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INTRODUCTION.
This flea receives its common name of oriental rat from the fact that its favorite hosts
are rats, especially the Norway rat which is thought to be of central Asian origin. This
flea's greatest importance is that it is the principal vector of bubonic plague and murine
typhus from rats to humans. Oriental rat fleas are of worldwide distribution and found
throughout the United States, but most commonly in seaport areas; scarce in northern areas
but found as far north as Washington, Minnesota, and New Hampshire.
RECOGNITION.
Adults about 1/16" (2-2.5 mm) long. Body laterally flattened (side to side);
wingless. Color reddish brown. Head with front rounded, ocular bristle inserted in front
of eye; genal comb lacking. Pronotat comb lacking; mesopleuron (side of mesothorax)
divided by a vertical rodlike thickening; thorax not reduced, dorsum (top) equal to or
larger than 1 st abdominal segment. Abdominal terga (dorsal plates) 2-6 with a single row
of bristles; spermatheca (internal sperm storage organ; towards rear of abdomen)
dark-colored, visible through exoskeleton in alcohol collected specimens. In addition,
antennae short, 3-segmented; ocalli lacking; legs long, coxae large, tarsi 5- segmented;
usually jumping insects; mouthparts piercing-sucking with well-developed palps. Mature
larvae about 1/8-1/4" (3-5.2 mm) long. Larvae whitish, slender, eyeless, and legless.
With a well-developed head. Anal struts/hooks 2, small. With moderately long,
backward-projecting hairs (setae) encircling each segment. Last abdominal segment (10th)
with 3 ventrolateral hairs (setae). Description is same as for dog and cat fleas.
SIMILAR GROUPS.
Human flea (Pulax irritans) with rnesopleuron (side of mesothorax)
not divided by a vertical thickening, and ocular bristle inserted below eye.
Sticktight flea (Echicnophaga gallinacea) and Chigoe flea (Tunga
penetrans) with front of head angular, dorsum (top) of thorax shorter than lst abdominal
segment dorsum; in addition, sticktight flea with a group of spinuies (short spines) on
inner side of hind coxas.
Polygenis gwyni (family Rhopalopsyllidae) with 2 rows of bristles on
typical abdominal segment.
BIOLOGY.
Females lay 4-8 eggs after each blood meal. Eggs are sticky but usually fall off the host
or are deposited in the nest. The minimum temperature for egg development is
54degreesF/12degreesC. Larvae usually feed on organic matter including droppings from
adult fleas but cannot develop solely on a blood diet; they can also successfully develop
solely on grain stored in grain sacks. Because the larvae lack a closing mechanism on
their spiracies, they require high humidity for development and move to areas of high
humidity. Exposure to 0% RH at 72degreesF/22degreesC for 24 hours is lethal but at 90% RH
the lethal temperature is 97 degrees F / 36 degrees C. Larvae go through 3 molts and then
pupate. Successful pupation and emergence requires 64-95degreesF/18-35degreesC and 60+%
RH. Females emerge 3-4 days before males. If well fed, adults may live for a year or more
in the lab, but probably only 2-4 weeks in the wild. The life cycle (egg to egg) can be
completed in as few as 4-8 weeks.
HABITS.
Unfed adults are attracted to light but fed adults shun light. Adults have responded
positively to the odor from a favorable host at up to 12" (30 cm) and were able to
distinguish it from nonhost species. Adults can jump as far as 94" (24 cm)
horizontally and 4.3" (1 1 cm) vertically. The favorite host is the Norway rat
(Rattus norvegicus (Berkenhout)), but the oriental rat flea is also found on the cofton
rat (Sigmodon hispidus Say & Ord), roof rat (R. rattus Linnaeus), the house mouse (Mus
musculus Linnaeus), cottontail rabbits (Sylvilagus spp.), and the California ground
squirrel (Spermophilus ap.). Oriental rat fleas readily bite and feed on humans. The
medical concern is that these fleas are the principal vector of both bubonic plague and
murine typhus. The transmission is primarily from rats to humans although other wild host
reservoirs of these disease organisms can be involved.
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