Ecdysteroids fromPycnogonum litorale (Arthropoda,Pantopoda) act as chemical defense againstCarcinus maenas (Crustacea,Decapoda)

Pycnogonum litorale (Ström) is unpalatable to the common shore crabCarcinus maenas, a generalist predator in the pycnogonid's habitat. A feeding bioassay reveals that the crabs are deterred by ecdysteroids that occur in high levels in all developmental stages ofP. litorale. The total ecdysteroids in the pycnogonids reach 5.9×10^–4 M. The 20-hydroxyecdysone 22-acetate (20E22A), which is the predominant ecdysteroid in the pycnogonids, and 20-hydroxyecdysone (20E), the arthropod molting hormone, were tested for their antifeedant effect onC. maenas. When contained in food pellets in homogeneous concentrations, 20E and 20E22A significantly reduced food consumption at 1.25×10^–4 and 5.0×10^–4 molar levels, respectively. The present results demonstrate for the first time chemical defense in arthropods in a marine predator-prey relationship. Furthermore, they provide evidence that ES contained in one animal can act as feeding deterrents on another animal.     

Biosynthesis and distribution of insect-molting hormones in plants—A review

Insect-molting hormones, phytoecdysteroids, have been reported to occur in over 100 plant families. Plants, unlike insects, are capable of the biosynthesis of ecdysteroids from mevalonic acid, and in several cases the biosynthesis of phytoecdysteroids was also demonstrated to proceedvia sterols.Spinacia oleracea (spinach) biosynthesizes polypodine B and 20-hydroxyecdysone, which is the predominant insect-molting hormone found in plant species. The onset of ecdysteroid production in spinach requires the appropriate ontogenetic development within the plant, which is related to leaf development. In spinach, lathosterol is the biosynthetic precursor to ecdysone and 20-hydroxyecdysone. Phosphorylated ecdysteroid intermediates, particularly ecdysone-3-phosphate, are required during biosynthesis. Polyphosphorylated forms of ecdysteroids are putative regulatory components of the pathway. During spinach development, the 20-hydroxyecdysone is transported from the sites of biosynthesis to the apical regions. An analysis of the physiological data available suggests that different species may synthesize ecdysteroids in various organs and distribute these ecdysteroids to other sites. Annual plants appear to concentrate ecdysteroids in the apical regions, including flowers and seeds. Perennial plants may recycle their ecdysteroids between their deciduous and their perennial organs over the growing season. Further investigations of ecdysteroid biosynthesis and physiology within plants will be required before an acceptable system can be designed to test phytoecdysteroid effectivenessin vivo against insect herbivory. Based on a paper presented at the Symposium on the “Regulation of Biosynthesis and Function of Isopentenoids,” Atlanta, Georgia, May 1994.     

Isolation and identification of apolar metabolites of ingested 20-hydroxyecdysone in frass ofHeliothis virescens larvae

A large amount of 20-hydroxyecdysone was orally administered to larvae of the tobacco budworm,Heliothis virescens, in order to investigate its detoxification mechanisms. Four major relatively nonpolar metabolites were isolated from their frass. These compounds were identified as the 22-linoleate, 22-palmitate, 22-oleate, and 22-stearate of 20-hydroxyecdysone using various forms of spectroscopy, including NMR. This is the first report of this type of metabolite from an insect.     

Fundamental aspects and potential roles of ecdysteroids in schistosomes an update overview

