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.     

Resistance of Bemisia tabaci (Homoptera: Aleyrodidae) to insecticides in southern Spain with special reference to neonicotinoids

The tobacco whitefly, Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) which occurs in various parts of the world, has developed a high degree of resistance against several chemical classes of insecticide, including organophosphates, carbamates, pyrethroids, insect growth regulators and chlorinated hydrocarbons. The present studies were done in order to monitor the susceptibility of whitefly populations in southern Spain to insecticides commonly used there. Systemic bioassays using Spanish field populations of B tabaci collected in 1994, 1996 and 1998 indicated an increase, albeit a slow one, in resistance to imidacloprid over this period. Comparative studies of other neonicotinoids using the same bioassay revealed a high degree of cross‐resistance to acetamiprid and thiamethoxam. Leaf‐dip bioassays with adult females from these populations revealed a high level of resistance to cyfluthrin, endosulfan, monocrotophos, methamidophos, and pymetrozine, each at 200 mg litre⁻¹. Buprofezin and pyriproxyfen were tested against second‐instar nymphs and eggs, respectively. Buprofezin also showed a lower efficacy against ESP‐98, a strain of B tabaci received from Almeria in 1998, but pyriproxyfen resistance was not obvious when tested against eggs of strain ESP‐98. Field trials in 1998 revealed good efficacy of imidacloprid in one farm in the Almeria region and two greenhouses in Murcia and Sevilla, but a loss of activity by imidacloprid in another farm in the Almeria region. Cross‐resistance between imidacloprid and thiamethoxam was also confirmed under field conditions. © 2000 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.     

Effects of buprofezin and diflubenzuron on various developmental stages of Asian citrus psyllid, Diaphorina citri

BACKGROUND: Diaphorina citri populations in Florida are developing resistance to commonly used neurotoxic insecticides. Alternatives to neurotoxins, such as insect growth regulators, are needed to control this season-long subtropical pest to prevent or delay development of insecticide resistance. In the present investigation, two insect growth regulators (IGRs), buprofezin and diflubenzuron, were evaluated against various developmental stages of D. citri. RESULTS: The 0–1-day-old D. citri eggs were more susceptible to buprofezin and diflubenzuron than the 3–4-day-old eggs. Adult emergence was completely suppressed by treating first- or third-instar nymphs with buprofezin or diflubenzuron at 30–240 or 23–184 µg mL⁻¹ rates respectively. Treatment of fifth-instar nymphs with diflubenzuron at a rate of 184 µg mL⁻¹ and with buprofezin at 30–240 µg mL⁻¹ rates resulted in approximately 20 and 15–80% reductions in adult emergence respectively. The mean number of eggs per plant was reduced at 5 days after topical treatment with diflubenzuron. Mean egg hatch per plant was reduced at 5 and 6–15 days after topical treatments with buprofezin and diflubenzuron respectively. CONCLUSION: Buprofezin and diflubenzuron effectively suppressed D. citri adult emergence. D. citri were more susceptible as early (first–third-instar) than late (fifth-instar) nymphs. Both IGRs inhibited egg production and egg hatch. Reduction in the number of subsequent offspring suggests reduced vertical transmission of Candidatus Liberibacter asiaticus, the pathogen thought to cause citrus greening disease. The present results indicate that both IGRs tested here should be effective tools for rotation in insecticide-based D. citri management programs. Copyright © 2012 Society of Chemical Industry     

