Smithsonian Science » entomology

Honeybees fascinate visitors at the National Zoological Park

John Barrat — Wed, 07 Jul 2010 11:51:01 +0000

Meet the Scientist: Dr. JoGayle Howard of the Smithsonian’s National Zoological Park
Japanese giant salamanders given to the National Zoo by Asa Zoological Park in Hiroshima

Slide Show: Smithsonian’s National Museum of Natural History is 100!

John Barrat — Tue, 22 Jun 2010 17:24:14 +0000

Since its doors first opened in 1910, the National Museum of Natural History has inspired curiosity and learning about the natural world and our place in it. Building upon the strong foundation of our extensive collections, the staff of the museum have been at the forefront of essential scientific exploration and research, and groundbreaking public exhibition and education. This slideshow and the website (www.mnh.si.edu/onehundredyears/) is a living documentary of the Museum’s 100-year history.

Tiny, new brains prove just as adept as large, mature brains among tropical orb-web spiders

John Barrat — Wed, 02 Jun 2010 19:18:24 +0000

When it comes to brains, is bigger better? For instance, can the tiny brain of a newly hatched spiderling handle problems as adeptly as the brain of a larger adult spider? One theory, known as the size limitation hypothesis, predicts that the miniscule brains of tiny creatures contain fewer neurons and thus have less capacity, making these creatures more prone to mistakes.

Photo right: An adult Nephila clavipes on its web with an insect it has captured.

To test this theory, Thomas Hesselberg of the Smithsonian Tropical Research Institute in Panama, recently examined and compared the designs of webs woven by newly hatched, mid-size and adult orb-web spiders of the species Nephila clavipes and Eustala illicita. (Nephila grow explosively and an adult can weigh up to 500 times more than it did when newly hatched.) He collected a number of spiders from each age group, induced them to weave webs on square frames in a laboratory and then took careful measurements of each web. He also conducted observations of the webs of both species in the wild. A paper on Hesselberg’s work was published recently in the scientific journal “Ethology.”

Photo left: An N. clavipes resting at the hub of its laboratory web.

Orb-web spiders have a fixed reserve of sticky capture spiral silk inside their bodies prior to web building. This reserve is thought to be entirely used up as the web is completed. “As orb spiders build the capture spiral from the outer periphery towards the hub [or center of the web], they need to match web size to silk reserves,” Hesselberg writes. Younger spiders that haven’t mastered this behavior, he reasoned, should have a larger area free of silk at their web’s center hub. Or, to cover for a miscalculation, a young spider may increase the distance between the spirals of its capture silk spun out nearer to the web’s hub.

In his observations of the different webs, he found no evidence that adult Nephila or Eustala spiders have any more brain power or build webs any more effectively than newly-hatched spiderlings. “Neither species showed clear signs of being behaviorally limited or more prone to committing errors as spiderlings than were older juveniles or adults,” Hesselberg concluded.

Photo right: The web of an E. illicita spider in the wild. (Photos by Thomas Hesselberg).

One miscalculation may lie, Hesselberg adds, in the human assumption that “the orb web is the result of a demanding computational behavioral process. Theoretical models suggest that the construction of the orb web might be achieved by following a few simple rules of thumb and thus not pose any significant computational challenge for the spider.”

–John Barrat

Transmitters unveil long-distance movements of orchid bees

John Barrat — Thu, 27 May 2010 17:42:51 +0000

In their daily search for food, blue-green orchid bees zip through increasingly scarce patches of tropical forest pollinating rare flowers. Now, for the first time ever, researchers at the Smithsonian Tropical Research Institute are able to track the routes of these creatures by gluing tiny transmitters to the backs of individual bees. The data they are collecting is yielding new insight into the role bees play in tropical forest ecosystems.

“When people disturb and destroy tropical forest they disrupt pollination systems,” says entomologist David Roubik, senior staff scientist at the Tropical Research Institute. “Now we can track orchid bees to get at the distances and spatial patterns involved in pollination—vital details which have completely eluded us in the past.”

