No abstract

No abstract

An account is given of an investigation made of the life-histories of Oscinella frit and its parasites in Ontario, Canada, with a view to the possible introduction of suitable parasites into England. The various Chloropid species associated with O. frit in North America are discussed.The life-history of the frit-fly in Ontario is similar to that in England except wheat, not oats, is attacked, and that there appears to be no regular grain-infesting generation, but the insect is never a major pest in Canada.The life-histories of the following six species of parasites are described : Hexacola sp. n., Polyscelis sp. n., Loxotropa sp., Cyrtogaster sp., Callitula bicolor and Spalangia drosophilae. Other hosts from which these parasites have been reared include Chloropids associated with O. frit in wheat, namely O. carbonaria, O. soror, O. minor and Meromyza americana.A brief account is given of the control exerted by these parasites on the population of frit-fly in Ontario and a comparison is made between the Canadian and English parasite complexes. From this it is concluded that S. drosophilae might exert some control of frit-fly if introduced into England.

In a previous paper (Simmonds 1946*) the biology of Phytodietus pulcherrimus (Cress.), a parasite of Loxostege sticticalis, L., the sugar-beet web-worm, has been described. This paper will be devoted to the habits and life-history of another important parasite of Loxostege in North America, Bracon vulgaris (Cress.). This species appears to be confined to the American continent, all of the records being from Canada and the U.S.A. It has been reared only from Loxostege sticticalis, L., and L. commixtalis, Wlk. From the former species it has been recorded by Paddock (1912), Swenk (1918), Jones, Hoerner and Corkins (1921), Pepper and Hastings (1941), and Simmonds (1946); from the latter species by Hoerner (1933). During the present work it has been reared from L. sticticalis, material from both Montana and Alberta.

Experiments were designed to determine the criteria by which an ovipositing female of Spalangia drosophilae Ashm. is attracted to an environment where suitable hosts may be found, and by which these hosts are selected.The results obtained indicate that ovipositing female Spalangia are attracted to and maintained in areas where suitable host puparia may occur by their reaction to sensory impressions. Thus females tend to be attracted to dampness and to soil level where, in grasses, host material is likely to be found. In such an area searching for hosts appears to be at random, but once an object that is a possible host is located there follows a careful examination and, if the object is “ considered ” a suitable host, oviposition follows. It appears that there are several definite criteria by which an object is accepted as a host suitable for oviposition. In general the hosts selected by the parasite are those which are suitable for the development of her progeny.