Butterflies tastes food with their feet

Chemosensory Basis of Host Recognition in Butterflies—Multi-component System of Oviposition Stimulants and Deterrents

  1. Ritsuo Nishida

+Author Affiliations

  1. Laboratory of Chemical Ecology, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan
  1. Correspondence to be sent to: Ritsuo Nishida, e-mail: ritz@kais.kyoto-u.ac.jp


Larvae of most butterfly species feed on a limited number of host species belonging to a single plant family. The choice of host plants is determined both at the egg-laying and larval-feeding stages (Schoonhoven et al., 1998). The choice of oviposition site by an adult female is crucial to the survival of their offspring, and thus the mother butterflies lay their eggs with great precision on the host plants. Although host recognition by phytophagous insects involves multiple sensory modalities, including visual, olfactory and gustatory cues, contact chemical stimuli from host and non-host plants play an important role at the final step of egg-laying behavior. The contact chemoreceptors responsible for detection of both host and non-host allelochemicals at oviposition are located on the foretarsi of the female butterfly (Roessingh et al., 1991; Nishida, 1995).

Oviposition stimulants

In recent years, suites of specific host-finding cues have been characterized for several families of butterfly species including Papilionidae, Pieridae and Nymphalidae (Honda and Nishida, 1999). Oviposition stimulants of the citrus swallowtail butterfly, Papilio xuthus(Papilionidae) were found to consist of multiple components which included flavonoids (1 and 2), a nucleoside (adenosine), alkaloids (3 and4), a cyclitol (5) and an amino acid derivative (6) (Nishida et al., 1987;Nishida, 1995) (Figure 1). None of the individual components elicited oviposition responses alone. The specific activity was provoked only when these components were applied as a mixture. Synergistic effects among stimulant components can be seen in several papilionid species (Honda and Nishida, 1999). The butterflies seem to perceive a subset of ingredients simultaneously as a ‘blend taste’ with the toothbrush-like chemosensilla densely distributed on the tarsal segments. However, its sensory mechanism—how the butterfly integrates the complex signal arising from the many components—remains unknown. We do not know whether the stimulants are perceived simultaneously as a chemical blend on each sensillum or separately with each specific chemoreceptor cell. A multi-component system of oviposition stimulants seems to provide a high specificity in host recognition. On the other hand, it also provides some flexibility in host choices, allowing them to lay eggs not only onCitrus but also on rutaceous hosts belonging to other genera (e.g.Poncirus and Xanthoxylum) that partially share some common subsets of ingredients (unpublished data). Related swallowtail species such as P. protenor and P. polyxenes (Feeny et al., 1988; Honda, 1990) also use the same classes of chemicals as the host-finding cues (e.g. flavonoid glycosides, phenethylamines and quinic acid derivatives). Such underlying chemical similarity may have provided a route to colonization on novel hosts among the papilionid butterflies (Feeny et al., 1988; Nishida, 1995;Honda and Nishida, 1999).

Figure 1 Multi-component systems of oviposition stimulants contained in a host plant, Citrus unshiu(left), and oviposition deterrents in a non-host rutaceous plant, Orixa japonica (right), for a Rutaceae-feeding swallowtail butterfly, Papilio xuthus. 1, hesperidin; 2, rutin; 3, bufotenine; 4, synephrine; 5,chiro-inositol; 6, stachydrine; 7, quercetin 3-O-(2G-β-D-xylopyranosylrutinoside); 8, 5-{[2-O-(β-D-apiofuranosyl)- β –D-glucopyranosyl]oxy}-2-hydroxybenzoic acid; and 9, disyringoyl aldaric acid ester.

Oviposition deterrents

Although P. xuthus feed on various rutaceous species, both the adult females and the larvae reject a rutaceous plant, Orixa japonica. A flavonoid triglycoside (7) was identified as one of the oviposition deterrents (Figure 1). Compound 7 is a xylosyl derivative of rutin (2), a positive stimulant for the butterfly (Nishida et al., 1990). This compound may disrupt the oviposition stimulant activity due to its structural resemblance and relatively high concentrations in the leaves, competing for the same receptor cells. Two hydroxybenzoic acid derivatives (8 and 9) were characterized as potent deterrents at both oviposition and larval feeding (Ono et al., 2004). Simultaneous occurrence of these compounds in O. japonica appears to provide an effective chemical barrier against the butterfly. Kairomones (stimulants) and allomones (deterrents) responsible for host recognition stimulate specific receptor cells in the tarsal chemosensilla of butterflies (Roessingh et al., 1991). It remains unclear, however, whether these deterrent compounds block the intrinsic activity of the stimulants or exert their effect by other mechanisms in P. xuthus.