The human digenic trematodeSchistosoma mansoni produces ecdysteroid hormones. Both ecdysone (22R)-2,3,14,22,25-pentahydroxy-cholest-7-en-6-one and 20-hydroxyecdysone (22R)-2,3, 14,20,22,25-hexahydroxycholest-7-en-6-one were detected during the critical development stages of this bisexual parasite: during the exponential growth phase to adult stage (day 11 postinfection) and during the sexual maturation of adult and egg laying (day 40 postinfection). The parasites released their ecdysteroid hormones in the biological fluids of the infected vertebrates as soon as six days postinfection. In addition, the time course of the ecdysteroid titer was correlated with the susceptibility or the innate resistance of the host to schistosome infection. Moreover, we demonstrated that after a schistomicide therapy, ecdysteroids from urine of infected children decreased markedly four days after drug administration. We also have demonstrated that immunization of rodents with an ecdysone-BSA complex led to the reduction of the worm burden. By in vitro studies, we have shown that the ecdysterone antibodies were able to kill the juvenile worms within 24 hr. In addition, we have demonstrated that the enzymes Superoxide dismutase (SOD, EC 1.15.1.1) were present in schistosomes and that the total Superoxide dismutase activities in both males and females could be correlated with the 20-hydroxyecdysone within parasites.     

双酰基肼类昆虫生长调节剂的作用机理及抗药性研究进展

双酰基肼类杀虫剂是近几年陆续开发的一类高效、选择性强、对环境友好的昆虫生长调节剂,其作用靶标与昆虫蜕皮激素(20E)一样,结合于蜕皮激素受体(EcR)——过剩气门蛋白(USP)的异源二聚体,诱导昆虫早期基因的转录,但由于双酰肼类化合物在昆虫体内的持续存在,使20E不存在情况下发生的事件不能进行,如多巴脱羧酶(DDC)等基因的表达受阻,不合成几丁质,羽化激素不能释放,最后使幼虫早熟脱皮而死亡。随着这类杀虫剂使用时间和范围的不断扩大,对其抗药性的研究也逐渐引起了重视。本文主要综述了这类新型杀虫剂作用机理及抗药性等方面的研究进展。     

Biosynthesis of sterols and ecdysteroids in Ajuga hairy roots

Hairy roots of Ajuga reptans var. atropurpurea produce clerosterol, 22-dehydroclerosterol, and cholesterol as sterol constituents, and 20-hydroxyecdysone, cyasterone, isocyasterone, and 29-norcyasterone as ecdysteroid constituents. To better understand the biosynthesis of these steroidal compounds, we carried out feeding studies of variously ²H- and ¹³C-labeled sterol substrates with Ajuga hairy roots. In this article, we review our studies in this field. Feeding of labeled desmosterols, 24-methylenecholesterol, and ¹³C₂-acetate established the mechanism of the biosynthesis of the two C₂₉-sterols and a newly accumulated codisterol, including the metabolic correlation of C-26 and C-27 methyl groups. In Ajuga hairy roots, 3α-, 4α-, and 4β-hydrogens of cholesterol were all retained at their original positions after conversion into 20-hydroxyecdysone, in contrast to the observations in a fern and an insect. Furthermore, the origin of 5β-H of 20-hydroxyecdysone was found to be C-6 hydrogen of cholesterol exclusively, which is inconsistent with the results in the fern and the insect. These data strongly support the intermediacy of 7-dehydrocholesterol 5α,6α-epoxide. Moreover, 7-dehydrocholesterol, 3β-hydroxy-5β-cholest-7-en-6-one (5β-ketol), and 3β,14α-dihydroxy-5β-cholest-7-en-6-one (5β-ketodiol) were converted into 20-hydroxyecdysone. Thus, the pathway cholesterol→7-dehydrocholesterol→7-dehydrocholesterol 5α,6α-epoxide→5β-ketol→5β-ketodiol is proposed for the early stages of 20-hydroxyecdysone biosynthesis. 3β-Hydroxy-5β-cholestan-6-one was also incorporated into 20-hydroxyecdysone, suggesting that the introduction of a 7-ene function is not necessarily next to cholesterol. C-25 Hydroxylation during 20-hydroxyecdysone biosynthesis was found to proceed with ca. 70% retention and 30% inversion. Finally, clerosterol was shown to be a precursor of cyasterone and isocyasterone.     

