Spodoptera exigua Oviposition and Larval Feeding Preferences for Pigweed, Amaranthus hybridus, over Squaring Cotton, Gossypium hirsutum, and a Comparison of Free Amino Acids in Each Host Plant

The beet armyworm, Spodoptera exigua (Hübner), can utilize a number of different host plants for oviposition and larval development, but some host plants are preferred over others. This study, using cage choice tests and olfactometer assays, demonstrates the beet armyworm's preference for pigweed, Amaranthus hybridus L., over cotton, Gossypium hirsutum L. Cage and olfactometer choice assays indicated that olfaction plays an important role in host selection by ovipositing females. First instars exhibited no feeding preference, but the more mobile third instars showed a significant feeding preference for excised pigweed leaves. The higher quantities and more diverse accumulations of free amino acids in pigweed might, in conjunction with other physiochemical and mechanical attractant and deterrent factors in the two-plant species system, play roles in the tendency of the beet armyworm to select pigweed over cotton and in providing a superior array of easily absorbed amino acids as compared to cotton.     

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.     

In vivo Volatile Emissions from Peanut Plants Induced by Simultaneous Fungal Infection and Insect Damage

Peanut plants, Arachis hypogaea, infected with white mold, Sclerotium rolfsii, emit a blend of organic compounds that differs both quantitatively and qualitatively from the blend emitted from plants damaged by beet armyworm (BAW; Spodoptera exigua) larvae or from uninfected, undamaged plants. Attack by BAW induced release of lipoxygenase products (hexenols, hexenals, and hexenyl esters), terpenoids, and indole. The plant-derived compound methyl salicylate and the fungal-derived compound 3-octanone were found only in headspace samples from white mold infected plants. White mold-infected plants exposed to BAW damage released all the volatiles emitted by healthy plants fed on by BAW in addition to those emitted in response to white mold infection alone. When BAW larvae were given a choice of feeding on leaves from healthy or white mold-infected plants, they consumed larger quantities of the leaves from infected plants. Exposure to commercially available (Z)-3 hexenyl acetate, linalool, and methyl salicylate, compounds emitted by white mold-infected plants, significantly reduced the growth of the white mold in solid-media cultures. Thus, emission of these compounds by infected plants may constitute a direct defense against this pathogen.     

Regulation of Oviposition in Anopheles gambiae s.s.: Role of Inter- and Intra-Specific Signals

Females of Anopheles gambiae Giles normally oviposit in a large number of fresh, small, sunlit, and spatially spread temporary pools. Such pools are associated with lower levels of predation compared to large, longer-lasting habitats. We compared oviposition levels on preferred (water collected from natural anopheline larval habitats) and non-preferred (distilled water) aqueous substrates by gravid females that contained different densities of conspecific eggs or early and late instar larvae. The presence of conspecific larvae, but not eggs, had a positive or negative effect on the ovipositional responses of gravid An. gambiae females, depending on the quality (preferred or non-preferred by the mosquito) of the oviposition water and the density of larvae. Presence of larvae, at all densities, in distilled water deterred oviposition. However, in natural anopheline pool water, a low density of larvae increased oviposition, whereas a higher density inhibited oviposition. Our results suggest that two signals produced by this mosquito may be involved in regulating oviposition: a volatile pheromone emitted by conspecific larvae, which augments the effect of a volatile signal emitted by preferred habitats, and a non-olfactory cue associated with high densities of larvae that deters oviposition.     

Investigation of oviposition deterrent in larval frass ofSpodoptera littoralis (Boisd.)

Previous experiments demonstrated an oviposition-deterring effect of larval frass in the Egyptian cotton leaf worm,Spodoptera littoralis (Boisd.). In this study, females were shown to perceive the oviposition-deterring substance(s) with their antennae. During dark, airtight, and cold (–10 °C) storage, the deterrent was persistent for at least 395 days. On the other hand, larval frass retained its activity for only two days when applied to cotton leaves. The deterrent activity of frass was independent of larval density. Frass of larvae reared at high densities deterred oviposition as well as frass of larvae feeding separately or in small groups. For significant oviposition deterrence, the minimum amount of frass was in the range of 5–10 mg frass per cotton leaf. An acetone extract of larval frass was highly deterrent, in contrast to extracts prepared with water, ethanol, chloroform, or pentane.     

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.     

