Larvicidal activity of neem and karanja oil cakes against mosquito vectors, Culex quinquefasciatus (say), Aedes aegypti (L.) and Anopheles stephensi (L.)

Larvicidal effect of neem (Azadirachta indica) and karanja (Pongamia glabra) oil cakes (individuals and combination) was studied against mosquito species. Both the oil cakes showed larvicidal activity against the mosquito species tested. The combination of neem and karanja oil cakes in equal proportion proved to have better effect than the individual treatments. The combination of the two oil cakes recorded an LC95 of 0.93, 0.54 and 0.77% against the mosquitoes, Culex quinquefasciatus, Aedes aegypti and Anopheles stephensi respectively The increase in efficacy of the combination treatment over individuals in all the mosquito larvae tested was found to range about 4 to 10 fold in terms of LC50 and 2 to 6 fold in terms of LC95.     

Larvicidal potential of different solvent extracts and oleanolic acid derivative from Coccinia indica against vector mosquitoes

The mosquito larvicidal activities of different solvent extracts (chloroform, ethyl acetate, and methanol) from the leaves of Coccinia indica were studied. Among the extracts tested, the methanol extract showed the highest larvicidal activity against early fourth instar larvae of Culex quinquefasciatus (LC₅₀?=?142?mg?L^?1), Aedes aegypti (LC₅₀?=?158?mg?L^?1) and Anopheles stephensi (LC₅₀?=?161?mg?L^?1) after 24?h of exposure period. The lowest larval mortality was observed with the ethyl acetate extract with the LC₅₀ values of 927, 872, and 730?mg?L^?1 against Cx. quinquefasciatus, Ae. aegypti, and An. stephensi, respectively. The chloroform extract showed the moderate larvicidal activity against the mosquito species tested with the LC₅₀ values from 446 to 546?mg?L^?1. A new triterpene was isolated from the methanol extract using bio-assay guided separation and identified as an oleanolic acid derivative by NMR, IR and mass spectral studies. The compound showed prominent larvicidal activity against Cx. quinquefasciatus, Ae. aegypti and An. stephensi with the LC₅₀ values of 5.6, 5.0, and 4.8?mg?L^?1, respectively. The results of the present investigation offer an opportunity for developing alternatives to rather expensive and environmentally hazardous organic insecticides.     

Larvicidal potential of Nerium indicum and Thuja oriertelis extracts against malaria and Japanese encephalitis vector

Ethanolic and acetone extracts of Nerium indicum and Thuja orientelis have been studied against III instar larvae of Anopheles stephensi and Culex quinquefasciatus. Ethanolic extract of N. indicum is found more effective than its acetone extract against anopheline larvae with LC50 values of 185.99 and 148.05 ppm for former and 229.28 and 149.43 ppm for the later after 24 and 48 hrs of exposure. The acetone extract with LC50 values of 209.00 and 155.97 ppm is more effective in case of culicine larvae than its ethanolic extract with LC50 494.07 and 194.49 ppm after 24 and 48 hours of treatment. Ethanolic extract of T. orientelis is more effective against both the larval species with LC50 values of 13.10 and 9.02 ppm after 24 and 48 hours for anopheline and 22.74 and 16.72 ppm against culicine larvae. The acetone extract showed LC50 values of 200.87 and 127.53 ppm against anopheline and 69.03 and 51.14 ppm against culicine larvae. Thus ethanolic extract of T. orientelis is an ideal potential larvicide for both types of mosquito larvae.     

Faecal shield chemical defence is not important in larvae of the tortoise beetle Chelymorpha reimoseri (Chrysomelidae: Cassidinae: Stolaini)

The most frequently investigated defence mechanism among larvae of tortoise beetles is protection by faecal shields, which generally present chemicals that are directly sequestered and/or modified from larval host-plants. In the present work we investigate the tortoise beetle Chelymorpha reimoseri that feeds on the leaves of Ipomoea carnea fistulosa (Convolvulaceae), seeking for the importance of this mechanism to their larvae. We show that 4th instar larvae suffer low predation regardless of the presence of shields in field and laboratory bioassays with ants and chicks. Chloroform extract from larvae without shields provided high protection against predation as shown in bioassays in the field, as well as against chicks, suggesting that C. reimoseri does not rely on the shield for protection. The aqueous extract of the shields did not show activity in such bioassays. The compounds responsible for this protection have yet to be identified, and it remains an open question as to whether they are sequestered from the host plant or de novo biosynthesized. This is the first record of chemical defence in cassidine beetles without the need for faecal shields. These findings indicate that more attention should be paid to chemicals present in the tissues of larvae and/or adults of tortoise beetles; the protective compounds sequestered from host plants or de novo biosynthesized can provide an alternative or complementary strategy against predation in these insects.     