A generalist herbivore in a specialist mode Metabolic,sequestrative, and defensive consequences

Adults of a generalist herbivore, the lubber grasshopper,Romalea guttata, can be converted to functional specialists by feeding them exclusively on catnip,Nepeta cataria. No obvious adverse effects on adult development resulted from this enforced monophagy. Notwithstanding the fact thatR. guttata has had no coevolutionary relationship with this Eurasian mint, it readily sequesters compounds that are identical to or derived from the terpenoid lactones that are characteristic ofN. cataria. R. guttata appears to both biomagnify minor allelochemicals and to sequester metabolites of theNepeta terpenes in its paired defensive glands. The levels of autogenously produced phenolics are not affected by feeding onN. cataria and the defensive secretions of catnip-fed grasshoppers are more repellent to ants than those of wild-fed acridids. Metabolites of theN. cataria monoterpenes are sequestered in the defensive glands when catnip is added to the natural diet ofR. guttata. The ability of a generalist,R. guttata, to facilely bioaccumulate a potpourri of foreign allelochemicals when feeding in a specialist mode is analyzed in terms of its biochemical, physiological, and functional significance. Sequestration is examined as a response to the enteric effronteries represented by the phytochemicals that can be characteristic of the overload in a monophagous diet.     

Induction of Plant Volatiles by Herbivores with Different Feeding Habits and the Effects of Induced Defenses on Host-Plant Selection by Thrips

Induced plant responses to attack by chewing insects have been intensively studied, but little is known about plant responses to nonchewing insects or to attack by multiple herbivores with different feeding habits. We examined volatile emissions by tobacco, Nicotiana tabacum, in response to feeding by the piercing–sucking insect western flower thrips (WFT), Frankliniella occidentalis, the chewing herbivore Heliothis virescens, and both herbivores simultaneously. In addition, we examined the effects of herbivore-induced plant defenses on host-plant selection by WFT. Plants responded to thrips feeding by consistently releasing five compounds. Simultaneous feeding by WFT and H. virescens elicited the same 11 compounds emitted in response to caterpillar feeding alone; however, two compounds, α-humulene and caryophyllene oxide, were produced in greater amounts in response to simultaneous herbivory. In choice tests, thrips consistently preferred uninduced plants over all other treatments and preferred plants damaged by caterpillars and those treated with caterpillar saliva over those treated with caterpillar regurgitant. The results are consistent with a previous finding that caterpillar regurgitant induces the release of significantly more volatile nicotine than plants damaged by caterpillars or plants treated with caterpillar saliva. A repellent effect of nicotine on WFT was confirmed by encircling unwounded plants with septa releasing volatile nicotine. Our results provide the first direct evidence that thrips feeding induces volatile responses and indicates that simultaneous herbivory by insects with different feeding habits can alter volatile emissions. In addition, the findings demonstrate that induced plant responses influence host-plant selection by WFT and suggest that the induction of volatile nicotine may play a role in this process.     

The fate of radiolabeled steroids in ovaries and eggs of the tobacco hornworm,Manduca sexta

To determine the precursors and the fate of 26-hydroxyecdysone in eggs, the fate of labeled putative ecdysteroid precursors was examined in the tobacco hornworm,Manduca sexta. Following injection of [¹⁴C]cholesterol, 22,25[¹⁴C]dideoxyecdysome or [³H]ecdysone into female pupae (day 16), only [¹⁴C]cholesterol was incorporated and metabolized. It was converted to labeled nonecdysteroid and ecdysteroid conjugates, of which the latter in ovaries and 48- to 64-hr-old eggs is mainly 26-hydroxyecdysone 26-phosphate (>85% in ovaries). Quantitation of the ecdysteroid conjugate by reversed-phase high performance liquid chromatography (RP-HPLC) showed that the levels of 26-hydroxyecdysone 26-phosphate were 31 μg/g of ovaries from 4-day-old females and 25 μg/g and 17 μg/g of 48- to 64-hr-old and 72- to 88-hr-old eggs, respectively. The RP-HPLC of the conjugate fraction of 48- to 64-hr-old eggs showed an additional peak of radioactive material eluting about three min before the 26-hydroxyecdysone 26-phosphate. The quantity of this material increased in the 72-to 88-hr-old eggs, though it was not detected in the analyses of the conjugate fraction from ovaries. Additional peaks of radioactive material eluting before the 26-hydroxyecdysone 26-phosphate peak were observed in the chromatogram of the conjugates of 72- to 88-hr-old eggs. These radioactive materials need to be identified to determine the ultimate fate of ecdysteroids in the developing embryos of the tobacco hornworm. No radioactive free ecdysteroids were detected in either egg age group.     

