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The dried twigs of Piper ribesioides were used to prepare various extracts in different solvents. Each extract was evaluated for their toxicity against 2nd instar larvae of Spodoptera exigua. The highest acute toxicity was observed for ethyl acetate extract with an LD50 of 3.25 and 2.50 μg/larva and LD90 of 9.19 and 8.15 μg/larva after 24 and 48 h post-treatment after topical application. Piperine, methyl piperate, N-cinnamoyl-(2-phenylethyl) amine, pinostrobin, pinocembrin, cinnamic acid, lemairamin, N,N-Diphenylcinnamide, and methyl cinnamate were isolated from this extract that was toxic to S. exigua larvae. Cinnamic acid was the most active compound with a LD50 of 0.17 μg/larva after 48 h of topical treatment. Piperine was significantly similar in activity (LD50 = 0.19 μg/larva), but toxicity decreased with the change in structural configuration as observed with methyl piperate (LD50 = 0.73 μg/larva). Other compounds were 3 to 11-fold less toxic than cinnamic acid and piperine. Growth of survived S. exigua larvae until adult emergence after topical application was recorded and maximum inhibition of about 70% was observed after the application of cinnamic acid. Egg hatch was only 29.11% after cinnamic acid treatment, compared to 97.38% in controls. Neither induction nor inhibition of detoxification enzymes due to treatment of extracts were statistically significant, however, individual compounds like cinnamic acid, methyl cinnamate, piperine, pinostrobin, pinocembrin, and lemairamin did show a moderate impact on these enzymes.

Background Thymol is a known natural product with insecticidal activity against several insect species. A recent study on structural modifications of thymol to thymyl esters and their efficacy against Spodoptera litura suggested that such an approach could develop generalized novel insecticides/insect growth inhibitors and requires further studies to establish the efficacy against lepidopterans. Results Thymol and structurally modified eight esters were evaluated against beet armyworm, Spodoptera exigua using the topical application. Thymyl butanoate was the most toxic compound with a median lethal dose (LD50 ) of 2.33 and 1.62 μg/larva after 24 and 48 h posttreatment, respectively. All thymyl esters were potentially better than the parent compound thymol, except thymyl dibromoacetate, in their efficacy against Spodoptera exigua. Essentially, there were three levels of activity vis-a-vis the compounds used, that is, with the LD50 range of 1.5 to 5.0, 7.0 to 15.0, and > 20 μg/larva, respectively. Ovicidal activity and reduction in larval growth were also determined by treating third instars at sub-lethal doses, that is, LD50 doses of second instars. Thymyl butanoate treated larvae inhibited glutathione S-transferase, carboxylesterase, and acetylcholinesterase activities, whereas the other thymyl esters induced these enzymes. Conclusion Thymyl butanoate exhibited higher toxicity against Spodoptera exigua and is the first to report about > 15.5× more toxicity than thymol and > 6.5× than thymyl cinnamate, which suggests that the efficacy was species-specific versus the chemical structural variation of the esters.

Coffea arabica parchment extracts and caffeine isolated from the plant were evaluated randomly against 1-week-old adults of red flour beetle, Tribolium castaneum for fumigant toxicity and repellent action under laboratory conditions. The effects on detoxification enzymes and neuroenzyme was also determined. Among the various extracts prepared sequentially using hexane, dichloromethane, ethyl acetate and methanol as solvents, the dichloromethane extract did repel insects on contact (EC50 = 4380.65 ppm). The repellence was more prominent when an olfactory response was measured (EC50 = 2571 ppm). The active ingredient isolated from dichloromethane extract was identified as caffeine which showed very strong repellency as compared to the extract. In terms of toxicity of this extract, a significant mortality was recorded in fumigation assay (LC50 = 5555 and 791 ppm, 24 and 48 h post-treatment, respectively). However, caffeine did not induce similar toxicity as the dichloromethane extract. The studies on the impact on detoxification enzymes of T. castaneum showed that dichloromethane extract inhibited carboxyl esterase activity, which possibly led to high toxicity. However, caffeine inhibited glutathione-s-transferase and induced carboxylesterase enzymes. It was, therefore, obvious that C. arabica parchment crude extracts have dual effects against T. castaneum adults, i,e, fumigant toxicity and repellent effects. However, the active compounds responsible for the two activities are surely different as caffeine could only induce repellent action against the beetles and the toxic compound needs to be identified, which is presently being investigated.

