Effect of pyriproxyfen,a juvenile hormone mimic,on egg hatch,nymph development,adult emergence and reproduction of the Asian citrus psyllid,Diaphorina citri Kuwayama

BACKGROUND: The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, is a vector of bacteria presumably responsible for huanglongbing (HLB) disease in citrus. In this laboratory study, an investigation was made of the activity of pyriproxyfen, a juvenile hormone mimic, on ACP eggs, nymphs and adults to evaluate its potential as a biorational insecticide for inclusion in an integrated pest management (IPM) program for ACP. RESULTS: Irrespective of egg age, timing or method of treatment, a significantly lower percentage of eggs (5–29%) hatched after exposure to 64 and 128 µg mL^?1 of pyriproxyfen. Only 0–36% of early instars (first, second and third) and 25–74% of late instars (fourth and fifth) survived to adults following exposure to 16, 32 and 64 µg mL^?1 of pyriproxyfen. However, 15–20% of adults that emerged following treatment as late instars exhibited morphological abnormalities. Furthermore, pyriproxyfen adversely affected reproduction (fecundity and fertility) of adults that emerged from treated fifth instars or that were treated topically with 0.04 µg as adults. CONCLUSIONS: Application of pyriproxyfen at 64 µg mL^?1 resulted in greater inhibition of egg hatch and suppression of adult emergence compared with lower rates. Pyriproxyfen also markedly reduced female fecundity and egg viability for adults that were exposed either as fifth instars or as newly emerged adults. The ovicidal, larvicidal and reproductive effects against ACP suggest that pyriproxyfen is suitable for integration into an IPM program for ACP. Copyright © 2009 Society of Chemical Industry     

Lethal and sub-lethal effects of a novel sulfoximine insecticide,sulfoxaflor, against Asian citrus psyllid and its primary parasitoid under laboratory and field conditions

The Asian citrus psyllid, Diaphorina citri Kuwayama, is the most important international pest of citrus because it transmits the bacteria that cause huanglongbing (HLB). HLB limits citrus production globally. We evaluated the toxicity of sulfoxalor against D. citri and its parasitoid, Tamarixia radiata Waterston. Sulfoxaflor was as toxic as imidacloprid to adult D. citri. The LC₅₀ values for sulfoxaflor and imidacloprid were 8.17 and 5.7 µg AI mL^?1, respectively. The LC₅₀ of sulfoxaflor for T. radiata adults was 3.3 times greater than for D. citri adults. Treatment with sulfoxaflor resulted in reduced oviposition, development of nymphs, and emergence of adult D. citri on plants, as compared with controls. The lowest concentration that reduced adult emergence was 0.6 µg AI mL^?1. There was reduced feeding by D. citri adults on leaves treated with sulfoxaflor. The residual toxicity of sulfoxaflor was equivalent to imidacloprid. Under field conditions, formulated sulfoxaflor reduced populations of D. citri compared with untreated controls. Sulfoxaflor is a novel mode of action and is an effective tool for D. citri management.     

Effect of Buprofezin onIcerya Purchasi andPlanococcus Citri

The effectiveness of buprofezin (aqueous suspensions from 25% wettable powder) on cumulative nymph mortality and reproduction of two homopterous pests,Icerya purchasi Maskell (Margarodidae) andPlanococcus citri (Risso) (Pseudococcidae), was investigated under laboratory conditions. Buprofezin was very effective against crawlers of both species. Dipping in concentrations of 0.002%, 0.01% and 0.05% (a. i.) resulted in 91–99% nymph mortality ofP. citri, whereas 100% mortality was recorded whenI. purchasi was treated at 0.05% (a. i.); the 3rd-instar nymphs ofI. purchasi were less susceptible to the chemical. Death of the larval stages occurred mainly during the molting process to the 2nd-instar nymphs. At 0.05%, buprofezin sprayed on adults slightly reduced fecundity and decreased egg hatch to 31% forI. purchasi and, depending on the exposure period of the females, to 49-7% forP. citri. Buprofezin at 0.05% exhibited strong ovicidal activity onP. citri, resulting in inhibition of over 80% egg hatch.     