Induced resistance in soybean toHelicoverpa zea: Role of plant protein quality

Resistance in soybean toHelicoverpa zea is comprised of both constitutive and inducible factors. In this study, we investigated the induction of resistance byH. zea in both greenhouse and field studies. In a greenhouse experiment, fourth-instarH. zea growth rates were reduced by 39% after 24 hr feeding and by 27% after 48 hr when larvae fed on previously wounded V3 foliage (cv. Forrest) compared with undamaged foliage. In a field study, the weight gain by larvae was more than 52% greater when larvae fed for 72 hr on undamaged R2/R3 soybean plants (cv. Braxton) compared to those that fed on previously wounded plants. A significant component of the induced resistance is due to a decline in the nutritional quality of foliar protein following foliar damage byH. zea. Foliar protein was extracted from damaged and undamaged foliage and incorporated into artificial diets. Larval growth was reduced 26% after four days and 49% after seven days on diets containing protein from damaged plants compared to larvae feeding on foliar protein from undamaged plants. Chemical analyses of protein quality also indicated a decline in quality in damaged plants compared to unwounded plants. Increases in lipoxygenase activity (53%), lipid peroxidation products (20%), and trypsin inhibitor content (34%) were observed in protein from wounded plants. Moreover, a 5.9% loss in free amines and 19% loss in total thiols occurred in protein from wounded plants. Larval feeding causes a significant increase in foliar lipoxygenase activity that varied among genotypes. Lipoxygenase isozymes were measured at pH 5.5, pH 7.0, and pH 8.5 in V3 stage plants of Forrest, Hark, D75-1069, and PI 417061 genotypes. Lipoxygenase activity in each genotype was significantly increased after 72 hr of larval feeding at each pH level tested, with the exception of lipoxygenase isozymes at pH 5.5 in genotype PI 417061. Larval feeding on R2/R3 stage plants (field-grown cv. Braxton) for six days also increased foliar lipoxygenase activity.     

Damage-Induced Accumulation of Phytoecdysteroids in Spinach: A Rapid Root Response Involving the Octadecanoic Acid Pathway

Some plant defenses are known to be rapidly induced following attack by phytophagous insects. Plant-produced insect molting hormones, termed phytoecdysteroids, are believed to aid plant resistance; however, their dynamics are poorly understood. Using spinach (Spinacia oleracea) as a model system, we examined the inducibility of phytoecdysteroids, primarily 20-hydroxyecdysone (20E), in an effort to characterize potential interactions with herbivorous insects. Rapid phytochemical induction was investigated using damage treatments and applications of defense-related plant-signal analogs, specifically methyl jasmonate (MJ) and methyl salicylate (MSA). Within two days, mechanically damaged roots exhibited two to three fold increases in phytoecdysteroid concentrations. Four days after root damage, small increases in shoot levels were also detectable. Unlike roots, foliar 20E concentrations were unaltered over a range of shoot treatments including insect herbivory (Spodoptera exigua), mechanical damage, and MJ applications. Additions of MJ (12.5–50 g/liter) to the root systems of hydroponically grown plants stimulated accumulations of root phytoecdysteroids in a dose-dependent manner, similar in magnitude to the response induced by root damage. Under identical conditions, MSA did not affect the accumulation of 20E when added to the hydroponic solutions of undamaged plants. Moreover, MSA inhibited the induction of 20E in wounded roots, but did not interfere with the action of applied MJ. In contrast to mechanical damage, roots did not induce 20E levels when challenged with two different fungal pathogens (Pythium aphanidermatum and Phytophthora capsici).We propose that wound-induced accumulations of 20E are generated in the roots, signaled via endogenous jasmonates, and may confer enhanced resistance against subterranean herbivorous insects.     

