The wheat bulb fly (Leptohylemyia coarctata, Fall.) has been causing failures and poor crops of wheat and rye for a number of years in many parts of Yorkshire. Broadly speaking, these attacks fall into two types, one on light sandy soil after second early or main crop potatoes, and the other on very heavy soil after fallows. The first type occurs commonly for many miles around Selby, but it has been a perennial problem well known to this department in the parish of South Duffield a few miles to the east of Selby. Although the soil is unsuited. to wheat, a satisfactory crop can be grown, provided the fly does not cause serious damage, after potatoes which have followed a ley. Rye was only slightly less affected than wheat, and it was not convenient to replace them by other cereals. Accordingly, at the suggestion of the Advisory Entomologist, Mr. H. W. Thompson, a study of the biology of the fly under local conditions was commenced in 1943. In 1944 attacks were much more serious and general and afforded an opportunity of extending the work and comparing observations in widely differing localities. It was then found that other districts were also centres of perennial attack resulting in reduced yields and sometimes failures. Damage after potatoes similar to that at South Duffield occurred on the Lincolnshire border at Dirtness Bridge Farm and surrounding farms on black sand.

With 4 Text-6gure-s) THIS work originated in experiments set up to stu'dy the utilization of organic katter in the soil by wireworms. As the work progressed certain curious facts were noted, e.g. sometimes a wireworm would feed appreciably, yet its weight would remain constant or even decrease; also starving wireworms might remain approximately constant in weight over long periods, whereas at times they might increase in weight without apparent reason. In view of these observations and of the known great variability in the results of experimental work on these insects, experiments were set up to iind a technique for rearing wireworms in such a way that the growth of individuals could be studied in detail, with particular attention to changes in weight in relation to food and soil moisture.The following technique was finally adopted. Wireworms were confined, individually, in glass vessels of varying size according to the size of the wireworm; for small wireworms, 1-20 mg. in weight, vessels 3 x I in. were very suitable, but for the larger ones, vessels 5 x I* in. were required. The vessels were one-third filled with soil of a known water content and after the wireworm and food had been introduced the vessels were tightly

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Wireworms rarely occur in permanent arable land @ sufficient numbers to cause serious damage to crops. Various workers (e.g. Roebuck, 1924;Hawkins, 1936; M i l e s 8z &hen, 1941) have noted the reduction in numbers of wireworms in successive years on ploughedout grassland. At Rothamsted reductions of 62 yo in one year and 85 % i n two years were recorded on plots on Highfield. This reduction is certainly due in part to the exposure of wireworms to their natural enemies and to the direct effect of disturbance by implements of cultivation. It has also frequently been suggested that the beetles prefer to oviposit on grassland or clover leys and to a lesser extent on cereal crops (Bryson, 1930; Rawlins, 1934; Balachowsky & Mesnil, 1935 ; Miles 8z Cohen, 1938). A laboratory experiment to test this point was accordingly carried out in June 1940. OVIPOSITION PREFERENCESrwenty-five wooden boxes of 12 x 8 in. area and 8 in. deep were each filled with 28) Ib. of sieved Rothamsted allotment soil and the surface lightly pressed down to within in. of the top of the box. Five boxes each were sown on 13 May with winter wheat (Wilma), kale (thousand-headed), grass (mixture) and wild white clover. The remaining five boxes were left unsown. The wheat and the kale were sown in three rows about 3 in. apart across the width of the boxes, and the grass and clover were sown thickly over the whole area. The boxes were arranged in the form of a Latin square and clamped together on the floor of a well-ventilated, unheated glasshouse. A frame was erected around the boxes up to about 18 in. above their tops and, when the plants were well established, the frame was covered with muslin and all cracks at the sides and between boxes were sealed with surgical tape. The boxes were watered normally throughout the experiment and the unsown, wheat and kale boxes were kept weeded.Between 8 and 13 June, 214 adults of Apiotes 0bscuru.s were introduced into the cage, eight or nine being placed in each box. A. obscurw was chosen because the previous year's observations showed that this species laid more readily in captivity than did A. sputator. The relative numbers of the sexes were not known as enough beetles could not be spared for dissection, and it was intended to make an examination of the survivors and the dead bodies at the end of the experiment. On 3 July the cage was opened, all crops were cut to ground level, and all beetles on the surface removed: two live beetles and seven dead ones were found.The technique adopted for counting the eggs was as follows. Two cylindrical tins 12b. high and 4f in. dim. were each filled about one-third full of the soil to be examined (approx. z t lb.).The tins were then filled to within I in. of the top with a solution of magnesium sulphate (sp. gr. 1-12) and stirred for 5 min. The level of the solution was then raised almost to the edge of the tin and it was allowed to stand for 10 min. The level was again raised by allowing the solution to trickle in from an aspirator and the foam which formed on the top made...