The relationship between the acute toxicity and feeding deterrent activity of ten compounds occurring commonly in essential oils was explored in order to determine whether they are acute toxins or antifeedants against stored-grain pests. Simultaneously, the objective was also to demonstrate the comparative efficacy against three post-harvest stored-grain pests. Thymol, carvacrol, eugenol and trans-anethole were specifically toxic, and linalool was a generalist feeding deterrent against all three species studied. Thymol was most toxic to Tribolium castaneum and Rhyzopertha dominica compared to carvacrol and eugenol but was least toxic to Sitophilus oryzae. Similarly, linalool deterred feeding of S. oryzae (FI50 = 0.025 mg/g of the wafer diet), T. castaneum (FI50 = 0.207 mg/g of the wafer diet) and R. dominica (FI50 = 0.482 mg/g of the wafer diet) at different concentrations; R. dominica beetles required about 20 times the concentration to deter feeding compared to S. oryzae and more than twice compared to T. castaneum. Comparison of toxicity and deterrent activity with respective artificial blends as binary mixtures revealed that synergism was not a generalized phenomenon, and the variations were both species as well as blend specific. Individual compound efficacy correlations were not ascertained, which suggests that artificial blends could be prepared to obtain potential mixtures for substantial control of stored-grain insect pests. The present study also implies that the compounds are mostly acute toxins, and whatever inhibition in feeding was obtained could be due to physiological toxicity rather than any interaction with gustatory receptors.

Nanotechnology is recognized as one of the key strategies that can contribute to sustainable and competitive agriculture. Several studies have reported an enhancement in the efficacy of certain biological substances on pests, a decrease in toxicity toward humans and the environment, and a reduction of losses due to physical degradation with the encapsulation of these substances in nanoparticulate systems. Thus, nanotechnology could contribute to the development of less toxic biopesticides with favorable safety profiles, increased stability of the active agents, enhanced activity on target pests, and increased adoption by end users. Research has shown that the use of nanoparticles is effective in protecting plant products and plant oils from rapid degradation, allowing a prolonged effect on target pests. Because the polymers used in this kind of formulation are biodegradable, continuous delivery of the active agent with low environmental harm is achieved. Though studies on the risk assessment of nanomaterials vis-a-vis biopesticides toward agroecosystem components after their release into the environment is lacking, it is imperative to add risk-assessment protocols into the strategies based on nanotechnology. Overall, nanobiotechnology seems promising in the direction of formulations that can be used to improve the stability and efficacy of natural products. Such formulations can provide controlled release of the molecules at the site of action, minimize potential toxic effects on nontarget organisms, and prevent degradation of the active agent by microorganisms. While there is certainly industrial activity aimed in this direction, the technology is still far from proven, with major questions persisting around release rates, storage stability, and cost effectiveness. Use of engineered nanomaterials (ENMs) is a widely known phenomenon in nanotechnology. However, relevant toxicity endpoints for ENMs need to be identified and safety evaluations need to be conducted before their application strategies are employed. Safety assessments are not easy because the application of ENMs will be relative to different selected organisms that will depict the sensitivity to the potential toxic effects.

The antifeedant and contact toxicity of Sphagneticola trilobata L. (Asterales: Asteraceae) extracts and isolated alkane compounds were investigated. Leaves of S. trilobata were sequentially extracted with hexane, dichloromethane, ethyl acetate, and methanol. Each extract and the compounds isolated were evaluated against the third instars of Spodoptera litura (F.) (Lepidoptera: Noctuidae), Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae), and Plutella xylostella L. (Lepidoptera: Yponomeutidae). Ethyl acetate extract and isolated alkanes were feeding deterrents as well as contact toxins against all the three species evaluated (FI50 ~ 0.27-2.34 mg/ml; LD50 ~ 0.88-4.2 µg/larvae for ethyl acetate extract, and FI50 ~ 0.06-4.35 mg/ml; LD50 ~ 0.72-3.54 Ethyl acetate extract for isolated alkane). Impact on detoxifying enzymes was variable. The ethyl acetate crude extract reduced carboxylesterase activity in S. litura and P. xylostella while in S. exigua the enzyme was induced. In contrast, glutathione-S-transferase activity was induced in S. exigua but no significant difference in P. xylostella and S.litura was observed. Our results suggest that the S. trilobata extracts have multiple biological activities that contribute to the toxicity in lepidopterans. Variable enzyme responses to the products evaluated in different lepidopteran species also confirm that some species-specific inductions do occur, suggesting the possibility of resistance development in the future, which cannot be summarily ignored. However, for this detailed biochemical studies are required. Multiple bioefficacies of S. trilobata makes it a potential botanical for further exploitation on larger scale so that field potential can be established in any integrated pest management (IPM) system.

