of all insecticides based on proper (early) timing resulted in the same efficacy as two applications of the same insecticides.     

The influence of the aphid-specific pathogen Conidiobolus obscurus (Entomophthoromycota: Entomophthorales) on the mortality and fecundity of bamboo aphids

Bioassays and scanning electron microscopy of Conidiobolus obscurus for bamboo aphids as well as its effects on the fecundity of bamboo aphids were carried out to estimate bamboo aphid biocontrol potential. Multi-concentration bioassay and fecundity assessment were performed on aphid species of Takecallis taiwanus, Takecallis arundinariae, Melanaphis bambusae, and Metamacropodaphis bambusisucta. C. obscurus can effectively infect four species of bamboo aphids, and most cadavers appeared in the first 2 days after inoculation. The final mortalities reached 74–91 % at high concentrations of conidia among the tested species. Based on the fitted time–concentration–mortality models, the estimates of the median lethal concentration (LC₅₀) of the fungal conidia differed significantly among different aphid species and decreased with observation days. The lowest LC₅₀ was estimated to be 57 conidia mm^?2 for T. taiwanus on day 5 after conidial shower. Moreover, the C. obscurus-infected aphids only produced 3.9–18.2 % progeny of the corresponding healthy aphids, which strongly presented fungal influence on host fecundity. In conclusion, C. obscurus has the ability of restraining the development of bamboo aphid populations, which is suitable for further application in aphid biocontrol in bamboo forests.     

Toxicity and antitermite activity of the essential oils from Cinnamomum camphora, Cymbopogon nardus, Melaleuca cajuputi and Dipterocarpus sp. against Coptotermes curvignathus

Efficacy of four different essential oils against the subterranean termite, Coptotermes curvignathus Holmgren, was assessed in various bioassays. Laboratory results indicate that the highest termite mortality was found in Dipterocarpus sp. essential oil after 24 h (LC₅₀ = 1.62 %) and the lowest in Melaleuca cajuputi (LC₅₀ = 4.60 %). The wood consumption in the filter paper treated with Dipterocarpus sp. oil is also smaller than for the other three essential oils tested. However, the other three essential oils also inhibited termite susceptibility of the specimens. Dipterocarpus sp. (keruing oil) was the most effective insect antifeedant and repellent against C. curvignathus. The results suggest that essential oils might have some beneficial activity of economic value and are considered good candidates for the development of new chemicals (repellents or antifeedants) for termite control.     

Susceptibility of the Mexican bean beetle <Emphasis Type="Italic">Epilachna varivestis</Emphasis> Mulsant (Coleoptera: Coccinellidae) to endemic isolates of <Emphasis Type="Italic">Beauveria bassiana</Emphasis> (Balsamo) Vuillemin (Hypocreales: Clavicipitaceae)

Entomopathogenic fungi represent excellent candidates for biological insecticides. Among the many entomopathogenic fungi, Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Clavicipitaceae) is one of the most promising species. Here, we report the results of infection studies performed using four B. bassiana native isolates (Bb37, Bb38, Bb40, and Bb45) compared with the commercial product Mycotrol^® (strain GHA) on adult Mexican bean beetle Epilachna varivestis Mulsant (Coleoptera: Coccinellidae), one of the most important pests of bean production in Mexico. First, single concentration (1 × 10⁸ conidia mL^?1) assays were carried out using all isolates applied using an immersion method. Examinations at 10 days after inoculation indicated that isolates Bb37, Bb38, and Bb40 significantly reduced adult survival, causing 60–75% mortality compared to the commercial strain GHA (33%) and control (29%). Second, using two selected isolates (Bb37 and Bb40), the mean lethal concentration values (LC₅₀) were estimated for third instar larvae and adult E. varivestis. The LC₅₀ values for Bb37 and Bb40 isolates decreased 5.26-fold and 3.19-fold, respectively, in third instars compared with adults. However, such difference for Bb40 isolate was not significant. Finally, an experiment, to compare the median survival time (MST) values between third instar and adult E. varivestis, was conducted using Bb37 and Bb40 at 1 × 10⁹ conidia mL^?1. MST values were significantly reduced against larvae (87 and 100 h) compared with adults (130 and 134 h) by Bb37 and Bb40, respectively. We conclude that native isolates of B. bassiana represent an important alternative for the control of E. varivestis. However, to demonstrate its effectiveness under field conditions, detailed studies are needed.     

