SEASONAL OCCURRENCE OF LYGUS SPP. (HETEROPTERA: MIRIDAE) ON ALFALFA IN SASKATCHEWAN

Abstract

Several species of Lygus (Hahn) that occur in Saskatchewan are serious and continuing pests of alfalfa grown for seed. They are readily controlled by any one of several insecticides, but the efficiency of this control is dependent upon knowing their seasonal development and occurrence on the crop.In the years 1976 and 1978, at three locations in Saskatchewan, populations of Lygus in alfalfa seed crops were sampled at 5-to 7-day intervals throughout the period of insect activity. In 1979 and 1980 samples of bugs were taken occasionally from the same locations, and in all years from other locations in the province. A sample consisted of 6 7 0 0 specimens collected by either a 38-cm sweepnet in not less than 25 and as many as 200 random sweeps, or a D-Vac sampler in not less than 3 m2 in spring and after harvest when sweep-sampling was not possible. Collected specimens were preserved in alcohol, sorted, and identified. Additional data, not previously published, were available from a similar mid-1950's study of Lygus seasonal occurrence in alfalfa seed crops in the Torch River district of northeastern Saskatchewan.Because the nymphs of the genus Lygus cannot be identified to species, the proportions of the various species collected were determined from the adults, identified according to Kelton (1975).At each sampling date when adults were present, a representative number of not less than 10 and not more than 50 female adults were collected, killed, and dissected. The females were classified as: reproductive-mated, some oogenesis, pre-laying or laying, and non-reproductive-teneral, not mated, absence of oogenesis, fat bodies hypertrophied, in diapause. Male adults were also dissected and classified as above, according to testicular and accessory glandular development.The extensive sampling has shown that Lygus adults generally do not overwinter in alfalfa fields. In the fall as the alfalfa matures they move to more succulent native autumn plants, then hibernate in the shelter of plant litter. In the spring they become active and feed on early-growing plants, and migrate to alfalfa when it becomes suitable for feeding and oviposition.The seasonal occurrence of Lygus nymphs and adults in alfalfa seed crops at three locations are illustrated in Fig. 1. The curves are the means of 4 years' data, expressed as the percent of the total population in nymphal and adult stages throughout the period of activity. Because first-and second-instar nymphs are difficult to distinguish fronl one another they are combined in a single curve. Occurrence can vary by as much as 7 days about these means, due to weather and possibly to species content of the Lygus population.At Moose Jaw, lat. 50°N, long. 105"W, in the shortgrass prairie region, the species composition of the adults was 84% Lygus borealis (Kelton), 13% Lygus desertinus Knight, and 3% Lygus lineolaris (Palisot de Beauvois). Hatch of eggs laid in the alfalfa stems by overwintered females begins about 10 May and is concentrated in a 3-week period. The peak of summer, first-gene...

Insecticidal control of late-season plant bug (Hemiptera: Miridae) infestations in Manitoba has no effect on alfalfa seed quantity and quality

“…When late instar nymphs and adults of lygus bugs attack the same host plant stages, nymphs were more injurious than adults in buckwheat (Mostafa 2007), but approximately equally injurious in beans (Khattat and Stewart 1975), strawberries (Easterbrook 2000) and cotton (Gutierrez et al 1977). At the end of the growing season in the Prairie Provinces, adult lygus bugs are in reproductive diapause (Craig 1983), and so may feed less as they prepare to over-winter. Thus, the lack of effect on yield of lateseason populations of plant bugs in our study may result from a combination of reduced plant vulnerability and diminished plant bug feeding activity.…”

“…lineolaris (Palisot), L. borealis (Knight) and L. elisus (Van Duzee) (Craig 1983;Timlick et al 1993;Braun et al 2001;Mostafa 2007).…”

“…Unlike alfalfa for hay, plant bugs in seed crops can find favoured feeding sites throughout most of the growing season, and mowing does not reduce their numbers through disturbance or habitat loss (Uddin 2005). Both alfalfa plant bugs and lygus bugs can complete development on alfalfa (Hughes 1943;Craig 1983;Gerber and Wise 1995), and alfalfa plant bugs are relatively restricted to this crop (Hughes 1943). In Manitoba, lygus bugs may also complete development on canola and other crops that mature early (Gerber and Wise 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

“…The simultaneous occurrence of more than one Lygus species on canola and other crops is common (Fye 1982;Craig 1983;Domek and Scott 1985;Butts and Lamb 1991;Schwartz and Foottit 1992;Timlick et al 1993). Colonizing adults, nymphs, or new-generation adults were present on the rosette, bud, flower, or pod development stages of canola, indicating that these species all reproduce and develop populations on this crop in Manitoba.…”

Damage to wheat seeds caused by a plant bug, Lygus lineolaris L.

“…(Heteroptera: Miridae), are pests of many crops in western Canada, reducing yield of canola (Wise and Lamb 1998) and seed alfalfa (Craig 1983) by damaging developing seeds (Butts and Lamb 1990). These plant bugs or related true bugs are suspected of causing damage to seeds of Canadian wheat, although the causative agent of the damage has not been confirmed.…”