Larval exposure to oviposition deterrents alters subsequent oviposition behavior in generalist,Trichoplusia ni and specialist,Plutella xylostella moths

The present study was undertaken to determine the effects of larval feeding experience on subsequent oviposition behavior of the resulting moths. Larvae of the cabbage looper (Trichoplusia ni, Noctuidae) and the diamondback moth (Plutella xylostella, Plutellidae) were exposed to the phenylpropanoid allelochemical trans-anethole (at 100 ppm fw in artificial diet) or the limonoid allelochemical toosendanin (10 ppm sprayed on cabbage leaves). Both compounds had been shown to deter oviposition in naïve moths in previous choice tests. Moths developing from experienced larvae (both sexes) showed a decrease in oviposition deterrence response when given a choice between control and treated leaves, unlike naïve moths. This phenomenon, analogous to habituation to feeding deterrents in lepidopteran larva, occurred irrespective of duration of feeding on the deterrent compound. We also observed that F₁larvae resulting from experienced moths (previously exposed to toosendanin as larvae) grew as well on toosendanin-treated foliage as on control foliage. In contrast, growth of F₁larvae from naïve moths was significantly impaired by toosendanin. These results demonstrate that host-selection behavior in cabbage looper (a generalist) and diamondback moth (a specialist) may be shaped by feeding experience according to Hopkins' Host Selection Principle in addition to chemical legacy.     

Deterrence of repeated oviposition in sorghum shootflyAtherigona soccata

The sorghum shootfly,Atherigona soccata, under low population density conditions lays one egg per sorghum plant. Possible regulatory mechanisms of this oviposition behavior are reported. The presence of an egg thoroughly washed and reattached to a leaf does not deter further oviposition, indicating the absence of visual cues. When washings from eggs were sprayed on sorghum plants, or when plants from which eggs had been removed were presented to a gravid female, significant deterrence was observed. Apparently a deterrent pheromone is associated with the water-soluble glue with which the females attach their eggs to the leaves. Some deterrent effect persists for at least 7 days.     

Feeding and oviposition deterrent activities of flower buds of globemallow,Sphaeralcea emoryi torrey,against boll weevil,Anthonomus grandis Boheman (Coleoptera: Curculionidae)

The globemallow,Sphaeralcea emoryi Torrey, a plant native to Arizona was evaluated as a source of feeding or oviposition deterrents to the boll weevil,Anthonomus grandis Boheman. Feeding and oviposition responses of reproductive weevils to the flower buds and artificial diets spiked with dry powder or extracts of the globemallow buds were determined. Boll weevils were deterred from feeding and ovipositing in the flower buds unless the calyxes were removed. Male and virgin female weevils were discouraged from feeding as much as gravid weevils. Secondary chemicals in the flower buds served primarily as feeding deterrents but also prevented oviposition. The concentration of these chemicals was highest in the calyxes of the buds, and potent deterrent activity could be extracted from the calyxes with methanol. Boll weevils were able to perceive the deterrents by contact chemosensory organs on the antennae, maxillary palps and labial palps.     

Chemical constituents ofErysimum cheiranthoides deterring oviposition by the cabbage butterfly,Pieris rapae

Avoidance ofErysimum cheiranthoides for oviposition byPieris rapae has been attributed to the presence of water-soluble deterrents. The active material was extracted inton-butanol and isolated by a series of HPLC separations. TLC of the active fraction and visualization of individual constituents with Kedde's reagent indicated that cardenolides are responsible for deterring oviposition. UV spectra were also characteristic of cardenolides. Bioassays of selected known cardenolides revealed a general lack of activity, except for cymarin, which was as strongly deterrent as the most prominent cardenolide isolated in pure form fromE. cheiranthoides. The results suggest that cardenolides in this plant can explain its escape from cabbage butterflies, but specific structural features of the glycosides are necessary for oviposition-deterring activity.     

Kairomones for the egg parasiteTrichogramma evanescens Westwood

In observation-cage experiments some new contact kairomones for the egg parasiteTrichogramma evanescens Westwood are demonstrated.T. evanescens females search significantly longer on cabbage leaves treated with the wing scales of two hosts,Pieris brassicae L. andP. rapae L. Further, egg washes ofP. brassicae containing an oviposition deterrent pheromone for the butterflies, were found to have a contact-kairomonal effect on the parasite.T. evanescens females search significantly longer on cabbage leaves sprayed with a methanol or water wash ofP. brassicae eggs than on leaves treated with the solvent only.Hymenoptera: Trichogrammatidae.Lepidoptera: Pieridae.     