The team trapped 17 iridescent blue-green orchid bees called Exaerete frontalis –a species common in the rainforest. “These bees easily carry a 300-milligram radio transmitter glued onto their backs,” says Martin Wikelski, director of the Max Planck Institute of Ornithology and a research associate at the Smithsonian. “By following the radio signals with a hand-held antenna, we have discovered that male orchid bees spend most of their time in small core areas, but will take off and visit areas farther away.

One male even crossed over the shipping lanes in the Panama Canal, flew 5 kilometres, and returned to Barro Colorado Island a few days later. Such long distance flights, the researchers say, support the claim that bees are major agents of gene flow, connecting widely-dsipersed orchids or other plants which they alone pollinate, over fragmented landscapes and for an extended time. This study proves that “bees are key evolutionary players in allowing orchids and other tropical plants to evolve into diverse taxa that are each spatially rare and thus require long-distance pollination,” the researchers write.

In the past, researchers have struggled to determine the distances that bees travel by following individuals marked with paint, or using radar, which doesn’t work well when trees are in the way. “Carrying a transmitter may reduce the distance that the bees travel. But even if the flight distances we record are the minimum distances that these orchid bees can fly, they are impressive, long-distance movements,” said Roland Kays, curator of mammals at the New York State Museum and a STRI research associate. “These data help to explain how the orchids these bees pollinate can be so rare.”

The Smithsonian Tropical Research Institute, the U.S. Environmental Protection Agency, the New York State Museum and the National Geographic Society all provided support for this study. Its co-authors are affiliated with the University of Arizona, Tucson, Cornell University, EcolSciences, Inc. and the New York State Museum.

Thepytus carmen, a newly described species of butterfly from Brazil

John Barrat — Tue, 13 Apr 2010 12:49:41 +0000

Thepytus carmen, a newly described species of butterfly from Brazil, was recently named in memory of Carmen Lúcia Buck in recognition of the gracious support of science that she and her husband Peter have provided to the Smithsonian Institution’s National Museum of Natural History. Described by Smithsonian entomologist Robert K. Robbins and Marcelo Duarte, Museum of Zoology, University of São Paulo. (Illustration by Vichai Malikul)

For sweat bees, being social builds a more developed brain

John Barrat — Thu, 25 Mar 2010 12:52:41 +0000

Females of the tropical sweat bee Megalopta genalisa exhibit a very primitive form of social behavior. Either a bee lives as a solitary queen, going out from her nest to forage for her own food, or she can be a social queen–a stay-at-home mom. In that case, one of her daughters goes out to forage for her. The daughter’s ovaries don’t develop, and she never leaves her mother to start her own colony.

Recently, scientists at the Smithsonian Tropical Research Institute in Panama discovered that the brain region responsible for learning and memory is larger in the social queens than in the solitary queens of this species. Their study is the first comparison of the brain sizes of social and non-social individuals of the same species.

Image right: A tropical sweat bee, Megalopta genalisa, in her nest.

“The idea is that to maintain power and control in groups you need more information, so the bigger the group, the bigger individuals’ brains need to be.” says William Wcislo, Smithsonian staff scientist.

“It was surprising to us that even though the social queens don’t have bigger brains overall, the fact that the area associated with learning and memory–the mushroom body–was more developed in the social queens than in the solitary bees suggesting that social interactions are cognitively challenging, as predicted by the social brain hypothesis,” said Adam Smith, postdoctoral fellow at STRI. “It’s interesting to see that a characteristic like brain development changes so immediately, even with this simple mother-daughter division of labor.”

This study was done in the Smithsonian Tropical Research Institute’s new insect neurobiology laboratory, built to take advantage of diverse tropical insect groups with a variety of brain sizes to understand how brain size and behavior are related

These results were published recently online in the journal Proceedings of the Royal Society B.

New Acquisition: Eighty-thousand bark beetles enter National Museum of Natural History collections

John Barrat — Tue, 23 Mar 2010 14:12:21 +0000

The Smithsonian’s National Museum of Natural History recently acquired an 80,000-specimen collection of bark beetles donated by the late Stephen L. Wood, Brigham Young University professor of Entomology, and former reigning expert on the bark beetles.