Suppression of Reproduction in Poekilocerus pictus (F.) using Penfluron and Diflubenzuron

Abstract

Penfluron and diflubenzuron, both chitin synthesis inhibitors known to be highly effective against nymphs of Poekilocerus pictus (F.), were tested against the adult for their possible effects upon reproduction. These compounds were found to have the maximum effect, when no eggs were laid, if both sexes were treated. The eggs of treated males × untreated females did not hatch and those of treated females × untreated males gave rise to nymphs which died before reaching maturity.     

Evaluation of alternative rice planthopper control by the combined action of oil-formulated Metarhizium anisopliae and low-rate buprofezin

BACKGROUND: High resistance of brown planthopper (BPH) Nilaparvata lugens Stål to common insecticides is a challenge for control of the pest. An alternative control strategy based on the combined application of fungal and chemical agents has been evaluated. RESULTS: Three gradient spore concentrations of oil‐formulated Metarhizium anisopliae (Metschnikoff) Sorokin (Ma456) were sprayed onto third‐instar nymphs in five bioassays comprising the low buprofezin rates of 0, 10, 20, 30 and 40 µg mL^?1 respectively. Fungal LC₅₀ after 1 week at 25 °C and 14:10 h light:dark photoperiod decreased from 386 conidia mm^?2 in the buprofezin‐free bioassay to 40 at the highest chemical rate. Buprofezin (LC₅₀: 1647, 486 and 233 µg mL^?1 on days 2 to 4) had no significant effect on the fungal outgrowths of mycosis‐killed cadavers at the low application rates. The fungal infection was found to cause 81% reduction in reproductive potential of BPH adults. In two 40 day field trials, significant planthopper (mainly BPH) control (54–60%) was achieved by biweekly sprays of two fungal candidates (Ma456 and Ma576) at 1.5 × 10¹³ conidia ha^?1 and elevated to 80–83% by incorporating 30.8 g buprofezin ha^?1 into the fungal sprays. CONCLUSION: The combined application of the fungal and chemical agents is a promising alternative strategy for BPH control. Copyright © 2010 Society of Chemical Industry     

Composition and biological activity of essential oils from Labiatae against Nezara viridula (Hemiptera: Pentatomidae) soybean pest

BACKGROUND: Plant essential oils have been recognised as an important natural source of insecticide. This study analysed the chemical constituents and bioactivity of essential oils that were isolated via hydrodistillation from Origanum vulgare L. (oregano) and Thymus vulgaris L. (thyme) against eggs, second instar and adults of Nezara viridula (L.). RESULTS: The major component of oregano was p‐cymene, and, for thyme, thymol. The ovicidal activity was tested by topical application; the essential oil from thyme was more effective. The fumigant activity was evaluated in an enclosed chamber; the LC₅₀ values for oregano were 26.8 and 285.6 µg mL^?1 for nymphs and adults respectively; for thyme they were 8.9 µg mL^?1 for nymphs and 219.2 µg mL^?1 for adults. To evaluate contact activity, a glass vial bioassay was used; the LC₅₀ values for oregano were 1.7 and 169.2 µg cm^?2 for nymphs and adults respectively; for thyme they were 3.5 and 48.8 µg cm^?2 respectively. The LT₅₀ analyses for contact and fumigant bioassays indicated that thyme was more toxic for nymphs and adults than oregano. Both oils produced repellency on nymphs and adults. CONCLUSION: These results showed that the essential oils from O. vulgare and T. vulgaris could be applicable to the management of N. viridula. Copyright © 2011 Society of Chemical Industry     

Response of citrus peelminer Marmara gulosa Guillén and Davis (Lepidoptera: Gracillariidae) stages to various insecticides

BACKGROUND: Egg and larval stages of citrus peelminer Marmara gulosa Guillén and Davis infesting zucchini squash Cucurbita pepo L. var ‘Revenue’ were exposed in the laboratory to a wide range of insecticide classes used in California citrus (organophosphate, carbamate, pyrethroid, neonicotinoid, insect growth regulator, fermentation products and sulfur) to determine peelminer response with and without a non‐ionic adjuvant or oil. RESULTS: All of the insecticides tested except sulfur reduced egg hatch and mine initiation. When the larval stage was treated, only buprofezin failed to reduce larval and pupal development. Cyfluthrin and spinosad, with the addition of adjuvant or oil, and abamectin combined with oil allowed no survivors at 7 days after treatment (DAT). The slower‐acting insect growth regulators pyriproxyfen and diflubenzuron applied in combination with adjuvant or oil allowed no survival of peelminer 21 DAT. A field trial showed 62.6–68.5% reduction in mined citrus fruit after two applications of diflubenzuron and no significant improvement of control with the addition of cyfluthrin. CONCLUSION: Bioassays indicate that M. gulosa is relatively susceptible to a wide range of insecticide classes in the laboratory. Lack of efficacy experienced in field trials would then be due to characteristics of the fruit or canopy that limit coverage, rather than to the effectiveness of the insecticides. Copyright © 2008 Society of Chemical Industry     

