Laboratory studies with antifeedants against larvae of Boarmia (Ascotis) selenaria on alfalfa

The antifeedant effect of five organotin compounds (fentin acetate, fentin hydroxide, fentin chloride, cyhexatin and fenbutatin oxide) and of three other compounds known to possess antifeeding activity (guazatine triacetate, 4′-chloroacetophenone isobutyrylhydrazone and thiram) was investigated by feeding treated alfalfa to larvae of Boarmia selenaria. The three fentins and cyhexatin were highly active at 0.1 g litre^?1, the order of activity at this concentration being fentin chloride > fentin hydroxide > fentin acetate ? cyhexatin, whereas the other compounds were practically inactive at either this or a somewhat higher concentration (0.5 g litre^?1). Guazatine triacetate had a concentration-independent antifeedant effect at much higher concentrations (5–20 g litre^?1).     

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.     

The effect of diflubenzuron upon larvae of the geometrid Boarmia (Ascotis) selenaria on avocado leaves

Small (70 mg) Boarmia selenaria larvae fed for 4 days on avocado leaves or alfalfa dipped in aqueous diflubenzuron suspensions suffered from severe developmental disturbances. Similar results were obtained with leaves sprayed in an avocado orchard, with which, in addition, the considerable persistence of diflubenzuron under field conditions could be demonstrated. The substance was also active by topical application against large (500–600 mg) B. selenaria larvae, whereas by contact it was only moderately toxic. Some other non-conventional control agents, viz., the antifeedant AC-24055 and several juvenile hormone analogues, were of medium and negligible activity, respectively, against this insect.     

The residual effect of a neem seed kernel extract sprayed on fodder beet against larvae ofSpodoptera littoralis

The residual effect of a dried methanolic extract of neem (Azadirachta indica A. Juss) seed kernels was investigated with larvae of the Egyptian cotton leafworm,Spodoptera littoralis (Boisd.), in field trials. Fodder beet was sprayed with 1% emulsions of the extract. The treated leaves were collected from the field 1, 3, 5 and 9 days after spraying and offered to the larvae for 48 h. Survival and mean weight of the larvae were recorded 2, 4, 6, 9 and 11 days from the start of exposure to the residues, and rate of pupation was calculated. The extract had a strong antifeedant effect and an intense insect growth-regulating (IGR) effect in field-treated leaves, especially with the 1- and 3-day-old residues. A positive correlation was found between the age of the residues and the mean percent of live larvae, larval weight and pupation rate of the larvae.     

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.     

Response ofSpodoptera littoralis (Boisd.) andEarias insulana (Boisd.) larvae to azadirachtin and salannin

The effect of azadirachtin and salannin, two triterpenoids isolated from seeds of neem (Azadirachta indica A. Juss), on the feeding response ofSpodoptera littoralis (Boisd.) andEarias insulana (Boisd.) larvae, was investigated. Styropor (foamed polystyrene) lamellae were painted on both sides with a mixture of 5% sucrose with different concentrations of either azadirachtin or salannin dissoled in methanol-water (3∶7). Azadirachtin strongly suppressed feeding inS. littoralis larvae even at 0.001%, whereas salannin showed some antifeedant activity at 0.005% and above. Larvae ofE. insulana were deterred from feeding on azadirachtin-treated lamellae even at 0.005%, whereas salannin was effective only at 0.01% and above. Azadirachtin applied on cotton leaves deterred larvae ofS. littoralis from feeding at all concentrations ranging between 0.001 and 0.02%.     

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.     

The effect of BAY SIR 8514 onspodoptera littoralis (Boisduval) eggs and larvae

The chitin biosynthesis inhibitor diflubenzuron and its analog BAY SIR 8514 are equitoxic for eggs ofSpodoptera littoralis. BAY SIR 8514 residues on alfalfa fed toSpodoptera larvae were more toxic than diflubenzuron residues, whereas BAY SIR 8514 topically applied to these larvae was consistently twice as toxic as diflubenzuron, according to different criteria.     

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).