The Stephen L. Wood collection brings the collection of bark beetles held in the Natural History Museum’s Department of Entomology to an impressive 180,000 specimens, making it one of the most extensive collections in world.

Image right: Bark beetle galleries or tunnels excavated in wood beneath the bark of an American elm. (Photo by Deborah Bell)

“The Smithsonian’s collection is arguably the most important bark beetle collection in the world,” says David Furth, entomology collections manager at the Natural History Museum. “We are proud to have the S. L. Wood beetles join our collection.”

Bark beetles, named for the fact that they live and reproduce in the inner bark of trees, are common pests of conifers, such as pine. Different species of bark beetles attack different species of trees, causing damage and spreading disease. Most bark beetle species are dark red, brown, or black, and about the size of a grain of rice. When viewed under magnification, their antennae are visibly elbowed with the outer segments enlarged and club-like. The antennae contain receptors that may detect tree resin odors, thus functioning as the beetle’s nose and enabling their ravenous appetites.

Image left: Entomologists Natalia Vandenburg and Dave Furth at the National Museum of Natural History with dozens of wooden drawers containing bark beetle specimens donated by Stephen L. Wood.

With more than 2,000 known species—some 200 are found in California alone—bark beetles are both ecologically and economically significant. Outbreak species of these tree-damaging beetles kill large areas of forests in western USA and may spread tree diseases like Dutch elm disease.

Dave Furth and other Entomology Department staff set out on a cross-country expedition, rental truck in tow, to bring Wood’s bark-beetle collection home to the Smithsonian. Consisting of some 181-specimen drawers, the collection was carefully transported from Provo, Utah to the Smithsonian in 2009.

Since that time, the Smithsonian’s entomology staff have brought the Wood’s bark beetles into the museum’s collection area and transferred and archived his massive library and correspondence records into the museum’s research library.

“We are pleased the S. L. Wood acquisition has joined the Smithsonian’s collection, and will contribute to the future study of the bark beetle,” Furth says. –Jessica Porter

Females shut down male-male sperm competition in leafcutter ants

John Barrat — Thu, 18 Mar 2010 18:25:30 +0000

Leafcutter ant queens can live for 20 years, fertilizing millions of eggs with sperm stored after a single day of sexual activity.

Danish researchers who have studied ants at the Smithsonian Tropical Research Institute in Panama since 1992 recently discovered that in both ant and bee species in which queens have multiple mates, a male’s seminal fluid favors the survival of its own sperm over the other males’ sperm. However, once sperm has been stored, leafcutter ant queens neutralize male-male sperm competition with glandular secretions in their sperm-storage organ.

“Two things appear to be going on here,” explains Jacobus Boomsma, professor at the University of Copenhagen and Research Associate at STRI. “Right after mating there is competition between sperm from different males. Sperm is expendable. Later, sperm becomes very precious to the female who will continue to use it for many years to fertilize her own eggs, producing the millions of workers it takes to maintain her colony.”

Image right: Leafcutter ant queen

With post-doctoral researchers Susanne den Boer in Copenhagen and Boris Baer at the University of Western Australia, professor Boomsma studied sperm competition in sister species of ants and bees that mate singly—each queen with just one male—or multiply—with several males.

Their results, published this week in the prestigious journal, Science, show that the ability of a male’s seminal fluid to harm the sperm of other males only occurs in species that mate multiply, and that their own seminal fluid does not protect sperm against these antagonistic effects.

Image left: A leafcutter ant carries a leaf fragment back to its nest. (USDA photo)

“Females belonging to many species—from vertebrates to insects– have multiple male partners. Seminal products evolve rapidly, probably in response to the intense male-male competition that continues even after courtship and mating have taken place,” said William Eberhard, Smithsonian staff scientist. “This study continues the STRI tradition of looking at post-copulatory selection in a very biodiverse range of organisms, following in the footsteps of people like Bob Silberglied, who asked why butterflies and moths have two kinds of sperm in the 1970’s.”

Similar sperm competition systems appear to have evolved independently in ants and in bees. Researchers now aim to discover how genes that control sperm recognition in bees and ants may differ, thus continuing to elucidate the details of a process key to reproduction and evolution.

