Ifluence of High Temperature and Light on Postdiapause Development of the Wheat Stem Sawfly1,2

Can. Enr. 114: 775-788 (1982) The effects of the major factors on populations of the wheat stem sawfly, Cephus cinctus Norton, were studied in the field at Lethbridge, Alberta between 1970 and1977. Fecundity of the females, which contain an average of 32.7 eggs, is influenced by the condition and variety of host plants in which they develop as larvae. Populations of the adults that emerge from infested crops cut 7-9% by the larvae in one year may infest 7@80% of the stems of adjacent crops in the following year. Increased adult densities, however, fail to increase markedly the percentage of stems' infested because the adults concentrate at field margins when they reinfest the most preferred stems. Because only one larva can mature in each stem, competition within stems that receive more than one egg causes a major drop in the population but not in the percentage of infested stems cut. Another major drop is caused by host plant resistance, which is influenced in both susceptible and resistant wheats by the weather during the growing season.On an average, all of the larvae die in 28% of the infested stems of two susceptible wheats and in 67% of those of a resistant wheat. The mortality in resistant wheats, however, is generally not sufficient to prevent economic infestations in subsequent years. Parasitism, which was a major factor in only 7 of 36 years in southern Alberta, is increased by weather conditions that cause delayed ripening of the wheat crops. The mortality of mature larvae and pupae averaged 21.3%. It is affected by extremes of moisture and temperature and can be ihcreased slightly by shallow tillage of infested stubble. ResumeEntre 1970 et 1977, on a Ctudie sur le terrain, B Lethbridge (Alberta), l'effet des facteurs principaux sur les populations de ctphes du blt (Cephus cinctus Norton). La ftconditk des femelles, qui contiennent en moyenne 32.7 oeufs, dtpend de l'ttat et de la variktk de la plante h6te dans lesquelles elles se sont dtveloppkes au stade larvaire. Les adultes qui tmergent des cultures infesttes, ayant une proportion de 7 i 9% des tiges coupkes par les larves durant l'annee, peuvent infester 70-B 80% des tiges des cultures adjacentes, l'annte suivante. Cependant, une plus grande densitk d'adultes n'a pas pour effet d'accroitre de f a~o n marquke le pourcentage de tiges infestkes, car les insectes se concentrent sur les pourtours des champs ou ils rtinfestent les tiges prtftrtes. Etant donnk qu'une seule larve peut atteindre la maturitt dans chaque tige, la concurrence B l'inttrieur des tiges qui re~oivent plus d'un oeuf entraine une chute marqute de la population, mais non du pourcentage de tiges coupies. Un autre facteur responsable de la diminution de la population est la rksistance de la plante h6te qui dtpend, tant chez les blBs sensibles que rtsistants, des conditions climatiques durant la pkriode de croissance. En moyenne, toutes les larves ont ptri dans 28% des tiges infesttes de deux blts sensibles et dans 67% de celles d'un blt rtsistant. Toutefois la mortalitt dans les bl...

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

POPULATION DYNAMICS OF THE WHEAT STEM SAWFLY, CEPHUS CINCTUS (HYMENOPTERA: CEPHIDAE), IN WHEAT

Holmes¹

1982

“…Climex sets the weekly population growth index to zero during weeks when the species is in diapause. At 10 °C, obligatory diapause lasted between 40 and 110 days (Salt 1946), 90 days (Holmes 1982), and 90–100 days (Villacorta et al 1971). All of these studies were conducted at temperatures between 5 °C and 10 °C and were warmer than temperatures that C. cinctus would be exposed to under North American field conditions.…”

Section: Model Developmentmentioning

confidence: 99%

“…Based on presence of larvae and termination of larval activity in the fall, final values were set to 15 hours (DPDO) and 8 °C (DPTO). Though the species is widely distributed, it does not occur south of 36°N (Villacorta et al 1971). A diapause-index value of zero would indicate that model conditions have not been met in order to induce and/or terminate diapause.…”

Section: Model Developmentmentioning

confidence: 99%

Bioclimatic assessment of abiotic factors affecting relative abundance and distribution of wheat stem sawfly (Hymenoptera: Cephidae) in western Canada

Olfert¹,

Weiss²,

Catton

et al. 2018

Wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), indigenous to North America, quickly adapted from host native grasses to wheat crops (Triticum Linnaeus (Poaceae)) with expansion of agriculture on the Great Plains of North America. Bioclimatic simulation tools, such as Climex, predict the potential geographic distribution and establishment of insects in ecosystems, based on climate. The ecoclimatic index, a measure of ecological suitability, integrates potential population growth with stresses to produce estimates of relative abundance. This simulation software was used to develop a bioclimate model for C. cinctus in western Canada. Results fostered a better understanding of how C. cinctus responded to selected climate variables. Two general circulation models were then applied to assess the response of C. cinctus populations to future climate. Relative to current climate, predicted changes in C. cinctus distribution and relative abundance were greatest for 2030, with a small further increase for 2070. Across the Prairies and Boreal Plains Ecozones, changes in ecoclimatic index were greater than in geographic distribution. Both general circulation models indicated most of this area would be categorised as very favourable. This suggests that the potential for pest populations could expand into areas that do not currently experience economic losses associated with C. cinctus.

“…feeding behavior but might have had an inhibitory effect on the spinning of cocoons and diapause initiation. Effects of light on postdiapause development of C. cinctus have been reported (Villacorta et al 1971), but effects on pre-diapause development remain unclear (Holmes 1975). In an attempt to determine the effect of light on diapause initiation of C. cinctus, in a previous study we (W.L.M., unpublished data) painted infested wheat stems black and observed no inhibitory effects on diapause initiation.…”

mentioning

confidence: 96%

Rearing the wheat stem sawfly on an artificial diet

Macedo

Peterson

et al. 2005

The wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), is an insect pest in dryland wheat cropping systems in the southern Canadian Prairies and the northern Great Plains of the United States (Morrill 1997). Yield losses caused by C. cinctus are due to reduced head weight (Holmes 1977; Morrill et al. 1992) and lodging, which decreases harvest efficiency. Estimates of yield losses in Montana alone are about US$25 million per year.