DEVELOPMENT OF ADULT AND NYMPHAL POPULATIONS OF LYGUS LINEOLARIS (PALISOT DE BEAUVOIS), L. ELISUS VAN DUZEE, AND L. BOREALIS (KELTON) (HETEROPTERA: MIRIDAE) IN RELATION TO SEEDING DATE AND STAGE OF PLANT DEVELOPMENT ON CANOLA (BRASSICACEAE) IN SOUTHERN MANITOBA

Abstract

The Canadian Entomologist 129: 777 -787 (1997) The development of adult and nymphal populations of Lygus lineolaris (Palisot de Beauvois), L. elisus Van Duzee, and L. borealis (Kelton) was studied in relation to seeding date and stage of plant development in four seedings of canola (cv. Westar) in field plots at Glenlea, Manitoba, in 1988 and 1989. Lygus lineolaris was the dominant species in all seedings and in both years. Colonizing adults (first-generation adults) of the t h e e Lygus spp. first invaded the plots at about the same time from the late rosette to the early flowering stages of plant development, and Lygus adult numbers reached maxima during flowering in all seedings. The stage of plant development, and not seeding date, was important in attracting colonizing adults of Lygus to canola. Second-generation nymphs first appeared at the flowering stage of canola. All nymphal instars reached maxima and median abundances during the late flowering and pod development stages in all seedings. Second-generation adults were present from early to late pod development stages. Median abundances of second-generation adults of L. lineolaris, L. elisus, and L. borealis usually were reached at the same plant growth stage in each seeding. Leferink, J.H.M., et G.H. Gerber. 1997. Dynamique des populations d'adultes et de larves de Lygus lineola~is, L. elisus, et L. borealis (Heteroptera: Miridae) en fonction des dates d'ensemencement et des stades de croissance des plants dans des cultures de colza (Brassicaceae) du sud du Manitoba. The Canadian Entomologist 129 : 777-787. RQum6 La dynamique des populations d'adultes et de larves de Lygus lineolaris (Palisot de Beauvois), L. elisusvan Duzee et L. borealzs (Kelton) a Ct C CtudiCe en fonction des dates d'ensemencement et des stades de croissance des plants dans quatre semis de colza (cv. Westar), 9 Glenlea, Manitoba, en 1988 et 1989. Lygus lineolaris a Ct C I'espbce dominante dans tous les semis, au cours des 2 annCes. Les adultes colonisateurs (premikre gCnCration d'adultes) des trois espkces de Lygus ont envahi les semis 9 peu prbs en m&me temps, entre le stade rosette et le dCbut de la floraison, et c'est au cours de la floraison que le nombre d'adultes de Lygus a atteint un maximum, dans tous les semis. C'est le stade de croissance de laplante, et non pas ladate d'ensemencement, qui est le facteur dCterminant de 1'anivCe des adultes de Lygus dans les semis de colza. Les larves de la seconde gCnCration sont apparues au cours de la floraison du colza. Tous les stades larvaires ont atteint leur abondance maximale et leur abondance mCdiane vers la fin de la floraison et durant le dCveloppement des siliques, dans tous les semis. Les adultes de la seconde gCnCration ont Ct C prCsents durant toute la pCriode de dCveloppement des siliques. L'abondance mCdiane des adultes de deuxibme gCnCrafiun de L. tineotaris, L. elisus et L. borealis Ctait gCnCralement atteinte au m&me stade de croissance des plants dans chacun des semis. [Traduit par la RCdaction] Contribution No. 1656...

ECONOMIC THRESHOLD FOR PLANT BUGS, LYGUS SPP. (HETEROPTERA: MIRIDAE), IN CANOLA

“…In Alberta, Butts and Lamb (1991a) found few plant bugs until the fourth-and fifth-instar nymphs appeared, which usually coincided with the end of flowering. In Manitoba, Leferink and Gerber (1997) collected increasing numbers of plant bug nymphs with a sweep net until the fourth and fifth instars appeared.and pods,.ri~ned. The results fxom these studies imply that sweep-net samples taken before pods begin to develop, i.e., growth stage 4.4 or earlier, may underestimate plant bug densities and are less reliable than samples taken at growth stages 5.1 and 5.2.…”

“…The three plant bug species are assumed to feed in similar ways on the crop. They complete a single generation on canola, when the crop is producing buds, flowers, and pods (Butts and Lamb 1991a;Gerber and Wise 1995;Leferink and Gerber 1997). Plant bugs reduce yield directly by damaging individual seeds, or indirectly by feeding on buds, flowers, stems, or leaves (Butts and Lamb 1990;Turnock et al 1995).…”

SAMPLING PLANT BUGS, LYGUS SPP. (HETEROPTERA: MIRIDAE), IN CANOLA TO MAKE CONTROL DECISIONS

“…Another factor which affects the precision of sampling is the differential efficiency of sweeping for the early and late instars of plant bugs. Butts and Lamb (1991b) and Leferink and Gerber (1997) captured very few early instar nymphs of plant bugs in canola with a sweep net. In our studies, most of the plant bugs collected were either late instars or adults when sampling occurred at the crop stages recommended for control.…”