Potential of Metarhizium anisopliae and Beauveria bassiana in the control of tea termite Microtermes obesi Holmgren in vitro and under field conditions

Two strains of Metarhizium anisopliae (Metschnikoff) Sorokin and two strains of Beauveria bassiana (Ballsamo) Vuillemin were evaluated for their potential use as biological control agents against the tea termite Microtermes obesi Holmgren. The strains were screened for relative pathogenicity, and the median lethal time eliciting 50% mortality (LT₅₀) was calculated. In general, the M. anisopliae strains were more virulent with lower LT₅₀ values than B. bassiana strains. The LT₅₀ values ranged from 1.6 to 3.7 days. The median lethal concentrations (LC₅₀) of all the isolates were also determined. The M. anisopliae strains had low LC₅₀ values compared to B. bassiana strains. The LC₅₀ values ranged from 35 to 140 conidia per termite. The strains were also tested for survival under laboratory nest conditions. All the isolates exhibited the ability to grow, sporulate and produce an epizootic in treated nest material. Field applications of the isolates also produced promising results.     

Field evaluation of an attract and kill strategy against western corn rootworm larvae

The larvae of the invasive maize pest Diabrotica virgifera virgifera (Coleoptera; Chrysomelidae, western corn rootworm) hatch in the soil in spring and search for maize roots following CO₂ gradients. CO₂ is one cue that might be used as an attractant towards soil insecticides, a mechanism already shown in laboratory experiments. This study compared the efficacy of several combinations of in or between-row applications of different rates of CO₂-emitting capsules and/or soil insecticides (here tefluthrin) aimed at preventing root damage by the pest larvae under field conditions. CO₂ emission of the capsules in the soil lasted up to 28 days with a peak after 21 days coinciding with the first larval hatch. The pest density in the soil was not high enough to cause root damage above the economic threshold. Furthermore all tefluthrin applications, regardless of whether at full, half or quarter rates effectively prevented root damage; thus CO₂ did not significantly further increase this efficacy. In-row applications of tefluthrin with or without CO₂-emitting capsules prevented root damage to a much larger extent (59–77 % on the node injury scale) than the between-row applications of tefluthrin with or without capsules (17–31 %). In conclusion, further research on belowground orientation and movement of D. v. virgifera larvae, as well as tests with combinations of CO₂-emitting capsules and lower rates of soil insecticide are needed to potentially develop attract and kill strategies as a management option against this maize pest.     

Effect of larval selection with two bioinsecticides on susceptibility levels and reproductive capacity ofAedes aegypti (L.)

Two bacterial insecticides,Bacillus thuringiensis H-14 andB. sphaericus 1593 were evaluated for larvicidal potency against mosquito larvae ofAedes aegypti. LC₅₀ values showed thatB.thuringiensis H-14 (4×10⁵ spores/ml) had a higher pathogenicity against fourth larval instars ofA. aegypti thanB. sphaericus (3.1×10⁶ spores/ml) by about 7.75 times. Larval selection with LC₉₀ of both pathogens for 8 successive generations caused a decrease in the susceptibility levels of selected strains ofA. aegypti as compared with the original strain. Moreover, the results indicated that the effect of larval selection with the above bioinsecticides led to an obvious reduction in the egg production and hatchability of eggs produced by mosquito adults that developed from surviving larvae.     

