Responses to prey chemicals by a lacertid lizard,Podarcis muralis: Prey chemical discrimination and poststrike elevation in tongue-flick rate

The ability to discriminate prey chemicals from control substances and the presence of a poststrike elevation in tongue-flicking (PETF) rate are experimentally demonstrated in the lacertid lizard,Podarcis muralis, The tongue-flick attack score, a composite index of response strength, was significantly higher in response to integumental chemicals from cricket than to cologne or distilled water. The cricket chemicals additionally elicited a significantly greater rate of tongue-flicking and higher proportion of attacks by the lizards than did control stimuli. PETF combined with apparent searching movements strongly suggest the presence of strike-induced chemosensory searching (SICS). Experimental evidence indicates that both PETF and SICS occur in insectivorous representatives of three families of actively foraging autarchoglossan lizards, suggesting their widespread occurrence in such lizards. The adaptive roles of chemosensory behavior in the foraging behavior of P.Muralis are discussed. It is proposed that these lizards may form chemical search images and that PETF and SICS may have been present in the lacertilian ancestors of snakes.     

A comparative analysis of scoring methods for chemical discrimination of prey by squamate reptiles

In studies of squamate responses to prey chemicals presented on cotton-tipped applicators, investigators typically record several responses, each of which gives only part of the overall picture. The tongue-flick/attack score (TFAS) is a widely used composite measure of response strength that accounts for attack, its latency, and number of tongue-flicks. We present data and analyses on these variables and investigate the utility of several other possible response variables. It is concluded, for both practical and theoretical reasons, that TFAS and two modifications of it are the best measures of response strength. Uses and statistical analyses of TFAS and variables derived from it are discussed. It is recommended that information on tongue-flick rate, number of individuals attacking, and latency to attack be presented.     

Selective improvement in responses to prey odors by the lobster,Homarus americanus,following feeding experience

Lobsters can detect odors from two natural prey species, the horse musselModiolus modiolus and the blue musselMytilusedulis. When lobsters fed exclusively on one of these two prey species for one month, their behavioral response threshold for the prey odor from this species was lowered relative to the threshold for odor from the nonexperienced prey.     

Discriminative Response to Animal, But Not Plant, Chemicals by an Insectivorous, Actively Foraging Lizard, Scincella lateralis, and Differential Response to Surface and Internal Prey Cues

Responses by the insectivorous, actively foraging scincid lizard, Scincella lateralis, to chemical cues from a plant food favored by herbivorous lizards, its ability to discriminate prey chemicals from control substances, and its relative response to internal and surface prey chemicals were studied experimentally. We presented chemical cues to the lizards on cotton swabs and recorded their tongue-flicks and biting attacks on the swabs. The lizards exhibited significantly greater tongue-flick rates and biting frequencies to prey surface cues than to plant surface chemicals from romaine lettuce, diluted cologne (pungency control), and deionized water. Responses to the plant stimuli did not differ from those to the two control stimuli, in contrast with strong responses to the same plant cues by herbivores. This finding provides the first information suggesting that chemosensory response may be adapted to diet, with responsiveness to plant stimuli evolving de novo in herbivores. Biting and tongue-flicking responses were significantly greater to cricket chemicals than to all other stimuli, among which there were no differences. Thus, the lizards are capable of prey chemical discrimination, which may be ubiquitous among actively foraging lizards. The lizards exhibited more frequent biting and higher tongue-flick rates to internal than surface prey chemicals. Although different methods of stimulus preparation are appropriate for different purposes, we conclude that prey surface chemicals available to foraging lizards are most desirable for studies bearing on location and identification of prey.     