Oviposition response of Chironomus tepperi to nitrogenous compounds and bioextracts in two-choice laboratory tests

Two-choice laboratory tests were used to investigate the oviposition response of Chironomus tepperi to a range of nitrogenous compounds and crude bioextracts. Responses to nitrogenous compounds varied in response to concentration. Ammonium nitrate did not influence oviposition at concentrations from 2 to 12 mg/liter. Hydroxylamine hydrochloride increased oviposition at 6 mg/liter, but had no effect at either 2 or 12 mg/liter. Sodium nitrate reduced oviposition at 2 mg/liter relative to the controls, but had no significant effect at 6 or 12 mg/liter. C. tepperi responded to many of the crude bioextracts, strongly avoiding oviposition in solutions containing homogenized chironomid larvae (1 final instar/100 ml; C. tepperi or Polypedilum nubiferum), and avoiding solutions conditioned by conspecificlarvae at concentrations down to the equivalent of 1 final instar/100 ml over 24 hr. Homogenates of adult conspecifics had no effect on oviposition site selection. Homogenates of larval Culex annulirostris (Culicidae) deterred oviposition, but only at high concentrations (3 final instars/100 ml). Our results demonstrate that chemical cues from larval populations deter oviposition by C. tepperi females searching for newly flooded habitats where larval competition will be minimized.     

Volatile Emissions Triggered by Multiple Herbivore Damage: Beet Armyworm and Whitefly Feeding on Cotton Plants

Plants are commonly attacked by more than one species of herbivore, potentially causing the induction of multiple, and possibly competing, plant defense systems. In the present paper, we determined the interaction between feeding by the phloem feeder silverleaf whitefly (SWF), Bemisia tabaci Gennadius (B-biotype = B. argentifolii Bellows and Perring), and the leaf-chewing beet armyworm (BAW), Spodoptera exigua Hübner, with regard to the induction of volatile compounds from cotton plants. Compared to undamaged control plants, infestation with SWF did not induce volatile emissions or affect the number and density of pigment glands that store volatile and nonvolatile terpenoid compounds, whereas infestation by BAW strongly induced plant volatile emission. When challenged by the two insect herbivores simultaneously, volatile emission was significantly less than for plants infested with only BAW. Our results suggest that tritrophic level interactions between cotton, BAW, and natural enemies of BAW, that are known to be mediated by plant volatile emissions, may be perturbed by simultaneous infestation by SWF. Possible mechanisms by which the presence of whiteflies may attenuate volatile emissions from caterpillar-damaged cotton plants are discussed.     

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.     

Influence of cnicin,a sesquiterpene lactone ofCentaurea maculosa (Asteraceae), on specialist and generalist insect herbivores

The sesquiterpene lactone cnicin was extracted fromCentaurea maculosa andCentaurea vallesiaca. We examined its effects on the ovipositional response and larval development of generalist and specialist insect herbivores associated withC. maculosa. For the oviposition trials, three plant species (C. maculosa, Achillea millefolium, andCichorium intybus), half of which were sprayed with 3% of cnicin, were exposed to the specialist mothsStenodes straminea, Agapeta zoegana, andPterolonche inspersa in field cages. All three species significantly preferredC. maculosa to other plants andP. inspersa significantly preferred cnicin-sprayed plants to untreated plants for oviposition. Tested over all species, cnicin significantly increased the number of eggs laid on a given plant. A larval diet test examined the toxicity of cnicin for larvae of the generalist noctuid mothSpodoptera littoralis. Cnicin concentrations of 3% and 6% were lethal and 1% and 0.5% seriously inhibited growth and development. The larvae of theC. maculosa specialistStenodes straminea survived at 6% cnicin, but none of the pupae hatched.Agapeta zoegana was able to survive at 1% and 3% cnicin. Both specialists had difficulties with the artificial diet, but weight increase and survival was not further reduced when cnicin was present compared with on the control diet. In conclusion, cnicin influenced host recognition by the specialist species, and larvae of the generalist did not survive on natural levels of cnicin. Growth and survival of the specialist were not influenced by cnicin but were considerably hampered on artificial diet.     

Plant response to eggs vs. Host marking pheromone as factors inhibiting oviposition byPieris brassicae

Pieris brassicae L. butterflies secrete miriamides onto their eggs. These avenanthramide alkaloids are strong oviposition deterrents when sprayed onto a cabbage leaf. However, these compounds could not be detected in cabbage leaves from which egg batches had been removed two days after deposition and that still showed oviposition deterrency. It was concluded that the miriamides were not directly responsible for the avoidance by females of occupied leaves while searching for an oviposition site. Evidence was obtained that cabbage leaves themselves produce oviposition deterrents in response to egg batches. Fractions containing potent oviposition deterrents could be isolated from surface extracts of leaves from which previously laid egg batches had been removed. The term host marking pheromone that was used previously is not applicable in this case.     

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.     

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.     

Oviposition preference of the diamondback moth (Plutella xylostelld) unaffected by the presence of conspecific eggs orBacillus thuringiensis

Neither toxins fromBacillus thuringiensis Berliner nor conspecific eggs deterred oviposition by the diamondback moth,Plutella xylostella (L.) (Lepidoptera: Plutellidae), in laboratory choice tests. The finding that toxins did not deter oviposition by moths from a susceptible line shows that oviposition preference and larval survival were not associated in this line. Selection for larval resistance to toxins did not significantly alter oviposition preference, which rules out a strong genetic correlation between larval performance and oviposition preference. Failure of conspecific eggs to deter oviposition may not represent lack of association of preference and performance because other evidence suggests that larval performance may not be greatly affected by larval density. These results suggest that the ability of refuges to slow evolution of physiological resistance toB. thuringiensis toxins will not be magnified by an oviposition preference for untreated foliage.     