Alarm response of the marine mud snail,Nassarius obsoletus: Specificity and behavioral priority

Nassarius obsoletus, N. vibex, andN. trivittatus were exposed to juices of conspecifics and taxonomically and ecologically related gastropod species. Conspecific juices caused the strongest alarm responses, while those from taxonomically related species (congeners) induced less pronounced responses. Juices from nonrelated species induced no alarm response with one notable exception, the strong alarm response ofN. trivittatus toUrosalpinx cinerea juices. Nonrelated gastropod species induced stronger feeding responses than more closely related species. The strongest feeding responses, however, were induced by juices from nongastropod mollusks. The apparent balance between feeding attraction to less related species and alarm response to more related species was further examined by manipulating the snails' diet. Starvation resulted in a great reduction of conspecific alarm responsiveness. Following the resumption of feeding, the original responsiveness was again observed. Although the alarm response is likely an antipredator device, conclusive evidence for its effectiveness in reducing predation is lacking. One of the predators ofNassarius obsoletus which may be responsible for maintenance of an alarm response is the green crab,Carcinus maenas.This paper is based in part upon a thesis submitted by D.S. to Boston University for the degree of Master of Arts.     

Occurrence and levels of ecdysteroids in spinach

The dominant ecdysteroid in spinach,Spinacia oleracea L., is 20-hydroxyecdysone (2β,3β,14α, 20R,22R,25-hexahydroxy-5β-cholest-7-en-6-one) with the presence of a smaller amount of polypodine B (2β,3β,5β,14α,20R,22R,25-heptahydroxycholest-7-en-6-one). Ecdysteroids are present in the seed embryo at 14 μg ecdysteroid/seed, and ecdysteroid levels increase, in the plant during growth and development. During the onset of ecdysteroid production, the ratio of ecdysteroid to total sterol shifts from a value of one to about ten over the course of a week. Spinach may serve as a model to study ecdysteroid biosynthesis in plants. Based on a paper presented at the symposium on Plant and Fungal Sterols: Biosynthesis, Metabolism and Function, held at the AOCS Annual Meeting, Baltimore, MD, April 1990.     

Nutritional Value of Various Ray Fish Liver Oils to the Pacific White Shrimp <Emphasis Type="Italic">Litopenaeus vannamei</Emphasis>

A 32-day comparative feeding trial was performed to evaluate the nutritional value of four different ray fish liver oils to the Pacific white shrimp Litopenaeus vannamei. Four feeds were prepared with liver oil extracted from Dasyatis brevis, Rhinoptera steindachneri, Aetobatus narinari, and R. bonasus. A control feed was prepared with Menhaden fish oil. Ray fish liver oils were mainly composed of poly- and highly unsaturated fatty acids and contained levels of 20:5n-3 and 22:6n-3 comparable in magnitude to those of Menhaden fish oil, except for A. narinari liver oil, which had moderately low concentrations of 20:5n-3 and 22:6n-3 but showed a particularly high level of 20:4n-6, more than six times greater than that of Menhaden fish oil. Dietary fatty acids significantly influenced the fatty acid composition of shrimp muscle tissue, e.g., the diet with Menhaden fish oil elicited significantly higher shrimp muscle DHA level than diets with oil from D. brevis, and A. narinari, but not than diets with oil from R. steindachneri and R. bonasus. In spite of these differences, all four ray fish liver oils evaluated were as efficient in promoting growth and survival of L. vannamei as Menhaden fish oil, an ingredient known for its adequate nutritional quality to shrimp and fish. This study demonstrated one of the many possible applications of a locally-available resource that is currently being wasted.     

