Host-marking pheromones in lepidoptera,with special reference to twoPieris spp

Adult females of several lepidopteran species avoid oviposition near conspecific eggs. Laboratory and field studies indicate that visual factors as well as chemical host markers may be involved in egg avoidance behavior. The oviposition-deterring pheromones (ODP) of two pierids,P. brassicae andP. rapae have been studied in considerable detail. The ODPs are probably produced in the female accessory glands and contain volatile and nonvolatile components. They are perceived by nonspecialized antennal or tarsal receptors, respectively. The ODP ofP. brassicae affects oviposition ofP. rapae females and vice versa. ODPs show promise for insect control programs, but more information on oviposition behavior in the presence of ODP under field conditions is required.     

The nature of the gregarizing signal responsible for maternal transfer of phase to the offspring in the desert locust Schistocerca gregaria

We examined aggregative behavior of hatchlings of the desert locust Schistocerca gregaria emerging from solitaria egg pods that had been incubated in sand previously used for consecutive ovipositions by gregarious females. Hatchlings derived from such eggs were significantly more gregarious than those derived from pods laid in clean sand. The gregarizing effect of the sand-associated factor originating from 3, 5, or 10 ovipositions by gregarious females increased in a dose-dependent fashion. Washing the sand with organic solvents following such ovipositions, or flushing it with nitrogen gas, led to substantial loss of its gregarizing effect, showing that the active signal is volatile and of medium polarity. The gregarizing activity of the exposed sand correlated with the presence of C-8 unsaturated ketones, (Z)-6-octen-3-one and (E,E)-3,5-octadiene-2-one and its E,Z isomer, previously shown by us to form part of the releaser pheromone system that mediates group oviposition in S. gregaria. These ketones were present in relatively large amounts in the eggs obtained from egg pods of gregarious females and were also detected in the extracts of accessory glands of gregarious females, a candidate source of the gregarization factor. It is proposed that the pheromone is secreted at the onset of oviposition. This would account for its distribution predominantly within the eggs and surrounding sand at the site of oviposition. The study sheds new light on the pheromonal mechanism associated with transgenerational transmission of gregarious characters in crowded S. gregaria populations and provides yet another case in this insect of dual releaser and primer roles played by the same pheromone blend.     

Dodecanoic Acid Is the Oviposition Pheromone ofLutzomyia longipalpis

The sandfly,Lutzomyia longipalpis (Lutz and Neiva), produces an oviposition pheromone in the accessory glands that is secreted onto the eggs during oviposition. This compound attracts and/or stimulates gravid females for egg-laying. The compound was identified as dodecanoic acid, using gas chromatography–mass spectrometry, gas chromatography, and chemical derivatizations. The synthetic analog induced the same behavioral response in gravid sandflies as the whole egg extract when present in biologically relevant quantities. When single sensillum recordings were taken from the ascoid on the antennae of female sandflies, the response to egg extract and dodecanoic acid was similar. There was a dose dependent response to dodecanoic acid and preferential sensitivity compared to other fatty acids. There was a strong additive interaction upon the behavior ofL. longipalpis when dodecanoic acid was tested in a bioassay with the known oviposition attractant apneumones from rabbit feces, hexanal, and 2-methyl-2-butanol. The results suggested that sandflies acquired hexadecanoic acid (palmitic acid) from the blood meal and over a period of four days this was converted to dodecanoic acid. The role of these token semiochemicals in sandfly oviposition is discussed with respect to additive interactions and the significance of their origin from larval food resources.     

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.     

Host-Plant Chemistry Influences Oviposition Choice of the Spicebush Swallowtail Butterfly

