Department of Entomology, Iowa State University, Ames, Iowa 50011, USA.
Insect antennae offer a sensitive way to detect the presence of odor plumes and to
monitor their fine structure, both in the laboratory and field, as first demonstrated by Baker
and Haynes (Physiol. Entomol. 14:1-12, 1989). Interest in using antennae to
quantify ambient concentrations of odor in the field has grown, as efforts to disrupt mating
of moths with sex pehromones have met with increasing success in recent years
(Sauer et al., Chem. Senses 17:545-553, 1992; Suckling et al., J. Econ.
Entomol. 87:1477-1487, 1994; Suckling and Angerelli, Environ. Entomol. 25:101-108,
1996). However, the usefulness and reliability of electroantennograms (EAGs) measured
from such antennal preparations are limited due to their inability to discriminate both
quality and quantity. A single EAG reading from a single antennal detector cannot
discriminate a small amount of a compound to which the antenna is optimally tuned from a
large amount of a compound to which it is sub-optimally tuned. Moreover, not only
pheromone components, but plant volatiles as well can depolarize or adapt (or both) the
antennal biosensor that is supposedly tuned to the pheromone, and prevent accurate
quantitative EAG readings to made. The EAG at present is useful in the field only for
monitoring relative concentrations of a known pheromone compound dispensed for mating
disruption or measuring concentration fluctuations within the fine structure of a plume of
known composition. It has also been used to successfully measure plume fluctuations from
a known source of host odor in the field from 60 meters away (Voskamp et al., Physiol.
Entomol. 23:176-183, 1998).
Recent interest by the U.S. Defense Department under the Controlled Biological Systems
Program of the Defense Advanced Research Projects Agency (DARPA) in detecting and
locating sources of anthropogenic compounds such as those emitted by unexploded
landmines, has spurred efforts by our laboratory to increase the sensitivity and
discrimination ability of insect antennal sensors. We have attempted to begin to overcome
the fundamental limitations of single antennal biosensors by deploying arrays of
differentially tuned insect antennae. Our initial results show that these arrays have the
ability to at least crudely discriminate plumes or puffs of a single compound representing a
single class of odor such as pheromone or host odor. These discriminatory assessments can
be made in real time from split-second recordings of single puffs or plumes.