Insecticide resistance status of Bemisia tabaci Q‐biotype in south‐eastern Spain

BACKGROUND: Bemisia tabaci Gennadius Q‐biotype has readily developed resistance to numerous insecticide classes. Studies in the Mediterranean area are needed to clarify the resistance status and cross‐resistance patterns in this invasive whitefly biotype. The levels of resistance in nymphs of seven strains of B. tabaci Q‐biotype from south‐eastern Spain to representative insecticides were determined. RESULTS: Six populations had low to moderate levels of resistance to azadirachtin (0.2‐ to 7‐fold), buprofezin (11‐ to 59‐fold), imidacloprid (1‐ to 15‐fold), methomyl (3‐ to 55‐fold), pyridaben (0.9‐ to 9‐fold), pyriproxyfen (0.7‐ to 15‐fold) and spiromesifen (1‐ to 7‐fold), when compared with a contemporary Spanish Q‐biotype reference population (LC₅₀ = 2.7, 8.7, 15.2, 19.9, 0.34, 20.9 and 1.1 mg L^?1 respectively). A single population collected from a greenhouse subject to intensive insecticide use exhibited generally higher resistance levels to the same array of compounds (31‐, 1164‐, 3‐, 52‐, 9‐, 19‐ and 3‐fold respectively). Pyridaben and spiromesifen were extremely effective against nymphs of all strains, with LC₅₀ values significantly below recommended application rates. CONCLUSION: In contrast to previous reports, high rates of efficacy exist for numerous insecticide classes against B. tabaci Q‐biotype populations in these intensive agricultural regions of south‐eastern Spain. This probably reflects the recent and significant reductions in exposure that have resulted from a wider uptake of IPM technologies and strategies. However, the continued presence of resistance genes also suggests that a reversion to levels of high insecticide exposure could result in a rapid selection for resistance. Copyright © 2009 Society of Chemical Industry     

Lack of fitness costs associated with pyriproxyfen resistance in the B biotype of Bemisia tabaci

BACKGROUND: The insect growth regulator pyriproxyfen has provided effective control of the whitefly Bemisia tabaci Gennadius in many countries. Here, whether or not fitness costs were associated with pyriproxyfen resistance in a laboratory‐selected resistant strain (QC02‐R) of the B biotype was determined. RESULTS: Mortality caused by pyriproxyfen and fitness traits over time were measured in unselected and selected hybrid strains, which were created by crossing individuals of the resistant strain with individuals of a susceptible strain. Fitness costs were not associated with resistance in QC02‐R, as mortality caused by pyriproxyfen did not increase over time in unselected hybrid strains and fitness traits were similar in unselected and selected hybrid strains. Using a new method to examine the inheritance of resistance, based on data from fitness cost experiments, it was estimated that pyriproxyfen resistance is controlled by two loci in the QC02‐R strain. CONCLUSION: The lack of fitness costs associated with pyriproxyfen resistance could promote the evolution of resistance in field populations with similar traits to QC02‐R. Copyright © 2008 Society of Chemical Industry     

Comparative testing of several juvenile hormone analogues in two species of locusts,Locusta migratoria migratorioides and Schistocerca gregaria

Effective treatment with juvenile hormone analogues (JHAs) of early penultimate or early last-instar locust hoppers induces a supernumerary ‘extra’ nymphal instar. These ‘extra’ nymphs, also termed ‘adultoids’, die in the course of, or shortly after, an ‘extra’ moult. Less effective treatment results in imperfect adults with crumpled twisted wings which presumably limit their flight and migratory abilities. Extremely effective treatment leads to death in the next moult. Comparing dose-response relations of (7S)-methoprene, fenoxycarb, pyriproxyfen and a new JHA, R70-1 (ethyl cis-N-{2-[4-(2-hydroxycyclohept-1-ylmethyl)phenoxy]ethyl}carbamate), we revealed that route of administration, instar of the recipient hopper, and species may alter over 1000-fold the ED₅₀ for the same JHA. Locusta migratoria migratorioides is much more susceptible to JHAs than Schistocerca gregaria. The lowest ED₅₀ found to induce adultoids and subsequent death in the ‘extra’ moult was 0·12 μg pyriproxyfen injected in olive oil to early penultimate instar hoppers of L. m. migratorioides (about 0·5 μg g^-1 fresh weight). R70-1 was more active than pyriproxyfen following the more practical topical application to early last-instar hoppers of L. m. migratorioides, 5·9 μg and 46 μg per hopper, respectively (about 10 μg g^-1 and 78 μg g^-1 fresh weight). The high susceptibility of last-instar L. m. migratorioides nymphs to topically applied R70-1 is promising from the practical standpoint. ©1997 SCI     

