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The tell-tale grasshopper

June 19, 2007 By Heidi Ledford This article courtesy of Nature News.

Can forensic science rely on the evidence of bugs?

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Lynn Kimsey was one of 137 witnesses called to testify in the murder trial of Vincent Brothers, who stood accused of killing his wife, mother-in-law and children in Bakersfield, California. Brothers said that he was in Ohio at the time of the murders; he had rented a car there, and driven it no further west than St Louis, Missouri.

When Kimsey took the stand, she revealed the identity of four key informants that would unpick this alibi: a grasshopper, a paper wasp and two 'true bugs'. All four told her that Brothers' rental car had been well beyond St Louis.

Kimsey, who was branded "the bug lady" by media covering the trial, is an entomologist at the University of California, Davis. She had been enlisted by the US Federal Bureau of Investigation to identify the insect carcasses plastered on the rental car's radiator and air filters, to see whether these could place where the vehicle had been driven. The four bugs she presented to the jury are, she said, only found west of Missouri. After hearing this and much more evidence, the jury found Brothers guilty on 29 May.

Law enforcement has been conferring with insect informants for centuries, typically focusing on the flies that colonize dead bodies. If the conditions are right, such bugs can reveal how long a body has been dead, if the victim was poisoned, or whether the body had been moved. Bugs can also help to track movement — a squashed bug plucked from someone's shoe treads or a revealing insect bite from a geographically limited pest can all be clues of where a suspect has been.

Forensic scientists perform similar analyses using pollen grains, which have shapes and compositions that are unique to specific plant taxa — and genetics sometimes specific to particular plants. Diatoms can point to aquatic crime scenes: a combination of diatom species in the right proportions can serve as a fingerprint for a specific body of water.

But, like most evidence, such forensic clues can be uncertain. And Kimsey says she worries that the skills entomologists rely on to quickly identify key bugs may be disappearing — potentially making such work even more uncertain.

Wrong place, wrong time

For Brothers' trial, defence attorneys brought in four witnesses to argue against Kimsey's bug analysis. One point of contention was whether the maps showing the distribution of these insects were accurate. Kimsey admits that these maps had been simplified for the understanding of the court, reducing fuzzy-edged bug habitats to distinct areas with hard boundaries.

Arwin Provonsha, a forensic entomologist from Purdue University in Indiana who questioned these maps on the stand, notes that some published evidence suggests that these insects can be found beyond the boundaries that Kimsey presented. But, he says, he still thinks that the insect evidence shows that the car was driven further west than St Louis.

Other experts highlight that bug distributions can change, which could make it hard to interpret some evidence. "We have classic publications about bug distribution from maybe 50 years ago that are quite good," says Jeffrey Wells, a forensic entomologist at West Virginia University in Morgantown, who was not involved with this case. "But some things have changed. Some distributional records are out of date."

Another difficulty when weighing entomological evidence is that individual bugs may wander outside of the distinct areas that make up their official habitat. Insects can even hitch cross-country rides in trains and trucks, taking them to areas of the country where they are not normally found.

Mistaken identity

Misidentification of insects can also lead forensic scientists astray, says Kimsey. At a recent North American Forensic Entomology meeting she assembled six blowfly specimens and asked attendees to identify them. "No one identified them all correctly," says Kimsey. "We were very discouraged. If you can't identify the blowfly correctly, then your estimation of the postmortem interval could be wrong."

When Provonsha looked at the insects in the Brothers case, he identified all but one the same as Kimsey.

Fewer young entomologists are interested in using classical morphology to identify species, Kimsey says, preferring modern molecular techniques based on DNA sequencing. But genetic sequencing will be of limited use for cases such as hers, she says. Most insects don't appear in genetic databases because their genes have not yet been sequenced.

Meanwhile, she says, the old-fashioned approach has its advantages over slower molecular techniques. "It's a lot more cost effective if you can say 'what is this?' and 30 seconds later someone can tell you what it is," says Kimsey. "It's a level of expertise that's going to be sorely missed if we lose it."


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