     

Azetidine-2-carboxylic acid: A naturally occurring inhibitor ofSpodoptera littoralis (boisd.) (Lepidoptera: Noctuidae)

Ruscus hypoglossum andUrginea maritima (Liliaceae) are highly resistant toSpodoptera littoralis. The foliage of these plants contains a proline analog, L-azetidine-2-carboxylic acid (AZA): inUrginea at a concentration of 1.7% of fresh weight and inRuscus at a concentration of 0.019%. The concentration of AZA inUrginea accounts for its lethal effects onS. littoralis larvae and for the direct effect of an acetone-soluble 80% methanol extract on adultS. littoralis, as evidenced by reduced viability of eggs deposited. The toxicity ofRuscus extracts is only partly attributable to AZA content.     

The use of Bacillus thuringiensis to control two lepidopterous insect pests (Agrotis ypsilon and Spodoptera littoralis)

An area of 50 feddans cultivated with soybeans was treated withBacillus thuringiensis (B.t.) baits againstAgrotis ypsilon and 60 feddans were sprayed withB.t. spray againstSpodoptera littoralis. WhenB.t. baits were used, the percentage of kill ofA. ypsilon reached 96.1–96.4% compared to 97.4–98% kill on using hostathion baits. WhenB.t. was sprayed againstS. littoralis, a percentage of larval kill 88.3% was obtained. This increased to 97.3% after the second application. On the other hand, the precentage of kill reached 96.8% when lannate was sprayed once. The average yield was 1.54 tons/fed. whenB.t. was sprayed twice againstS. littoralis and 1.42 tons/fed. when sprayed once. Areas, treated with lannate gave 1.44 tons/fed., while in the untreated area the yield was comparatively low being 0.83 tons/fed.Mith 4 tables     

Field evaluation of purified Z-9, E-11-tetradecadienyl acetate as an attractant for males ofSpodoptera littoralis (Boisd.) (Lepidoptera,Noctuidae)

The efficiency of 100% purified Z-9, E-11-tetradecadienyl acetate, the major sex attractant for males ofS. littoralis, was evaluated in a field test. A trap (17-cm diameter) baited with 2 mg of the purified attractant dispensed in polyethene vials, was significantly less efficient in attractiveness than a trap baited with one virgin female. The importance of a synergistic component for improving the efficiency of theS. littoralis sex pheromone is discussed.     

The efficacy of Bacillus thuringiensis var. israelensis against larvae of the blackfly Odagmia ornata (Meig.) (Simuliidae) at low temperatures

The effect of the suspension of Bacillus thuringiensis var. israelensis spores on larvae of the blackfly Odagmia ornata was studied in the laboratory and under field conditions of a natural biotope in southern Bohemia. The preparation Moskitur was used and its effect was tested in laboratory at temperatures 0.1-2.9 degrees C and 17-19 degrees C. Although O. ornata larvae were able to filter feed on a lethal dose of the preparation even at a lower temperature than 2.9 degrees C, no marked manifestation of mortality was observed at low temperatures in comparison with a control sample.     

Efficiency of the synthetic sex attractant and the effect of trap size on captures ofSpodoptera littoralis males in water traps and in dry funnel traps

The efficiency of the synthetic sex attractant ofS. littoralis and the effect of trap size on male captures in water traps and in newly designed dry traps were investigated. The synthetic attractant was less efficient in attractiveness than virgin females in both small (17 cm) and large (60 cm) traps. Trap size did not affect male captures in traps baited with either virgin females or synthetic pheromone. The dry trap tested was as efficient as the water trap, easier to handle, and highly suitable for monitoring or for mass trapping ofS. littoralis.     

