The effectiveness ofBacillus thuringiensis Berliner onBoarmia (Ascotis) Selenaria Schiff. (Lepidoptera,Geometridae) in laboratory tests and field trials

The effectiveness of a commercial preparation ofBacillus thuringiensis Berliner (Dipel) against eggs and larvae ofBoarmia (Ascotis) selenaria Schiff. of different age was examined in laboratory and in field tests. The mortality rate ofB. selenaria was proportional to the concentration ofB. thuringiensis and inversely related to the age of the treated larvae. In neonate larvae, 100% mortality was obtained even with a low concentration (0.5%). Egg hatch was not affected, but the survival rate of larvae hatched from treated eggs was very low (2.2%). No phytotoxicity of the commercial microbial preparation was observed on fruit or leaves of avocado. High doses ofB. thuringiensis persisted on avocados, probably because of specific conditions:i.e., absence of rainfall, moderate temperatures and limited penetration of sunlight. Tests carried out in large commercial orchards, using motor-guns and helicopters, yielded good results.     

The residual effect of some products from Neem (Azadirachta indica A. Juss) seeds upon larvae ofBoarmia (Ascotis) selenaria Schiff. in laboratory trials

The effect of Neem on the development ofBoarmia (Ascotis) selenaria Schiff. was investigated. Young leaves of avocado were treated in the laboratory with varying concentrations of Neem seed kernel suspensions or with emulsions of some Neem oil products, and offered to larvae of different size. Furthermore, avocado plants in flower pots were sprayed with Neem suspensions and the residues allowed to age in different locations. Leaves from the different treatments were offered to larvae of various sizes in laboratory tests and the larval weight, pupation rate and mortality were recorded. 0.3% Neem was highly effective on laboratory-treated leaves. A negative correlation was found between the concentration of the Neem suspensions on the one hand and the rate of growth and pupation on the other hand. No activity was found with the emulsion of either Neem extractive or Neem oil obtained from Neem kernels after extraction. In larvae kept for four days on avocado leaves treated with 0.3% Neem suspension, the growth and pupation rate was nearly as low as in larvae fed on treated leaves throughout their life span. The experiment with Neem-sprayed plants kept at different locations indicated the following order of activity of the residues: laboratory ? shade > sun.     

Potency and effect ofBacillus thuringiensis preparations against larvae ofSpodoptera littoralis andBoarmia (Ascotis) selenaria

The potency of two newBacillus thuringiensis (B.t.) preparations (coded ABG 6104 and ABG 6105) and of Dipel (B. thuringiensis var.kurstaki) was determined againstSpodoptera littoralis (Boisd.) 5th-instar larvae on a calcium-alginate diet. With this bioassay, the newB.t. products were more than twice as potent as Dipel. They were also 2–3 times more active than Dipel on alfalfa and cotton leaves in the laboratory. When applied in an alfalfa field at the rate of 312 mg/m², ABG 6104 and ABG 6105 caused 40% mortality of 5th-instar larvae and reduced the weight of the survivors to 30–40% of the control; only half of this activity was obtained with Dipel. On cotton, the activity of all theB. t. products was low. NeonateS. littoralis larvae were effectively controlled on avocado seedlings; however, there was high mortality also in the untreated controls. All threeB. t. preparations had a similar effect onBoarmia (Ascotis) selenaria Schiff. on avocado leaves in the laboratory. Addition of a chitinase enzyme did not increase the pathogenicity of the microbial preparations in the latter tests.     

Toxicity of the chitin synthesis inhibitors,diflubenzuron and its dichloro-analogue,to Spodoptera littoralis larvae

The activities of the chitin synthesis inhibitors, diflubenzuron and PH 60–38, against Spodoptera littoralis larvae were assayed by feeding treated alfalfa or poisoned wheat bran baits, by allowing the larvae to imbibe sucrose-containing aqueous dispersions of the compounds, and by injection into larvae. PH 60–38 was less active than diflubenzuron. On alfalfa, diflubenzuron had to be fed for at least 2 days to prevent formation of normal pupae and emergence of adults. For very big (480–540 mg) larvae, feeding diflubenzuron at concentrations of 50 mg/litre for 2 days or 2.5 mg/litre for 3 days prevented adult emergence. For 200–250 mg larvae, this was achieved by feeding concentrations of 100 mg/litre for 2 days, 5 mg/litre for 3 days or 3.5 mg/litre for 4 days. In all larvae > 150 mg, mortality in feeding experiments occurred in the prepupal or the pupal stage. Only with 30–50 mg and 100–150 mg larvae was there considerable mortality during moults between larval instars, the larvae being unable to liberate themselves from the old larval skins and head capsules. Diflubenzuron incorporated into wheat bran baits at concentrations of from 2.5 to 10 000 μg/g killed approximately 70–90% of the insects. When imbibed, diflubenzuron was much less toxic as a wettable powder than as a liquid formulation but the two formulations were equitoxic when injected into the larvae.     