The spicebush swallowtail, Papilio troilus (L.), lays its eggs on plants in the family Lauraceae. Sassafras [Sassafras albidum (Nutt.) Nees], spicebush [Lindera benzoin (L.) Spreng.], redbay (Persea borbonia (L.)] and camphortree [Cinnamomum camphora (Nees) Eberm.] are four of its known host plants. In one-choice tests, free-flying spicebush swallowtail females laid eggs on chemical extracts of the leaves of each of these four hosts. In two-choice experiments, females always preferred to oviposit on an extract of sassafras compared to extracts of the other three hosts. It was shown for spicebush extract that this response was not due to oviposition experience. Previously we had identified one of the host plant chemicals acting as an oviposition stimulant in sassafras extract as 3-caffeoyl-muco-quinic acid (3-CmQA). Extracts of the other three hosts did not contain this compound. The addition of 3-CmQA alone to spicebush extract did not increase oviposition activity. It did, however, increase discrimination between hosts and nonhosts. When a fraction of sassafras extract containing 3-CmQA and other synergistic stimulants was added to spicebush extract, preference for sassafras extract was no longer recorded. These results show existing differences in oviposition chemistry among host plants of the spicebush swallowtail and how these differences can influence oviposition choice in bioassay experiments.     

Does the imported cabbageworm,Pieris rapae,use an oviposition deterring pheromone?

Eggs ofPieris rapae (L.) contain a water- and methanol-soluble oviposition-deterring pheromone (ODP) that is avoided by ovipositing females offered treated and untreated cabbage leaves in a choice situation. Water extracts of female accessory glands also deter oviposition. Egg washes and gland extracts stimulate a contact chemoreceptor in sensilla on the fore tarsi. Electroantennogram (EAG) recordings show that antennal receptors respond to volatiles from conspecific eggs, but not to volatiles from eggs ofMamestra brassicae. No differences were detected between North American and European insects with regard to production and perception of ODP. These results differ from conclusions in the literature based upon field observations. It is concluded that this discrepancy in due to methodological differences.     

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.     

Host selection byBlepharipa pratensis (Meigen), a tachinid parasite of the gypsy moth,Lymantria dispar L.

The host selection process ofBlepharipa pratensis (Meigen), a tachinid parasite of the gypsy moth,Lymantria dispar L., was investigated. Once in the host's habitat, and following contact with a recently damaged leaf edge (cut, torn, eaten), the fly orients perpendicular to the edge and moves back and forth with the front tarsi grasping the damaged edge. Oviposturing (oviposition intention) may occur. Leaf exudates appear to arrest the fly on the leaf and increase tarsal examination (searching). If an edge of a gypsy moth-eaten leaf is contacted, oviposition usually occurs. Significantly more eggs are laid when host-browsed foliage is encountered, compared to mechanically cut or damaged foliage, indicating response to a cue left by the host during feeding. The number of host-damaged leaf clusters in an area significantly enhances oviposition there; in field-cage tests, significantly more eggs (7911) were laid in simulated-crown areas with all clusters browsed, compared to the adjacent areas containing 1/2 browsed (4200 eggs) and undamaged clusters (2209 eggs). A host selection sequence is suggested and discussed.     

Discrimination of occupied host fruit by plum curculio females (Coleoptera: Curculionidae)

Larval survival of plum curculios (PCs),Conotrachelus nenuphar (Herbst), was found to decrease with increasing egg density per fruit. Subsequently, we assayed PCs for propensity to avoid egg-laying at sites (immature plums) already occupied by conspecific eggs. Laboratory choice tests showed PCs made an equal number of visits to and ovipositions in fruit with a single oviposition as in clean fruit. Although there was a trend toward more visits to fruit which contained four or eight oviposition wounds and eggs or eight artificial punctures than to clean fruit, PCs oviposited less frequently into these than clean fruit. Results suggest that wounding of fruit may enhance the ability of ovipositing PCs to locate fruit, but at the same time may furnish cues allowing some degree of discrimination against heavily infested fruit for oviposition.     

Oviposition in Delia platura (Diptera, Anthomyiidae): The Role of Volatile and Contact Cues of Bean

The choice of a suitable oviposition site by female insects is essential for survival of their progeny. Both olfactory and contact cues of the oviposition site may mediate this choice. The polyphagous Delia platura (Diptera: Anthomyiidae), a severe agricultural pest of numerous crops, lays eggs in the soil close to germinating seeds. Maggots feed upon the cotyledons. Only little is known about the cues guiding oviposition behavior. In this study, the effects of both olfactory and contact cues of beans (Phaseolus vulgaris) on oviposition of D. platura females were tested. Egg deposition on germinated beans was preferred to egg deposition on ungerminated beans or on beans in different postgerminating developmental stages. Olfactory cues of germinating beans alone stimulated female flies to lay eggs. Additional contact cues of germinating beans seemed to enhance the response, but the difference was not significant. Surface extracts of germinating beans sprayed on surrogate beans showed that both polar and nonpolar substances stimulated oviposition of D. platura flies. Gas chromatography-electroantennographic detection recordings of head space samples of germinating beans showed positive response of females to different compounds. We conclude that olfaction plays a major role when D. platura females are searching for oviposition sites. Volatile compounds released from germinating beans such as 4-hydroxy-4-methyl-2-pentanone, 1-hepten-3-one, 1-octen-3-ol, and 3-octanone should be considered as key compounds that mediate oviposition behavior. The use of different sensory modalities by closely related species of Delia is discussed.     