Do European Corn Borer Females Detect and Avoid Laying Eggs in the Presence of 20-Hydroxyecdysone?

European corn borer larvae detect and avoid feeding in the presence of phytoecdysteroids (PEs) such as 20-hydroxyecdysone (20E). Therefore, we hypothesized that females would have taste receptors similar to larvae and avoid laying eggs in the presence of 20E. We found female-specific taste sensilla on the tarsi that respond to 20E at concentrations as low as 10⁻⁶ M, a threshold comparable to that of larvae. However, in choice tests, females laid a similar number of eggs on 20E-treated and on nontreated artificial substrates (filter paper, glass, and nylon), although they spent significantly more time in behavioral sequences related to substrate assessment when 20E was present. In contrast, when given a choice between maize plants (eight leaves) sprayed with 20E or only the solvent, females laid 70% fewer eggs on the treated than on control plants. These observations suggest that other chemical cues of plant origin must be present at the same time as 20E for females to modify their oviposition behavior.     

20-Hydroxyecdysone Deters Oviposition and Larval Feeding in the European Grapevine Moth, Lobesia botrana

European grapevine moth females (Lobesia botrana, Lepidoptera Tortricidae) select an oviposition site by tasting the host plant surface and then gluing a single egg on berries from grapes or from several other host plant species. In doing so, females should avoid ovipositing on plants that are detrimental to their progeny. Do they sense the same deterrent compounds as larvae, despite the fact that they do not have access to the same compartments of the plants? We tested this hypothesis with 20-hydroxyecdysone (20E), purified from Leuzea carthamoides. Phytoecdysteroids are usually found inside plant tissues and accessible to larvae in an aqueous phase, while adults would access them only through the epicuticular wax. We first confirmed that larvae avoid feeding on 20E and that they taste 20E with their lateral sensilla styloconica, at a threshold of 10^?6 M. Then, we tested whether adult females avoid ovipositing on glass spheres sprayed with 20E. When given a choice, females avoided laying eggs on a treated surface, at a threshold of 8 ng/cm². In addition, they deposited significantly fewer eggs in the presence of 20E. Presuming that legs play an important role in assessing the oviposition substrate, we assessed the sensitivity of their taste receptors. In females, 14 taste sensilla are located on the ventral side of the last tarsus of the prothoracic leg. One group of these sensilla house one neuron that is sensitive to 20E, with a detection threshold of about 10^?7 M. The same molecule is thus sensed both in larvae and adults of L. botrana where it respectively inhibits feeding and oviposition.     

A Comparison of Semiochemically Mediated Interactions Involving Specialist and Generalist <Emphasis Type="Italic">Brassica</Emphasis>-feeding Aphids and the Braconid Parasitoid <Emphasis Type="Italic">Diaeretiella rapae</Emphasis>

Diaeretiella rapae, a parasitoid that predominately specializes in the parasitism of Brassica-feeding aphids, attacks Lipaphis erysimi, a specialist feeding aphid of the Brassicaceae and other families in the Capparales, at a greater rate than the generalist-feeding aphid, Myzus persicae. In this study, we investigated the orientation behavior of D. rapae to the volatile chemicals produced when these two aphid species feed on turnip (Brassica rapa var rapifera). We showed no significant preference orientation behavior to either aphid/turnip complex over the other. Isothiocyanates are among the compounds emitted by plants of the Brassicaceae in response to insect feeding damage, including by aphids. We assessed parasitoid orientation behavior in response to laboratory-formulated isothiocyanates. We tested two formulations and discovered significant orientation toward 3-butenyl isothiocyanate. We also assessed plant and aphid glucosinolate content, and showed large levels of glucosinolate concentration in L. erysimi, whereas there was little change in plant content in response to aphid feeding. Our results suggest that during the process of host location, similar cues may be utilized for locating L. erysimi and M. persicae, whereas the acceptance of hosts and their suitability may involve aspects of nonvolatile aphid chemistry.     

