Losses of canola seeds from feeding by Lygus species [Heteroptera: Miridae] in Manitoba

Abstract

Pods of canola plants (Brassica napus L., mostly cv. Westar) were sampled annually from 11–40 canola fields in Manitoba in 1985–1991. The effects of temperature, precipitation, and lygus bug density (in 1989 and 1990) on seed classes (normal, aborted, and collapsed) were determined. In 1991, all pods from 10 racemes sampled from each of 11 canola fields in Manitoba were examined, and the collapsed seeds were classified as injured by lygus bugs or not. The proportion of aborted seeds was not related to lygus bug densities or to weather conditions. The proportion of collapsed seeds varied from 2 to 53% among fields and was related to the number of lygus bugs in the field at the time the pods were collected. Collapsed seeds increased by 1.5% for each lygus bug per sweep. In 2 yr, the proportion of collapsed seeds increased with the mean monthly temperature and decreased with the total precipitation in July, but these weather factors accounted for little of the variation in the proportion of collapsed seed in most years. Collapsed seeds occurred at low frequency in many pods at all canopy levels, but they were most common in small pods in the upper part of the canopy. The proportion of seeds injured by lygus bugs was estimated to be 3–5%, on average, and in some fields, 20%. In addition, lygus bug feeding on other parts of the host plant may induce seed collapse. Key words: Insecta, Lygus, Brassica napus, seed damage, canola

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

“…Plant bugs in the genus Lygus damage canola (oilseed rape, Brassica napus L., and Brassica rapa L.) growing in western Canada (Butts and Lamb 1991b;Turnock et al 1995). Three species, Lygus lineolaris (Palisot de Beauvois), Lygus borealis (Kelton), and Lygus elisus Van Duzee, are common on canola and alfalfa in Manitoba, although L. lineolaris is often the most abundant (Schwartz and Foottit 1992;Timlick et al 1993).…”

“…The three plant bug species are assumed to feed in similar ways on the crop. 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). 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).…”

“…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). An economic threshold for insecticidal control has not been established, because the relation between plant bug abundance and canola yield loss is difficult to quantify (Butts and Lamb 1991b;Turnock et al 1995). An economic threshold for insecticidal control has not been established, because the relation between plant bug abundance and canola yield loss is difficult to quantify (Butts and Lamb 1991b;Turnock et al 1995).…”

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

“…Three species of Lygus are pests of canola: L. lineolaris (Palisot de Beauvois), L. borealis (Kelton), and L. elisus Van Duzee (Timlick et al 1993). Yearly field losses of seed from Lygus feeding are at least 3-5% and in some fields reach 20% (Turnock et al 1995). Butts and Lamb (1991) and Gerber and Wise (1995) described the number of generations and seasonal occurrence of Lygus species in northern Alberta and southern Manitoba, respectively.…”

Suitability of Brassica juncea (Brassicaceae) as a host plant for oviposition for Lygus lineolaris (Palisot de Beauvois) (Heteroptera: Miridae)

“…Cutlass) were 8.4 times lower than from the inflorescence of B. napus, indicating that the differences in oviposition on these species were due to the presence of an antixenosis-type of plant resistance factor(s) in the inflorescence of B. juncea. (Schwartz and Foottit 1992;Timlick et al 1993;Gerber and Wise 1995;Turnock et al 1995). Crop resistance, based on oviposition non-preferences (antixenosis) of Lygus bugs on species of Brassica and Sinapis, is of interest because this crop protection strategy might prove important in population suppression of these pest insects and in reduction of damaged seeds and yield loss.…”