Insecticidal activity against Aedes aegypti of m-pentadecadienyl-phenol isolated from Myracrodruon urundeuva seeds

BACKGROUND: Myracrodruon urundeuva Fr. Allemao is a common tree in the Caatinga that has been widely used for various medical purposes. Previous studies showed that the ethanol seed extract of M. urundeuva has potent activity against the larval stage of the dengue vector Aedes aegypti. Given this potential insecticidal activity, bioguided separation steps were performed in order to isolate the active compound(s). RESULTS: The isolation process resulted in only one active chemical compound, identified by infrared spectroscopy and mass spectrometry as m-pentadecadienyl-phenol. This compound presented potent larvicidal and pupicidal activity (LC₅₀ 10.16 and 99.06 µg mL⁻¹ respectively) and great egg hatching inhibitory activity (IC₅₀ 49.79 µg mL⁻¹). The mode of action was investigated through observations of behavioural and morphological changes performed in third-instar larvae treated with m-pentadecadienyl-phenol solution after 1, 6, 12, 16 and 20 h of exposure. Some changes were observed as flooding of the tracheal system, alterations in siphonal valves and anal gills and lethargy, probably caused by the strong anticholinesterasic activity reported previously. CONCLUSION: The compound isolated from M. urundeuva seeds, m-pentadecadienyl-phenol, showed potent activity against immature stages of dengue vector, Ae. aegypti, being considered the main larvicidal principle. Copyright © 2012 Society of Chemical Industry     

Aqueous solubilities,photolysis rates and partition coefficients of benzoylphenylurea insecticides

The aqueous solubilities and octanol–water partition coefficients (K_OW) of the benzoylphenylurea (BPU) insecticides teflubenzuron, chlorfluazuron, flufenoxuron and hexaflumuron were determined in comparison with the more extensively studied diflubenzuron. Both teflubenzuron and hexaflumuron were substantially less water‐soluble (9.4 (± 0.3) µg litre⁻¹ and 16.2 (± 0.5) µg litre⁻¹ in water, respectively) than the value previously reported for diflubenzuron (89 (± 4) µg litre⁻¹ in water). Log K_OW values for diflubenzuron, teflubenzuron, hexaflumuron, flufenoxuron and chlorfluazuron were 3.8, 5.4, 5.4, 6.2 and 6.6, respectively, as determined using reverse‐phase HPLC. Photodegradation of hexaflumuron, teflubenzuron and diflubenzuron in water indicated hexaflumuron to be the most rapidly degraded of the three compounds at pH 7.0 (t_1/2 = 8.6 (± 0.4) h) and pH 9.0 (t_1/2 = 5 (± 1) h); diflubenzuron was the slowest of the three pesticides to degrade in pH 7.0 (17 (± 4) h) and pH 9.0 (8 (± 2) h) buffered water. In a solar simulator using river water buffered to pH 9.0, teflubenzuron, hexaflumuron and diflubenzuron half‐lives were 20 (± 4), 15 (± 2) and 12 (± 1) h, respectively; dark controls showed no loss of parent BPU over similar time periods. © 2000 Society of Chemical Industry     

Pyriproxyfen,a novel insect growth regulator for controlling whiteflies: Mechanisms and resistance management