Terpenes and biogenically related phenols commonly found in plant essential oils are known to be toxic to insect pests. Accordingly thymol was tested for acute toxicity via topical application to diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae) and its parasitoid, Cotesia plutellae (Kurdjunov) (Hymenoptera: Braconidae under laboratory conditions. Topical application to adult female parasitoids versus second instars of P. xylostella showed that thymol was about 62 times less toxic to the parasitoid than to the host larvae with 24 h LD50 of 0.052 and 0.0008M, respectively. Although thymol was less toxic to the parasitoid, some biological parameters of the progeny at sublethal doses of surviving parasitoids were impaired such as rate of emergence and development time of larvae and pupae. The impact on detoxification enzymes was also studied and there was no significant induction in cytochrome P450 and carboxylesterase activities in both treated male and female wasps. Results obtained sugge...

The insecticidal activity of various extracts prepared from the dried stem of Bauhinia scandens var. horsfieldii was determined against Plutella xytostella second instars via topical application. The best activity was observed in case of dichloromethane extracts with an LD50 of 2.76 and 2.15 μg/larva after 24 and 48 h, respectively. Further processing of this extract provided a mixture of long chain alkanes as active material exhibiting a LD50 of 2.81 μg/larva, 48 h post-treatment. Further screening of this mixture showed that heptacosane and hexacosane were the major compounds and were toxic to P. xylostella larvae with respective LD50 of 1.58 and 2.58 μg/larva after 48 h of treatment. This suggested that both compounds have additive effect in the alkane mixture. Combined evaluation of heptacosane and hexacosane proved that they were additive in activity when the two compounds were mixed in a natural ratio in which they occur in the alkane mixture. The impact of these compounds on detoxification enzymes was determined to show the possibility of resistance development against these compounds.

Essential oils are by-products of plant metabolism that are now known to interfere with basic metabolic, physiological and behavioral functions of insects, thereby having promise for use as pest control agents. Accordingly, four essential oil compounds, thymol, 1,8-cineole, linalool and pulegone, were evaluated against the diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Yponomeutidae), to determine their acute toxicity. Thymol and 1,8-cineole were highly toxic to third instars with a LD50 of 0.22 and 0.41 μg/larva, respectively. Linalool and pulegone were moderately active against this insect species, exhibiting

Comparative bioefficacy of five compounds in terms of acute toxicity and feeding and oviposition deterrence was determined against Helicoverpa armigera (Hubner), Spodoptera litura (F.) and Chilo partellus Swinhoe. Thymol was universally the most active compound, though with variable LD50 values depending upon the species evaluated. S. litura was the most susceptible with an LD50 of 28.5 μg/larva followed by C. partellus with an LD50 of 189.7 μg/larva and H. armigera with an LD50 = 290.8 μg/larva. Comparative trend of acute toxicity, however, showed a significant overlap in activity for C. partellus and H. armigera when treated with various compounds. There was a reverse trend for feeding deterrence where H. armigera and S. litura gustatory response was similar in comparison to C. partellus, a specific maize borer that exhibits positive phototropism. Thymol and linalool were synergistically toxic against all the 3 species and carvacrol was antagonistic in all combinations. Response of S. litura was definitely different compared to the other 2 species. All the compounds deterred oviposition and were ovicidal too. Overall, thymol was the most active compound as an acute toxicant, oviposition deterrent, ovicide or a feeding deterrent against all the three insects. Other than thymol, 1,8-cineole and linalool were effective ovicidal compounds with an LC50 = 4.0 and 3.3 mg/ml, respectively against H. armigera eggs but less active as oviposition deterrents than thymol; however, this deterrence was similar to the one observed in S. litura moths. 1,8-cineole and linalool were similar in deterring oviposition of C. partellus moths. Anethole was the least active as oviposition deterrent against all the 3 species evaluated and ODI50 values were 2.5–5-fold higher for this compound in both choice and no-choice situation.