Developmental profile of sinalbin (p-hydroxybenzyl glucosinolate) in mustard seedlings,Sinapis alba L., and its relationship to insect resistance

Sinalbin was identified as a chemical component of insect anti-xenosis and antibiosis resistance mechanisms in seedlings ofSinapis alba by DEAE-Sephadex chromatography, HPLC, treatment with sulfatase and myrosinase, various feeding tests using artificial and natural substrates, and by measuring sinalbin concentrations in cotyledons and leaves during seedling development. The effects of sinaibin on feeding were dependent upon the insect species and upon the rapidly changing profile of sinaibin concentrations in the developing seedling. The high concentrations of sinalbin found in young cotyledons (up to 20 mM) and leaves (up to 10 mM) deterred the feeding of the flea beetle,Phyllotreta cruciferae Goeze and larvae of the bertha armyworm,Mamestra configurata Walker. The protection that sinalbin confers upon the vulnerable, newly emerged seedling (and upon tiny, young leaves) appears critical for the first few days of survival ofS. alba under feeding pressure from flea beetles in the field. The lower concentrations of sinaibin found in older cotyledons and leaves (2–3 mM) offer little or no protection againstP. cruciferae and may actually stimulate the feeding of this crucifer specialist. These concentrations of sinaibin, however, are still effective in reducing the level of feeding by larvae of the more generalist feederM. configurata.     

Processing of iridoid glycoside antirrinoside fromMaurandya antirrhiniflora (Scrophulariaceae) byMeris paradoxa (Geometridae) andLepipolys species (Noctuidae)

The iridoid glycoside antirrinoside was found to be sequestered by highly aposematic larvae of the geometrid mothMeris paradoxa and two noctuid mothLepipolys species feeding onMaurandya antirrhiniflora (Scrophulariaceae), a natural food plant from southern Arizona. The antirrinoside content of leaves and petioles being consumed, eariy-instar larvae, late-instar larvae, larval frass, regurgitant, reflex-bleeding emission (Meris paradoxa), cocoons, pupae, meconium emitted upon eclosion, and adult moths was determined. Larvae, other than the earliest instars, did not excrete antirrinoside in the frass, but sequestered it in amounts of 3–11 % of the dry weight. Small amounts of antirrinoside remained in various pupal or cocoon parts and some was emitted in the meconium upon eclosion. The total antirrinoside accounted for was, however, considerably below that expected based upon the remarkably high 20% content of the leaves and petioles being consumed. The adult cryptic moths of both species contained little or no antirrinoside. This is the first report of a natural food plant and larval stages forM. paradoxa and a previously undescribedLepipolys species. It is also the first report of antirrinoside sequestration and utilization by insects.Chemistry of the Scrophulariaceae. 20. Paper 19: Stermitz, F.R., Ianiro, T.T., Robinson, R.D., and Gardner, D.R. 1991.J. Nat. Prod. 54:626–628.     

Effects of Plant Diet on Detoxification Enzyme Activities of Two Grasshoppers, Melanoplus differentialis and Taeniopoda eques

The polyphagous grasshoppers Melanoplus differentialis and Taeniopoda eques use different foraging patterns: over time M. differentialis tends to reduce the variety of host plants it feeds on and specialize on particular plants (diet components), whereas T. eques mixes host plants to achieve a very diverse diet. We tested the hypothesis that these differing behaviors are correlated with differing patterns of detoxification enzymes. The activities of midgut, fat body, and malpighian tubule detoxification enzymes were determined in last instars of the two grasshoppers, reared for five days on single-or mixed-plant diets. Significant differences in several cytochrome P450 activities and glutathione S-transferase were evident for nymphal grasshoppers feeding on different plant diets. However, the behavioral differences between the two species could not be explained by an underlying flexibility of detoxification response in M. differentialis, but lacking in T. eques. This is the first reported evidence that detoxification enzyme activities are affected by plant diet in polyphagous orthopterans.