Pyriproxyfen, a novel juvenile hormone mimic, is a potent suppressor of embryogenesis and adult formation of the sweetpotato whitefly, Bemisia tabaci (Gennadius), and the greenhouse whitefly, Trialeurodes vaporariorum (Westwood). Dipping of cotton or tomato seedlings infested with 0 to 1-day-old eggs in 0.1 mg litre^?1 resulted in over 90% suppression of egg hatch of both B. tabaci and T. vaporariorum. Older eggs were affected to a lesser extent. Exposure of whitefly females to cotton or tomato seedlings treated with pyriproxyfen resulted in oviposition of non-viable eggs. The LC90 values for egg viability of B. tabaci and T. vaporariorum exposed to treated plants were 0.05 and 0.2 mg litre^?1, respectively. Treatment of whitefly larvae with 0.04–5 mg litre^?1 resulted in normal development until the pupal stage; however, adult emergence was totally suppressed. Second instars of B. tabaci exposed to 5 mg litre^?1 pyriproxyfen, excreted honeydew at a level similar to the control level until the fourth instar (pupation), after which a strong reduction was observed. Inhibition of egg-hatch on the lower surface of cotton leaves was observed when their upper surface was treated with 1–25 mg litre^?1, indicating a pronounced translaminar effect. These findings indicate that pyriproxyfen is an efficient control agent of both B. tabaci and T. vaporariorum. The compound has been used successfully for controlling whiteflies in Israeli cotton fields since 1991. Adults of B. tabaci collected from a rose greenhouse and from adjacent cotton fields were monitored during 1991–1993 for their susceptibility to pyriproxyfen. A high level of resistance was recorded in whiteflies collected from a greenhouse after three successive applications of pyriproxyfen. Based on LC50 values, the resistance ratio for egg-hatch suppression was 554-fold and, for adult emergence failure, 10-fold. However, a single treatment of pyriproxyfen in cotton fields during the summer season (according to an insecticide resistance management (IRM) strategy) did not alter appreciably the susceptibility of B. tabaci to this compound. In order to prevent development of resistance, an attempt should be made to restrict its use to one treatment per crop season applied during the peak activity of the pest. Pyriproxyfen can be alternated with other novel compounds such as buprofezin and diafenthiuron for controlling whiteflies in cotton, vegetables and ornamentals as part of integrated pest management (IPM) and IRM strategies. In pyriproxyfen- or buprofezin-resistant strains of B. tabaci or T. vaporariorum, no appreciable cross-resistance was observed among pyriproxyfen, buprofezin and diafenthiuron.     

Effects of pymetrozine, an antifeedant of Hemiptera, on Asian citrus psyllid, Diaphorina citri, feeding behavior, survival and transmission of Candidatus Liberibacter asiaticus

BACKGROUND: Vector‐borne plant disease management can be enhanced by deployment of antifeedants in addition to the use of broad‐spectrum neurotoxic insecticides. The effects of pymetrozine on Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, feeding behaviour, survival and transmission of Candidatus Liberibacter asiaticus (Las), the presumed causal pathogen of huanglongbing, were investigated. RESULTS: Pymetrozine applied at 52 and 104 µg mL^?1 to citrus plants [Swingle citrumelo (X Citroncirus webberi Ingram and Moore)] modified the feeding behavior of ACP and increased the amount of time spent performing non‐penetration behaviors while decreasing the time spent performing ingestion behaviors compared with the controls 1 day after treatment. However, the antifeedant effect of pymetrozine subsided 5 days after application. Pymetrozine reduced the survival of both adults and nymphs on treated plants compared with the control. However, it had a greater impact on survival of nymphs than on survival of adults. Pymetrozine applied at 52 and 104 µg mL^?1 on Las‐infected ‘Valencia’ sweet orange plants [Citrus sinensis L. (Osbeck)] reduced acquisition (12 and 21% respectively) and transmission (11 and 18% respectively) of Las by feeding ACP adults compared with the controls; however, these reductions were not statistically significant. CONCLUSIONS: Pymetrozine exhibited moderate antifeedant effects by modifying the feeding behavior of ACP adults with short residual activity. The impact of pymetrozine on survival of nymphs was greater than on adults at the higher concentrations tested. Pymetrozine also reduced the acquisition and transmission of Las by feeding ACP adults up to 21 and 18%, respectively, compared with untreated controls. Copyright © 2010 Society of Chemical Industry     

Evaluation of some selective insecticides and their combinations with summer oil for the control of the pear psyllaCacopsylla pyri

A field trial was carried out to evaluate the efficacy of several selective insecticides for the control of pear psyllaCacopsylla pyri (L.) (Hemiptera: Psyllidae) in two successive years. Three insect growth regulators (IGRs) — diflubenzuron, pyriproxyfen and teflubenzuron, and an amin-hydrazine derivative — amitraz, were evaluated singly and in combination with summer oil (1%). All insecticides were applied at recommended label rates in both years. When compared with the untreated control, all insecticides alone and their combinations with summer oil, except for pyriproxyfen alone, provided control of young (1st and 2nd instars) nymphs. However, combined applications of these insecticides and summer oil were more effective than either insecticide alone for controlling the egg and young nymph stages of the pest. The products were less effective against older (3rd–5th instars) nymphs, even in combination with summer oil, and failed to suppress the population of older nymphs. Adding oil to sprays also delayed oviposition by winterform and summerform females. With the exception of oil with amitraz, combinations of insecticides with summer oil did not cause any phytotoxicity during the study.     