Specialist Weevil, Rhyssomatus lineaticollis, Does Not Spatially Avoid Cardenolide Defenses of Common Milkweed by Ovipositing into Pith Tissue

Rhyssomatus lineaticollis is a milkweed specialist whose larvae feed upon pith parenchyma in ramet stems of the common milkweed, Asclepias syriaca. Compared with other specialist insect herbivores on milkweeds, this curculionid beetle is unusual in that it is cryptically colored and does not sequester cardenolides characteristic of milkweed chemical defense. Based upon optimal defense theory, we predicted that pith tissue would be low in defensive compounds and that oviposition into the pith would spatially avoid cardenolides. We rejected this hypothesis because we found that pith tissue has a relatively high cardenolide concentration compared to cortex, epidermis, and leaf tissues. Moreover, we found total plant cardenolide concentration was lower in plants that contained the beetle eggs. Cardenolide concentrations were different among tissues in intact stems without the pith herbivore compared to stems where it was present. Furthermore, the overall polarity of the cardenolides present varied among plant tissues and between plants with and without R. lineaticollis eggs. Although we found lower concentrations of cardenolide in piths where the eggs were present, the cardenolides present in the pith contained more nonpolar forms, indicating that the plant may be responding to herbivory by increasing toxic efficacy of cardenolide defenses while lowering the total concentration. We suggest that preoviposition behavior by female beetles, which includes feeding on new leaves of the plant, is a mechanism by which females manipulate plant chemistry and assess quantitative and qualitative changes in cardenolide chemistry in response to herbivory prior to oviposition.     

Evidence for a Host-Marking Pheromone in White Spruce Cone Fly, Strobilomyia neanthracina

Cone flies (Strobilomyia spp.) lay eggs on coniferous cones, and larvae must complete development within the cone on which the eggs are laid. Previous field surveys showed that egg distributions of several species are uniform, suggesting that females avoid ovipositing on cones with conspecific eggs or larvae. In both the field and laboratory, S. neanthracina females walked around cones following oviposition, touching their mouthparts to the cone as they walked. In laboratory bioassays, where females were presented with a cone on which they or another female had oviposited and touched with mouthparts, or one without an egg, females laid preferentially on cones without eggs. However, females laid randomly when presented with a cone on which a female had oviposited but been prevented from touching with her mouthparts following oviposition or another cone without an egg. This indicates that females deposit a host-marking pheromone with their mouthparts following oviposition and that this deters further oviposition on marked hosts. Laboratory and field bioassays indicated that the host-marking pheromone is located in the head and thorax of female flies.     

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.     

Experience Induces a Phytophagous Insect to Lay Eggs on a Nonhost Plant

Experience of nonhost plants by phytophagous insects may alter their foraging and oviposition responses to these plants. Using the diamondback moth (DBM) Plutella xylostella (L.), its host-plant Chinese cabbage, and a nonhost-plant Pisum sativum (pea) as a model system, we examined whether experience of the nonhost plant by adults can induce oviposition on the nonhost plant. Naive DBM females did not accept pea for oviposition in either no-choice or choice conditions, whereas females with prior experience of pea laid up to 20% of their eggs on this plant. Naive females reduced their oviposition, but experienced females did not refrain from laying eggs in a nonhost-plant environment. Such habituation to nonhost plants could lead to host range expansion in phytophagous insects and increase mortality of pest insects in diversified crop systems.     

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.     

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.     