The role of chemosensory cues in discrimination of prey odors by the amphisbaenianBlanus cinereus

Responses of amphisbaenians (Blanus cinereus) to deionized water, a control for pungency (cologne), and integumental prey odors (coleopteran larvae and adult ants) on cotton swabs were studied in experiments with a randomized blocks design to discover whether amphisbaenians use chemical cues to detect and identify prey. No individual bit the applicators. Amphisbaenians tongue-flicked at lower rates than epigean saurians, which are active foragers. Tongue-flick rate differed among treatments, but responses to prey odors were not significantly different from those to cologne. The number of directed tongue-flicks emitted during the 60-sec trials was, however, lower in response to deionized water than in response to cologne or prey odors. Response details, the low rate of tongue-flick, and absence of biting are discussed in relation to the foraging behavior and fossoriality of amphisbaenians. Evidence from this study indicates that the vomeronasal sense is used by amphisbaenians to identify odors, but our experiments failed to demonstrate that amphisbaenians discriminate between prey and nonprey odors.     

Responses to major categories of food chemicals by the lizard Podarcis lilfordi

Many lizards are capable of identifying food using only chemical cues from food surfaces, but almost nothing is known about the types of compounds that are effective stimuli. We experimentally studied lingual and biting responses by a lacertid lizard, Podarcis lilfordi, to single representatives of three major categories of food chemicals, sucrose as a carbohydrate, pure pork fat as a mixture of lipids, and bovine gamma globulin as a protein. In 60-sec trials in which stimuli were presented on cotton swabs, the lizards detected all three stimuli, exhibiting more tongue-flicks, licks, or bites, or a greater tongue-flick attack score (TFAS; overall measure of response strength to prey stimuli) than to deionized water. The initial response to all stimuli was tongue-flicking, but the lizards discriminated among the types of chemical stimuli. After preliminary tongue-flicks, the lizards responded to sucrose solutions by licking at high rates, to pure pork fat by biting, and to protein by a combination of additional tongue-flicks and biting. Biting is a feeding response to prey or solid plant material. Licking is a feeding response to sugars in nectar or ripe fruit. Its frequency increased with sucrose concentration. Our data suggest that lizards can identify several types of chemicals associated with food and direct feeding attempts to sources of such chemicals in the absence of visual cues.     

Role of prey odor in food recognition by rock crabs,Cancer irroratus say

Rock crabs,Cancer irroratus, respond to food odors in low concentration as measured by changes in antennular flicking rate. The responses of rock crabs to prey odor were tested in the presence and absence of visual cues to determine the role of chemical cues in prey recognition. Crabs were attracted to the source of mussel odor introduced into one arm of a Y maze. Natural and artificial prey shells and resin boxes were presented to crabs with and without the presence of mussel extract. The crabs were able to see, handle, and manipulate these objects. Crabs opened and consumed contents that emitted chemosensory cues and ignored identical objects that did not. Rock crabs were attracted to food odors and are capable of utilizing chemical cues to detect, locate, and identify food items.     

Kairomones and their use for management of entomophagous insects: II. Mechanisms causing increase in rate of parasitization byTrichogramma spp.

When the effect of the kairomone, tricosane, on parasitization byTrichogramma achaeae Nagaraja and Nagarkatti of eggs ofHeliothis zea (Boddie) was studied in petri dish tests, the greatest percentage parasitization ( = 64%) was obtained if the entire filter paper was treated. Treatment of smaller areas (about the eggs) resulted in decreased parasitism. In the greenhouse, highest parasitization ( = 71%) byT. pretiosum (Riley) ofH. zea eggs placed on pea seedlings grown in pie pans was obtained if the whole pan was treated; lowest parasitism ( = 29%) occurred when the pans were untreated. Parasitization was intermediate ( = 52%) in other pans treated only at selected spots. Dissections ofH. zea eggs collected from kairomonetreated and untreated field plots revealed that eggs ofTrichogramma spp. were more efficiently distributed (less superparasitism) among host eggs in treated plots. These kairomones increase parasitization ofTrichogramma spp. by releasing and continuously reinforcing an intensified searching behavior rather than by attracting and guiding the parasite directly to the host.Hymenoptera: Trichogrammatidae.In cooperation with the University of Georgia College of Agriculture Experiment Station, Coastal Plain Station, Tifton, Georgia.Mention of a proprietary product in this paper does not constitute an endorsement of this product by the USDA.     

