40 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 47 



LILAC 



Lilac Borer, Podosesia syringae syringae (Harr.), fig. 30. — 

 The larva of this insect is a major pest of lilac. The adults are 

 moths that have transparent rear wings. Holes made in the bark 

 of lilac by the grubs are likely to be numerous and are charac- 

 terized by protruding sawdust, oozing sap, and, in the spring, by 

 brown pupal cases at the entrances of emergence holes. Eggs 

 deposited by the female in early summer on rough bark give rise 

 to the white grubs that bore through the bark into the wood be- 

 neath, where they feed and grow until winter brings their activi- 

 ties to a halt. 



Control Measure h (end of circular) . 



Oystershell Scale, fig. 5. — This is a major pest of lilac. See 

 under Ash. Control Measure 5 (end of circular) in late winter 

 or Control Measure 3 in early summer. 



LINDEN 



Elm Spanworm, Ennomos subsignarius (Hbn.). — The adult 

 form of this species is sometimes called the snow-white linden 

 moth. Both male and female are pure white. The larva or cater- 

 pillar is a gray and brown looper with irregular yellow marks. 

 Outbreaks of this insect occur at intervals of 10 to 20 years. The 

 female moth deposits eggs in the summer on tree branches. The 

 eggs do not hatch until the next spring. When outbreaks occur, 

 the caterpillars are present in such numbers that they defoliate 

 linden and several other kinds of trees. 



Control Measure 1 or 2 (end of circular) . 



LOCUST 



Locust Borer, Megacyllene robiniae (Forst.). — Black locust 

 is particularly susceptible to the larva of this insect. The larva 

 is white, cylindrical, and up to 1 inch long. At first it mines 

 the bark and sapwood of the locust, but later it bores into the 

 heart of the tree, often causing so much damage that the trunk 

 breaks. Growth, pupation, and transformation of the insect take 

 place in the wood. The adults are beetles that emerge in autumn 

 and feed on the pollen of goldenrod. Each is about three-fourths 

 inch long, black, and has zig-zag yellow lines across the back. 