We explored the potential of Burma rosewood, Dalbergia oliveri in dengue fever vector control by evaluating various extracts as larvicides and growth disruptors of Aedes aegypti Linnaeus (Diptera: Culicidae) under laboratory conditions. Third instars and pupae of the mosquito were tested using WHO guidelines. Highest larvicidal effect was obtained with dichloromethane and hexane extracts (LC 50 = 289.1 and 325.3 ppm, respectively) within 24 h post-treatment. However, toxicity was about 1.78-fold more in dichloromethane extracts than hexane extract, if treatment was given for longer duration of 48 h (LC 90 = 5048.5 ppm for hexane and 2848.1 ppm for dichloromethane extracts, respectively). In these treatments moderate inhibition of pupation was also seen with some larvae staying as 4th stage larvae for 8 days before dying. There were no significant differences in the sex ratio of emerged adults compared with the controls. Dichloromethane extract, being most active, was subjected to sequential chemical separation to obtain series of isoflavonoids. Three compounds (+)-medicarpin, formononetin and (±)-violanone were identified as active larvicides of Ae. aegypti . Significant pupal mortality was observed with dichloromethane extract treatment of 1–3 h old pupae after 48 h post-treatment (LC 50 = 1004.5 ppm). Isoflavonoid medicarpin (LC 50 = 296.72 ppm) was most active compound against pupae. Eclosion inhibition (EI) was also observed in pupae treated with dichloromethane extract (EI 50 of 668.7 ppm). Thus, naturally occurring larvicides can be particularly effective where larval habitats are readily identifiable. Results obtained should be of value in the search for new natural larvicidal compounds from other extracts as well and represent the first report of this plant species being used to control a mosquito vector.

Azadirachtin is a known botanical insecticide with multiple modes of action. Whether these effects have any relation with the modes of application, specifically during ecdysis process, has been the objective of the present study and accordingly the impairment, if any, among cuticular proteins of Spodoptera litura (Fab.) was determined. Azadirachtin was applied topically, via injection or oral administration. Azadirachtin administered via injection and topical applications severely impaired the ecdysis by 86.67 and 80.0%, respectively. However, this impairment via oral administration was significantly lower (73.33%). Using SDS-PAGE, the cuticular proteins were determined for treated insects under all the three modes of application. In all cases 6 protein bands (MW 9-34 kDa) were identified using markers as standard. In all treatments 3 induced proteins (MW. ~16, 20 and 23 kDa) and 1 reduced protein (~19 kDa) were observed. In case of the topical treatment a different induced protein of ~18 kDa was identified. The change in cuticular proteins, their possible role in ecdysis impairment vis-a-vis the mode of application of azadirachtin is being correlated. This will help in understanding the mode-of-action at cuticular level and also will allow developing a suitable application strategy under field conditions in insect pest management.

A series of biorational glycol diesters were prepared which have similar characteristics as sugar esters. From 62 glycol diesters prepared, 35 compounds were active in the range of 1–10 mg/ml concentration in diet that inhibited larval growth of second instars of Spodoptera litura and Helicoverpa armigera . The most inhibitory compounds to growth were ethylene, diethylene and triethylene glycol dialkanoates with EC 50 range of 1–5 mg/ml for S. litura and 2–6.5 mg/ml for H. armigera . Comparatively, sucrose octanoate, the known insecticidal sugar ester, was least active (EC 50 = 10.76 and 9.02 mg/ml for S. litura and H. armigera , respectively). Toxicity induced by glycol diesters is not mediated through feeding inhibition as relative consumption rate was never significantly reduced but the relative growth rate was reduced by 25–54% in S. litura and 26–44% in H. armigera . Efficiency of conversion of ingested food (ECI) was also significantly reduced. Obviously, these results do not implicate any absolute antifeedant effect, but a toxicity effect due to a reduced ECI. This was surprisingly opposite to sucrose octanoate action, where a significant effect on consumption and not the ECI was observed after oral administration, which suggests an antifeedant effect. From structure/activity point of view, increasing the chain length of molecules decreased the activity. This is obvious from least activity obtained in molecules like propane, methyl propane and pentane derivatives. Second, the deviation from open chain compounds to cyclohexyl alkanoates also reduced the activity substantially. Therefore, an open chain glycol diester of C-8 carbon length is required for the said activity against lepidopterans.