Toxicity of spiromesifen to the developmental stages of Bemisia tabaci biotype B

BACKGROUND: Spiromesifen is a novel insecticidal/acaricidal compound derived from spirocyclic tetronic acids that acts effectively against whiteflies and mites via inhibition of acetyl‐CoA‐carboxylase, a lipid metabolism enzyme. The effects of spiromesifen on the developmental stages of the whitefly Bemisia tabaci (Gennadius) were studied under laboratory conditions to generate baseline action thresholds for field evaluations of the compound. RESULTS: Adult B. tabaci mortality rate after spiromesifen treatment (5 mg L^?1) was 40%. Treatment with 0.5 mg L^?1 reduced fecundity per female by more than 80%, and fertility was almost nil. LC₅₀ for eggs was 2.6 mg L^?1, and for first instar 0.5 mg L^?1. Scanning electron microscopy revealed that eggs laid by treated adult females had an abnormally perforated chorion, and females were unable to complete oviposition. Light and fluorescent microscopy showed significantly smaller eggs following treatment, and smaller, abnormally formed and improperly localized bacteriomes in eggs and nymphs. The number of ovarioles counted in females treated with 5 mg L^?1 was significantly reduced. Spiromesifen showed no cross‐resistance with other commonly used insecticides from different chemical groups, and resistance monitoring in Israel showed no development of field resistance to this insecticide after 1 year of use. CONCLUSION: The strong effect on juvenile stages of B. tabaci with a unique mode of action and the absence of cross‐resistance with major commonly used insecticides from different chemical groups suggest the use of spiromesifen in pest and resistance management programmes. Copyright © 2008 Society of Chemical Industry     

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     

Biochemical and molecular mechanisms of diafenthiuron resistance in the whitefly,Bemisia tabaci

B-biotype Bemisia tabaci has developed high levels of resistance to many insecticides. To investigate the risks and explore possible mechanisms of resistance to diafenthiuron in B. tabaci, a 32.8-fold diafenthiuron-resistant strain (R-DfWf) was established after selection for 36 generations compared with the susceptible strain (S-Lab). Biochemical assays showed that the activity of cytochrome P450 towards p-NA was significantly higher (4.37-fold higher) in the R-DfWf strain than in the S-Lab strain. Similarly, the carboxylesterase (COE) activity and glutathione S-transferase (GST) activity were also significantly higher (3.12- and 1.83-fold higher, respectively) in the R-DfWf strain than in the S-Lab strain. The expression of five of seven P450 genes was significantly higher (>3-fold) in the R-DfWf strain than in the S-Lab strain. The expression of COE2 was significantly higher (>2.5-fold) in the R-DfWf than in the S-Lab strain. The expression of GST and GST2 was significantly higher (>2.3-fold) in the R-DfWf than in the S-Lab. Thus, cytochrome P450, COE and GST may appear to be responsible for the resistance to diafenthiuron in B. tabaci. It is also valuable for usage of insecticides for resistance management and control of this species.     

Beet armyworm (Spodoptera exigua) resistance to spinosad

Susceptibility to spinosad (Success®/Tracer®) of beet armyworm (Spodoptera exigua) from the southern USA and Southeast Asia was determined through exposure of second‐ and third‐instar larvae to dipped cotton leaves. LC₅₀ estimates of susceptibility of second‐ and third‐instar larvae of field populations ranged from 0.279 to 6.14 and 0.589 to 14.0 mg spinosad litre⁻¹, respectively. A Thailand population was 22‐ and 24‐fold less susceptible than the six other US field populations evaluated, and 85‐ and 58‐fold less susceptible than a reference laboratory population, respectively. From these results, we initiated experiments to test the hypothesis that the Thailand population was resistant to spinosad. F₁ crosses between the resistant Thailand population and a susceptible reference strain yielded individuals that were 22‐fold less sensitive to spinosad than the susceptible parent. This same resistant strain exhibited significantly greater survivorship on plants treated with spinosad in the field. Lastly, selection of an Arizona population resulted in a significant reduction in susceptibility to spinosad, further substantiating the hypothesis of a genetic basis for resistance to spinosad. These findings indicate a vulnerability of this new insecticide to resistance development in beet armyworm and should serve as a warning against excessive use of it. © 2000 Society of Chemical Industry     