A laboratory evaluation of the effectiveness of diflubenzuron against Dermestes maculatus De Geer and other storage insect pests

The chitin synthesis inhibitor diflubenzuron, applied as a wettable powder spray to woven polypropylene at 100–500 mg m^?2, was effective against Dermestes maculatus De Geer for at least 12 weeks. D. maculatus was unable to develop on ox hide dipped in a suspension of diflubenzuron (125 mg litre^?1), or on fishmeal dusted at 1–10 mg of active ingredient kg^?1. Diflubenzuron prevented the development of infestations of Callosobruchus maculatus (L.) on peas and of Acanthoscelides obtectus (Say) on beans dusted at 1–5 mg kg^?1. The compound was also very effective against early instar larvae of Trogoderma granarium Everts on wheat. The persistence and activity of diflubenzuron at low dosage rates against D. maculatus appear to justify larger scale trials.     

Contact activity of diflubenzuron against Spodoptera littoralis larvae

The effect of diflubenzuron as a residue on glass or applied topically to Spodoptera littoralis larvae was investigated. Diflubenzuron was active as a residue on glass against 100 and 200 mg larvae; the toxicity of residues was identical whether a dispersable formulation or a wettable powder or the technical substance were used. By topical application, diflubenzuron had an ED₅₀ for cumulative percentage mortality up to the adult stage of 004 and 0066 μg/larva for 100 and 200mg larvae respectively. Neither the site of the topical application nor whether the larvae were kept singly or in groups of ten after the treatment had an influence on toxicity. The data indicate that diflubenzuron has contact toxicity to at least one insect species as well as the known stomach poison action.     

Morphogenetic effects of diflubenzuron,an inhibitor of chitin deposition,on the coconut black-headed caterpillar (Nephantis serinopa myer)

Feeding the last instar larvae of Nephantis serinopa, the coconut black-headed caterpillar, on coconut leaves that had been dipped in diflubenzuron suspensions (0.2-4.0 g litre^?1) and dried, inhibited the moulting process and caused morphogenetic deformities of their pupae. The inhibition of moulting ranged from 27.5 to 75% The maximum effect was produced by suspensions of 4.0 g litre^?1 when only 5% of the larvae survived to become adults against 97.5% of untreated larvae.     

Effect of insecticide—synergist combinations on the survival of Spodoptera exigua

The chitin synthesis inhibitors diflubenzuron and teflubenzuron have recently become ineffective for the control of Spodoptera exigua in floricultural crops. An extended laboratory test with second-instar larvae of S. exigua on Vicia faba plants was carried out to determine the influence of synergists on the biological activity of three benzoylphenyl ureas (BPUs). The co-application of piperonyl butoxide, an oxidase inhibitor, did not increase the activity of diflubenzuron, teflubenzuron or hexaflumuron. The best results were obtained with diethyl maleate, for suppressing glutathione S-transferase activity, and with dimethoate, as a hydrolase inhibitor. A joint application of diflubenzuron (at a concentration which resulted in 43% survival) with diethyl maleate or dimethoate gave only 6.2 and 8.9% surviving larvae, respectively. In addition, development to fourth-instar larvae was inhibited. The more stable teflubenzuron was synergized by both compounds to a much lesser extent than diflubenzuron. None of the synergists had a significant effect on the activity of hexaflumuron, which was the most potent insecticide of the three BPUs tested against S. exigua.     

