Field experiments on the control of wheat bulb fly, Leptohylemyia coarctata (Fall.)

Abstract

Although damage by wheat bulb fly, Leptohylemyia coarctata (Fall.), can be prevented or reduced by various cultural measures these are not always practicable (Gough, 1957) and chemical methods were therefore investigated. Preliminary experiments suggested that seed dressings would be the simplest and most promising approach as Gough & Cohen (1954) found that spraying to kill adults was unsatisfactory.Seed dressings containing 20 per cent, -y BHC to prevent wireworm damage were introduced commercially about 1949-50, but observations on fields where this treatment was used indicated that it had little effect on attack by wheat bulb fly, and higher rates were therefore tested at the outset. About the same time, aldrin and dieldrin became available for experimental purposes, and seed dressings containing these materials were used in the first trial; other materials were introduced for comparison or as they became available and, in the later stages of the work, chemicals found promising by Bardner (1958Bardner ( , 1959 were included. Methods.Fields on commercial farms were usually selected for experiments on the basis of a fairly high egg count of wheat bulb fly, preferably over one and a half million per acre; these egg counts were based on 20 four-inch cores per field, the samples being examined by a flotation process (Cockbill & others, 1945). All cultivations, including sowing, were carried out by the farmer or his staff with his own equipment. Smaller trials were drilled with a hand machine.Dry seed dressings only were used and all seed was treated in a small barrel-type dressing machine, usually within 24 hours and invariably within a few days of sowing. Except where otherwise stated, all insecticidal seed dressings also contained a suitable quantity of organo-mercurial fungicide and the seed on all control plots in experiments where the insecticide was combine-drilled was treated with an organo-mereurial fungicide (O.M.). The rate of dressing was either 2 or 3 oz./bushel (equivalent to 2 or 3 g./kg.). Where possible, seed-drills were calibrated beforehand so that the sowing rate of the seed or any material combine-drilled would fall within the chosen range. The rates were checked after the drilling of each treatment by noting the difference between the weight of seed or material put in the drill and the residue.Counts of attacked and healthy plants and shoots were made on sample areas of two adjacent rows each 1 ft. long on one or more occasions and the number and condition of the larvae in the attacked shoots (or a sample thereof) were recorded. The number of samples taken depended on circumstances but was usually three to five per plot. Usually these samples were brought back to the laboratory for examination and dissection under a low-power binocular microscope though sometimes it was possible to make total-plant and damaged-shoot counts in the field.

Persistence and distribution of insecticidal seed‐dressings for control of the wheat bulb fly, Leptohylemyia coarctata

“…Dieldrin and y-BHC seed-dressings have been used for more than 10 years to control wheat bulb fly. Results of many trials have shown that y-BHC acts mainly by preventing larvae entering the plants and kills few larvae that succeed in entering, whereas dieldrin acts mainly by killing larvae after they enter (Gough & Woods, 1954;Bardner, 1958;Way, 1959;Maskell & Gair, 1961 ;Gough, Woods, Maskell & Towler, 1961). Both materials are less effective in organic soils than in mineral soils (Gough et al, 1961.…”

Development of a pest threshold decision support system for minimising damage to winter wheat from wheat bulb fly,Delia coarctata

“…This contrast in accuracy could be related to specific environmental factors that limited shoot production such as soil capping or water logging (Robertson et al, 2009). Our revised thresholds for D. coarctata in winter wheat demonstrate that the current D. coarctata pest threshold of 250 eggs m -2 (Gough et al, 1961) is too simplistic and for many crops this likely represents either an overestimation of the potential pest damage, an underestimation of the amount of damage that can be tolerated by a winter wheat crop, or a combination of both factors. Sensitivity analysis (achieved by adjusting each parameter used in Equation 2 from its likely minimum value to its maximum value; Fig.…”

“…Crop tolerance, or the economic injury level, can be broadly defined as the amount of pest damage that a crop can withstand before an economic consequence is observed (Stern et al, 1959). The most recent D. coarctata pest thresholds of 250 or 100 eggs m -2 , for crops sown before the end of October and from November, respectively, were devised c. 60 years ago by Gough et al (1961) and only take account of pest abundance with no consideration of crop tolerance. Adjusting various agronomic factors, such as sowing date and seed rate, has been used to successfully achieve tolerance against other stem-boring pests of wheat, including the gout fly, Chlorops pumilionis (Bjerkander) (Bryson et al, 2005) and wheat saw fly, Cephus cinctus Norton (Beres et al, 2011).…”

Some aspects of the wheat bulb fly problem The fifth Barnes Memorial Lecture

“…Following the work of Gough (1946, 1947) on wheat bulb fly infestations in Yorkshire and the widespread and severe outbreaks of wheat bulb fly damage in the eastern counties in 1952 and 1953, entomologists in the National Agricultural Advisory Service, at Rothamsted and elsewhere, started much work on the biology, ecology and chemical control of wheat bulb fly. This work included such studies as those on diapause in the egg (Way, 1959a(Way, , 1960, effects of soil conditions on oviposition (Raw, 1955), estimation of crop losses (Raw & Lofty, 1957), host plant location (Stokes, 1956; Long, 1958), alternative hosts (Stokes, 1955), adult behaviour (Dobson, Stephenson & Lofty, 1958;Long, 1959;Dobson & Morris, 1960), parasites and predators, (Dobson, 1961), laboratory rearing (Bardner & Kenten, I957), and methods of controlling the pest with chemicals (Bardner 1958; Way, 1959b;Gough et al, 1961).…”