Speed of action and toxicity of acylurea insect growth regulators against Spodoptera exempta (Walk.) and Spodoptera littoralis (Boisd.) larvae: Effect of inter-moult age

Ultra-low volume (ULV) spray bioassays at droplet densities (20–80 drops cm^?2) corresponding to field deposits were used to determine the efficacy of two acylurea insect growth regulators, teflubenzuron (‘Nomolt®’) and flufenoxuron (‘Cascade®’) against three different age groups of third-instar Spodoptera exempta and Spodoptera littoralis larvae. While no response (mortality and/or abnormal moulting with impaired ability to feed) was observed with one-day-old larvae until 48 h after treatment, two-day-old larvae showed some response (27–93% abnormal moulting and 3–10% mortality when larvae were sprayed; 80–100% abnormal moulting and up to 83% mortality when larvae and plants were sprayed) after 24 h and up to 100% mortality at 120 h. Studies with non-feeding, pre-moult larvae showed that cuticular uptake of acylureas was sufficient to affect an appreciable proportion of larvae after 24 h, with up to 100% mortality at 120 h. More detailed studies with pre-moult S. littoralis larvae showed that, while a few larvae which moulted between 1 and 5 h after treatment showed abnormal moulting to the L4 stage, a much larger proportion of larvae which moulted 6–20 h after treatment were affected. Previous studies with S. exempta have shown that different larval instars show similar levels of sensitivity to acylureas. The present work suggests that, while the age distribution within instars has little influence on the end-point mortality of acylureas, it can profoundly modify the speed of response, the majority of larvae within an instar being effectively controlled at the moult following treatment. The significance of these observations in relation to the crop protection activity of acylureas against field populations of Spodoptera larvae is discussed.     

Beetle-specific Bacillus thuringiensis Cry3Aa toxin reduces larval growth and curbs reproduction in Spodoptera littoralis (Boisd.)

Application of Bacillus thuringiensis tenebrionis (Bt) and expression of the Bt protein Cry3Aa in genetically modified crops are used for targeted control of the Colorado potato beetle Leptinotarsa decemlineata (Say). The Cry3A proteins are selectively toxic for the beetles but the present study describes effects of Cry3Aa on the Egyptian armyworm, Spodoptera littoralis (Boisduval). Cry3Aa expressed in potatoes or added to an agar-base wheat-germ diet reduced the growth of S. littoralis caterpillars and the fertility of adults. The effect of 1.4 mg kg(-1) Cry3Aa in potato leaves was comparable with that of 3.3 mg kg(-1) in the diet. This difference in activity was correlated with better digestibility and higher conversion efficiency of the diet that also supported higher reproduction rate: S. littoralis grown on the potatoes reached a similar size to those on the diet but laid only 702 instead of 1077 eggs per female. Cry3Aa consumption reduced body growth as a consequence of lower food intake without significantly affecting food digestibility and the conversion efficiency of nutrients. The 11% and 5% body weight reductions caused by 1.4 mg kg(-1) Cry3Aa in potatoes and 3.3 mg kg(-1) in the diet, respectively, were associated with 74% and 65% reduction in the number of progeny; S littoralis grown on a diet with 9.1 mg kg(-1) Cry3Aa were 10% smaller and produced no viable progeny. These data suggest that the curtailment of reproduction was not caused by a general shortage of nutrient reserves but by a more direct Cry3Aa effect on the reproduction process.     

Antifeeding effect of cypermethrin and permethrin at sub-lethal levels against Pieris brassicae larvae

An antifeeding (feeding deterrent) response by first- and fifth-instar larvae of Pieris brassicae was shown to be significant at sub-lethal levels of cypermethrin and permethrin, using leaf-discs treated with the pyrethroids by dipping. Permethrin was slightly more effective than cypermethrin both as an insecticide and as an antifeedant against fifth-instar larvae, but the reverse order of effectiveness was observed, with a marked difference in mortality, against newly-hatched larvae. When 1-day-old fifth-instar larvae were continuously given leaf discs treated with a solution of the pyrethroid (1 mg litre^?1), up to the time of pupation, both cypermethrin and permethrin induced a significant extension of the larval period, with a reduction in the maximum larval and pupal weights, as well as a reduction in the total leaf-area consumed. However, at higher levels of both pyrethroids, lowering the temperature induced some irritancy, as indicated by regurgitation and frequent uncoordinated wriggling movements of the fifth-instar larvae. The advantages of cypermethrin as a protectant and as an antifeedant over permethrin are discussed.