404 
Psyche 
[December 
Mature Catharosia larvae emerge by rupturing the intersegmental 
membrane between the eighth abdominal segment and the pygo- 
phore in male hosts, and the seventh sternum and the first valvifers 
in female hosts. After the larva has passed through, the host’s 
sclerites typically fall back into place, making it difficult to 
recognize that a parasitoid has emerged. During our study one larva 
died while emerging from a female L. diffusus, providing an 
opportunity to examine closely how an exit is achieved (Fig. 3). 
Bugs sometimes lived for several days after the emergence of a fly 
larva, and Ashlock and O’Brien (1964) reported one female lygaeid 
(sp?) living for a month after the emergence of a Catharosia lustrans 
larva. This bug produced five eggs, but development of the 
parasitoid may have been abnormal since the larva died without 
forming a puparium. Other dissections by these authors and all of 
our dissections revealed that fully developed gonads are not present 
in parasitized hosts. 
Upon emerging from the host the mature larva moves a short 
distance away and pupates. Puparia were occasionally found lying 
in the open on the substrate. However, pupation usually occurred 
beneath some sort of cover. 
The high rate of parasitism found in the Wood Co. L. diffusus 
population when sampled on 19 June 1978 (60%) and the laboratory 
dissections, which indicate that Catharosia sterilizes its host, suggest 
that this fly may play an important role in controlling seed bug 
populations. 
Summary 
Fifty-one adults of Catharosia sp. (Diptera: Tachinidae) were 
reared from Ligyrocoris diffusus (Uhler), L. sylvestris (L.) (new host 
record for the genus Catharosia), Perigenes constrictus (Say), 
Sphaerobius insignis Uhler, and Zeridonius costalis (Van Duzee) 
that were collected in Wisconsin in 1977 and ’78. Sixteen flies were 
reared through a complete life cycle on laboratory cultured L. 
diffusus. Rates of parasitism in field collected L. diffusus were 60% 
on 19 June and 16% on 22 August 1978. The fourth sternum of 
female flies is modified with spined plates that may help hold the 
host during oviposition. Both adults and nymphs are parasitized, 
but parasitoids emerge only from adult hosts. Total parasitoid 
development time can be as short as 18 days. Mature Catharosia 