Larval gustatory responses to plant allelochemicals

The chemosensory mechanisms of oviposition and larval feeding must be intrinsically coordinated, for females usually select the plants the larvae accept. However, the nature of such gustatory responsiveness to allellochemicals at both larval and adult stages is not well understood. The fact that both oviposition and larval feeding are elicited (or deterred) by the same subset of chemicals suggests a congruent sensory mechanism between the tarsal chemoreceptors of adults and the gustatory chemoreceptors of larvae (Nishida, 1995; Ono et al., 2004). Electrophysiological responses of the host kairomones and non-host allomones were examined against tarsal and larval mouthpart chemosensilla in P. xuthus. Both larval feeding stimulant (e.g. quinic acid) and deterrent (e.g. gentisic acid glycoside 8) components evoked large numbers of spikes, probably stimulating different receptor cells of medial and lateral styloconic sensilla of the fifth instar larvae (unpublished). A comparison of the chemosensory components used by these butterflies to make food and oviposition choices reveals their evolutionary route to chemosensory adaptation at the insect–plant interface.


Bats and Echolocation

Bats are not blind; in fact they can see almost as well as humans. But to fly around and hunt for insects in the dark, they use a remarkable high frequency system called echolocation.

Echolocation works in a similar way to sonar. Bats make calls as they fly and listen to the returning echoes to build up a sonic map of their surroundings. The bat can tell how far away something is by how long it takes the sounds to return to them.

These calls are usually pitched at a frequency too high for adult humans to hear naturally. Human hearing ranges from approximately 20Hz (cycles per second) to 15 to 20 kHz (1000Hz) depending on age. In comparison, some bats can hear sounds up to 110 kHz in frequency. By emitting a series of often quite loud ultrasounds that either sweep from a high to low frequency or vary around a frequency, bats can distinguish objects and their insect prey and therefore avoid the object or catch the insect.

Individual bat species echolocate within specific frequency ranges that suit their environment and prey types. This means that we can identify many bats simply by listening to their calls with bat detectors.


Dolphins natural Sonar, called Echolocation

The Dolphin Defender

by Irene Tejaratchi

Dolphins use sound to detect the size, shape, and speed of objects hundreds of yards away. Fascinating and complex, the dolphin’s natural sonar, called echolocation, is so precise it can determine the difference between a golf ball and a ping-pong ball based solely on density. Although humans have researched these intelligent marine mammals for decades, much of their acoustical world remains a mystery.

One of the keys to dolphin echolocation is water’s superb conduction of sound. Sound waves travel 4.5 times faster in water than they do in the air. Dolphins use this to their advantage, in ways that would make a superhero envious. Using nasal sacs in their heads, dolphins send out rapid clicks that pass through their bulbous forehead, or “melon.” The sound is focused, then beamed out in front of the dolphin. The sound wave speeds through the water, bounces off the object under investigation, and is reflected back to the dolphin. Fat-filled cavities in the dolphin’s lower jaw receive this information and auditory nerves conduct it to the middle ear and brain, where an acoustic picture is created.

Scientists say that dolphins may also use clicking to communicate with one another. Although dolphins do not possess vocal cords, they still “speak” using sounds such as whistles, squeaks, and trills. A mother dolphin may whistle to her newborn for days, apparently to imprint a signature whistle upon her baby that will enable it to recognize her. It is believed that dolphins use whistles to identify one another and possibly for other functions, such as communicating strategic alerts while hunting in a group, but scientists have yet to crack the code. Many doubt, however, that dolphins have a formal language akin to that of humans.

In the 1950s, researcher John C. Lilly helped pioneer the systematic study of dolphin vocalization. A strong advocate of interspecies communication, Lilly wrote several books about dolphins, inspired the film Day of the Dolphin (1973), and was a supporter of the Marine Mammal Protection Act of 1972. Another pioneer of dolphin research, Kenneth S. Norris, first obtained evidence of dolphin echolocation by blindfolding a bottlenose to test its ability to locate an object underwater.

Since the 1960s, American military scientists have studied dolphins, and have trained them to perform such tasks as attaching explosives and eavesdropping devices to enemy ships or submarines. In the mid-1980s, the U.S. Navy began training dolphins to search for mines using their echolocation. In 2003, dolphins were deployed for the first time in a real war situation to probe the seafloor for mines near the Iraqi port of Umm Qasr. For decades, animal activists have opposed the use of dolphins for entertainment or military activities, citing questionable training methods and the stress-related illnesses, such as ulcers, that the animals can manifest in such situations.