Discrimination of Prey, But Not Plant, Chemicals by Actively Foraging, Insectivorous Lizards, the Lacertid Takydromus sexlineatus and the Teiid Cnemidophorus gularis

Sampling environmental chemicals to reveal prey and predators and to provide information about conspecifics is highly developed in lizards. Actively foraging lizards can discriminate between prey chemicals and control stimuli, but ambush foragers do not exhibit prey chemical discrimination. Recent experiments on a few species of herbivorous lizards have also demonstrated an ability to identify plant food chemicals. We studied chemosensory responses to chemicals from prey and palatable plants in two species of actively foraging, insectivorous lizards. Both the lacertid Takydromus sexlineatus and the teiid Cnemidophorus gularis exhibited strong responses to prey chemicals, but not to plant chemicals. These findings increase confidence in the relationship between prey chemical discrimination and foraging mode, which is based on data for very few species per family. They also provide data showing that actively foraging insectivores in two families do not respond strongly to plant cues. Such information is essential for eventual comparative studies of the relationship between plant diet and responses to food chemicals. The traditional method of presenting stimuli by using hand-held cotton swabs worked well for T. sexlineatus but could not be used for C. gularis due to repeated escape attempts. When stimuli were presented to C. gularis on ceramic tiles and no experimenter was visible, the lizards responded readily. Presentation of stimuli on tiles in the absence of a visible experimenter may be a valuable approach to study of food chemical discrimination by active foragers in which antipredatory behavior interferes with responses to swabs.     

TrappingDendroctonus brevicomis Changes in attractant release rate,dispersion of attractant,and silhouette

A sticky trap with 3 m² surface area was modified by changes in attractant release rate, vertical dispersion of the attractant, and addition of a tree trunk silhouette to the trap axis. As attractant release rate increased, the number ofDendroctonus brevicomis caught at the source of attractant and at 1.5 and 5.2 m above ground on two vertical silhouettes 4.5 m away increased. In one experiment, more beetles were caught at a dispersed source of attractant than at a point source. Fewer beetles were caught at the lower traps on the two outlying silhouettes when a silhouette was at the source, than when no silhouette was at the source. As attractant release rate increased, the catch of a predator,Temnochila chlorodia, increased at the source.Coleoptera: Scolytidae.Based in part on a thesis submitted by Paul E. Tilden to the University of California, Berkeley, in partial fulfillment of the requirements for the Master of Science degree in entomology, December 1976. These studies were supported by the Forest Service, U.S. Department of Agriculture, and in part by the Rockefeller Foundation and a joint grant (NSF GB-34718/BMS 75-04223) from the U.S. National Science Foundation and the U.S. Environmental Protection Agency to the University of California. The findings, opinions, and recommendations are not necessarily those of the funding agencies or the University of California.Mention of trade names is for information only and is not an endorsement by the funding or sponsoring agencies.     

Behavioral (Feeding) Responses of the Crayfish, Procambarus clarkii, to Natural Dietary Items and Common Components of Formulated Crustacean Feeds

