Ecologists have quantified Orthoptera (grasshoppers and crickets) density in a wide variety of conservation studies. Objective determination of Orthoptera population size is possible using mark-release recapture techniques but these are time-consuming and of little use for all but the smallest scale studies. Therefore, a wide range of sampling techniques have been devised to quantify population density and the most commonly used methods include sweep netting and quadrat counts. It is the aim of this paper to critically review studies that have used these techniques and to provide useful suggestions for non-specialists on which method may be most applicable to their study site. This paper reviews a selection of the extensive literature reporting studies estimating the abundance of grasshoppers (Acrididae) in a wide range of grassland ecosystems. Where possible, studies on bush-crickets (Tettigoniidae) and crickets (Gryllidae) are included reflecting their overall contribution to assemblage diversity in grassland ecosystems and to highlight the need for further investigations of sampling efficiency on these two under-researched families.

Review of the Methods Frequently Used to Estimate the Abundance of Orthoptera in Grassland Ecosystems

Breeding Wheat for Resistance to Insects

Marker-assisted breeding provides an opportunity for wheat breeders to introgress/pyramid genes of interest into breeding lines and to identify genes and/or quantitative trait loci in germplasm to be used as parents. Molecular markers were deployed to assist selection for disease resistance, agronomic and quality traits in several wheat cultivars released for commercial cultivation in Canada. Marker-assisted breeding is routinely used in most wheat breeding programmes for rust resistance (leaf, stem and stripe rust), orange wheat blossom midge resistance, high grain protein concentration, Fusarium head blight and common bunt resistance. Markers are being used selectively within breeding programmes to target traits that relate to market class or regional adaptation. For example, marker-assisted breeding for low lipoxygenase activity and low grain cadmium is being performed in durum breeding programmes and for enhancing stem solidness in programmes targeting resistance to the wheat stem sawfly. Markers are also being utilized for ergot resistance in durum wheat. Increased gluten strength is being selected with a marker for the overexpression of the Bx7 high-molecular-weight glutenin subunit. Marker-assisted breeding is also being used to pyramid resistance genes against a group of stem rust races related to TTKS (Ug99), a disease that poses a serious threat to global wheat production. Development of tightly linked diagnostic markers and high-throughput genotyping with SNP markers will result in more effective molecular wheat breeding in the near future and will open the door to genomic selection.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/pbr.12057

Application of molecular markers to wheat breeding in Canada

Larvae of the wheat midge, Sitodiplosis mosellana (Gehin) feed on the surface of wheat seeds for about 10 days beginning when pollination occurs. A few wheats have a high level of antibiotic resistance to the larvae, which suppresses their growth and development. Nearly all larvae develop successfully on susceptible wheats. Analysis by HPLC of seed extracts produced by alkaline hydrolysis revealed rapid changes in the levels of p-coumaric and ferulic acids during early seed development. Seed infested by wheat midge larvae showed induced changes in the dynamics of these phenolic acids. The most resistant wheats had a higher constitutive level and a more rapid induction of ferulic acid than susceptible wheats. Levels of ferulic acid exceeding 0.35 μg/g fresh weight were associated with a high mortality of newly hatched larvae. In one wheat line, resistance also was associated with induced production of p-coumaric acid. The induction of ferulic acid was similar in wheat from the laboratory and field, except in one resistant wheat that produced higher levels in the field. In ripe seeds, resistant and susceptible wheats had similar levels of phenolic acids.

