1048 Water H. WELLHOUSE 
They furnish food for nearly all of the insects studied. A few excep- 
tions, such as the snowy tree cricket (Oecanthus niveus) and the damsel 
fly Lestes viridis, procure their food elsewhere and use the hawthorn 
branches merely to shelter their eggs from the weather and their enemies. 
Every part of the tree furnishes food for some species of insect, as may be 
seen from the following outline: 
Trunk-and ‘branches... 45054 ne hl leg ks ace ue re AO species 
A. External feeders (scales, aphids, and cthers), 19 
B. Internal feeders (borers), 21 
Roots (aphids)itiais\ RNG. Ris Genta OAC ONES i. Se Re sDReO ae ak ik a rr 1 
Thorns (weevils)................. ean Mrs aU EMD IRE ILO ooo 5 in 6 « 1 
BEET ists hrate ate aae I oal ean WD Ria a a oS UA EOI Wah RRC PAN ee gw 9-00 0 292 
A. External feeders (miscellaneous), 235 
B. Miners (tineids, weevils, sawflies), 37 
C. Gall makers (aphids, mites, cecidomyiids), 20 
Flowers (thrips, maggots, caterpillars, beetles, and others).................... 12 
Fruit (caterpillars, bugs, maggots, grubs)...............0 000000020 cece eee 30 
The other basic need of insects which a host plant may supply is 
shelter. Most of the insects included in this paper are sheltered to some 
extent by the hawthorn, although the completeness of the shelter varies 
with the habits of each species of insect. Some are protected only by their 
position on the surface of the tree. Others are partially sheltered in rolled 
leaves, bark crevices, and the like. Still others are securely housed within 
the plant tissues. The degree of shelter secured by those species living 
externally on the surface of the plant varies so greatly and so gradually 
that no distinct lines of division can be drawn in so general a statement as 
this. The more distinct groups of internal feeders (borers, leaf miners, 
and gall makers) are indicated above and are distinguished from the 
external feeders, which receive less complete shelter. 
The fact that so many species of insects feed at the expense of the haw- 
thorns suggests the idea that these trees are in danger of extinction. Such 
is not the case, however, for the hawthorns when not weakened by drought 
or flood are very hardy, long-lived trees. Some indications as to why they so 
successfully withstand the feeding of the insects may be seen from a study of 
the following data, which are based on statistics given in the last sections of 
this paper: 
APPROXIMATE FEEDING PERIOD OF HAwTHORN INSECTS 
Species Species 
Mian hiss, Sayan io ne suren ies ee rere s 1 August. 3307.2. 30 ee ee 117 
PACT bers, coe teen tene,  oiraneceet pee come ire ee bats 54 - » September... .. 5.435 eee 124 
Dilaniy cen ae No a SRE a Me et 190..: ‘October! Ho ee eee 80 
Tune tee eget. eo ea nana ce 232. November. (0.0.3 .en eee 23 
AUDA ieee tama nie ee Arun, heh Revenues tenes 131 Time of feeding unknown........... 58 
Foop Puants or HawtHorn INSEcTS 
Food’ plants restricted to Crataegus. os... 14. cls. 4.6 ee) Eee eee 57 species 
Food plants including other related or associated groups.................+..5- 325 species 