Behavior ofHeliothis virescens (F.) in presence of oviposition deterrents from elderberry

Extracts prepared from elderberry,Sambucus simpsonii Rehd., leaves with either acetone, dichloromethane, distilled water, ethanol, hexane, or methanol deterred oviposition byHeliothis virescens (F.) on treated substrates in the laboratory. Doses of the aqueous extract equivalent to as little as 0.8 mg of leaves/cm2 of oviposition substrate were effective in reducing egg deposition. There was no significant difference in the mean number of landings on extract-treated and untreated surfaces. When either the antennae, proboscis, or the metathoracic legs were removed from female moths, there was no significant effect on oviposition on paper towels treated with elderberry leaf-water extract in laboratory bioassays, but in field cages, moths without these appendages deposited significantly fewer eggs on treated leaves of tobacco plants, a preferred host. There was no evidence that elderberry leaf-water extract affected mating byH. virescens.Lepidoptera: Noctuidae.Mention of a commercial or proprietary product does not constitute an endorsement by the USDA.     

Chemical and experiential basis for rejection ofTropaeolum majus byPieris rapae larvae

Rejection of nasturtium,Tropaeolum majus, by cabbage-reared larvae ofPieris rapae has been explained by the presence of feeding deterrents in the nastrutium foliage. Sensitivity to the deterrents develops as neonate larvae feed on cabbage. The most prominent deterrent compound, which is present in nasturtium at a concentration of 40 mg/100 g fresh leaves, was identified as chlorogenic acid. When neonate larvae were fed on a cabbage leaf treated with high concentrations of deterrent-containing extracts of nasturtium foliage, they remained insensitive to the deterrents, so they accepted nasturtium when transferred as second instars. When neonate larvae were reared on a cabbage leaf treated with 0.1 mg chlorogenic acid, ca. 35% of the second instars accepted nasturtium. Similar dietary exposure of neonates to the subunits of chlorogenic acid, caffeic acid and quinic, acid resulted in much less or no effect on the rejection behavior of second instars. The results suggest that the combined effects of specific chemical constituents of nasturtium can explain the rejection of this plant by larvae ofP. rapae, but if larvae are continuously exposed to these compounds immediately after hatching, they apparently become habituated to the feeding deterrents. The lack of activity of the subunits of chlorogenic acid suggests that specific structural features are necessary for a dietary constituent to cause such habituation or suppression of sensitivity development.     

Identification and bioassay of kairomones forHelicoverpa zea

Hexane extracts of leaves of 307 accessions from 73 host plant species ofHelicoverpa zea were analyzed by gas chromatography (GC) and used forH. zea oviposition and neonate larvae orientation bioassays. The gas chromatographic (GC) retention times of compounds statistically associated with behavioral activity were identified by correlation of GC peak area with oviposition and larval orientation preferences. Although taxonomically diverse in their origin, compounds for study were purified from extracts of species of the genusLycopersicon, due to their relative abundance. The structures of eight long-chain alkanes associated with oviposition preference were assigned by mass spectrometry, and the structures of five similarly associated organic acids and a terpenoid alkene were identified by¹H and¹³C nuclear magnetic resonance spectroscopy. The structures of a number of other phytochemicals from the plant leaves were identified for comparative purposes, including a previously unknown terpene, 7-epizingiberene. Bioassays were performed on the isolated acids and on the alkane wax fractions of severalLycopersicon species, and significant differences were found in oviposition stimulation for both classes of compounds. Of the hundreds of compounds found in the extracts, none were observed to act as oviposition deterrents. The results of these bioassays may be useful in explaining the broad host range ofH. zea, as well as the process and evolution of host plant selection for oviposition.     

Generalization of a Habituated Feeding Deterrent Response to Unrelated Antifeedants Following Prolonged Exposure in a Generalist Herbivore, Trichoplusia ni

The possibility of generalization of habituated response to unrelated feeding deterrents following prolonged exposure was examined in third instar Trichoplusia ni (Lepidoptera: Noctuidae) larvae by rearing them on antifeedants and then testing with other unrelated antifeedants. We introduced neonate larvae (<24-hr old) onto cabbage leaves treated with crude seed extracts of Melia volkensii (Meliaceae) or oil of Origanum vulgare (“oregano”) (Lamiaceae) and allowed them to feed until early in the third instar. Naïve larvae were reared on cabbage leaves treated with carrier solvent alone. Both experienced and naïve larvae were tested for feeding deterrent response with the same and the different extracts in a leaf disc choice bioassay. Habituation was generalized to both M. volkensii and oregano following prolonged exposure to either plant extract and also to a pure allelochemical, thymol, following prolonged exposure to either digitoxin or xanthotoxin. However, there was no generalization of the habituated response to oregano following prolonged exposure to digitoxin or thymol, or to thymol or xanthotoxin following prolonged exposure to oregano or M. volkensii. Our results demonstrate that habituated response to feeding deterrents in a polyphagous insect herbivore can be generalized among and between plant extracts and pure allelochemicals, but not in all situations. The implications of such behavioral plasticity in herbivorous insects for the use of antifeedants as crop protectants or for host plant shifts is discussed.     

