Bioefficacy and mode-of-action of some limonoids of salannin group fromAzadirachta indica A. Juss and their role in a multicomponent system against lepidopteran larvae

Biological activities of the salannin type of limonoids isolated fromAzadirachta indica A. Juss were assessed using the gram pod borerHelicoverpa armigera (Hubner) and the tobacco armywormSpodoptera litura (Fabricius) (Lepidoptera: Noctuidae). Inhibition of larval growth was concomitant with reduced feeding by neonate and third instar larvae. All three compounds exhibited strong antifeedant activity in a choice leaf disc bioassay with 2.0, 2.3 and 2.8 (μ/cm² of 3-O-acetyl salannol, salannol and salannin, respectively deterring feeding by 50% inS. litura larvae. In nutritional assays, all three comounds reduced growth and consumption when fed to larvae without any effect on efficiency of conversion of ingested food (ECI), suggesting antifeedant activity alone. No toxicity was observed nor was there any significant affect on nutritional indices following topical application, further suggesting specific action as feeding deterrents. When relative growth rates were plotted against relative consumption rates, growth efficiency of theH. armigera fed diet containing 3-O-acetyl salannol, salannol or salannin did not differ from that of starved control larvae (used as calibration curve), further confirming the specific antifeedant action of salannin type of limonoids. Where the three compounds were co-administered, no enhancement in activity was observed. Non-azadirachtin limonoids having structural similarities and explicitly similar modes of action, like feeding deterrence in the present case, have no potentiating effect in any combination.     

Repellent,antifeedant and toxic effects of Ageratum conyzoides (Linnaeus) (Asteraceae) extract against Helicovepra armigera (Hübner) (Lepidoptera: Noctuidae)

Repellent, antifeedant and toxic effect of crude hexane extract of Ageratum conyzoides were investigated against Helicoverpa armigera. In orientation bioassay, the extract exhibited dose-dependent repellency against neonates. Extract significantly increased the mortality and decreased growth of different larval stages when administrated orally in artificial diet. EC₅₀ value was at 0.11% for larval growth inhibition. Toxicity of the extract was manifested by high mortality of first instar larvae after 7 days of feeding on diet containing 0.05–0.4% of extract with LC₅₀ of 0.17%. Under choice bioassay, extract showed strong antifeedant activity against fifth instar larvae with DI₅₀ of 0.21%. In nutritional bioassay, extract significantly reduced RCR, RGR, ECI and ECD of fifth instar larvae with increased AD. When RGR were plotted against RCR, the growth efficiency of larvae fed on treated diet was significantly lower than the control fed larvae suggesting the antifeedant and toxic effect of extract.     

Bioefficacy and mode-of-action of aglaroxin A from Aglaia elaeagnoidea (syn. A. roxburghiana) against Helicoverpa armigera and Spodoptera litura

The bioefficacy of aglaroxin A from Aglaia elaeagnoidea (syn. A. roxburghiana) was assessed using the gram pod borer, Helicoverpa armigera (Hübner), and Asian armyworm, Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae). The compound exhibited strong growth inhibition in a diet bioassay, with 0.67 p.p.m: and 0.78 p.p.m. of the compound reducing growth by 50% in H. armigera and S. litura neonate larvae, respectively, whereas a growth inhibition of 95% was achieved at 2.36 p.p.m: and 2.41 p.p.m., respectively; this was comparable to azadirachtin treatments used as a control. Aglaroxin A was toxic to various stadia. Nutritional analysis revealed the antifeedant properties of the compound; however, nutritional indices indicated that the reduction in growth of the larvae was not entirely due to starvation, but partly due to the toxic effects of the ingested compound. This was further confirmed in topical treatments. When relative growth rate was plotted against relative consumption rate, the growth efficiency of larvae fed on a diet containing aglaroxin A was significantly less than that of control larvae. These results further indicate that aglaroxin A acts as both antifeedant and chronic toxin. Morphologically deformed or partially pupated insects were obtained after 5th instar larvae were treated with aglaroxin A. Such developmental inhibition during ecdysis was not due to depletion of the moulting hormone, as treated larvae, when provided with exogenous 20‐hydroxyecdysone, did not show any recovery from the effect. However, it is obvious from the present findings that aglaroxin A activity does not absolutely follow the pattern of azadirachtin or the more related compound rocaglamide known in lepidopterans.     