Cuscuta hyalina Roth., an insect development inhibitor against common house mosquito Culex quinquefasciatus Say

A preliminary screening of crude acetone extract of Cuscuta hyalina Roth. was conducted against the laboratory reared preadult stages of common house mosquito Culex quinquefasciatus (Say) (Diptera: Culicidae). 24 h LC50 of third and fourth instar larvae and pupae were 303 ppm, 306.44 ppm and 97.66 ppm respectively. The extract completely restrained the adult mosquito emergence at sublethal doses (50 ppm for third instar and 75 ppm for fourth instar), by disrupting the normal morphogenesis. The extract was found to be an effective oviposition deterrent at 80 ppm. The plant was also found to be effective in suppressing the adult emergence when directly sprinkled as dry powder on the water surface.     

Effect of Pb,Cd and Cu on survival and development of Culex quinquefasciatus (Diptera: Culicidae)

ABSTRACT

The present research aimed to determine the lowest levels of three heavy metals (Pb, Cd and Cu) to which the larvae of Southern House Mosquito, Culex quinquefasciatus are susceptible in water. The study also aimed to investigate the effects of these heavy metals on the development of Cx. quinquefasciatus at concentrations set by Pakistan Environmental Protection Agency (Pak-EPA) as permissible levels for liquid industrial effluents. The 2nd instar larvae of Cx. quinquefasciatus were exposed to different concentrations of Pb, Cd and Cu and their effects on oviposition preference, egg hatching rate and larval development were studied. The LC₅₀ values of Pb, Cd and Cu were 12.6, 6.3 and 2.6?ppm, respectively. Gravid female mosquito adults deposited a significantly lower number of egg rafts in containers containing 0.50?ppm Pb or 1.0?ppm Cu in water. Each of the heavy metals in water resulted in significantly (p?<?0.05) lower egg hatching rate, prolonged time to pupation, lower pupation rate, prolonged time to adult emergence, lower adult emergence rate and higher female to male ratio. It is concluded that the 2nd instar larvae of Cx. quinquefasciatus are susceptible to Pak-EPA permissible levels of Pb, Cd and Cu in municipal and liquid industrial effluents.     

Larvicidal,repellent, and histopathologic effects of Citrullus colocynthis against the malaria vector

Abstract

This research is conducted to determine the larvicidal, repellent and pathological effects of fruit extracts of C. colocynthis on malaria vector mosquito, Anopheles stephensi Liston, 1901. The fruit water and ethanol extract of C. colocynthis were concentrated for larvicidal and repellent activities on human volunteer against An. stephensi. The temephos larvicide was tested as the positive control. A concentration of 300?mg/L had full-scale mortality and the most toxic effect. The LC₅₀ and LC₉₀ values of C. colocynthis water and ethanol extracts were 180and 283?mg/L, respectively. The LC₅₀ and LC₉₀ values of temephos were 0.2706 and 1.6932?mg/L, respectively. The ED₅₀ and ED₉₀ values of the plant extract were 0.2 and 1.3?mg/cm², respectively. Thin sections from treated larvae exhibited gross histopathologic effects of C. colocynthis fruit extracts on gut epithelial cell layer by vacuolization of foregut cuboidal and midgut columnar cells. This study suggested that the fruit extracts of C. colocynthis had significant larvicidal and repellent activity to be used as an ideal approach to control the malaria vector mosquito.     