The application of insecticides to control oriental fruit fly, Bactrocera dorsalis Hendel (Diptera: Tephritidae), is a principal component of the current management of these fruit flies. However, we evaluated four extracts of Alpinia galanga Wild Linn (Zingiberaceae) rhizomes against adult flies and found hexane and ethanol extracts to be most effective (LC50 = 4,866 and 6,337 ppm, respectively, after 24 h). This suggested that both nonpolar and polar compounds could be active in the candidate plant. Accordingly, the hexane extract was further processed to isolate nonpolar active compounds from this plant source. Two compounds, (E)-p-acetoxycinnamyl alcohol and (E)-p-coumaryl alcohol ethyl ether, were identified as active ingredients and found to be more active than total hexane extract (LC50 = 3,654 and 4,044 ppm, respectively, after 24 h). The data suggested that the compounds were not synergistic but may have some additive effect in a mixture. The activity of the hexane extract against detoxification enzymes, carboxylesterase (CE) and glutathione transferase (GST) also was determined in vitro. CE was inhibited by 70%, whereas GST was not significantly inhibited. Insect CEs mediate insecticide resistance via their induction; therefore, inhibition of these enzymes by plant allelochemicals could be a useful alternative approach for the management of the pest in the field.

Pesticides based on microorganisms and their products have proven to be highly effective, species specific and eco-friendly in nature, leading to their adoption in pest management strategies around the world. The microbial biopesticide market constitutes about 90% of total biopesticides and there is ample scope for further development in agriculture and public health, although there are challenges as well. This article reviews the various microbial biopesticides that are commercially available, the different approaches for their production and development, the recent technological advances and the challenges faced by the microbial biopesticide field in the future.

Eight essential oil compounds were evaluated against the maize borer, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae), to determine their influence on oviposition and feeding behavior. Thymol was the most active compound against C. partellus when evaluated as an oviposition deterrent (ODI 50 = 1.36 mg ml -1 ), an ovicide (LC 50 = 2.06 mg ml -1 ), or a feeding deterrent (FI 50 = 141.8 μg cm -2 ) in laboratory experiments. The results corroborated with greenhouse experiments, in which egg laying on maize plants was inhibited significantly when the treatment was 15 times the concentration used in the laboratory experiments. However, there was neither any correlation between oviposition deterrence and feeding inhibition, nor between oviposition deterrence and ovicidal action. Apparently, toxicity per se or ovicidal action does not play any role in choice of oviposition in C. partellus. This was more obvious when the efficacy of compounds was compared in greenhouse experiments where ODI values and number of eggs laid on the treated leaves did not differ significantly in choice and no-choice situations. Apparently, toxicity plays an important role in predicting host plant choice, but behavioral response in terms of oviposition preference is independent of toxic action, particularly for non-host toxins. Thus, the same compounds affecting oviposition behavior on the one hand and having ovicidal or feeding deterrent properties on the other could be useful in field situations in any area-wide integrated pest management model.

We report the toxicological effects of new series of biorational glycol esters and compare the efficacy with the known commercial sugar ester, sucrose octanoate. Ethylene glycol diesters were easy to prepare without any isomeric constraints and very safe compounds that were applied as sprays or as residues. The compounds were equally toxic to mustard aphid, Lipaphis erysimi nymphs and adults and the activity was significantly comparable with sucrose octanoate activity. In spray assays LC50 of various compounds ranged from 1.32 to 11.5 mg/ml and in residual assay the range was 20.3‐51.4 lg/cm 2 . In residual assay, ethylene glycol di-2-ethylhexanoate (5) and dioctanoate (6) were as effective as sucrose octanoate. Structure activity relationship suggested that higher number of carbon chains in these two compounds may be playing a role in the stability of compounds under residual operation of the insecticide. Based on these results, glycol esters would be useful and easy to prepare biorational compounds in integrated pest management. J. Appl. Entomol.