Effects of some conventional insecticides and insect growth regulators on different phenological stages of the white wax scale,Ceroplastes destructor Newstead (Hemiptera: Coccidae), and its primary parasitoid,Aprostocetus ceroplastae (Girault) (Hymenoptera: Eulophidae)

The toxicity of two juvenile hormone analogues, pyriproxyfen (Nemesis^®) and fenoxycarb (Insegar^®), and two contact insecticides, methomyl (Lannate) and methidathion (Ultracide), was evaluated against immature stages (LI, LII, LIII) of Ceroplastes destructor Newstead in the field. The effects of these chemicals and one moulting inhibitor, triflumuron (Alsystin^®), and three insecticides: methyl-parathion (Penncap-M), profenofos (Selecron) and prothiofos (Tokuthion), on Aprostocetus (= Tetrastichus) ceroplastae (Girault) were assessed in the laboratory. Development of the first and second instar nymphs of C. destructor was completely arrested by the chemicals. Less than 1% of scales sprayed with pyriproxyfen at LII stage survived to adult female. Survival to the adult stage varied significantly between chemical treatments, and between chemicals and untreated controls for scales sprayed at the LIII stage. Female fecundity, fertility and body sizes of survivors of treatments applied at the LIII stage were not significantly affected by any of the chemicals. All the chemicals exhibited high toxicity to A. ceroplastae. Only triflumuron was slightly harmful, while methomyl was the most toxic (harmful), causing 100% mortality in the first 30 min after treatment. Although all the chemicals evaluated had effectively arrested the first and second instars of C. destructor, none of them exhibited sufficient selectivity to A. ceroplastae to warrant recommendation for integrated management of C. destructor in citrus orchards in South Africa, where A. ceroplastae plays an important role.     

Elucidating resistance in cotton genotypes to whitefly, <Emphasis Type="Italic">Bemisia tabaci,</Emphasis> by population buildup studies

Plant resistance has become an important component of integrated pest management (IPM) for management of whitefly, Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), an important pest of cotton in India. The present studies were undertaken to standardize the plant stage and identify resistant cotton genotypes against whitefly. Nine plant stages of F846, a susceptible cotton genotype, were exposed to whitefly for 25 days under no-choice conditions. The population buildup (eggs, nymphs, pupae and adults) was recorded. The 12-, 14- and 16-leaf stages were suitable for plant resistance studies against whitefly, and the 14-leaf stage was taken for further studies. Ten cotton genotypes of Gossypium hirsutum and two of G. arboreum were covered with split cages in which five pairs of B. tabaci (F₁) were released. The population buildup was recorded to categorize genotypes as resistant, moderately resistant, moderately susceptible or susceptible. The experiment was repeated with F₂ and F₃ generation whiteflies. Based on overall average score of three experiments, LD694 was rated as resistant; LK861, Supriya, RS2013, CNH911 and PA183 as moderately resistant; IS-376/4/1/20/72, NHH44, TxMaroon2-78, Bt 6304 and RS2098 as moderately susceptible; and F846 as susceptible. LD694 was found to be resistant in three consecutive generations of whitefly.     

Susceptibility pattern and development of resistance in the diamondback moth,Plutella xylostella L,to Bacillus thuringiensis Berl var kurstaki in India

Base‐line susceptibility for six‐day‐old larvae of the diamondback moth, Plutella xylostella, against Bacillus thuringiensis var kurstaki (Biobit^®) was studied by a cabbage leaf disc dip bioassay technique. Diamondback moth from 13 locations in seven different states spread over a distance of about 3000 km longitudinally was used for these studies. Forty‐eight‐hour LC₅₀ values varied from 1.0 to 10.97 mg AI litre⁻¹. Further investigations on the development of resistance under laboratory conditions showed an increase in LC₅₀ from 2.76 (for unselected F₁ generation) to 5.28 mg AI litre⁻¹ (for selected F₉ generation), using a selection concentration of 6.4 mg AI litre⁻¹. This suggested a possibility of the development of resistance under field conditions if there were to be extensive and indiscriminate use of B thuringiensis. These findings are discussed in relation to integrated pest management and the mechanisms of resistance in resistance management tactics. © 2000 Society of Chemical Industry     