Lethal and sublethal effects of spirotetramat on the mealybug destroyer, Cryptolaemus montrouzieri

Spirotetramat is a new systemic insecticide listed in Group 23 of the IRAC mode-of-action classification scheme as an inhibitor of lipid biosynthesis. Side effects assessment on key natural enemies is necessary before incorporating a pesticide in IPM programs. Herein, lethal and sublethal side effects of spirotetramat on adults and larvae of Cryptolaemus montrouzieri Mulsant (Coleoptera: Coccinellidae) were evaluated under laboratory conditions by topical application and by ingestion of treated individuals of Planococcus citri Risso (Hemiptera: Pseudococcidae). The lethal and sublethal effects of spirotetramat were compared to those of chlorpyriphos and pyriproxyfen, two insecticides commonly used in Spanish citrus. Spirotetramat resulted harmless: (1) when directly applied on larvae and adults of C. montrouzieri, since it did not affect survival, longevity, fecundity, egg hatching, and offspring survival. In contrast, chlorpyriphos was classified as moderately toxic for adults due to its effects on fecundity, egg hatching and offspring survival. Pyriproxyfen was classified as harmful for larvae due to the acute effect on pupal mortality. When larvae and adults of C. montrouzieri were fed with treated prey, spirotetramat was also classified as harmless. Adults of C. montrouzieri fed with pyriproxyfen-treated prey exhibited increased fecundity but no eggs hatched. Moreover, the larvae fed on pyriproxyfen-treated prey did not reach the adult stage. The results of this study indicate that spirotetramat may be compatible with augmentative releases of C. montrouzieri in citrus.     

Assessing toxicity of post-emergence herbicides to the Spilarctia obliqua Walker (Lepidoptera: Arctiidae)

The lethal and sublethal effects of three post-emergence herbicides, 2,4-D ethyl ester (Weedkill 80WP), imazethapyr (Pursuit 10EC) and quizalofop ethyl (Tergasuper 5EC) fortified with artificial diets were studied on larvae of Spilarctia obliqua Walker (Lepidoptera: Arctiidae). Quizalofop ethyl and imazethapyr caused significant reduction of pest survival at almost all levels; however, 2,4-D ethyl ester was nontoxic. Interestingly, LC₅₀ data (0.230 and 0.855% for quizalofop ethyl and imazethapyr, respectively) obtained from probit analysis were almost equal to labeled doses (x) of quizalofop ethyl (x = 0.16%) and imazethapyr (x = 0.625%), which shows the high toxicity of these compounds against S. obliqua larvae. Among the three herbicides, imazethapyr caused sublethal effects on this pest, increasing the larval period at almost all concentrations tested in the artificial diet. Considering the markedly significant effect of quizalofop ethyl on pest survivorship with no sublethal effect, we suggest incorporating it into the integrated pest management module for S. obliqua in legumes or oilseed crops with other biorational insecticides. Based on toxicity, imazethapyr can be a potential candidate for integrated management of S. obliqua. However, because of its sublethal effects, we advocate caution while using it in the presence of pest infestations.     

Pheromone-based decision support tools for management of <Emphasis Type="Italic">Halyomorpha halys</Emphasis> in apple orchards: development of a trap-based treatment threshold

The invasive brown marmorated stink bug, Halyomorpha halys (Stål), has become a serious pest in mid-Atlantic apple orchards. Because no decision support tools exist for H. halys management, calendar-based insecticide applications have been the only successful technique for mitigating H. halys injury in orchards. Following the identification of the two-component aggregation pheromone of H. halys, we conducted a study to determine whether biological information generated by traps baited with this pheromone and pheromone synergist could be used to make management decisions. In this study, experimental apple orchards were treated with a H. halys-targeted insecticide only when a predetermined cumulative threshold of either 1, 10, or 20 adults per trap was reached. Once threshold was reached, two alternate row middle sprays 1 week apart were triggered and the threshold was reset. For comparison, some orchards were also subjected to a weekly alternate row middle spray or left untreated as controls. At harvest, significantly less fruit injury was observed when treated weekly or using a threshold of 1 or 10 H. halys adults per trap to trigger insecticide applications. Orchards treated using a cumulative threshold of 20 adults per trap or when left unsprayed had significantly higher fruit injury. In addition, insecticide applications were reduced by 40% using a threshold of 10 adults per trap. Our results suggest that baited pheromone traps can be used as decision support tools to trigger insecticide applications when needed to mitigate risk and effectively manage H. halys in apple orchards.