The effect of neem allelochemicals on nutritional physiology of larval Spodoptera litura

Neem allelochemicals azadirachtin, salannin, nimbinene and nimbin were administered to different larval instars of the tobacco armyworm, Spodoptera litura orally in artificial diet, topically or via injection. Nutritional analyses revealed strong antifeedant and growth regulatory effects of azadirachtin which were independent of each other. While salannin and nimbinene induced concentration dependent feeding deterrence only; nimbin was inactive to the 1000 ppm level against this insect species. One of the causes of the reduced growth rate of azadirachtin treated insects was due to an increase in the costs associated with growth. This was relative to a drastic reduction in the activity of gut trypsin. Salannin and nimbinene, however, did not interfere with the trypsin activity of the gut. These results and those from nutritional studies suggest that salannin and nimbinene have no toxicity mediated effects on S. litura larvae and antifeedant activity is a result of the effects on deterrent and other chemoreceptors. The fact that azadirachtin directly or indirectly inhibits the secretion of trypsin by the enzyme-secreting cells of the gut is discussed.     

Avidin expressed in transgenic tobacco leaves confers resistance to two noctuid pests,Helicoverpa armigera and Spodoptera litura

Fertile transgenic tobacco plants with leaves expressing avidin in the vacuole have been produced and shown to halt growth and cause mortality in larvae of two noctuid lepidopterans, Helicoverpa armigera and Spodoptera litura. Late first instar H. armigera larvae and neonate (<12-h-old) S. litura larvae placed on leaves excised from T₀ tobacco expressing avidin at 3.1–4.6M (moles/kg of fresh leaf tissue) had very poor growth over their first 8 days on the leaves, significant numbers had died by days 11 or 12 and all were dead by day 22 (H. armigera) or day 25 (S. litura). Similar results were obtained when late first instar H. armigera larvae were placed on leaves from T₁ plants expressing avidin at six different average concentrations, ranging from 3.7 to 17.3M. Two larvae on the lowest expressing leaves survived to pupation, but there was total mortality among the other groups and no relationship between avidin concentration and the effects on the larvae. Synergistic effects between avidin-expressing tobacco plants and a purified Bt toxin, Cry1Ba, were demonstrated. Late instar H. armigera larvae fed with leaves from T₂ plants expressing avidin at average concentrations of either <5.3 or >12.9M, and painted with Cry1Ba protein at a rate equivalent to an expression level of 0.5% of total leaf protein, died significantly faster than larvae given either of the two treatments alone. Larvae fed with avidin-expressing leaves painted with the protease inhibitor, aprotinin, at a rate equivalent to 1% of total leaf protein had mortality similar to those given avidin-leaves alone. There was no evidence of antagonism between these two proteins.     

Antifeedant and toxic activity of Adhatoda vasica leaf extract against Spodoptera littoralis (Lep., Noctuidae)

Abstract: The effect of crude methanolic extracts of Adhatoda vasica leaves on the feeding and performance of Spodoptera littoralis larvae was investigated in the laboratory. Feeding on fresh leaves resulted in 100% mortality of larvae after 26 days of unsubstantial growth. The extract exhibited strong antifeedant and toxic activity against the larvae when applied either on leaf discs or incorporated into artificial diet. Under choice conditions the antifeedant index calculated over 72 h for neonate larvae increased significantly (from 71.5 ± 3.2 to 92.1 ± 4.2) as the concentration of extract in the treated diet increased from 200 to 1000 ppm. Consumption by the sixth instar larvae of leaf discs dipped in 0.01, 0.1 and 0.2% extract solutions was significantly lower than consumption of control discs in both choice and no-choice tests. The latter two concentrations deterred feeding by 63.4 and 90.4%, respectively, under choice conditions, while only the 0.2% extract solution deterred feeding by 56.8% in the no-choice test. Toxicity of the extracts was manifested by a high mortality, reduced growth rates, and low weight gain by larvae fed on diets containing 200–2000 ppm of the extract. No larvae survived to pupation under the latter concentration. The time to pupation increased from 15.8 ± 0.4 to 37.9 ± 4.1 days as the extract concentration in diet increased from 0 to 1000 ppm. When fed to the fifth instar larvae, the crude extract significantly reduced consumption, growth, utilization of ingested and digested food, and approximate digestibility. The consumption-dependent growth efficiency of animals fed on extract-free diet was significantly higher than the growth efficiency of animals fed on extract-containing diets, suggesting both antifeedant and toxic activities of the extract.     