Insecticidal activity of surfactants and oils against silverleaf whitefly (Bemisia argentifolii) nymphs (Homoptera: Aleyrodidae) on collards and tomato

The insecticidal activities of four surfactants (Cide‐kick, Silwet L‐77, M‐Pede and APSA‐80), a dishwashing detergent (New Day), a mineral oil (Sunspray oil), a cotton seed oil and a vegetable oil, alone or in combination, were tested against nymphs of Bemisia argentifolii Bellows & Perring on collards and tomato. Silwet L‐77 was more effective (>95% mortality) than Cide‐Kick or APSA‐80 at rates from 0.25–1.00 g AI litre⁻¹ but caused severe phytotoxicity to tender tomato leaves at all but the lowest rate. New Day dish detergent at 2.0 ml litre⁻¹ caused mortality (95%) comparable to M‐Pede insecticide soap at 10‐fold greater concentration. A New Day ingredient, cocamide DEA, was considerably more active than the other ingredients or the commercial mixture. Additional surfactants added to Sunspray oil increased efficacy in some treatments, but not others. Toxic responses of 2nd‐ and 3rd‐ instar whiteflies to vegetable oil and cotton seed oil at 5.0 and 10.0 ml litre⁻¹ plus 0.4 g AI litre⁻¹ APSA‐80 ranged from 22.1 to 79.9% and 66.3–88.7% mortality, respectively. Whitefly mortality was greater on tomato than on collard in six of seven instances when differences between host plants were significant. Our results indicate that the these surfactants and oils have good potential for controlling B argentifolii. © 2000 Society of Chemical Industry     

Laboratory Evaluation of the Novel Naturally Derived Compound Spinosad against Ceratitiscapitata

Laboratory studies were conducted to determine the effect of the naturally derived compound spinosad on Ceratitis capitata Wied. (Diptera, Tephritidae). The organophosphate fenthion was used as a standard. Direct dose-dependent mortality and reduced fecundity were observed in oral treatment of adults with spinosad. The LC₉₀ values 14 h and seven days after treatment were 19·50 and 0·49 mg litre⁻¹ respectively. Fenthion was less active (the LC₅₀ eight days after treatment was 1·17 mg litre⁻¹) and did not affect the fecundity of the fly. Adults were also very susceptible to spinosad and fenthion via residual contact. For spinosad, 100% mortality was recorded 48 h after treatment for a dose of 10 mg litre⁻¹. Spinosad was more effective than fenthion in suppressing larval development when neonate larvae were reared on treated diet supplemented with a range of concentrations from 0·02 to 0·83 mg kg⁻¹ diet. Last-instar larvae were much less susceptible to spinosad or fenthion when exposed via dipping or when they pupated in treated medium and both products had similar performance. A lack of ovicidal activity was observed in direct egg-treatments with spinosad but significant reductions from 1 mg litre⁻¹ onwards were recorded for fenthion.     

In-vitro and in-vivo nematicidal activities of the cyclic dodecapeptide omphalotin A

Omphalotin A, a cyclic dodecapeptide produced by submerged cultures of the basidiomycete Omphalotus olearius, exhibited in-vitro and in-vivo nematicidal activity. Meloidogyne incognita was the most sensitive nematode. At 2.0 mg litre⁻¹, 50% of the nematodes were dead after one hour. Heterodera schachtii, Radopholus similis and Pratylenchus penetrans were affected at higher concentrations. Incorporated into agar, the compound prevented infection of cucumber seedlings by M. incognita at concentrations of 1 mg litre⁻¹ and higher. In glasshouse tests, complete protection of cucumbers and lettuce was achieved between 2.5 and 10 mg litre⁻¹. No insecticidal activity was observed when Plutella xylostella, Phaedon cochleariae or Spodoptera frugiperda were fed material containing 4 g kg⁻¹ of omphalotin A. © 1999 Society of Chemical Industry     