Egg dispersion in codling moth: Influence of egg extract and of its fatty acid constituents

Codling moth females (Cydia pomonella, Lepidoptera: Tortricidae) (CM) usually lay single eggs and have a tendency to disperse. In a first experiment we observed that single females exposed to 20 apples distribute their eggs regularly among apples, suggesting a dispersive oviposition behavior. In a dual-choice situation, isolated females avoided oviposition on areas of cardboard treated with a methylene dichloride egg extract at the dose of ca. 1.0 egg equivalent/cm². A strong avoidance was obtained in response to a 20-fold dose, which was accompanied by a significant reduction of total oviposition. Seven major compounds found by GC analyses in the methylene dichloride extract of 2 to 3-day-old eggs were saturated or unsaturated C₁₄-C₁₈ straight-chain fatty acids: myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid. This was confirmed by GC-MS analysis of an extract made by ethyl ether. Smaller amounts of three methyl esters were also identified as methyl myristate, methyl palmitate, and methyl stearate. A blend of the seven fatty acids (FA) mimicked rather well the avoidance provoked by the extract, and this avoidance was confirmed by choice between treated and untreated fruits by single females. The treatment of apples with the 7FA mixture induced an aggregative distribution of the eggs among apples. We also found that the amounts of fatty acids harvested in the extract depend on the egg age. Amounts of fatty acids increased until eggs were 4 days old and then decreased before hatching. In this paper we discuss the possible role of simple molecules, such as fatty acids and their esters, as semiochemicals indicative of juvenile tissues.     

Iridoid glycosides as oviposition stimulants for the buckeye butterfly,Junonia coenia (Nymphalidae)

Females ofJunonia coenia (Nymphalidae), a specialist on plants that contain iridoid glycosides, were found to use aucubin and catalpol, iridoid glycosides typical of a host plant,Plantago lanceolata (Plantaginaceae), as oviposition cues. Incorporating dried ground leaf material or pure iridoid glycosides into agar disks proved to be a very effective method of testing. In no-choice tests and choice tests, females laid more eggs on disks withP. lanceolata leaf material or iridoid glycosides, compared to agar controls. There was variation among individual females in preference for disks withP. lanceolata leaf material versus disks with iridoid glycosides. Females given a choice of three different concentrations of iridoid glycoside (0.2, 0.5, 1.0%) in the agar disks and a control laid more eggs on the disk with the highest concentration of iridoid glycoside.     

Aggregated oviposition inDelia antiqua (Meigen): A case for mediation by semiochemicals

Experiments conducted in the laboratory tested the hypotheses that aggregated oviposition by onion maggot flies,Delia antiqua (Meigen), is caused by stimuli associated with ovipositing females, newly laid eggs, or both. Using a paired oviposition station bioassay that eliminated visual stimuli associated with the treatment under study, 67% of the eggs laid by caged females were in response to the odor of females already ovipositing on an onion slice, as opposed to 33% of the eggs laid in response to an onion slice alone. When newly laid eggs were transferred to onion slices and held for either 24 or 48 hr before being bioassayed against similarly aged untreated onions, 74% and 97% of the eggs were laid at the egg-treated onion stations, respectively. Similar results were achieved when an aqueous wash of newly laid eggs was applied to the onion slice. When the egg wash was processed through a bacterial filter or when eggs were present but not in contact with onions, all response was eliminated. These results implicate microorganisms transmitted on the egg surface in creating an attraction for ovipositing females. Heptane extracts of ovipositor tips from mated, ovipositing females induced 72% of the test females to oviposit near points at which extracts were applied to the oviposition station floor. A behavioral sequence for an optimal host-selection strategy is hypothesized, whereby host-seeking female onion flies respond to host-derived alkyl sulfides at long range and metabolic by-products of microbially infested hosts and visual cues at short range (ca. l m), with final selection of oviposition sites potentially reinforced by contact with an aggregation pheromone released or left on the substrate by ovipositing females.     

Response of the ichneumonid parasiteNemeritis canescens to Kairomones from the flour moth,Ephestia kuehniella

2-Acylcyclohexane-1,3-diones, a novel class of compounds in the larval mandibular glands ofEphestia(=Anagasta) kuehniella Zeller, act as kairomones. Their relative activities in eliciting oviposition responses from the larval parasiteNemeritis(=Venturia) canescens (Grav.) are reported.