Cloning and expression inEscherichia coli of entomotoxic protein gene fromBacillus thuringiensis subspecieskurstaki

A plasmid borne larvicidal crystal protein gene from B.thuringiensis subspecieskurstaki was cloned inEscherichia coli using a specific 20-mer oligonucleotide probe. The gene expressed inE. coli at a high level. TransgenicE. coli cells produced large irregular bodies which looked bright under phase contrast microscopy. The phase bright bodies released by sonic disruption of cells could be pelleted by centrifugation. Toxicity trials on the larvae ofSpodoptera litura showed that the pellet was antifeedant and toxic to the larvae. The supernatant was only mildly antifeedant. Even short term feeding of larvae on the toxin delayed the onset of pupation.     

Secretory avocado idioblast oil cells: evidence of their defensive role against a non-adapted insect herbivore

We tested the hypothesis that avocado idioblast oil cells play a defensive role against herbivorous insects. Toxicities of the intact avocado idioblast oil cells and the extracted idioblast oil were compared for three insect herbivores. Spodoptera exigua (Hübner) larvae are generalists that do not feed on avocados. By contrast, Sabulodes aegrotata (Guenée) and Pseudoplusia includens (Walker) larvae are generalist herbivores that readily feed on avocados. All bioassays were performed at a naturally occurring concentration of idioblast oil cells (2% w/w). Choice experiments showed that S. exigua larvae avoided diet treated with avocado idioblast oil cells and consume more control than treated diet. In contrast, idioblast oil cells had no significant antifeedant effects on the adapted S. aegrotata and P. includens larvae. Subsequent experiments designed to assess resistance mechanisms separated pre-ingestive (behavioral) and post-ingestive (physiological) effects of the avocado idioblast oil cells, and the extracted idioblast oil, on the two adapted herbivores. Post-ingestive adaptation was the mechanism that allows feeding. Because the impact of the avocado idioblast oil cells was greatest on the performance of non-adapted S. exigua, additional experiments determined that larvae fed diet containing the oil cells had higher mortality and reduced larval growth compared to controls. Developmental times were significantly prolonged for the survivors. Thus, increased mortality, reduced developmental rates, and antifeedant activity in the non-adapted insect indicate that defense against non-adapted herbivores may be an important function of idioblast cells in avocados.     

Parasitism of an insect Manduca sexta L. alters feeding behaviour and nutrient utilization to influence developmental success of a parasitoid

The effects of macronutrient balance on nutrient intake and utilization were examined in Manduca sexta larvae parasitized by Cotesia congregata. Insects fed an artificial diet having constant total macronutrient, but with varied ratios of protein and carbohydrate, with altered diet consumption in response to excesses and deficiencies of the individual macronutrients. Bivariate plots of protein and carbohydrate consumption for non-parasitized larvae demonstrated a curvilinear relationship between points of nutrient intake for the various diets, and the larvae grew best on carbohydrate-biased diets. The relationship was linear for parasitized larvae with the growth uniform across diets. On protein-biased diets, the larvae regulated the nitrogen content, containing similar amounts of nitrogen regardless of consumption. Efficiency of nitrogen conversion in non-parasitized larvae was greatest on carbohydrate-biased diets, while nitrogen conversion by parasitized larvae was greatest with intermediate nutrient ratios. Accounting for carbohydrate consumption, the lipid content decreased as dietary carbohydrate increased, but parasitized larvae contained significantly less lipid. The total biomass of parasites developing in individual host larvae was positively correlated with host protein consumption, but the individual parasites were similar in size. Parasitism influences host nutrient consumption in a manner that achieves uniform host growth under diverse nutritional regimes, thereby constraining blood nutrient concentrations within limits suitable for parasite growth and development.     

Differential toxicity of a phenolic glycoside from quaking aspen to Papilio glaucus butterfly subspecies,hybrids and backcrosses