Effectiveness of thiamethoxam and imidacloprid seed treatments against Bemisia tabaci (Hemiptera: Aleyrodidae) on cotton

BACKGROUND: Bemisia tabaci (Gennadius) biotype B is one of the most important pests on cotton around the world. Laboratory, greenhouse and field experiments were conducted to determine the efficacy of thiamethoxam and imidacloprid seed treatments against B. tabaci on cotton. RESULTS: Under laboratory conditions, the two treatments caused whitefly adult mortality, reduced oviposition and increased mortality of nymphs at 10, 20, 30 and 40 days after germination (DAG). The longer the adults fed on plants from treated seeds, the higher the mortality. The two treatments did not have any effect on eggs. The efficacy of the treated seeds against B. tabaci gradually decreased from 10 to 40 DAG, being the lowest at 40 DAG. In laboratory experiments, the efficacies between the two treatments were similar. In greenhouse experiments, the two treatments were equally effective with lower numbers of whiteflies than untreated controls. With both treatments the concentrations of the active ingredient were gradually reduced with aging of the plants and from the bottom to the top leaves of the plants. Numbers of live whiteflies were well correlated with the dosage of active ingredients. Under field conditions, the seeds treated with both insecticides exhibited similar efficacy against B. tabaci for up to ～2 months. CONCLUSION: Cotton seeds treated with imidacloprid and thiamethoxam were effective against B. tabaci for up to 45 days under laboratory and greenhouse conditions, and up to ～2 months under field conditions. Use of imidacloprid‐ and thiamethoxam‐treated seeds can be an important alternative for management of whiteflies on cotton. Copyright © 2010 Society of Chemical Industry     

Fumigant Toxicity of Citruspeel Oils against Adult and Immature Stages of Storage Insect Pests

The biological action of citruspeel oils was shown to depend on a strong fumigant action. Bioassays conducted in air-tight glass chambers showed that all the six citrus oils tested had vapour toxicity towards adults of Callosobruchus maculatus F., Sitophilus zeamais Motsch. and Dermestes maculatus Deg. The 24-h LC₅₀ value of limepeel oil (a typical citrus oil) vapour against C. Maculatus was 7·99 μl litre⁻¹ which made it 1·5 and 1·6 times less toxic against the smaller S. zeamais and the larger D. maculatus adult insects. When immature stages were fumigated, limepeel oil vapour had 24-h LC₅₀ values of 7·8 and 21·5 μl litre⁻¹ against eggs of C. maculatus and D. maculatus respectively, and 9·1, 17·8 and 23·1, 23·9 μl litre⁻¹ against early larvae, pupae of C. maculatus and late larvae, pupae of D. maculatus respectively. X-ray studies showed that fumigated C. maculatus larvae within cowpea grains died immediately without further development. The bioactivities of five other citruspeel oils were similar to that of limepeel oil. Bioassays showed that sorption of citruspeel oil fumes occurred in the presence of grains or strips of dried fish, and that this tended to reduce the amount available for fumigant action outside the materials. The problems presented by sorption may hinder the development of citrus oils into practical fumigants for large-scale treatments of stored commodities.     

The ovicidal properties of the juvenile hormone mimic sumitomo S-31183 (SK-591) to insects

S-31183 was assayed against preimaginal stages of the tobacco whitefly,Bemisia tabaci (Genn.), and eggs of the Egyptian cotton leafworm,Spodoptera littoralis (Boisd.). The compound was found to be an ovicide forB. tabaci eggs in both preinfestation and postinfestation treatments. FreshS. littoralis eggs were very susceptible to the compound at 0.05 ppm a.i., response was much poorer with 1-2-day-old eggs and 2-3-day-old eggs were not affected even by 100 ppm. Publication of the Agricultural Research Organization. No. 2271-E, 1988 series.