Comparative larvicidal potential of different plant parts of Withania somnifera against vector mosquitoes in the semi-arid region of Rajasthan

Larvicidal potential of the extracts from different parts viz. green and red fruits, seeds, fruit without seeds, leaves and roots of Withania somnifera in different solvents was evaluated against larvae of Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus, the important disease vectors prevalent in the semi-arid region. Experiments were carried out on late 3rd or early 4th instar larvae of these mosquitoes using standard WHO technique. 24 and 48 hr LC50 values along with their 95% confidence limits, regression equation, chi-square (chi2)/heterogeneity of the response have been determined by log probit regression analysis. The 24 hr LC50 values as observed for whole green fruits in water, methanol and petroleum ether were 350.9, 372.4, 576.9; 115.0, 197.1, 554.6; 154.9, 312.0, 1085.0 while corresponding values for red fruits were 473.5, 406.4,445.2; 94.7, 94.5, 1013.0; 241.8, 535.0, 893.3 mg l(-1) for An. stephensi, Ae. aegypti and Cx. quinquefasciatus respectively showing that methanol extracts were more effective against anophelines as compared to culicines when whole fruits were taken. The 24 hr LC50 values as observed for seeds in acetone, methanol and petroleum ether were 188.1, 777.5, 822.5; 245.5, 769.0, 1169.0; 140.3, 822.9, 778.4 and for fruit without seeds were 80.2, 97.6, 146.6; 88.4, 404.4, 1030.0; 30.0, 44.5, 54.2 mg l(-1) for the above mosquito species respectively showing that extract of fruit without seeds were most effective in petroleum ether followed by acetone and methanol extracts. However, experiments conducted with methanol extracts of leaves and roots of this plant species did not show any appreciable larvicidal activity and a 20-40% mortality was observed up to 500 mg l(-1) of the extracts. Overall larvae of anophelines were found more susceptible as compared to culicines to all the extracts tested. Petroleum ether extract of fruit without seeds was found most effective against all the mosquito species showing that active ingredient might be present in this part of the plant species. The study would be of great importance while planning vector control strategy based on alternative plant derived insecticides.     

Variable predation risk and the dynamic nature of mosquito antipredator responses to chemical alarm cues

Summary. Predation is a pervasive selective agent highly variable in space and time. Due to the costs associated with antipredator responses, prey would be at a selective advantage if they respond to predation threats with an intensitfy matching the threat posed by the predator. Many aquatic organisms have been shown to use chemical alarm cues present in the water to assess the level of risk in their environment. This includes mosquito larvae which show antipredator responses to conspecific alarm cues. In this study, we investigated the nature of the responses of larval mosquitoes Culex restuans to those cues. In our initial observations, we showed pond/population differences in the response intensity of C. restuans to alarm cues. In experiment 1, we showed that the response intensity to alarm cues could be increased by increasing the background level of risk in the mosquitoes’ environment (by adding salamander predators) and once turned on, the response intensity to alarm cues was likely maintained for the remainder of the mosquitoes’ aquatic life. In experiments 2 and 3, we investigated if the increase in response intensity to alarm cues was directly correlated with the level of background risk in the mosquitoes’ environment. When given increasing levels of background risk, mosquito larvae subsequently showed a graded response to conspecific alarm cues. This series of experiments demonstrates that the response intensity of larval mosquitoes to a standard concentration of alarm cues is not fixed, but rather dependent on the background level of risk in the environment. An understanding of the background level of risk is particularly important for comparing antipredator responses of prey between habitats.     

Evaluation of the larvicidal efficacy of extracts from three plants and their synergistic action with propoxur against larvae of the filarial vector Culex quinquefasciatus (Say)

Petroleum ether extracts of Piper longum, Curcuma aromatica, and Ocimum basilicum were tested for their larvicidal activity against Culex quinquefasciatus, a filarial vector using WHO standard procedures. Among the three plants, extract of P. longum was found to be highly effective with LC₅₀ and LC₉₀ being 0.89 and 1.49 ppm, respectively. C. aromatica also showed significant larvicidal activity with LC₅₀ and LC₉₀ being 11.41 and 17.36 ppm, respectively. The LC₅₀ and LC₉₀ for O. baslicum were 76.67 and 200.56 ppm, respectively. Propoxur, a carbamate was also studied for its larvicidal activity, which showed LC₅₀ to be 0.09 ppm and LC₉₀ to be 0.16 ppm. Synergistic studies of all three plant extracts with propoxur revealed P. longum as a more efficient synergist with synergistic factor (SF) of 4.13 for LC₅₀ value and 1.68 for LC₉₀. Both C. aromatica and O. basilicum exhibited antagonistic activity at their respective LC₉₀ values with propoxur. At 1 : 1 ratio of the phytoextracts and propoxur, P. longum and C. aromatica showed synergism whereas O. basilicum displayed additive effect. Thus, P. longum was found to be a better larvicidal and synergistic agent at all tested ratios. Evidence indicates that mixed formulations of phytoextracts with insecticides might reduce the concentration of the chemicals to be applied for vector control.     