Inducible Production of Phenolic Acids in Wheat and Antibiotic Resistance to Sitodiplosis mosellana

The wheat midge Sitodiplosis mosellana (Gehin) occurred in all wheat-growing areas of Manitoba during 1993–1997, with 95% of spring wheat fields having some seeds infested by larvae. The level of infestation varied, but each year in excess of 20% of seeds were infested in some fields. Infestation levels in adjacent fields were more similar than in fields separated by a few kilometres. Within fields, the infestation was similar at the edge and near the centre. Wheat midge larvae also overwintered in, and adults emerged from, fields in all wheat-growing areas of Manitoba. Adults emerged from the end of June to the end of July most years, and the peak period for adult flight was mid-July, about 1 month later than in parts of Europe where winter wheat predominates. The timing of the emergence was similar from place to place and year to year. Females constituted 95% of insects caught in a flight trap. The first 10% and 50% of the flight occurred on 9 and 16 July, respectively, and the timing of the flight was not related to growing degree-days. In early August, mature larvae began dropping from wheat heads. The timing of infestation of spring wheat was variable among years because of differences in timing between midge flights and the susceptible heading stage of the crop. Nevertheless, the wheat midge flight usually coincided with the susceptible stage of the spring wheat crop.

Distribution and seasonal abundance of Sitodiplosis mosellana (Diptera : Cecidomyiidae) in spring wheat

Losses in yield of spring wheat due to infestations of Sitodiplosis mosellana (Gehin) were determined for 700 000 ha of arable land in northeast Saskatchewan, Canada in 1983. The proportion of kernels infested (y) was a power function of the number of wheat-midge larvae (x) (y = 35.3x0.725). One, 2, 3, and 4 larvae per kernel resulted in a level of infestation of 38, 58, 78, and 96%, respectively. There was no significant difference between infestation levels from fields sampled at the heading stage of crop growth and the estimates of infestation levels for these fields at harvest time. Yield of grain (y) was negatively exponential to an increase in level of infestation (x) (ln y = 5.7−0.017x). Infestations of 30, 60, and 90% reduced yields of spring wheat by 40, 65, and 79%, respectively. The average decrease in crop yield in the study area was about 30%, which resulted in estimated losses in total gross revenue of about $30 million.

Relationship between infestation levels and yield loss caused by wheat midge, sitodiplosis mosellana (géhin) (diptera: cecidomyiidae), in spring wheat in saskatchewan

Evaluation of Nosema locustae (Microsporida) as a control agent of grasshopper populations in Saskatchewan

The spatial and statistical distribution of eggs and larvae of the wheat midge, Sitodiplosis mosellana (Gehin), in wheat in northeastern Saskatchewan were investigated. The highest number of each stage occurred in the top third of the head and the lowest in the bottom third. Because of this the entire wheat head is considered an adequate sample unit for density estimates of the two life stages. Sample sizes required to estimate egg and larval populations with given levels of precision were determined. A sequential sampling plan for larval populations was derived using Green’s and Iwao’s methods. Both methods gave similar results; however, the number of samples required to reach a decision was higher using Green’s method than using Iwao’s.

Development of sampling designs for egg and larval populations of the wheat midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae), in wheat.

Bran treated with four different insecticides was field-tested as a crop protection measure against mainly third instar grasshopper populations composed mostly of Melanoplus sanguinipes (Fab.). The order of toxicity of these four insecticides was dimethoate 〉 fenvalerate 〉 propoxur 〉 pyridaphenthion. Five dosages of dimethoate were tested against mainly adult grasshopper populations. Rates of mortality due to both aqueous sprays (previously published results) and bran baits were compared. Degradation of both dimethoate and fenvalerate mixed with bran was small when stored in the laboratory at either 1°C or 20°C.

Evaluation of insecticide-treated bran baits for grasshopper control in Saskatchewan (Orthoptera: Acrididae).

Sampling distribution and sequential sampling for subterranean stages of orange wheat blossom midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae) in spring wheat.

M.K. Mukerji

Papers

Relationship between infestation levels and yield loss caused by wheat midge, sitodiplosis mosellana (géhin) (diptera: cecidomyiidae), in spring wheat in saskatchewan

Evaluation of Nosema locustae (Microsporida) as a control agent of grasshopper populations in Saskatchewan

Development of sampling designs for egg and larval populations of the wheat midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae), in wheat.

Evaluation of insecticide-treated bran baits for grasshopper control in Saskatchewan (Orthoptera: Acrididae).

Sampling distribution and sequential sampling for subterranean stages of orange wheat blossom midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae) in spring wheat.