Toxicity of formic acid to red imported fire ants, Solenopsis invicta Buren

BACKGROUND: Ants often compete with other ants for resources. Although formic acid is a common defensive chemical of formicine ants, it does not occur in any other subfamilies in Formicidae. No information on toxicity of formic acid to red imported fire ants, Solenopsis invicta, is available. This study examined its contact and fumigation toxicity to S. invicta in the laboratory. RESULTS: In a contact toxicity bioassay, 24 h LD₅₀ values of formic acid for workers ranged from 124.54 to 197.71 µg ant⁻¹. Female alates and queens were much less sensitive to formic acid than workers. At a concentration of 271.72 µg ant⁻¹, which killed 81.09 ± 16.04% of workers, the 24 h mortality was up to 39.64% for female alates and 38.89% for queens. In fumigation bioassays, 24 h LC₅₀ values ranged from 0.26 to 0.50 µg mL⁻¹ for workers, 0.32 µg mL⁻¹ for male alates and 0.70 µg mL⁻¹ for female alates. Complete mortality (100%) in queens occurred 24 h after they had been exposed to 1.57 µg mL⁻¹ of formic acid. At a concentration of 2.09 µg mL⁻¹, KT₅₀ values ranged from 23.03 to 43.85 min for workers, from 37.84 to 58.37 min for male alates, from 86.06 to 121.05 min for female alates and from 68.00 to 85.92 min for queens. CONCLUSION: When applied topically, formic acid was significantly less toxic than bifenthrin to red imported fire ants. Although its fumigation toxicity was lower than that of dichlorvos, formic acid had about an order of magnitude higher toxicity to S. invicta than to other insects studied so far. It may be worth investigating the use of formic acid for managing imported fire ants. Published 2012 by John Wiley & Sons, Ltd.     

The response of pyriproxyfen-resistant and susceptible Bemisia tabaci Genn (Homoptera: Aleyrodidae) to pyriproxyfen and fenoxycarb alone and in combination with piperonyl butoxide

Pyriproxyfen was effective against susceptible Bemisia tabaci eggs at a LC₅₀ of 0.003 mg litre⁻¹ and against nymphs at 0.02 mg litre⁻¹. In comparison, eggs of a laboratory selected, pyriproxyfen-resistant B tabaci strain, originating in an Israeli greenhouse, exhibited 6500-fold resistance and nymphs exhibited 1100-fold resistance. Eggs and nymphs of a strain from an Israeli sunflower field exhibited 450 and 210-fold resistance in comparison to the susceptible standard. Fenoxycarb was generally less effective than pyriproxyfen against B tabaci eggs and nymphs but was unaffected by pyriproxyfen resistance. Piperonyl butoxide (PB) was antagonistic to pyriproxyfen, and this increased with increasing pyriproxyfen resistance. PB had no effect on the toxicity of fenoxycarb. Collectively, these data imply that the modes of action of pyriproxyfen and fenoxycarb are distinct, despite the structural similarities of these molecules. Possible reasons for the antagonism of PB against pyriproxyfen are discussed. © 1999 Society of Chemical Industry     

Insecticide resistance management of Bemisia tabaci (Hemiptera: Aleyrodidae) in Australian cotton – pyriproxyfen,spirotetramat and buprofezin

BACKGROUND

Bemisia tabaci is a globally significant agricultural pest including in Australia, where it exhibits resistance to numerous insecticides. With a recent label change, buprofezin (group 16), is now used for whitefly management in Australia. This study investigated resistance to pyriproxyfen (group 7C), spirotetramat (group 23) and buprofezin using bioassays and available molecular markers.