Cardenolides fromErysimum cheiranthoides: Feeding deterrents toPieris rapae larvae

Larvae of the cabbage butterfly,Pieris rapae, refuse to feed on the wild mustard,Erysimum cheiranthoides, due to the presence of alcoholextractable deterrents. The active components were extracted inton-BuOH, and this extract was separated into four fractions (I–IV) by reverse-phase HPLC. Fractions III and IV retained the feeding deterrent activity. The activity of fraction III was found to be due to the cardenolide diglycosides 1 and 2, which were previously reported as oviposition deterrents for gravidP. rapae butterflies. Three active compounds were isolated from fraction IV by column chromatography on silica gel followed by reverse-phase HPLC. These compounds were identified as a monoglycoside, digitoxigenin 3-O--D-glucoside (4), and two diglycosides, glucodigigulomethyloside (5) and glucodigifucoside (6). An additional cardenolide isolated from fraction II was identified as cheirotoxin (7). All compounds were identified by UV, NMR (¹H and¹³C), and mass spectrometry, as well as hydrolysis experiments. The feeding deterrent activity of these compounds was compared with that of related commercially available chemicals and other compounds isolated fromE. cheiranthoides.     

Induction of Plant Synomones by Oviposition of a Phytophagous Insect

Earlier investigations of host habitat location in the egg parasitoid Oomyzus gallerucae have shown that oviposition of the elm leaf beetle (Xanthogaleruca luteola) induces the field elm (Ulmus minor) to emit volatiles that attract the egg parasitoid. In this study we investigated the mechanism of this induction by testing the effects of differently treated elm leaves on O. gallerucae in a four-arm olfactometer. First we investigated which sequence of the herbivore oviposition behavior is necessary for the synomone induction. The following major sequences were observed: (1) Prior oviposition, the gravid female gnawed shallow grooves into the leaf surface. (2) After gnawing upon the leaf surface, the female attached about 20–30 eggs with oviduct secretion in the grooves. We experimentally mimicked the shallow grooves on the leaf surface by scratching the leaf surface with a scalpel (= scratched leaves). Volatiles from such scratched leaves did not attract the egg parasitoid. However, as soon as eggs with oviduct secretion, or only oviduct secretion, was applied to these scratched leaves, they emitted attractive volatiles. Application of oviduct secretion and eggs on undamaged leaves did not elicit release of attractive synomones. Thus, an elicitor is located in the oviduct secretion, but becomes active only when the leaf surface is damaged. Jasmonic acid is known as a mediator of plant responses induced by feeding of herbivorous arthropods, and we demonstrate that it mediates production of elm synomones that attract O. gallerucae. The plant's reaction to oviposition was systemic, and leaves without eggs near leaves with eggs emitted attractants.     

Jasmonic Acid-Induced Changes in <Emphasis Type="BoldItalic">Brassica oleracea</Emphasis> Affect Oviposition Preference of Two Specialist Herbivores

Jasmonic acid (JA) is a key hormone involved in plant defense responses. The effect of JA treatment of cabbage plants on their acceptability for oviposition by two species of cabbage white butterflies, Pieris rapae and P. brassicae, was investigated. Both butterfly species laid fewer eggs on leaves of JA-treated plants compared to control plants. We show that this is due to processes in the plant after JA treatment rather than an effect of JA itself. The oviposition preference for control plants is adaptive, as development time from larval hatch until pupation of P. rapae caterpillars was longer on JA-treated plants. Total glucosinolate content in leaf surface extracts was similar for control and treated plants; however, two of the five glucosinolates were present in lower amounts in leaf surface extracts of JA-treated plants. When the butterflies were offered a choice between the purified glucosinolate fraction isolated from leaf surface extracts of JA-treated plants and that from control plants, they did not discriminate. Changes in leaf surface glucosinolate profile, therefore, do not seem to explain the change in oviposition preference of the butterflies after JA treatment, suggesting that as yet unknown infochemicals are involved.     