We have examined the behavioral (feeding) response of Procambarus clarkii to natural dietary items (zooplankton, live fishes, dead fishes, and fish eggs) and common components of formulated feeds used in the aquaculture industry (soybean meal, fish meal, corn meal, alfalfa meal, and vitamin C). The feeding response by P. clarkii was determined using an ordinally ranked, whole-animal bioassay that included the following behaviors: (1) movement of the maxillipeds for longer than three seconds, (2) increased movement of the walking legs with dactyl probing, (3) movement of walking legs to the mouth, and (4) orientation of the entire body towards the odor source. Feeding behavior was determined in response to intact items, bathwater containing aqueous leachates from intact items, water and methanol fractions of bathwater eluted through a C₁₈ resin flash chromatography column, and size fractions of bathwater containing either molecules 10,000 Da or molecules >10,000 Da. All fractions tested were significantly stimulatory. Zooplankton was the most stimulatory of the natural dietary items tested. However, the C₁₈ water fraction of the soybean meal bathwater before size fractionation (containing molecules both <10,000 and >10,000 Da) was the most stimulatory of the common feed components and more stimulatory than the zooplankton. Proximate analysis indicated that the compounds present in this fraction were ca. 51% soluble carbohydrate, 4% soluble protein, and 45% unknown (assumed to be insoluble carbohydrates, insoluble proteins, and ash). We hypothesize that the primary compounds in soybean meal responsible for eliciting a feeding response in P. clarkii are soluble carbohydrates and/or glycoproteins.     

Control of chemically stimulated feeding behavior in sand fiddler crabsUca pugilator: Evidence for hemolymph feeding inhibitory factor

Uca pugilator, the sand fiddler crab, is a deposit-feeder. It feeds on exposed sand flats as the tide recedes. Feeding movements are evoked by stimulation of chemoreceptors on the dactyls. Previous studies have demonstrated that a proteinaceous factor associated with the sinus gland region inhibits chemically-stimulated feeding behavior. Here, that work is extended to show the existence of a similar inhibitory factor present in the hemolymph of fed crabs in the laboratory and in the hemolymph of crabs returning from feeding in the field. The factor is not detected in fasted laboratory crabs or in field crabs walking from burrow areas to feeding sites. Injection of glucose results in inhibition of feeding activity in intact crabs. Injection of glucose, but not galactose, stimulates feeding in eyestalk-ablated crabs. We suggest that neural responsiveness is stimulated by glucose, and that elevated glucose in intact crabs results in release of feeding inhibitory factor from the sinus gland. Release of feeding inhibitory factor into the blood enables crabs to return to burrow areas without stopping when they encounter food-laden sediments.     

Phenolic compounds on the pod-surface of pigeonpea,Cajanus cajan,mediate feeding behavior of Helicoverpa armigera larvae

A methanol extract of the pod surfaces of Cajanus cajan, a feeding stimulant for fifth-instar Helicoverpa armigera, was shown to contain four main phenolic compounds. Three of these were identified as isoquercitrin, quercetin, and quercetin-3-methyl ether, by comparing UV spectra and HPLC retention times with authentic standards. The fourth compound was isolated by semipreparative HPLC and determined to be 3-hydroxy-4-prenyl-5- methoxystilbene-2-carboxylic acid (stilbene) by NMR spectroscopy and mass spectrometry. Quercetin, isoquercitrin, and quercetin-3-methyl did not affect the selection-behavior of fifth-instar H. armigera. However, larvae were deterred from feeding on glass-fiber disks impregnated with the stilbene. Furthermore, larvae exposed to quercetin-3-methyl ether consumed significant amounts of both disks. In a binary-choice bioassay, a combination of quercetin-3-methyl ether and the stilbene on one disk and pure quercetin-3-methyl ether on the other disk resulted in increased consumption of both glass-fiber disks by larvae. In contrast, consumption was reduced if the combination was presented to larvae on one disk with purified stilbene on the other disk. Cajanus cajan cultivars that varied in their susceptibility to H. armigera were surveyed for the presence of the four phenolic compounds. An absence of quercetin and higher concentrations of isoquercitrin than the cultivated variety characterized pod surface extracts of pod-borer-resistant cultivars. In addition, the ratio of the stilbene to quercetin-3-methyl ether was greater in the pod-borer-resistant cultivars. These findings are discussed in relation to the identification of chemical characters that can be used for crop improvement.     