RESULTS

Bioassay and selection testing of B. tabaci populations detected resistance to pyriproxyfen with resistance ratios ranging from 4.1 to 56. Resistance to spirotetramat was detected using bioassay, selection testing and sequencing techniques. In populations collected from cotton, the A2083V mutation was detected in three populations of 85 tested, at frequencies ≤4.1%, whereas in limited surveillance of populations from an intensive horticultural region the frequency was ≥75.8%. The baseline susceptibility of B. tabaci to buprofezin was determined from populations tested from 2019 to 2020, in which LC₅₀ values ranged from 0.61 to 10.75 mg L⁻¹. From the bioassay data, a discriminating dose of 200 mg L⁻¹ was developed. Recent surveillance of 16 populations detected no evidence of resistance with 100% mortality recorded at doses ≤32 mg L⁻¹. A cross-resistance study found no conclusive evidence of resistance to buprofezin in populations with high resistance to pyriproxyfen or spirotetramat.

CONCLUSIONS

In Australian cotton, B. tabaci pest management is challenged by ongoing resistance to pyriproxyfen, while resistance to spirotetramat is an emerging issue. The addition of buprofezin provides a new mode-of-action for whitefly pest management, which will strengthen the existing insecticide resistance management strategy. © 2023 Commonwealth of Australia. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Pathogenicity and host‐parasite relationships of the root‐knot nematode Meloidogyne incognita on celery

Pathogenicity and host‐parasite relationships in root‐knot disease of celery (Apium graveolens ) caused by Meloidogyne incognita race 1 were studied under glasshouse conditions. Naturally and artificially infected celery cv. D’elne plants showed severe yellowing and stunting, with heavily deformed and damaged root systems. Nematode‐induced mature galls were spherical and/or ellipsoidal and commonly contained more than one female, males and egg masses with eggs. Feeding sites were characterized by the development of giant cells that contained granular cytoplasm and many hypertrophied nuclei. The cytoplasm of giant cells was aggregated along their thickened cell walls and consequently the vascular tissues within galls appeared disrupted and disorganized. The relationship between initial nematode population density (Pi) and growth of celery plants was tested in glasshouse experiments with inoculum levels that varied from 0 to 512 eggs and second‐stage juveniles (J₂) mL^?1 soil. Seinhorst's model y = m + (1 – m)z^P–T was fitted to height and top fresh weight data of the inoculated and control plants. The tolerance limit with respect to plant height and fresh top weight of celery to M. incognita race 1 was estimated as 0·15 eggs and J₂ mL^?1 soil. The minimum relative values (m) for plant height and top fresh weight were 0·37 and 0·35, respectively, at Pi ≥ 16 eggs and J₂ mL^?1 soil. The maximum nematode reproduction rate (Pf/Pi) was 407·6 at an initial population density (Pi) of 4 eggs and J₂ mL^?1 soil.     

Ovicidal,larvicidal and juvenilizing activity of a picolinephenoxyanilide against Cydia pomonella

N‐(4‐phenoxyphenyl)‐2‐pyridinecarboxamide (1) was synthesized from commercially available materials and its ovicidal and larvicidal activity against Cydia pomonella (L) was tested. The compound showed a LC₅₀ of 0.98 mg ml⁻¹ when eggs less than 24 h were sprayed using a Potter Tower, but it had no effect when eggs older than this were sprayed. The compound did not have larvicidal activity when larvae were treated with 1200 µg g⁻¹. However, the larval head capsules were smaller than those in the controls when treated at this concentration. To assess its possible juvenile‐hormone‐like activity, the compound was topically applied to young pupae of Tribolium confusum duVal, where it produced clear juvenilization effects, which were dependent on the applied dose. © 2000 Society of Chemical Industry     

The ovicidal action of insecticides and insect growth regulator/insecticide mixtures on the eggs of various ages of susceptible and diflubenzuron-resistant strains of Spodoptera littoralis boisd