Lonicera Implexa Leaves Bearing Naturally Laid Eggs of the Specialist Herbivore Euphydryas Aurinia have Dramatically Greater Concentrations of Iridoid Glycosides than other Leaves

We tested in the field the hypothesis that the specialist butterfly Euphydryas aurinia (Lepidoptera: Nymphalidae, Melitaeinae) lays eggs on leaves of Lonicera implexa (Caprifoliaceae) plants with greater iridoid concentrations. We conducted our investigations in a Mediterranean site by analyzing leaves with and without naturally laid egg clusters. There were no significant differences in iridoid glycoside concentrations between leaves from plants that did not receive eggs and the unused leaves from plants receiving eggs, a fact that would seem to indicate that E. aurinia butterflies do not choose plants for oviposition by their iridoid content. However, the leaves of L. implexa that bore egg clusters had dramatically greater (over 15-fold) concentrations of iridoid glycosides than the directly opposite leaves on the same plant. These huge foliar concentrations of iridoids (15% leaf dry weight) may provide specialist herbivores with compounds that they either sequester for their own defense or use as a means of avoiding competition for food from generalist herbivores. Nevertheless, it may still be possible that these high concentrations are detrimental to the herbivore, even if the herbivore is a specialist feeder on the plant.     

Comparative physiological responses in Chinese cabbage induced by herbivory and fungal infection

Fungal infection of Chinese cabbage leaves by Alternaria brassicae has earlier been shown to have detrimental effects on larval development of the chrysomelid beetle Phaedon cochleariae. Furthermore, adults of this leaf beetle avoid fungus-infected Chinese cabbage leaves for oviposition and feeding. However, herbivory had no impact on fungal growth. In this study, we investigated physiological responses of the host plant to herbivore attack and fungal infection in order to elucidate the mechanisms of the described ecological interactions between the fungus and the herbivore. Changes in primary factors (water, C/N ratio, protein, sucrose) and defense-related plant compounds (glucosinolates, anthocyanins, peroxidase) were measured. Herbivory and fungal infection reduced the sucrose concentration of leaves and increased amounts of indole glucosinolates as well as total anthocyanins. In addition, water content was slightly lower in insect-damaged but not in infected leaves. Higher levels of peroxidase activity resulted exclusively from fungal infection. The C/N ratio and total protein content remained unaffected by either treatment. The implications of the induced plant changes on the herbivore are discussed.     

Influence of trichome exudates from species ofLycopersicon on oviposition behavior ofHeliothis zea (Boddie)

Cage experiments revealed that accessions of the wild tomato speciesLycopersicon hirsutum were preferred sites for oviposition byHeliothis zea. Hexane extracts from the leaves ofL. hirsutum were also preferred sites of oviposition in choice experiments among extracts from severalLycopersicon species. Extracts ofL. hirsutum were still biologically active several days after application, indicating that the phytochemical(s) involved are relatively stable and of low volatility. Gas Chromatographic analysis of leaf hexane extracts from 12 different accessions of theL. hirsutum complex and three tomato cultivars revealed substantial qualitative and quantitative variation in the chemical composition of these extracts. Comparison of these results with extract oviposition studies implicate a group of structurally related compounds as the active agents. Mass spectroscopy has tentatively identified these compounds as sesquiterpenes with the chemical formula C₁₅H₂₂O₂. These compounds are apparently synthesized and secreted from glandular trichomes on the leaf surface. These phytochemicals did not stimulate ovipositional behavior in females of the cabbage looper,Trichoplusia ni. The existence of genetic variation for the presence and amount of kairomones that serve as cues for insect orientation and oviposition could be utilized in a breeding program to develop tomato cultivars with genetically modified allelochemic profiles that would disrupt the sequential behavioral processes of insect host-plant selection.     

Volatile Stimuli Related to Feeding Activity of Nonprey Caterpillars, Spodoptera exigua, Affect Olfactory Response of the Predatory Mite Phytoseiulus persimilis

The effect of volatiles related to feeding activity of nonprey caterpillars, Spodoptera exigua, on the olfactory response of the predatory mites Phytoseiulus persimilis was examined in a Y-tube olfactometer. At a low caterpillar density (20 caterpillars on 10 Lima bean leaves), the predators were significantly more attracted to volatiles from infested leaves on which the caterpillars and their products were present or from infested leaves from which the caterpillars and their products had been removed when compared to volatiles from uninfested leaves. The predators, however, significantly avoided odors from 20 caterpillars and their products (mainly feces) removed from bean leaves. In contrast, at a higher caterpillar density (100 caterpillars on 10 Lima bean leaves), the predators avoided volatiles from caterpillar-infested bean leaves. Volatiles from infested leaves from which the caterpillars and their products had been removed were not preferred over volatiles from uninfested leaves. Volatiles from feces collected from 100 caterpillars were strongly avoided by the predators, while the behavior of the predatory mites was not affected by volatiles from 100 caterpillars removed from a plant. The data show that carnivorous arthropods may avoid nonprofitable herbivores. This avoidance seems to result from an interference of volatiles from herbivore products with the attraction to herbivore-induced plant volatiles.     