Polyphenols in brown algaeFucus vesiculosus andAscophyllum nodosum: Chemical defenses against the marine herbivorous snail,Littorina littorea

Polyphenols from two brown algae,Fucus vesiculosus (L.) andAscophyllum nodosum (L.) Le Jolis, inhibited feeding by the herbivorous snail,Littorina littorea. The active compounds were characterized as phloroglucinol polymers with a wide molecular weight range (mol wt <30,000 to >300,000) by spectroscopic, Ultrafiltration, thin-layer chromatographic, and chemical degradation data. As little as 1% (dry wt) polyphenol in food reduced feeding by more than 50%, and polyphenolic extracts inhibited feeding entirely when present in concentrations of 2–5% (dry wt). Commercially available phloroglucinol dihydrate and gallotannin, which are known herbivore feeding deterrents in terrestrial plants, inhibitedL. littorea feeding when added to food media in concentrations similar to those above. We conclude that polyphenols inF. vesiculosus andA. nodosum are functionally similar to terrestrial plant polyphenols (tannins) in providing chemical defenses against herbivores. This research is the first demonstration that chemical compounds defend these two dominant, perennial marine algae from the major herbivore found in their community.     

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.     

Tongue-flicking and biting in response to chemical food stimuli by an iguanid lizard (Dipsosaurus dorsalis) having sealed vomeronasal ducts: Vomerolfaction may mediate these behavioral responses

In the iguanid lizardDipsosaurus dorsalis, chemical food stimuli were discriminated from other odorants by vomerolfaction. This was demonstrated in a 2 × 3 experiment in which groups of lizards with sealed vomeronasal ducts or sham-sealed vomeronasal ducts responded to carrot chemical stimuli, cologne, and distilled water presented on cotton-tipped applicators. Abilities to detect and discriminate food chemicals were abolished in lizards having sealed vomeronasal ducts. For tongue-flick attack score and number of lizards biting, the sham-sealed group responded more strongly to carrot stimuli than to the control stimuli, but the group having sealed ducts did not. Lizards having sham-sealed ducts responded more strongly to carrot stimuli than did lizards having sealed ducts; responses by the two groups of lizards to control stimuli did not differ. Tongue-flicking occurred when the vomeronasal system detected a chemical stimulus from either carrot or cologne. Biting occurred only when the vomeronasal organ detected food stimuli (from carrot). Most duct-sealed lizards opened their mouths, some repeatedly. Mouth-opening thus occurs when the vomeronasal organ does not detect chemicals. It may be an attempt to stimulate or prime the vomeronasal organ or to dislodge the sealant.     

Using wood extracts to determine the feeding preferences of the western drywood termite,Incisitermes minor (Hagen)

Nymphs of the western drywood termite,Incisitermes minor (Hagen), were tested for their feeding preferences on wood and extracts of 11 tree species. The amount of wood consumed was inversely proportional to its specific gravity, but methanol extracts of least preferred woods were also least preferred when termites were confined to paper treated with extracts. In choice tests, only paper treated with extract of wood from which the colony developed and untreated and methanol-treated controls were significantly fed upon. Ponderosa pine extract applied to Douglas fir and sugar pine significantly decreased the amount of wood consumed. Resistance to termite feeding appeared to depend on the presence of repellent chemicals in the wood.     

Effects of secondary metabolites from marine algae on feeding by the sea urchin,Lytechinus variegatus