A grant from the Danish National Research Foundation and an Australian Research Council Fellowship supported this work. Permits for ant collection and export were issued by Panama’s Autoridad Nacional de Ambiente (ANAM).

The Smithsonian Tropical Research Institute, headquartered in Panama City, Panama is a unit of the Smithsonian Institution. The institute furthers the understanding of tropical nature and its importance to human welfare, trains students to conduct research in the tropics and promotes conservation by increasing public awareness of beauty and importance of tropical ecosystems. www.stri.org --Beth King

Leafcutter ants—first in agiculture and antibiotics

John Barrat — Mon, 01 Mar 2010 13:37:48 +0000

Females shut down male-male sperm competition in leafcutter ants

Laboratory tests reveal precise way to measure vertical lift in bumblebees and other small insects and birds

John Barrat — Thu, 28 Jan 2010 20:01:27 +0000

Birds do it. Bees do it. And in a laboratory in northern California, scientists using bumblebees recently figured out the best way to measure it. For biologists who study flight, knowing the maximum vertical lifting strength of a species can lead to a better understanding of how an animal escapes predators, pursues or flees potential mates, and transports its food. Yet calculating the vertical lifting capacity of a small bird or insect is no simple matter.

Photo right: A bumbleebee lifts a string of weights in an experiment in the Animal Flight Laboratory at the University of California. The grid behind the bee enables researchers to measure exactly how high the bee ascends from the ground. (Photo courtesy Robert Buchwald)

Recently, scientists Robert Buchwald and Robert Dudley of the Animal Flight Laboratory at the University of California, Berkeley (Dudley is also a Research Associate at the Smithsonian Tropical Research Institute in Panama), tested the accuracy of two different methods of calculating an insect’s load lifting ability on bumblebees (Bombus impatiens). They found that bumblebees can lift (in addition to their own bodies), on average, 53 percent of their body weight. Yet one of the methods they tested underestimated the bees’ strength by 18 percent.

Scientists began using the cumulative method of measuring lift in 1987. It involves attaching one tiny weight to the abdomen of an insect with a string. Each time the insect flies and raises the weight into the air, additional weight is added until the insect can no longer raise it from the ground. The weight of the final load lifted and the weight of the maximum load not lifted are averaged together and added to the body weight of the insect to determine its maximum vertical lift.

This slow-motion video shows a bumblebee lifting a string of weights in the Animal Flight Laboratory at the University of California, Berkeley. The left side of the screen shows the testing chamber from above, looking down upon the experiment. The right side is a lateral view of the chamber as seen in a mirror set at a 45-degree angle. The mirror lets the scientists see how high the bee is flying. Slowing down the audio recording of this experiment enables the researchers to calculate the wingbeat frequency of a bee during periods of maximum vertical lift. (Video courtesy Robert Buchwald)

A second method established in 2004, the asymptotic method, involves attaching a long string of tiny, evenly spaced weights to a bee’s petiole or midsection. As the bee rises it pulls the string of beads up with it until the chain becomes too heavy to lift further, at which point the bee hovers. The weight of the beads lifted from the ground, the weight of the string and the bee’s body weight are added together to determine the bee’s vertical lifting strength. Data from this method, on average, indicated bumblebees had an 18 percent higher vertical lifting ability than data gathered using the cumulative method.

Why is knowing the vertical lifting strength of a bumblebee important to biologists?

“Escape and chasing performance for flying animals can profoundly influence survival and, in some cases, mating success,” Dudley says. “Identification of the physiological and biomechanical limits to flight performance can indicate more general features of the behavior, ecology, and evolution of flying animals.”

Orchid bees tested in Panama lifted about 100 percent of their body weight using the same [asymptotic] method, Dudley explains, so bumblebees are on the low side of vertical lifting strength among bees. “They aren’t really high-performance fliers, rather better at transporting nectar and pollen loads—typically less than 50 percent of their body weight—back to the nest at regular intervals.”

A paper by Buchwald and Dudley describing these results was published in a recent issue of the Journal of Experimental Biology. —John Barrat