286 Journal of Agricultural Research voi. m,No.4 



THE ADULTS 



On the 17th of June the first observations of the adult Agrilus bilineatus 

 were made in the vicinity of Lake Elmo, Minn. Early in the after- 

 noon two or three could sometimes be seen at one time on a dying tree. 

 On the same day an adult was taken from its pupal cell in the bark, and 

 a lar\-a was found preparing to pupate. Since no adults were seen two 

 days earlier while the author was collecting in the same locality, it seems 

 that these observations fix the appearance of the adults quite definitely 

 for this section in a normal year. 



The adult borers increased in numbers until they reached their greatest 

 abundance about the ist of July, when as many as 10 were seen at one 

 time on a small area of bark. In the afternoon of June 26, 80 specimens 

 were collected near Savage, Minn. There was a noticeable decline in 

 numbers after the first week in July, and by July 20 the last record of 

 the adults was made. Continued careful search in the field after that 

 time was not rewarded. 



During the last days of the adults' flight many instances of apparent 

 feebleness became evident. On one occasion, while watching Agrilus 

 beetles, a female was seen to fly slowly toward a tree apparently intend- 

 ing to alight on it as usual, but the insect fell to the ground as if unable 

 to cling to the bark. The borer then made a second attempt, which 

 was also unsuccessful, and it was picked up from the ground where it 

 was lying apparently exhausted. The behavior of other chestnut borers 

 in the field and in the insectary leads to the belief that the last chapter 

 of their history is marked by the feebleness of old age. 



Agrilus adults lived about 12 days in the insectary, where they were 

 kept in a cage inclosing an oak tree. The conditions were so favorable 

 in the insectary that many details of the various habits could be studied 

 to great advantage, and continuous observations throughout the season 

 were made possible in spite of weather conditions. 



The habits of the Agrilus beetles were governed with such regularity 

 that a seemingly definite program was discovered which ser^-ed as a 

 guide for later observations. At no time during the season were beetles 

 found, even on the sunny side of the trunks, until nearly noon. On 

 July 7 in a place near Savage, Minn., where the adult borers were very 

 abundant, a careful search was begun shortly after 9 o'clock in the 

 morning and but one specimen was found at 9.30 a. m., a few at about 

 10 o'clock, and not until 1 1 o'clock were the}' found in their usual num- 

 bers. From this time until shortly after noon they increased in num- 

 bers; then they gradually disappeared until few were to be seen late in 

 the day. The latest field obser\^ation was made about 6 o'clock. In 

 the insectary the beetles were inactive in the bottom of the cage until 

 about 8 a. m., when they would begin to fly about and feed on the foliage 

 of the tree. Many were also obser^'ed courting during the early forenoon. 

 The absence of the beetles from the tree trunks, which they frequent laterin 