Diflubenzuron: Some aspects of its ovicidal and larvicidal mode of action and an evaluation of its practical possibilities

Diflubenzuron, 1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea, possesses larvicidal and ovicidal activities. On larvae it acts mainly as a stomach poison, yet it sometimes exhibits important contact activity. Though all instars can be controlled, older instars are generally less susceptible than younger ones. Histological inspections of Leptinotarsa decemlineata larvae revealed that after ending exposure to the compound, distortions in newly deposited cuticular layers decreased gradually. Ovicidal effects resulted from direct contact of diflubenzuron with eggs or from contamination of females by contact or feeding. Electron microscopic observations of embryos of Leptinotarsa decemlineata, contaminated via the female, also showed disturbed cuticule formation, suggesting a similar activity of the compound in larvae and in eggs. Spraying the eggs of Leucoptera scitella shows the compound to be mainly ovidical at a rate of 100 mg litre^?1, whilst with lower concentrations (10 and 1 mg litre^?1) the young larval instar will be killed. The levels of cross-resistance to diflubenzuron as a larvicide are low and the compound can be used effectively in the field against populations that are highly resistant to conventional insecticides. Laboratory and field results, based on larvicidal and ovicidal activities of diflubenzuron, are discussed in respect of species belonging to the Diptera, Lepidoptera, Coleoptera, Acarina (Phyllocoptruta oleivora) and Hemiptera (Eurydema oleraceum and Psylla piri).     

Residues of diflubenzuron on horse chestnut (Aesculus hippocastanum) leaves and their efficacy against the horse chestnut leafminer, Cameraria ohridella

Residues of the insect growth regulator diflubenzuron were quantified on horse chestnut (Aesculus hippocastanum L.) leaves treated with a diflubenzuron 480 g litre^?1 SC, Dimilin. To analyse the samples, an analytical procedure was developed involving a simple extraction step followed by high‐performance liquid chromatography on an octadecyl‐modified silica column with methanol + 0.01 M ammonium acetate mobile phase. The results showed diflubenzuron to be highly stable on horse chestnut leaves; more than 4 months (127 days) after application, 38% (on average) of the insecticide still remained on/in the leaves. The data confirmed biological observations showing diflubenzuron's long‐term efficacy against the horse chestnut leafminer, Cameraria ohridella Deschka & Dimi?, which is the most important pest of the horse chestnut in Europe. The hypothesis of possible penetration of diflubenzuron into the leaf mass is explored and discussed. Copyright © 2006 Society of Chemical Industry     

Laboratory selected resistance to diflubenzuron in larvae of aedes aegypti

The variation in tolerance to diflubenzuron [1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea] was examined in fourth instar larvae of seven strains of Aedes aegypti, some of which were resistant to DDT and permethrin. The difference between the least and the most tolerant to diflubenzuron was approximately two-fold. There was no correlation with resistance to the other insecticides. A DDT-resistant strain (T8) was selected 10 times (during 12 generations) with diflubenzuron. The LC₅₀ to diflubenzuron had increased 3.3 times by the S₈ generation but there was no further increase in later generations despite further selection. Associated with this increase, a marked decrease in resistance to DDT was observed but no change in permethrin tolerance. A genetically enriched strain (Hotchpotch) was synthesised from 35 strains of different geographic origin and crossed to the selected T8 strain before subsequent generations were selected five times with diflubenzuron. This procedure resulted in an 8 to 12-fold increase in the LC₅₀ value over that for unselected T8, accompanied by a decrease in the slope of the log dose against probit mortality line.     

Mechanisms of resistance to diflubenzuron in the house fly, Musca domestica (L.)

The mechanisms of resistance to the chitin synthesis inhibitor diflubenzuron were investigated in a diflubenzuron-selected strain of the house fly (Musca domestica L.) with > 1000 × resistance, and in an OMS-12-selected strain [O-ethyl O-(2,4-dichlorophenyl)phosphoramidothioate] with 380 × resistance to diflubenzuron. In agreement with the accepted mode of action of diflubenzuron, chitin synthesis was reduced less in larvae of the resistant (R) than of a susceptible (S) strain. Cuticular penetration of diflubenzuron into larvae of the R strains was about half that of the S. Both piperonyl butoxide and sesamex synergized diflubenzuron markedly in the R strains, indicating that mixed-function oxidase enzymes play a major role in resistance. Limited synergism by DEF (S,S,S-tributyl phosphorotrithioate) and diethylmaleate indicated that esterases and glutathione-dependent transferases play a relatively small role in resistance. Larvae of the S and R strains exhibited a similar pattern of in vivo cleavage of ³H- and ¹⁴C-labeled diflubenzuron at N₁C₂ and N₁C₁ bonds. However, there were marked differences in the amounts of major metabolites produced: R larvae metabolized diflubenzuron at considerably higher rates, resulting in 18-fold lower accumulation of unmetabolized diflubenzuron by comparison with S larvae. Polar metabolites were excreted at a 2-fold higher rate by R larvae. The high levels of resistance to diflubenzuron in R-Diflubenzuron and R-OMS-12 larvae are due to the combined effect of reduced cuticular penetration, increased metabolism, and rapid excretion of the chemical.     