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.     

Effects of Drought Stressed Cotton, Gossypium hirsutum L., on Beet Armyworm, Spodoptera exigua (Hübner) Oviposition, and Larval Feeding Preferences and Growth

The beet armyworm, Spodoptera exigua (Hübner), has been anecdotally reported to oviposit more on drought stressed than on nonstressed cotton plants. Using potted cotton plants in cages, this study demonstrated that beet armyworms deposited 3.3, 4.6, and 2.3 times more (P 0.05) eggs on cotton plants that were grown on 1500, 1000, and 750 ml water/wk, respectively, than on cotton plants grown in well watered (4000 ml water/wk) soil. Third instars, however, showed no preference for stressed cotton foliage over nonstressed foliage. Third instar beet armyworms raised on well watered cotton plants were 1.5, 2.3, and 2.6 times heavier than those reared on cotton grown in the 1500, 1000, and 750 ml water/wk plants (P 0.05), respectively. Physiochemical analyses showed that drought stressed leaves had significantly greater accumulations of free amino acids that are essential for insect growth and development. Soluble protein and soluble carbohydrates were also more abundant in stressed leaves compared to nonstressed leaves. Despite the apparent increase in nutritional quality in drought stressed plants, larval survival was reduced, probably because the limiting factor became water. Greater amounts of cotton leaf area were consumed from drought stressed leaves (P 0.05) than from nonstressed leaves, probably because the larvae had to metabolize greater portions of assimilated energy to supplement body water with metabolic water derived from respiration. The association of greater host plant nutritional quality to oviposition preference, and conversely, to reduced survivorship, is discussed.     

House fly oviposition inhibition by larvae ofHermetia illucens,the black soldier fly

Wild populations of house flies were inhibited from ovipositing into poultry manure containing larvae of the black soldier fly,Hermetia illucens (L.). A laboratory strain of house fly responded differently, readily ovipositing into manure with lower densities of soldier fly larvae, but avoiding the higher densities tested. The amount of timeH. illucens larvae occupy the manure prior to an oviposition test influences ovipositional responses of house flies. Manure conditioned byH. illucens larvae for 4–5 days did not significantly inhibit house fly oviposition. We suggest that some type of interspecific chemical communication (allomone) is present.Diptera: Stratiomyidae.Portion of an MS thesis by S.W.B.Research partially supported by State and Hatch funds.     

Aqueous extracts from indigenous plants as oviposition deterrents forHeliothis virescens (F.)

In laboratory and field tests, water extracts from plant foliage deterred oviposition byHeliothis virescens (F.). A maximum reduction of 93% was attained in laboratory oviposition cages. When females were allowed free choice of treated or untreated tobacco plants in field cage and field tests, maximum reductions in oviposition were 71 and 83%, respectively.Lepidoptera: Noctuidae.Mention of a commercial or proprietary product does not constitute an endorsement by the USDA.     

A neolignoid feeding deterrent againstLuehdorfia puziloi larvae (lepidoptera: Papilionidae) fromHeterotropa aspera,a host plant of sibling species,L. japonica

A feeding deterrent against larvae of a papilionid butterfly,Luehdorfia puziloi (Parnassiinae), a specialist onAsiasarum plants (Aristolochiaceae), was isolated from another aristolochiaceous plant,Heterotropa aspera. Antifeedant activity was exhibited by then-hexane-soluble fraction that proved to contain at least two active components. One of the deterrents was identified as a neolignan compound, asatone. The concentration of asatone inH. aspera was estimated at approximately 225 ppm, and larval feeding ofL. puziloi was significantly deterred at concentrations over 90 ppm. By contrast, asatone was not detectable (< 1 ppm, if any) in its host plant,Asiasarum sieboldii.     

Chemical constituents of an unacceptable crucifer,Erysimum cheiranthoides,deter feeding byPieris rapae

The wild cruciferErysimum cheiranthoides was found to contain extractable constituents that deterred feeding by larvae of the crucifer specialistPieris rapae when applied to cabbage leaf disks in both choice and nochoice bioassays. High-performance liquid chromatography was used to separate the extract into several fractions, two of which retained the feeding deterrent activity of the extract. UV-absorption spectra of the fractions suggested that one contained cardenolides similar or identical to those reported to deter oviposition byP. rapae onE. cheiranthoides. The other active fraction evidently contains a compound that deters larval feeding but not adult oviposition. The results suggest that the chemical defense ofE. cheiranthoides depends on two types of compounds acting on separate developmental stages of the insect.