Many plant extracts or allelochemicals show a broad spectrum of activity against pests and such products have long been touted as attractive alternatives to synthetic chemical pesticides for pest management because they pose little threat to the environment or to human health. The studies available suggest that plant-based materials do affect arthropod pests, vectors and other pathogens, yet only a handful of botanicals are currently used in agriculture in the industrialized world, and there are few prospects for commercial development of new botanical products. Secondary allelochemicals from plants are usually commercialized as single, concentrated compounds, despite research showing that compound mixtures reduce pest resistance better than single compounds. Several factors appear to limit the success of botanicals, most notably regulatory barriers and the availability of competing products of microbial origin and fermentation products that are cost-effective and relatively safe compared with their predecessors. In the context of agricultural pest management, botanical pesticides are best suited for use in organic food production in industrialized countries but can play a much greater role in the production and post-harvest protection of food in developing countries. It is in developing countries that are rich in endemic plant biodiversity where these pesticides may ultimately have their greatest impact in future integrated pest management (IPM) programmes, given their safety to non-target organisms and the environment. However, there is a need to organize natural sources, develop quality control, adopt standardization strategies and modify regulatory mechanisms.

Plants based pest control agents have long been touted as alternatives to synthetic chemicals for integrated pest management. Such phytochemicals reputedly pose little threat to the environment or to human health. Bioactivity of plant-based compounds is well documented in literature and is a subject of increasing importance. An antifeedant approach for insect control has been extensively studied, at least at laboratory level, though only a handful of plant-based compounds are currently used in agriculture. The known active plant-based antifeedants belong to groups like chromenes, polyacetylenes, saponins, quassinoids, cucurbitacins, cyclopropanoid acids, phenolics, alkaloids, various types of terpenes and their derivatives etc., and each insect species may process these allomones in a thoroughly idiosyncratic way, so that the same compound may have very different fates and consequences in different species of insects, thus pointing to different mechanisms involved in antifeedant action. It can also be vis...

Recently, the role of plant-based pest control agents has been considered to have significant potential to act as an alternative to synthetic chemicals for integrated pest management as they pose little threat to the environment or to human health. Bioactivity of plant-based compounds is well documented in the literature and is a subject of increasing importance. An antifeedant approach for insect control has been extensively studied, at least at laboratory level, though only a handful of plant-based compounds are currently used in agriculture. The known active plant-based antifeedants belong to groups like chromenes, polyacetylenes, saponins, quassinoids, cucurbitacins, cyclopropanoid acids, phenolics, alkaloids, and various types of terpenes and their derivatives, which have been comprehensively discussed in numerous reviews and books. Therefore, this chapter will not discuss various classes of compounds but will emphasize some of the latest isolated molecules that have significant potential for inducing feeding deterrence in insects. It is also obvious from various studies that each insect species may process these allomones in a thoroughly idiosyncratic way, so that the same compound may have very different fates and consequences in different species of insects, thus pointing to different mechanisms involved in antifeedant action. It can also be visualized that insect feeding deterrents may be perceived either by stimulation of specialized deterrent receptors or by distortion of the normal function of neurons, which perceive phagostimulating compounds. Some plant antifeedants influence the feeding activity through a combination of these two principal modes of action. From a commercial point of view only a few highly active antifeedants have been researched, which makes it impossible to systemize or to predict any molecular motifs in feeding inhibition. Impairment in deterrence resulting from habituation has been suggested that could pose different implications for pest management than does decreased deterrence resulting from increased tolerance to toxic substances. Genetically modified plants, which could produce the active antifeedant substances in amounts high enough to protect the plants from further herbivorous damage, could be a possibility in the future.

The efficacy of neem (1500 ppm azadirachtin (AI)), Delfin®WG™, a biological insecticide based on selected strain ofBacillus thuringiensisBerliner (Bt) subspecieskurstaki, and Cry1Ac protein, either individually or in combination, were examined against first to fourth instarHelicoverpa armigera(Hübner) larvae. Using an oral administration method, various growth inhibitory concentrations (EC) and lethal concentrations (LC) were determined for each bioagent. Combinations of sublethal concentrations of Bt spray formulation with azadirachtin at EC50or EC95levels not only enhanced the toxicity, but also reduced the duration of action when used in a mixture. The LC20and LC50values for Cry1Ac toxin were 0.06 and 0.22 μg ml−1, respectively. Bt–azadirachtin combinations of LC50+EC20and LC50+EC50result in 100% mortality. The mortality also was significant in LC20+EC20and LC20+EC50mixtures. These studies imply that the combined action is not synergistic but complimentary, with azadirachtin particularly facilitating the action of Bt. The Bt spray–azadirachtin combination is more economical than combinations that involve isolating the toxic protein, as the Bt spray formulations can be combined in a spray mixture with neem. These combinations may be useful for controlling bollworm populations that have acquired resistance to Bt as they may not survive the effect of mixture. Azadirachtin may be useful as a means of reducing the endotoxin concentrations in a mixture, to promote increased economic savings and further reduce the probability of resistance development to either insect control agent.