Energetic cost of development through metamorphosis for the seastar<Emphasis Type="Italic"> Mediaster aequalis</Emphasis> (Stimpson)

Rates of oxygen consumption were measured for embryos, larvae and juveniles of the seastar Mediaster aequalis for 76 days post-fertilization. The rate increased from 0.65 nmol O₂ ind^–1 h^–1 at 6 h after fertilization to 2.8 nmol O₂ ind^–1 h^–1 at day 35. Larvae became competent to metamorphose around day 35 post-fertilization and began to decrease their metabolic rate after this time. Metamorphosed juveniles consumed 0.74 nmol O₂ ind^–1 h^–1. Eggs contained 138.6 µg lipid ind^–1 and 12.1 µg protein ind^–1. Lipid levels decreased in concentration throughout development while protein levels increased slightly. The lipid levels decreased by 88.5 µg from eggs to day 76 larvae, accounting for 3.5 J of energy. Total oxygen consumption to this point was 3.74 µmol O₂ ind^–1, accounting for 1.84 J. The energetic demand up to day 76 was met completely through the use of lipid reserves. Metamorphosed juveniles expended 0.5 J more than larvae at the same age. Tubes of the polychaete Phyllochaetopterus prolifica were able to induce metamorphosis in M. aequalis larvae and a non-polar extract of these tubes also triggered metamorphosis. Larvae that are delayed to metamorphose can sustain their metabolic rate with lipid reserves for a limited, yet undetermined, period.Communicated by P.W. Sammarco, Chauvin     

Neurotoxicity and oxidative stress induced by permethrin in gills of the freshwater mussel Unio ravoisieri

Pyrethroids are contaminants found in the aquatic environment, and their toxicological effects on aquatic organisms have received extensive attention. However, the impact on freshwater bivalve of exposure to these chemicals is still largely unknown. Freshwater mussels Unio ravoisieri were exposed to two nominal permethrin (PM) concentrations C1?=?50?µg/L and C2?=?100?µg/L during 7 days. The measured concentrations of PM using gas chromatography (GC/ECD) in the treated aquariums were, respectively, 28.7–62.3?µg/L. Catalase (CAT), Glutathione-S-transferase (GST), and Acetylcholinesterase (AChE) activities, Glutatione (GSH) and Malondialdehyde (MDA) levels were determined in gills of U. ravoisieri. Significant increase in CAT activity by the lowest concentration and decrease by highest concentration were observed. Additionally, GST activity was increased in a concentration-dependent manner. However, statistically significant decrease in GSH levels (about 39%) was observed only at high concentration of this compound (100?µg/L). PM generated an increase in MDA levels reaching the highest value at the high concentration. AChE activity of mussel ranging from 51% inhibition at lowest concentration 50?µg/L to 89% inhibition at highest concentration 100?µg/L. The results indicated that oxidative stress and cell damage might be one of the main mechanisms of PM toxicity to freshwater mussels.     

Toxicological and larvicidal activities of Alzanzalakhet,Melia azedarach against cucurbit fly,Dacus ciliatus at Hail Province in Saudi Arabia

Alzanzalakhet, Melia azedarach L. (Sapindales: Meliaceae) is a common medicinal plant which is found in Hail desert in Saudi Arabia and traditionally used for various purposes. In this study, toxin effectiveness of the ethanolic, acetonic, and aqueous extracts of M. azedarach leaves was tested to determine a larvicidal activity against the cucurbit fly, Dacus ciliatus (Loew) (Diptera: Tephritidae). Different treatments with M. azedarach extracts varied significantly in their impact on mortality of D. ciliatus larvae. Results showed that all tested extracts in the three solvents exerted a positive pattern for reducing larvae of D. ciliatus. However, the ethanolic M. azedarach extract was the most potent compared with other tested solvents. The highest mortality of the D. ciliatus larvae was shown to be 94%, 74%, and 68% when the concentration was 1?×?10⁵?ppm for ethanolic, acetonic, and aqueous extracts, respectively. In contrast, the concentration 1?×?10¹?ppm resulted in the lowest mortality of D. ciliatus larvae at 40%, 34%, and 12% for ethanolic, acetonic, and aqueous extracts, respectively. Overall, the results of this study suggest that the ethanolic extract of M. azedarach leaves may be used as a sustainable method for controlling D. ciliatus larvae.     

