Specific Characters and Character Variants in Adults and Larvae 
of the Genus Paratrombium Bruyant 1910 (Acari, Trombidiidae), 
with Descriptions of Two New Species from Western North America 
Irwin M. Newell 1 
The genus Paratrombium was established by 
Bruyant for a larval mite, which he named P. 
egregium , found in a vial containing Diptera, 
Coleoptera, and possibly other insects. The 
outstanding characteristics of this larva as in- 
dicated in the drawings provided by Bruyant 
were: (1) the large postscutal dorsal plate, 
(2) the characteristically striate anterior por- 
tion of the scutum, (3) the form and orienta- 
tion of the heavy, sharp prosensillar setae 
which appear to arise from the end of long 
canals, (4) the swollen, bilobed tip of the 
rostrum, (5) the elongate, pectinate tritoros- 
tral setae, (6) the heavy rakelike inner setae of 
coxae I, (7) the presence of a single pair of 
intercoxal setae, (8) the number (four) and 
orientation of the setae between coxae III 
and the anus, (9) the presence of only two 
scythe-shaped claws on tarsus III. In all of 
these features, the species described by Bru- 
yant resembled so closely the one described 
below as Paratrombium bidactylus n. sp. as to 
indicate that these are congeneric. 
It should be pointed out that the original 
description of P. egregium differs from P. 
bidactylus n. sp. in three important respects: 
(1) the presence of a pair of slender, elongate 
setae between the sensilla and prosensillar 
setae of the scutum, (2) a coxal setal formula 
in the larva of 2-1-1 compared with 2-2-1 in 
P. bidactylus , and (3) the possible absence of 
the four characteristic elongate setae at the 
posterior margin of the body. The first of 
these apparent differences is based on an 
artifact; for the transverse suture which par- 
tially divides the scutum into anterior and 
posterior portions appears so sharp and deli- 
1 University of California, Riverside, California. 
Manuscript received May 13, 1957. 
cate that Bruyant unquestionably mistook it 
for a fine seta. With regard to the second of 
these characters it should be pointed out that 
Oudemans (1910) represented this species as 
having two setae on each of coxae II of the 
larva; and moreover showed only four pairs 
of setae on the scutum, including the single 
pair of sensilla. Oudemans’ somewhat more 
detailed figures were apparently prepared from 
Bruyant’s own material, hence, the original 
description of P. egregium was in error on this 
point also. With regard to the third point 
mentioned above, neither Bruyant nor Oude- 
mans showed the characteristic setae at the 
posterior end of the hysterosoma which are 
found in the larvae of P. bidactylus. It should 
be pointed out, however, that the writer’s 
drawings have been made from unengorged 
larvae while those drawn by Bruyant and 
Oudemans were of engorged larvae. Both 
Bruyant and Oudemans showed a total of 28 
postscutal and postcoxal setae whereas in P. 
bidactylus there are 30. This could be a true 
specific difference or it might possibly be due 
to the loss of one of the pairs of setae during 
the period of feeding in the specimens from 
which the available figures of P. egregium were 
drawn. At any rate, the close morphological 
similarity between P. egregium and the two 
species described below as P. bidactylus n. sp. 
and P. quadriseta n. sp. is so close as to indi- 
cate beyond reasonable doubt that they are 
congeneric. 
The differences between the two larvae de- 
scribed below appear to be adequate to indi- 
cate that two distinct species are involved, 
and since they were obtained from known 
adult females, it is possible to determine what 
adult characters, if any, show variations of a 
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