The biology of Lygus spp. (Heteroptera: Miridae) on oilseed rape in Manitoba
Leferink, Johannes H. M.
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The seasonal development of species of Lyqus Hahn was studied on oilseed rape (Brassica napus L.) in the field and laboratory in Manitoba. In the field experiments, four seedings of oilseed rape (cv. Westar) were made at regular time intervals in 1988 and 1989 at Glenlea, Manitoba. The experiment was conducted in four replicate plots in 1988 and five in 1989, with each p1ot, measuring 5 by 20 m. The species composition of the lygus bugs was determined. Lysus lineolaris (Palisot de Beauvois) accounted for 82.9 and 55.2% of the adult lygus bugs on oilseed rape in 1988 and 1989, respectively. Lyqus desertinus Knight and L. borealis (Kelton) together accounted for 17.1% of the adult lygus bugs in 1988 and for 7.7 and 37.1%, respectively, in 1989. Rearing of the nymphs resulted in adults of all three species, which indicated that all three species reproduced on this crop. Adult. lygus bugs first appeared on oilseed rape at the beginning of flowering stage. Nymphs appeared from 1 to 3 weeks later. Peak abundances and median of the nymphal instars and peak abundances and timing of median of the new adults occurred during the pod development stages. New adults of L. desertinus usually reached median and peak abundances earlier than L. borealis. The median of L. desertinus was from 8.2 days earlier to 0-2 days later than that of L. borealis, and from 6.5 days earlier to 1.6 days later than that of L. lineolaris. The peak of L. desertinus was from 3 to 10 days earlier than that of L. borealis and L. lineolaris. The effect of temperature on the rate of development of L. lineolaris was determined in the laboratory. Lyqus lineolaris was reared from egg hatching to the adult stage at five different temperatures ranging from 15.6* to 22.1*C. All rearing was at 80 + 5% R.H., and 16 h L : 8 h D photoperiod. The relation between temperature and rate of development of each nymphal instar was linear. Developmental time was negatively related to temperature: at 22.1*C the average time for development was 19.6 (SD = 1.3) days and at 15.5*C it was 41.8 (SD = 1.9) days. Threshold temperatures for development were estimated at 6.1, 8.3, 9.8, 10.7, and 11.4*C for the first, second, third, fourth, and fifth nymphal instar, respectively. The daily average air temperatures in the field were used as a parameter to estimate the expected times for development of L. lineolaris in the field in 1988 and 1989. The starting point for the estimated developmental times was the observed time of the median of the first nymphal instar. The observed times of the median of the adult stage were from 0.4 later to 22.3 days earlier than the expected times during the two years.