Summary Papilio glaucus subspecies, hybrids and backcrosses exhibit greatly different abilities to use quaking aspen (Populus tremuloides) and other members of the Salicaceae as host plants. This study was conducted to test the hypotheses that phenolic glycosides account for the differences in larval performance, and that differential performance is correlated with differential larval esterase activities. To test the hypotheses we conducted first instar survival trials and fourth (penultimate) instar feeding trials with tremulacin, a phenolic glycoside. We also conducted assays of -glucosidase, esterase, and glutathione transferase activities, using midgut enzyme preparations from fifth instars. First instar survival on the tremulacin treated diet generally improved with a higher proportion of Papilio glaucus canadensis genes in the genotype, although survival in one backcross treatment was surprisingly low. Penultimate instars of P.g. glaucus and P.g. australis fed tremulacin treated black cherry leaves experienced a severe reduction in growth rate relative to larvae fed control leaves. This seriously suppressed growth was partially due to reduced consumption rates and reduced conversion efficiencies, however, approximate digestibility was not affected. In contrast, P. g. canadensis and hybrids showed no differences in growth rates between tremulacin treated and control leaves. Reciprocal backcrosses of hybrids with P. g. glaucus resulted in slightly suppressed growth on treated versus control leaves. The results suggest that after a certain threshold, increased proportions of P. g. glaucus genes resulted in poorer growth performance with tremulacin in the diet. Soluble esterase activities generally increased with the proportion of Papilio glaucus canadensis genes in the genotype, and paralleled overall trends in larval survival and feeding performance. We conclude that phenolic glycosides such as tremulacin are responsible for differential performance of Papilio glaucus subspecies, hybrids and backcrosses fed plants in the Salicaceae, and that detoxification of phenolic glycosides by midgut esterase explains why some Papilio glaucus genotypes can effectively utilize these plants.     

Pre-ingestive and post-ingestive effects of soya bean extracts and rutin on Trichoplusia ni growth

Total ethanolic crude extracts from soya bean (Glycine max L. Merrill) PI 227687 and `Davis', three purified fractions (A, B and C) from PI 227687, and pure rutin were tested for their effect on the growth of Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae) larvae, from egg hatching to pupation. Analysis of covariance (ANCOVA), followed by bicoordinate utilisation plots, was used to remove the effect of feeding time from consumption and weight of pupae and to separate pre- ingestive and post- ingestive effects of different diets on T. ni growth. Survival, pupal weight, and feeding time of T. ni were all negatively affected by PI 227687 total extracts. Pupal weight and consumption remained affected by diet, after removing the effect of feeding time by ANCOVA. Larvae fed on the `Davis' extract diet grew larger and consumed more rapidly a larger amount of food than those fed on PI 227687 and control diets. T. ni pupal weight was strongly influenced by consumption. In general, those insects that consumed more food were heavier but larvae fed on diet containing PI 227687 extract grew less than the others, irrespective of the amount of ingested and digested food. The feeding time was adversely affected by PI 227687 fraction A, composed of two flavonol glycosides (rutin and quercetin 3-O-glucosylgalactoside) and of an isoflavone glycoside (genistin). Survival and pupal weight were not affected, although the consumption and assimilation of ingested food was lower when larvae were fed on fractions A and C. The toxicity of the higher rutin concentration (2%) was similar to that observed when the insects were fed on unfractioned PI 227687, except that effects on food consumption were not observed. Results indicated that the feeding deterrence of PI 227687 must be caused by other compounds from fractions A and C. Moreover, rutin, acting as an antibiotic, appears to account for the adverse effects of PI 227687 on the physiology of T. ni.     

Selective Feeding of <Emphasis Type="Italic">Helicoverpa armigera</Emphasis> (Hübner) and <Emphasis Type="Italic">Spodoptera litura</Emphasis> (Fabricius) on Meridic Diet with <Emphasis Type="Italic">Bacillus thuringiensis</Emphasis> Toxins

Laboratory experiments were conducted to evaluate the behavior of Helicoverpa armigera (Hübner) and Spodoptera litura (Fabricius) larvae on meridic diet with different concentrations of Bt spray formulation Delfin or isolated Cry1Ac protein or the foliage and bolls from transgenic cotton, Bollgard hybrid RCH-317 Bt. Both insect species selectively fed on nontreated diet compared with the diet treated with Delfin. While H. armigera exhibited concentration response with Cry1Ac, this protein did not affect S. litura larvae. In general Helicoverpa selected diet with low concentrations (EC₂₀ and EC₅₀ levels) of Cry1Ac compared with higher concentrations of Cry1Ac. In order to develop appropriate management strategies, a thorough understanding of the behavioral mechanisms leading to the responses of insects to the proteins in transgenic varieties is required. Thus, based on results of the insects fed individually on the leaf discs or bolls from transgenic cotton plants alone or under choice situation with meridic diet revealed that H. armigera larvae preferred meridic diet to transgenic leaves or bolls expressing Cry1Ac protein. H. armigera larvae preferred meridic diet to plant material; more than 70% larvae were seen on the meridic diet, and average larval weight gain was in the range of 121.7–130.5 mg. However, in case of S. litura the larvae showed no significant discrimination between meridic diet and the leaf discs. In fact more than 60% larvae preferred leaf discs for feeding, though Cry1Ac expression in leaf discs was in the range of 0.9–2.18 μg/g. Thus differences in behavioral response could potentially impact the level of efficacy of crop cultivars that have been genetically engineered to produce these proteins.     