The bioefficacy of aglaroxin A from Aglaia elaeagnoidea (syn. A. roxburghiana) was assessed using the gram pod borer, Helicoverpa armigera (Hubner), 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.

Biological activities of the salannin type of limonoids isolated from Azadirachta indica A. Juss were assessed using the gram pod borer Helicoverpa armigera (Hubner) and the tobacco armyworm Spodoptera 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 microg/cm(2) of 3-O-acetyl salannol, salannol and salannin, respectively deterring feeding by 50% in S. litura larvae. In nutritional assays, all three compounds 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 the H. 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.

Head space volatiles, including 73% di-n-propyl disulfide, were collected from freshly crushed neem seeds. This compound along with previously reported diallyl disulfide (di-2-propenyl disulfide) were toxic when applied topically or as a fumigant to Tribolium castaneum adults and 8-, 12-, and 16-d-old larvae, and Sitophilus oryzae adults. Di-n-propyl disulfide significantly decreased the growth rate and dietary utilization with moderate inhibition of food consumption in both insects. The total coefficient of deterrence for this compound ranged between 68.5 and 178.6, which suggests that it has medium to very good deterrent activity vis-a-vis the treatment concentration and instar. Di-n-propyl disulfide and diallyl disulfide presented a similar effect on efficiency of conversion of ingested food, which is reduced 3-fold; this implies that both compounds are physiological toxicants. Present studies clearly demonstrate that di-n-propyl disulfide could be a potent toxicant, fumigant, and feeding deterrent for stored grain pests, if a suitable formulation and application procedure are developed.

The biological activity of azadirachtin, nimbocinol, azadiradione and salannin isolated from Azadirachta indica A. Juss. (neem) was assessed alone and in combination against the cotton bollworm, Helicoverpa armigera (Hubner) and cluster caterpillar, Spodoptera litura (F) (Lepidoptera: Noctuidae). Nimbocinol exhibited growth inhibitory activity in artificial diet bioassays with 82.4 and 92.2 mg kg−1 concentrations inhibiting growth by 50%, respectively, in the two species. This efficacy was almost comparative to azadiradione (EC50 = 109.6 and 102.1 mg kg−1) and salannin (EC50 = 72.2 and 70.2 mg kg−1). Azadirachtin was the most active neem allelochemical against both insect species. In nutritional analysis, only nimbocinol and azadiradione reduced the efficiency of conversion of ingested food (ECI) in feeding experiments, indicating toxic rather than antifeedant effects. In a combination, when azadirachtin was present in a mixture, it always dominated in its efficacy and EC50 values did not deviate much from the individual efficacy of azadirachtin (0.23 and 0.21 mg kg−1, against H. armigera and S. litura larvae, respectively). However, enhanced activity among structurally variable molecules was observed, i.e., when salannin combines with nimbocinol or azadiradione, rather than structurally similar molecules like nimbocinol with azadiradione. The activity among nonazadirachtin limonoids in specific combination as opposed to the structural chemistry having explicitly two different modes of action, like feeding deterrence and chronic toxicity, may be playing a significant role in the multicomponent system.

L-Canavanine isolated from seeds of Canavalia ensiformis was found to produce antifertility in the adults of Periplaneta americana. Although there was no significant effect on body weight and food consumption index, yet 0.05 and 0.1 percent concentrations of canavanine in food produced significant sterility index of 88.3 and 100.0 respectively. Zusammenfassung L-Canavanin aus Canavalia ensiformis-Samen: Wirkungen auf die Fertilitat von Periplaneta americana (L.) (Orthopt., Blattidae) Das aus den Samen von Canavalia ensiformis isolierte L-Canavanin erwies sich als Antifertilitatsmittel fur die Adulten der Schabe Periplaneta americana. Obgleich es keine spezifischen Wirkungen auf das Korpergewicht und den Nahrungsindex zeigte, fuhrten 0,05 bzw. 0,1% des Wirkstoffes, mit der Nahrung gegeben, zu einem Sterilitatsindex von 88,3 bzw. 100.