Dolphin advocates also object to the navy’s use of manmade sonar, which is used to scan and investigate the ocean depths, claiming that it is harming dolphins and other marine mammals. They point to incidents such as the beaching of four different whale species off the coast of the Bahamas in March 2000, following navy sonar exercises in the area. Marine mammals strand themselves for a variety of reasons, but investigations confirmed that navy sonar caused the Bahamas stranding. Researchers are not exactly sure how manmade sonar affects marine mammals. Some believe the intense sounds may scare or disorient them and cause them to rapidly flee to the water’s surface, resulting in a sort of decompression sickness that damages sensory organs and causes internal bleeding.

If technological sonar can be implicated in the death of dolphins, it would be a tragic irony, considering that the sonar is based in part upon nature and dolphins’ superior echolocation capability. Efforts to replicate dolphin echolocation continue to fall short, as humans have yet to achieve the complexity and precision that 50 million years of evolution has bestowed upon dolphins. Perhaps if scientists could understand dolphin-speak they’d have more luck, but for now the true nature of dolphin communication remains mysterious.


Homing Pigeons & Navigation

Pigeons Navigate Using Brain Cells That Gauge Earth’s Magnetic Fields, Scientists Say

Posted: 04/27/2012 4:25 pm EDT Updated: 04/27/2012 4:25 pm EDT

Release a pigeon thousands of kilometers from home, and it’ll fly across seas, forests, or deserts to return. It’s not sight or smell that allows this amazing navigation; migratory birds can sense the magnetic fields that vary across Earth’s surface. Now, scientists have identified a collection of brain cells that let pigeons interpret these magnetic fields. They hope the findings will help reveal how the birds sense the magnetism in the first place, and shed light on this mysterious sixth sense.

“This is very exciting,” says biologist John Phillips of Virginia Polytechnic Institute and State University in Blacksburg, who was not involved in the new study. “There have been very few clear-cut findings in the past.”

Debate on how birds sense geomagnetic fields has largely revolved around magnetite particles found in various parts of their heads. Scientists have hypothesized that magnetite, a form of iron that’s the most magnetic of naturally occurring minerals, is the key ingredient in specialized cells that react to changes in magnetism. And the presence of magnetite in birds’ beaks had led some researchers to believe that this structure was key to birds’ homing abilities.

But earlier this month, a team of scientists showed that the iron in birds’ beaks isn’t magnetite—it’s balls of another, less magnetic, form of iron accumulated in white blood cells that are cleaning toxins out of the animals’ bodies.”That whole story just crashed and burned,” says Phillips.

At Baylor College of Medicine (BCM) in Houston, Texas, biologist David Dickman had previously found magnetite in the inner ears of pigeons, offering an alternate hypothesis for where the magnet-sensing cells are located. Last year, he discovered that four areas of the brain that are largely linked to inner ear function each showed a broad change in activity when pigeons were exposed to magnetic stimulation.

In the new study, published online today in Science, Dickman and BCM biologist Le-Qing Wu placed seven homing pigeons (Columba livia) in a dark room in the center of a cube-shaped set of magnetic coils. As the cube was rotated, the intensity of the magnetic field felt by the pigeon in the center varied. The scientists turned it in every direction, testing out the effect of various magnetic fields found on Earth. As they did this, Dickman followed the activity of 329 neurons in one of the areas of the brain he’d previously implicated. Fifty-three of the brain cells showed significant changes in activity as the coils rotated, reacting to field strength and polarity. The properties of the neurons allow them to have a unique activity pattern for every different spot on Earth, the scientists realized. Not only can the neurons allow the pigeons to pinpoint their longitude and latitude, says Dickman, but they can differentiate the Northern Hemisphere from the Southern Hemisphere and tell the pigeons which direction they’re facing.

The data don’t reveal which cells detect the magnetic fields, but, when combined with Dickman’s previous results, they suggest that the inner ear is key. Some scientists still hold that the magnetic sensing cells will be found in the beak, or in birds’ eyes, but working backward from the brain will help sort it out, says Dickman. “We now have a tool to study this with. We can go back and ask what cells and organs are feeding into this circuitry.”

The new findings could apply to other animals as well, says Phillips. Sea turtles, fish, and vertebrates including mice, cattle, and deer have been found to be sensitive to geomagnetic fields. But whether it applies directly to humans is unknown, he says. “There’s no evidence for that now. But there could be some kind of unconscious magnetic sense that helps us sense direction and spatial orientation.”

ScienceNOW, the daily online news service of the journal Science