Toxicity of the limonoid allelochemical cedrelone to noctuid larvae

The limonoid cedrelone, a constituent of Cedrela toona and C. odorata (Meliaceae) was evaluated as a larval growth inhibitor for the polyphagous noctuids Peridroma saucia and Mamestra configurata by examining its effects on development and feeding behaviour. Cedrelone significantly inhibited growth of different larval instars when administered orally (in artificial diet), topically or via injection. Nutritional analyses revealed that both growth inhibition and reduced consumption are a consequence of postingestive malaise rather than a peripherally-mediated antifeedant effect. Cedrelone administered via injection to sixth instar P. saucia larvae also inhibited growth, delayed development, and resulted in considerable larval mortality. However, all larvae which survived treatment pupated successfully. The present study suggests that the toxicity of cedrelone does not likely involve the endocrine system.     

Differential effect of tannic acid on two tree-feeding Lepidoptera: implications for theories of plant anti-herbivore chemistry

Summary Feeding efficiencies of ultimate instar larvae of two polyphagous tree-feeding Lepidoptera, Malacosoma disstria (Lasiocampidae) and Orgyia leucostigma (Liparidae), were measured on artificial diets containing from 0% to 8% tannic acid. Relative growth rate (RGR) of O. leucostigma was not affected by up to 8% tannic acid, suggesting that O. leucostigma has evolved an effective counteradaptation to hydrolyzable tannins. In contrast, as little as 0.5% tannic acid caused a significant reduction in RGR of M. disstria, due both to reduced efficiency of conversion of digested food (ECD) and reduced relative consumption rate (RCR), and caused a significant increase in mortality during the pupal stage. Moreover, when reared from hatching on tannin-containing diets, no M. disstria larvae survived past the fourth instar.Although tannins are commonly referred to as digestibility-reducing substances, tannic acid did not reduce the ability of M. disstria or O. leucostigma larvae to digest either the whole diet or nitrogen contained in the diet. For M. disstria, tannic acid acts as a toxin and a feeding deterrent, but not as a digestibility-reducing substance. Growing evidence that tannins commonly act as toxins warrants a reassessment of their role in anti-herbivore chemistry.     

An improved leaf-disk antifeedant bioassay and its application for the screening of Hokkaido plants

In the course of our search for new insect antifeedant substances from plants, we have devised an improved antifeedant leaf-disk bioassay. Our system allows an accurate measurement of consumed disk surfaces, using a video camera interfaced with a computer. The scanned image of the leaf disks is stored, and the eaten areas are measured with the help of a video-image analysis software. This new method allows for precise quantification of insect antifeedant activity tested on leaf material. This method was applied to the screening of Hokkaido plants for antifeedant activity. Out of 206 samples, seven demonstrated significant activity against larvae of the tobacco cutworm,Spodoptera litura.     

Development of a chemically defined diet for ants

A chemically defined diet is a useful tool for the study of nutritional physiology of organisms. We have developed such a diet for Camponotus carpenter ants to facilitate experiments on nutritional requirements of these ants. Worker colonies of Camponotus floridanus were fed with a chemically defined diet, containing all essential minerals, amino acids, vitamins, growth factors and sucrose in an agar matrix. After 13 weeks, neither the number of raised pupae, their dry weight, nor the mortality of workers in subcolonies fed with this diet differed significantly from control colonies fed with Bhatkar-Whitcomb-agar, in addition to cockroaches and diluted honey. Therefore, this diet is adequate for a normal brood production and a maximal growth rate of C. floridanus larvae, at least for a period of three months. This diet should be suitable for ants that are able to feed on agar-based food resources in general. Received 6 September 2006; revised 5 October 2006; accepted 18 October 2006. An erratum to this article is available at .     

Insect feeding deterrents from the medicinal plant Tylophora asthmatica

Alkaloid extractables of Tylophora asthmatica (Asclepiadaceae) have been tested for the antifeedant activity against Spodoptera litura by incorporating them in semisynthetic and cellulose diets. The alkaloid extractables at 0.01% concentration inhibited feeding of the larvae. Three compounds, tylophorine, tylophorinine and pergularinine, were isolated; and their EC₅₀ values were found to be 2.9, 8.6 and 12.00 ppm, respectively.     