The ovicidal action of four insecticides and three insect growth regulators, on eggs of various ages of the susceptible (S) strain of Spodoptera littoralis, was investigated. The results revealed that diflubenzuron was the most toxic compound tested on 0-1-day-old eggs, followed by triprene and then methoprene; chlorpyrifos came next in its toxicity, followed by cypermethrin then fenvalerate; methomyl was the least effective. With the progress of embryonic development, 1-2-day-old eggs showed slight tolerance to the action of the pesticides and juvenoids, but apparently resisted the action of diflubenzuron. Eggs 2-3 days old showed increased tolerance to the insecticides and diflubenzuron and, to a lesser extent, to the action of the two juvenoids. A total of 21 insecticide or insect growth regulator-insecticide mixtures, based on their toxicity equivalents (LD₂₅ + LD₂₅), were applied jointly on 0-1-day-old eggs of the S strain. The mixtures which produced high synergism on this stage could be arranged, according to their decreasing order of potentiation, as follows: fenvalerate/diflubenzuron, cypermethrin/triprene, methomyl/methoprene, cypermethrin/methoprene, fenvalerate/ methoprene, cypermethrin/methomyl, cypermethrin/diflubenzuron, fenvalerate/triprene, diflubenzuron/methoprene and methomyl/triprene. The mixtures that produced synergistic effects on 0-1-day-old eggs were also tested against the 1-2 and 2-3-day-oldeggs of the S strain. Theresults indicated that themixtures fenvalerate/diflubenzuron, and cypermethrin with either triprene or diflubenzuron, when tested on 1-2-day-old eggs, produced levels of synergism nearly similar to those achieved on newly deposited eggs. On the other hand, the mixtures cypermethrin/methomyl, and fenvalerate with methoprene or triprene, showed comparatively lower levels of synergism. However, the synergistic action of the mixture cypermethrin/methoprene, previously detected on newly deposited eggs, became an additive effect on 1-2-day-old eggs. Only the mixtures fenvalerate/diflubenzuron, cypermethrin/triprene and fenvalerate/methoprene showed synergism on 2-3-day-old eggs. The mixtures which showed synergistic effects on 0-1-day-old eggs of the S strain were further tested on eggs of various ages of the diflubenzuron-resistant (R_d) strain. As regards 0-1-day-old eggs, only the combinations cypermethrin/triprene, methomyl/methoprene and fenvalerate/methoprene produced additive effects. The mixture cypermethrin/diflubenzuron was still synergistic against newly deposited eggs of the R_d strain, in a manner similar to that indicated with the S strain. Apparent levels of antagonism were shown to the other insecticide-juvenoid mixtures as well as to the diflubenzuron/methoprene combination. The combinations cypermethrin/methomyl and fenvalerate/diflubenzuron had some effect on the freshly deposited eggs of the R_d strain but produced lower levels of potentiation. With the increase in age of the eggs, the mixture cypermethrin/diflubenzuron showed a lower level of synergism on the 1-2 day-old eggs than was observed in younger eggs. The additive effects, previously detected with some of the mixtures on newly deposited eggs became an antagonistic effect for the 1-2-day-old eggs. The eggs at this stage were more able to resist thejoint action of the other mixtures tested. Moreover, with further increase in the age of the eggs, the combination cypermethrin/diflubenzuron produced a lower level of potentiation on 2-3 day-old eggs, followed by fenvalerate/diflubenzuron at an even lower level, while the other mixtures showed various levels of antagonism.     

Spirodiclofen and spirotetramat bioassays for monitoring resistance in citrus red mite, Panonychus citri (Acari: Tetranychidae)

BACKGROUND: Citrus red mite, Panonychus citri (McGregor), is a key pest of San Joaquin Valley California citrus. Spirodiclofen was registered for mite control in 2007, and spirotetramat for scale control in 2008. Because of the potential for resistance to spirodiclofen to develop in spider mites, and cross‐resistance to spirotetramat used for other citrus pests, bioassay methods for resistance monitoring were developed. RESULTS: The responses of four populations of adult female, egg and larval stages of P. citri to spirodiclofen were compared to determine the most robust bioassay method for this pesticide. Adult females responded with a higher LC₉₉ and larval stages exhibited higher control mortality and a lower slope of response compared with the egg stage. Thus, the egg stage was found to be the most suitable stage for testing. Egg production and egg shape were significantly affected by spirodiclofen treatment of adult female mites. Bioassays with the related compound spirotetramat revealed that P. citri egg hatch was less affected by this compound, requiring the assessment of mortality to be extended to 11 days after treatment when the hatched larvae succumbed to the pesticide. Discriminating concentrations of 10 ppm for spirodiclofen and 31.6 ppm for spirotetramat in an 11 day bioassay were tested against eight field populations of P. citri, and 99–100% mortality resulted. CONCLUSION: These results provide a baseline for the response of P. citri to spirodiclofen and spirotetramat that will aid resistance management in California citrus. Copyright © 2011 Society of Chemical Industry