September, 1941 
the distribution of the bugs to be limited to 
areas where the host species grow. No doubt 
in times of migration and when buffeted by 
strong winds, many individual bugs may be 
carried far from their normal host and hence 
perish without successful reproduction. It 
appears that several species of Miridae are 
so restricted by ecological factors that their 
distribution is more limited than the host 
upon which they live. This is certainly true 
of the apple redbug, Lygidea mendax, which 
normally breeds on species of Crataegus; 
but the Crataegus grows far south and west 
of the areas where L. mendax can be found. 
While making a close study of Lygidea 
mendax the author noted that the bugs were 
never found on isolated trees exposed on 
high ground where the sun was hot and the 
atmosphere very dry. The bugs seemed to 
thrive only in valley areas where the humid- 
ity rarely dropped to desiccating levels. The 
nymph of L. mendax is very delicate, the 
body wall evidently only thinly chitinized; 
so it can live only where the humidity is high 
enough to prevent desiccation. The writer 
believes that the southward distribution of 
this species is limited chiefly by the high 
KNIGHT: PLANT Bucs, or Miripag, oF ILLINOIS 5 
temperatures and desiccating atmosphere 
frequently encountered west of the Missis- 
sippi and south of the Ohio rivers. It seems 
likely that other Miridae of the Boreal 
region may have their southern distribution 
limited for the same reasons. 
In contrast to the above, we may take 
another species, Heterocordylus malinus, of 
which the favorite wild host is Crataegus. 
This insect is more widely distributed than 
Lygidea mendax, for it is frequently found 
on Crataegus in Texas and Mississippi, 
apparently able to live wherever the host 
plants thrive. If we examine nymphs of H. 
malinus we find the body wall is more 
heavily chitinized than in L. mendax. The 
nymphs are not subject to fatal desiccation 
when the leaves of the host plant wilt under 
the heat of a hot, dry day. Some years ago 
the writer reared in breeding cages many 
nymphs of both species, and at that time 
first observed the more delicate nature of 
L. mendax. When both species are kept in 
cages on host plant foliage, and the host 
leaves are allowed to dry out, L. mendax 
will die immediately whereas H. malinus 
will live for several hours. 
Distribution and Habitat Preference* 
In Illinois the distribution patterns of the 
Miridae are linked primarily with those of 
their plant host species. Other factors also 
play a very important part in determining 
mirid distribution patterns, but the influence 
of these is not always obvious from a study 
of such a limited area as one state. The 
greater part of the uncultivated areas of 
Illinois is covered with either oak-hickory 
forests or prairie and the various types of 
community which lead up to them. There 
are certain restricted areas, however, in 
which we find mirid hosts found nowhere 
else in Illinois. These are the result of the 
rather axial geographic position of Illinois. 
This state is a long, narrow area, the north- 
ern end just bordering some of the conifer- 
ous communities which are common in Wis- 
consin and its southern end extending slightly 
into conditions typical of the southern states. 
In respect to east and west, Illinois is the 
mingling ground of the eastern deciduous 
forests and the western grasslands, with here 
and there an invasion of typical western 
*This section is the work of Herbert H. Ross, Sys- 
tematic Entomologist, Illinois Natural History Survey. 
plants in some of the sand areas. Small 
areas of peculiar interest are marked on the 
accompanying maps. 
Mirids in Restricted Areas 
The tamarack bogs, fig. 3E, are remnants 
of the glacial bogs. In Illinois they are 
restricted to the small area in the vicinity 
of Volo and Antioch in the extreme north- 
eastern portion of the state. They have been 
encroached upon by agriculture to a con- 
siderable extent, but a few remain which 
have preserved their flora and fauna prac- 
tically intact. These bogs, fig. 4, are the 
only place in this state where occurs native 
tamarack, Larix laricina, which is the exclu- 
sive host of the following plant bugs in this 
state: Deraeocoris laricicola Knight, Piloph- 
orus uhleri Knight, Plagiognathus larici- 
cola Knight. These species do not feed on 
other species of larch used for ornamental 
planting in various localities, so that our 
records for the larch mirids are confined to 
the northern bogs, fig. 5. 
Along the shore of Lake Michigan, north 
of Waukegan, is a narrow sand area, fig. 