The effects of a harmful alga on bivalve larval lipid stores

Marine invertebrates often have complex life histories that include a swimming planktivorous larval stage, at which time they are vulnerable to a variety of stressors, including those associated with nutritional stress and harmful algal blooms. Lipid stores have been shown to be especially important for post-metamorphic survivorship and growth in a variety of marine invertebrates. We investigated the effects of the harmful brown tide alga Aureococcus anophagefferens on the lipid stores and growth of larvae of the hard clam (northern quahog, Mercenaria mercenaria), a dominant bivalve in many western Atlantic bays and estuaries. M. mercenaria was the dominant bivalve in Great South Bay, Long Island, until the mid-1970s, but very few larvae are presently found in these waters. Recent brown tide blooms have been hypothesized to pose a barrier to recovery of M. mercenaria populations and hinder recent restoration efforts by negatively affecting clam larvae. To test whether a diet of the brown tide alga affects the accumulation of beneficial lipid stores, we fed larvae one of three diets representing equal biovolumes of Isochrysis galbana, a nutritious control alga; A. anophagefferens, the brown tide alga for which nutritional quality is not presently known; or a mixture of the two. Larvae fed only brown tide had significantly less lipid stores than those in the other dietary treatments. In addition, brown tide negatively affected larval size. We also tested for evidence of tradeoffs between larval growth and lipid stores, predicting that when the diet was less nutritious as in the brown tide treatments, larval size and lipids would be negatively correlated. In contrast, we found that larvae fed a mixed algal diet or only A. anophagefferens showed a significant positive correlation between lipid stores and size, suggesting that some larvae were simply better at obtaining food and associated nutrients. Larval success likely depends on a complex interplay between genetic and environmental factors. Our study suggests that poor nutrition associated with a harmful alga can have negative effects on larval size and lipids stores, which in turn are mediated by the inter-individual variability in the ability to grow and accumulate necessary lipid stores. Phytoplankton quality is likely to be important for the sustainability of bivalve populations even when it primarily impacts the larval phase; and a diet of brown tide algae may have lasting legacies for juveniles and adults.     

Effect of CryIC toxin from Bacillus thuringiensis on larval feeding behavior of Spodoptera exigua

The lack of data on the effect of Bacillus thuringiensis (B.t.) toxins on larval feeding behavior of the pest Spodoptera exigua (Hübner) (Noctuidae: Amphypyrini) prompted us to investigate the effect of three delivery systems of CryIC, a commercial formulation, inclusion bodies, and the activated CryIC toxin. The commercial formulation was the least and CryIC toxin the most lethal form to neonates of susceptible colonies. All but two of the treatments in choice tests with neonates and third instars showed significant avoidance of B.t. treated diet, with greater proportion of larvae from susceptible (UCR-S and AUBURN-S) and resistant (AUBURN-R) colonies on untreated diet than on diet treated with any of the CryIC forms and concentrations tested. Furthermore, third instars consumed significantly more control than treated diet for all CryIC forms, colonies and concentrations. The avoidance of CryIC toxin by neonates and third instars strongly suggests that CryIC, which also is present in the commercial formulation and in the inclusion bodies, is responsible for eliciting avoidance behavior by S. exigua larvae. Behavioral observations of third instars in a no-choice test on either treated or control diet indicated that questing behavior in susceptible larvae appears to be positively related with presence of CryIC toxin in the diet. Furthermore, resistant third instars were on the whole more active than susceptible thirds on both treated and control diet. Resistant thirds raised on CryIC treated diet (AUBURN-RC) spent more time eating treated diet than resistant larvae raised on control diet (AUBURN-R), suggesting that diet conditioning plays an important role on feeding behavior of S. exigua. The implications of these results are discussed.     

Insecticidal compound isolated from Syzygium lineare Wall. (Myrtaceae) against Spodoptera litura (Lepidoptera: Noctuidae)

A new crystal compound 2,5-diacetoxy-2-benzyl-4,4,6,6-tetramethyl-1,3-cyclohexanedione was isolated from the leaves of Syzygium lineare. The insecticidal activity of the compound was assessed against fourth instar larvae of Spodoptera litura. Its activity was better than the positive control azadirachtin. The compound was responsible for growth inhibition on S. litura. It induced larval, pupal and adult deformities even at low concentration. The compound may be useful as a botanical pesticide.