Impact of Botanical Pesticides Derived from Melia azedarach and Azadirachta indica Plants on the Emission of Volatiles that Attract Parasitoids of the Diamondback Moth to Cabbage Plants

Herbivorous and carnivorous arthropods use chemical information from plants during foraging. Aqueous leaf extracts from the syringa tree Melia azedarach and commercial formulations from the neem tree Azadirachta indica, Neemix 4.5^®, were investigated for their impact on the flight response of two parasitoids, Cotesia plutellae and Diadromus collaris. Cotesia plutellae was attracted only to Plutella xylostella-infested cabbage plants in a wind tunnel after an oviposition experience. Female C. plutellae did not distinguish between P. xylostella-infested cabbage plants treated with neem and control P. xylostella-infested plants. However, females preferred infested cabbage plants that had been treated with syringa extract to control infested plants. Syringa extract on filter paper did not attract C. plutellae. This suggests that an interaction between the plant and the syringa extract enhances parasitoid attraction. Diadromus collaris was not attracted to cabbage plants in a wind tunnel and did not distinguish between caterpillar-damaged and undamaged cabbage plants. Headspace analysis revealed 49 compounds in both control cabbage plants and cabbage plants that had been treated with the syringa extract. Among these are alcohols, aldehydes, ketones, esters, terpenoids, sulfides, and an isothiocyanate. Cabbage plants that had been treated with the syringa extract emitted larger quantities of volatiles, and these increased quantities were not derived from the syringa extract. Therefore, the syringa extract seemed to induce the emission of cabbage volatiles. To our knowledge, this is the first example of a plant extract inducing the emission of plant volatiles in another plant. This interesting phenomenon likely explains the preference of C. plutellae parasitoids for cabbage plants that have been treated with syringa extracts.     

Chemical stimulants and deterrents regulating acceptance or rejection of crucifers by cabbage butterflies

GravidPieris rapae butterflies oviposit on many, but not all, crucifers. Rejection ofErysimum cheiranthoides andCapsella bursa-pastoris was initially explained by the presence of chemical deterrents in the plants. Analyses and bioassays of plant extracts indicated the absence of oviposition stimulants inC. bursa-pastoris, but similar chemical separation ofE. cheiranthoides extracts revealed the presence of stimulants as well as deterrents. Choice tests illustrate how acceptance or rejection of a plant by an insect may depend on the balance of positive and negative chemical stimuli within the plant.     

Deterrence of repeated oviposition by fruit-marking pheromone inCeratitis capitata (Diptera: Tephritidae)

During ovipositor dragging on the fruit surface following egg laying in hawthorne fruit,Ceratitis capitata (Wiedemann) females deposit an unidentified pheromone that deters repeated oviposition attempts in that fruit. The pheromone proved water soluble and, when collected and sprayed in aqueous solution onto uninfested fruits in laboratory cages, effectively deterred boring attempts byC. capitata females of wild origin for at least 6 days (termination of test). A laboratory population ofC. capitata cultured on artificial media for more than 200 generations deposited pheromone that proved equally as deterrent to wild fly oviposition as pheromone from wild flies. However, lab fly oviposition was not effectively deterred by the presence of pheromone. The ecological significance of the pheromone is discussed.     

Isolation and identification of oviposition deterrents to cabbage butterfly,Pieris rapae,fromErysimum cheiranthoides

Avoidance of some crucifer species by the crucifer specialist,Pieris rapae, has been attributed to the presence of oviposition deterrents in these plants. Studies on one such unacceptable plant,Erysimum cheiranthoides, have resulted in the isolation ofn-butanol-soluble deterrents from the alcoholic extract of foliage. The active fraction contained three cardiac glycosides, which were isolated by reversed-phase HPLC and by open column chromatography on silica gel. Chemical and spectral evidence (UV, [¹H]NMR, and FAB-MS) led to the characterization of these compounds as erysimoside (1), erychroside (2), and erycordin (3). Erysimoside and erychroside were strongly deterrent toPieris rapae, but erycordin was inactive. Both active compounds have the same aglycone, strophanthidin (5) and the inner sugar in both cases is a 2,6-dideoxy hexose to which the outer sugar is attached at position C-4. These structural features, which are absent in the inactive compound (3), may represent specific requirements for oviposition deterrent activity.