Attraction ofTrichogramma platneri to eggs of some lepidopterous pests of avocado

The attraction ofTrichogramma platneri Nagarkatti (Hymenoptera: Trichogrammatidae) to eggs of two lepidopterous avocado pests,Boarmia sel-enaria (Schiffermüller) (Geometridae) andCryptoblabes gnidiella (Millière) (Phycitidae), was evaluated in olfactometer tests. The mobility of the wasp as measured by a mobility index was 0.6 for males and 1.8 for females; the males had a lower mobility and a lower search capacity index than the females. Frozen and fresh youngB. selenaria eggs had the greatest attraction forT. platneri, which diminished with increasing age of the eggs. The eggs ofC. gnidiella were also attractive to the parasitoid. Contribution from the Agricultural Research Organization. No. 2704-E, 1989 series.     

Biological data onApanteles cerialis Nixon (Hymenoptera: Braconidae), a parasite ofBoarmia (Ascotis) selenaria Schiff. (Lepidoptera: Geometridae)

Apanteles cerialis Nixon, a thelytokous braconid parasitoid ofBoarmia (Ascotis) selenaria Schiff., attacks young caterpillars (preferably 2–5 days old) of this pest in avocado plantations of Israel. At 27±1°C, oviposition rate is 2.04 progeny per day and 18.3 progeny over the entire life span. The development time of preimaginal stages is 16.1 and 15.2 days at 25° and 30°C, respectively, and increases to 37.3 days at 17°C. The pupal stage averages 4.4 days at 30°C and 13.5 days at 17°C. The average longevity of adults is 24.2 and 7.9 days at 30° and 17°C, respectively. In avocado orchardsA. cerialis appeared in considerable numbers in late summer and autumn; it was slightly hyperparasitized by the ichneumonid waspStictopisthus sp. (1 and 2% of the samples at one site).

     

An effective strain ofBacillus thuringiensis against fourth-instar caterpillars ofBoarmia selenaria

A strain ofBacillus thuringiensis Berliner effective against fourth-instarBoarmk selenaria Schiffermüller (Lepidoptera: Geometridae) was found. Strain HD-251 of the varietykurstaki H-serotype 3a, 3b was more effective than the standard HD-1-S-1980 in laboratory bioassays. The potency of HD-251 is two to four times higher than that of the standard, and varies from 19,821 to 68,645 IU/mg. Two other strains of the varietyaizawai H-serotype 7,viz., HD-249 and T63L4, were inferior to HD-251, with potencies of 6,982 and 13,714 IU/mg, respectively, against first-instar larvae.     

Phagostimulants enhancing the efficacy ofBacillus Thuringiensis formulations against the Giant Looper,Boarmia (Ascotis) Selenaria,in avocado

In both laboratory and field trials, as well as in semicommercial scale applications, the minimum concentration ofBacillus thuringiensis (B.t.) required to secure satisfactory larval mortality ofBoarmia selenaria could be halved, from 0.5% to 0.25%, by addition of 1% of the commercial phagostimulant Coax. Another phagostimulant product, Gustol, was inactive. Coax did not attract caterpillars from a distance. However, individual, Coax-treated spots on the avocado leaf surface were consumed by the larvae to a significantly greater extent than control. The same difference in palatability was recorded when the spots were treated with a mixture of Coax and aB.t. formulation. This explains, at least partially, the aforementioned advantageous effect of Coax in practical control of the looper byB.t.     

丁布胁迫对亚洲玉米螟氧化还原系统的影响

为探明丁布胁迫对亚洲玉米螟氧化还原系统的影响,采用酶活力测定方法和实时荧光定量PCR技术,研究了取食丁布含量差异显著的3个玉米品种登海662、浚单20和隆玉602叶片及模拟其叶片丁布含量的人工饲料后,玉米螟3龄幼虫氧化还原系统主要酶活性和谷氧还蛋白(Grx)mRNA转录表达的变化。结果显示:取食3个玉米品种叶片24 h后,亚洲玉米螟幼虫过氧化物酶和超氧化物歧化酶活性均显著高于对照,且在3个品种处理间差异显著,由大到小依次为登海662(118.30 U/mg和182.19 U/mg)、浚单20(107.13 U/mg和90.02 U/mg)和隆玉602(77.54 U/mg和93.59 U/mg)。取食浚单20可显著促进幼虫脂肪体Grx的表达,取食登海662可显著促进其中肠Grx的表达;取食模拟登海662叶片丁布含量的人工饲料12 h后,幼虫脂肪体中Grx表达量高于对应玉米叶片饲喂处理,而中肠部位则低于对应玉米叶片饲喂处理;取食模拟浚单20的结果与模拟登海662相反。表明亚洲玉米螟氧化还原系统在防御丁布胁迫过程中发挥着重要作用。     