A bioassay was developed to test the hypothesis that secondary metabolites from marine algae affect feeding by sea urchins. During experiments measuring chemoreception and gustation, feeding by the regular sea urchin,Lytechinus variegatus (Lamarck), was inhibited by extracts from the green marine alga,Caulerpa prolifera (Forsskal) Lamouroux andCymopolia barbata (Linneaus) Lamouroux. Cymopol, a monoterpene-bromohydroquinone component ofC. barbata, was partially responsible for the inhibited feeding observed in tests of theCymopolia crude extract. Caulerpenyne, an oxygenated sesquiterpene fromC. prolifera, was responsible for all of the urchin feeding inhibition observed in tests of theC. prolifera crude extract. Feeding was not affected by: (1) extracts from several otherCaulerpa species includingC. mexicana (Sonder) J. Agardh,C. ashmaedii Harvey,C. racemosa v.macrophysa (Kutzing) Taylor, andC. racemosa v.laetevirens (Montagne) Weber-van Bosse; (2) caulerpin, an indole-containing pigment isolated from all of theCaulerpa species exceptC. mexicana; and (3) an extract from the red marine alga,Gracilaria foliifera v.angustissima (Harvey) Taylor, which has no known secondary metabolites. Feeding inhibition was independent of the test diameter which correlated with the reproductive state of the urchins. Feeding inhibition was also independent of the starvation periods between experiments, and the temperature and salinity in ranges tolerated byL. variegatus obtained from the Florida Gulf Coast. The data strongly suggest that at least one alga,Caulerpa prolifera, is chemically defended against a dominant omnivore in its community.     

Different food sources affect the gustatory response of Anaphes iole,an egg parasitoid of Lygus Spp

The gustatory response of female Anaphes iole wasps to naturally occurring carbohydrates, a commercial food source, and host (Lygus lineolaris) frass was determined. Wasps responded to all 14 of the sugars at the highest concentration tested (2 M). At this concentration, sucrose, glucose, maltose, melezitose, fructose, and erlose all elicited <90% acceptance. The lowest concentration that evoked a response (=acceptance threshold) for these sugars was >1/256 M, with the exception of glucose, which was 1/16 M. Raffinose, trehalose, mannose, galactose, melibiose, rhamnose, stachyose, and lactose led to >50% gustatory response by the wasps at 2 M, and were categorized as moderately stimulatory sugars. The acceptance threshold for these sugars was <1/4 M, with the exception of raffinose, which was 1/256 M. In trials with moderately stimulatory sugars combined with either sucrose or maltose, only the rhamnose+maltose mixture significantly inhibited the gustatory response of A. iole. Food and water deprived parasitoids readily accepted the moderately stimulatory sugars. Eliminade^TM, a commercial food supplement, was readily accepted (92%) by A. iole. Conversely, the wasps did not feed on host frass. Chemical analysis of L. lineolaris frass demonstrated the presence of glucose, sucrose, fructose, trehalulose, and melezitose, apparently at concentrations below those perceived by A. iole. The latter two compounds were previously known only from homopteran honeydew (trehalulose and melezitose) and bacteria (trehalulose). With respect to gustatory response to nectar and honeydew sugars, A. iole differs markedly from other hymenopterans that have been studied in that this parasitoid accepted all the naturally occurring sugars with which it was tested. Moreover, this parasitoid had lower acceptance thresholds than other hymenopterans for many of the sugars. This broad and sensitive range of gustatory perception might be helpful in the development of a food source for the wasp that is not exploited by the host.     

Taste Sensitivity of Insect Herbivores to Deterrents is Greater in Specialists Than in Generalists: A Behavioral Test of the Hypothesis with Two Closely Related Caterpillars

Sensitivity of caterpillars of Heliothis virescens, a generalist, and H. subflexa, a specialist, to eight different plant secondary compounds was examined behaviorally. The compounds were nicotine hydrogen tartrate, hordenine, caffeine, sinigrin, linamarin, arbutin, chlorogenic acid, and salicin. All compounds deterred feeding, at least at the higher concentrations, but the generalist was less affected than the specialist. Thus the hypothesis that specialists have greater sensitivity to deterrents than generalists was supported. In most cases deterrence occurred on first encounter, indicating that the response was sensory; in some cases short-term postingestive effects also appeared to play a role. The larger quantities of deterrent-containing food ingested by H. virescens sometimes resulted in measurable postingestive effects during the second control test. This did not occur in H. subflexa, which more commonly rejected the deterrent-containing food on first contact. The contrast between the species is discussed in relation to tradeoffs involved in different diet breadths.