Effects of Cd2+ exposure on key life history traits and activities of four metabolic enzymes in Helicoverpa armigera (Lepidopteran: Noctuidae)

Cadmium (Cd) is a toxic non-essential element accumulated easily in living organisms due to its non-biodegradable nature. A slight increase in Cd levels will threaten the health of terrestrial and aquatic organisms. Therefore, Cd contamination and its effects on the ecosystems and organisms have become a major topic of eco-toxicological research. The present study investigated the eco-toxicological effects of Cd-supplemented diet on some life history traits and specific enzyme activities of carboxylesterase (CarE), glutathione S-transferase (GST), acetylcholinesterase (AChE) and cytochrome P450 monooxygenases (P450s) in the cotton bollworm, Helicoverpa armigera. The results showed that Cd significantly decreased larval survival, pupation and emergence, and reduced body mass of the sixth instar larvae, pupae, adult moths and female fecundity. Cd-supplemented diet also delayed the development of larvae and pupae and shortened the life span of the cotton bollworm moth. In addition, dietary Cd inhibited the activities of GST, CarE and P450, but increased AChE activity of the sixth instar larvae. We concluded that life history traits and metabolic enzymes are sensitive to Cd stress in the cotton bollworm. These parameters are potential biomarkers for monitoring environmental stress in Lepidopteran insect pests.     

Effects of the organophosphorous insecticides temephos (Abate®) and chlorpyrifos (Dursban®) on populations of the salt-marsh snail Melampus bidentatus

The effects of 2 organophosphorous insecticides, temephos (Abate^®) and chlorpyrifos (Dursban^®), on populations of the salt-marsh snail Melampus bidentatus Say (Basommatophora: Melampidae) were investigated in a series of field experiments. These toxicants were aerially applied to mosquito breeding areas in New Jersey salt marshes in the manner normally used in biting-fly control operations. No significant change in the population density of M. bidentatus was observed in response to multiple treatments of granular formulations of either temephos or chlorpyrifos. However, there was a highly significant (P<0.01) depression in population density observed in the plot exposed to multiple treatments of a temephos emulsion. This depression was followed by a resurgence in density levels, beginning 3 weeks after the last treatment. The specific mechanism for thisperturbation is not known. However, it is hypothesized that it might involve some combination of indirect insecticide effects coupled with age-specific effects. Tests of age structure of the affected population using the chi-square distribution supported this hypothesis.Paper of the Journal Series, New Jersey Agricultural Experiment Station. This research was supported, in part, by a grant from the New Jersey Mosquito Control Commission.     

Potential toxicity of flubendiamide in Drosophila melanogaster and associated structural alterations of its compound eye

Flubendiamide, a comparatively new insecticide, is used against lepidopteran insect pests and presumed safe for non-target Drosophila melanogaster (D. melanogaster). In this study, treatment concentrations (0.5, 1, 2 5, 10, and 20 μg/ml) of flubendiamide, lower than agricultural concentrations (rice 50μg/ml or cotton 100 μg/ml), were able to inhibit acetylcholinesterase activity in third instar larvae of D. melanogaster indicating a neurotoxic potential. In addition, larvae exposed to flubendiamide also manifested increased amounts of stress protein hsp70. The larvae expressing such stress response when allowed to emerge as adults displayed severe eye structure deformities found by scanning electron microscopy. These findings indicate a toxic potential for flubendiamide in D. melanogaster.     

The selective advantages of cannibalism in a Neotropical mosquito

We investigated the benefits of larval cannibalism in the Neotropical mosquito Trichoprosopon digitatum. The clutch size of the mosquito in the field was strongly correlated with adult female size, indicating a fitness advantage to being large. In controlled laboratory experiments, we compared the survivorship and eventual adult sizes of larvae that were given the opportunity to cannibalise conspecifics throughout their lifetimes with the survivorship and adult sizes of larvae that were prevented from cannibalising. Since the benefits of cannibalism are likely to depend on the context in which it occurs, the experiment was conducted at two levels of alternative food availability. When food availability was high most larvae survived to adulthood, females cannibalised more than males and there was no measurable advantage to cannibalism in terms of survival rate, emergence time or adult size. Larvae were significantly more cannibalistic when food availability was lower, although under these conditions no larvae survived to adulthood. Nevertheless, under low food an important fitness benefit to cannibalism was revealed: individuals which had the opportunity to cannibalise survived significantly longer as larvae than those which did not. This increased longevity is likely to provide an important advantage to mosquito larvae when they wait for the input of unpredictable food sources. Received: 7 October 1995/Accepted after revision: 13 April 1996     