Overwintering of the Japanese bayberry whitefly,parabemisia myricae,in Israel

The Japanese bayberry whitefly,Parabemisia myricae (Kuwana), was discovered in Israel on citrus and avocado trees in 1978. In order to clarify its mode of overwintering, observations and counts were carried out during the winters of 1979/80, 1982/83 and 1983/84, with the following findings. Larvae and adults were detected on citrus and avocado trees throughout the winter; only females were found. The oviposition rate ofP. myricae in winter was low, and rose steeply in spring. The density of larvae on the lower side of leaves was higher than on the upper side. Substantial numbers of larvae survived the winter on avocado trees. Emergence of adults became intensified at the end of February, reached a peak in early March, and ceased at the end of March or beginning of April.     

The pattern of cross-resistance to insecticides and juvenile hormone analogues in a diflubenzuron-resistant strain of the cotton leaf worm Spodoptera littoralis boisd

The rate of development of resistance to diflubenzuron in a laboratory susceptible strain of the cotton leafworm Spodoptera littoralis Boisd., the pattern of cross-resistance exhibited by the resistant strain to several insecticides and juvenile hormone analogues, as well as the synergistic action of piperonyl butoxide (PB) and S, S, S-tributyl phosphorotrithioate (TBP) with insecticides or diflubenzuron on both strains, were investigated. Resistance to diflubenzuron increased slightly in the first eight selected generations and was enhanced by further selection until in generation 30, the selected strain attained the high level of resistance of 290.7-fold, compared with the parent strain. The resistant strain when challenged with either insecticides or juvenile hormone analogues at selected generations (5, 10, 15, 20, 25 and 30) exhibited different levels of resistance to several insecticides representing organochlorine and organo-phosphorus compounds, carbamates and pyrethroids, but a clear case of negative correlation was indicated between resistance to diflubenzuron and juvenile hormone analogues. With regard to the synergistic action of PB and TBP on the toxicity of either diflubenzuron or insecticides against the fourth-instar larvae of the susceptible strain, methomyl showed slight levels of synergism when it was combined with them. With the exception of cypermethrin, which was not affected by the two synergists, lower levels of synergism were observed with the compounds endrin, diflubenzuron and fenvalerate when they were combined with the same synergists. These two synergists however, antagonised the toxic action of the organophosphorus compounds phosfolan and chlorpyrifos. Against the resistant strain, endrin was moderately synergised by TBP but only slightly by PB. Slight levels of synergism were observed when methomyl, phosfolan and diflubenzuron were combined with either synergist, but both antagonised chlorpyrifos and fenvalerate. Resistance to diflubenzuron and to the other tested chemicals in the resistant strain was scarcely affected by the two synergists.     

The effect of CME 134 onSpodoptera Littoralis Eggs and larvae

CME 134, a new benzoylphenyl urea chitin synthesis inhibitor, was less active than diflubenzuron and BAY SIR 8514, when tested againstSpodoptera littoralis eggs by a dipping method. AgainstS. littoralis larvae the compound was tested by feeding treated alfalfa, topical application and contact with crystalline residues on glass, followed by observation until the adult stage. With both 200–250 and 360–440-mg larvae 100% mortality was obtained by one-day feeding of alfalfa treated with 0.15 ppm a.i. Topical application to 100- and 200-mg larvae showed CME 134 to be about five and nine times more active than BAY SIR 8514 and diflubenzuron, respectively. These differences were even much greater in the contact tests. Cotton field plots were sprayed with either CME 134 or diflubenzuron formulations, leaves were collected at different intervals and fed for one day toS. littoralis larvae in the laboratory. 0.0009% a.i. CME 134 residues gave complete kill of 30–50-mg larvae after 5 and 20 days, and 86% kill after 28 days of aging. With 0.003 and 0.009% a.i., complete kill was obtained in 200–250-mg larvae until 50 days after spraying.