144 PIMPLINE ICHNEUMONIDAE 



I have not seen the type of Rhyssa skinneri Viereck, as already- 

 stated, but from the description, it does not seem impossible 

 that it may be a form of this species. 



Habits of Rhyssa 



The Rhyssae by means of their ovipositors bore into trees 

 infested with borers and there deposit their eggs. They are 

 primary parasites on Sirex, Monohammus and Urocerus cyaneus. 

 As their life from hatching to adult is spent within the trunks 

 of trees, it has made a study of their history practically impossible. 

 It has been generally assumed that they were external parasites, 

 but H. J. Erne ^^ gives an account of raising Rhyssa from Sirex. 

 According to him the eggs were laid within the larvae. It has 

 been clearly shown that in the closely related genus Megarhyssa, 

 the eggs are external to the larvae. The tip of the ovipositor 

 is constructed for sawing into wood and not for piercing other 

 insects. It does not seem probable that the members of one 

 genus live as external while those of so similar a genus should live 

 as internal parasites. Yet the only published evidence that has 

 been found asserts that Rhyssa live as internal parasites. Erne's 

 observations will be given here though their accuracy is doubted. 



"In studying Serropalpiis I had an opportunity to observe 

 Pimpla persuasoria. The eggs of Pimpla were usually laid in 

 the larva of a species of Sirex, which were very inactive on that 

 account, and did not put up any resistance. After they hatched 

 the little larva remained in the Sirex larva until the latter died. 

 The larva of Pimpla had by this time attained a size of two or 

 three lines. 



"They left the Sirex larva after it was dead, and from time 

 to time fed on the remains. If the Sirex larva is large the Pimpla 

 larva has food enough, but if it is small, the food supply is not 

 sufficient, and since the Pimpla does not try any other nourish- 

 ment it dies in the wood. Frequently the Sirex larva with the 

 parasite larva in its body, penetrates deeply into the wood, so 

 that the developed Pimpla has to bite its way out of the wood 

 from a depth of two lines in order to get free. For a space of 

 three days it thus works itself forward; if it does not get free 

 in three days its strength' becomes weakened and it dies in the 



" Mittheil. Schweiz. Entom. Gesell., iv, 1876, p. 9, p. 518. 