Comparative efficacy of certain plant extracts alone and combination with profenofos against Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae)

Ethyl alcohol, acetone, and petroleum ether extracts of three plant species belonging to three different botanical families [Strychnos nux-vomica (Loganiaceae), Euphorbia lathyrus (Euphorbiaceae), and Datura stramonlum (Solanaceae)], a chemical insecticide; profenofos and their combinations were tested against second and fourth instars of Spodoptera littoralis under lab conditions. Results revealed that the ethanol extract of S. nux-vomica was the most effective among all plant extracts, where the corrected mortality% were 92, 81, 58, and 27% to 2nd instar and 89, 74, 34, and 11% to 4th instar at concentrations 0.5, 0.25, 0.125, and 0.0625%, respectively. Calculated LC₅₀'s were 0.11, 0.22, and 0.34% to 2nd instar and 0.17, 0.37, and 0.52% to 4th instar for ethanol, petroleum ether, and acetone extracts, respectively. Acetone extracts of all plants were of lower effect. The chemical insecticide profenofos displayed higher efficacy than plant extracts (LC₅₀ = 0.002 and 0.003% for S. littoralis 2nd and 4th larval instars, respectively). The co-toxicity factor reached 76 and 60 when mixing S. nux-vomica + profenofos and D. stramonlum + profenofos at ratio 1:1 against S. littoralis 2nd instar larvae, thus indicating a potentiating effect. While treatment of the 4th instar larvae by the same mixtures resulted in a co-toxicity factor below 20 at all mixing ratios indicating, only, an additive effect against this instar.     

Laboratory and field evaluation of Metarhizium anisopliae for the control of Dengue vector,Aedes aegypti (Insecta: Diptera: Culicidae)

Biological control at the larval stages of development of mosquitoes is one of the techniques that afford a non-expensive, easy-to-use, and environment-friendly method for mosquito control. In this study, investigations were undertaken on microbial product to develop a strategy to control mosquito larval and pupal population in the lab and field. Highest larval mortality was evident in the lab with LC₅₀ and LC₉₀ at 0.25 and 0.5 at 24?h for Aedes aegypti. In the field study, to kill mosquito larval population resulting in 100% mortality of A. aegypti required 5 days duration. The dose-dependent mortality was calculated using a lethal time of approximately 1–5 days test period. The number of mosquito bites (%) (vectorial capacity) decreased at increasing concentration of fungal insecticide. Data indicate that the fungal pathogen interacting with mosquito larvae controlled mosquitoes in the lab and field.     

Induction of host specificity in larvae of Manduca sexta: chemical dependence controlling host recognition and developmental rate

Summary. The tobacco hornworm, Manduca sexta L. (Lepidoptera: Sphingidae) is a specialist on Solanaceae. This host specificity is induced as the larva feeds on solanaceous foliage, so that solanaceous-reared larvae will refuse to feed on other plants. Experiments were designed to determine the role of dietary constituents on the induction of host specificity and the effects of these on development of M. sexta. Choice assays using leaf discs of cowpea, Vigna sinensis (Fabaceae), were used to monitor the isolation of relevant chemical cues from foliage of potato. An aqueous extract of potato foliage strongly stimulated feeding. This extract was partitioned with n-butanol under alkaline conditions to obtain a highly active butanol extract. Reversed phase flash chromatography with a water-methanol gradient gave an active fraction that was used as a supplement for wheat germ-based artificial diet. Larvae reared on this s-diet became dependent on potato allelochemicals for initiation and continuation of feeding activity. These larvae also developed faster than larvae reared on the control p-diet, but no effect on adult mass was detected. Further flash chromatography of the active fraction under alkaline conditions provided a highly active sub-fraction, and semi-preparative HPLC using gradients of water and acetonitrile resulted in the isolation of a single compound. Bioassays indicated that this compound alone can account for host recognition by solanaceous-reared larvae. The results suggest that the mechanism of induced host specificity in M. sexta involves development of dependence on this compound. Received 21 December 1999; accepted 14 March 2000