Leaf disc choice test bioassay demonstrated that formulated neem seed extracts were highly deterrent and growth regulatory to rose aphid,Microsiphum rosae (L.) and Chrysanthemum aphid,Macrosiphoniella sanbornii (Gillete). Effective concentrations to produce 50% feeding deterrence was 0.80 and 0.84% respectively for 2nd instar nymphs irrespective of bioassay duration. The disruption of aphid feeding was related to the presence of azadirachtin concentration in the extract. The toxicity on contact from the leaf surface or via topical application due to azadirachtin was significantly different and topical treatment was at least 7 times more effective for both species. Thus growth regulatory effects of azadirachtin were influenced by the host plant and the stage of treatment. Field evaluation with formulated neem extracts revealed the effect to be more of growth regulatory nature thereby showing that azadirachtin is a physiological toxin for aphid species. Neem seed extracts reduced the population of aphid on respective host plants significantly, EC50 values being 0.88 and 0.96% forM. rosae andM. sanbornii respectively.

Foliar and twig extracts of three species of Aglaia were screened for larval growth inhibiting and antifeedant effects against the polyphagous lepidopteran larvae of Spodoptera litura and Helicoverpa armigera. A. elaeagnoidea and A. odorata crude ethanolic extracts were at par in their activity at an initial treatment level of 5 mg/g of dry diet weight, while A. roxburghiana was half as active as the other two species. Detailed investigation of A. elaeagnoidea species revealed the presence of complex limonoid fractions responsible for this activity. The nutritional analyses showed impaired diet consumption and dietary utilization at 200 ppm level of treatment when limonoid fractions Fr 2 J and Fr 6 K were provided orally to S. litura larvae, indicating centrally mediated anorexic effect. The isolation of the limonoid complex from A. elaeagnoidea should provide useful starting point for the development of a botanical anti-insect preparation.

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.

The excretion, retention, and tissue distribution of [3H]-dihydroazadirachtin was investigated in the variegated cutworm, Peridroma saucia (Noctuidae). The candidate compound was rapidly cleared from the hemolymph following either oral exposure or topical administration, with maximum concentrations at 6 h post-treatment and peak appearance of label in the frass at 12 h. However, approximately 45 and 55% of the labelled material was retained in the body at 72 h in respective treatments. Major depots for retained radioactivity were the gut (24% of the administered oral dose, 18.8% of the administered topical dose) and integument (12.2% of the oral dose and 30.7% of the topical dose). The variation in tissue distribution of dihydroazadirachtin with respect to the mode of application is discussed. A single polar metabolite fraction was obtained from the frass of dihydroazadirachtin-fed larvae. The physiological and behavioral effects of 22,23-dihydroazadirachtin and azadirachtin are quantitatively similar. © 1994 Wiley-Liss, Inc.

Eight essential oil compounds were used for study of larvicidal and growth inhibitory effects against the maize stem borer, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae). It is the most prevalent key pests, and is one of the limiting factors in the successful cultivation of the maize crop in India. Two dietary bioassays; on-diet and in-diet, were used. The bioassays showed different tenden- cies and LC 50 values were on the lower side in on-diet tests compared to in-diet assays. Thymol was the most active in both laboratory and greenhouse experiments. In greenhouse conditions, thymol was significantly active at a 10 x LC 50 level of treatment. Overall mor- tality due to thymol was 41.66% in 4 days and larvae failed to bore into the plant and could not feed until 48 h post-treatment. After 72 h there was some degree of feeding and boring in the plants by insects, but still < 45% of that in the controls. The present study suggests that larvicidal and growth inhibitory activity by the essential oil compounds could be beneficial as a possible control of the maize borer. This is especially true about thymol which has potential in field situations. It is effective if a proper delivery system and the appropriate time of sprays is established. A 4 day-interval spray of thymol against C. partellus can control the pest significantly and can be used in any integrated pest management system. On the basis of compound structure, no specific trend was observed.