Nysius huttoni (Hemiptera: Lygaeidae) : life history and some aspects of its biology and ecology in relation to wing development and flight.

Abstract

Aspects of the life history, general biology and wing polymorphism of the Lygaeid bug, N. huttoni are examined in this thesis. The effect of temperature on development of N. huttoni was studied in the laboratory at 5 constant temperatures (15, 20, 25, 30, and 35°C) and lab temperature (range 12.5- 29.5°C, mean 20.3°C). Time required for development from egg to adult ranged from 108 days at 15°C to 17.8 days at 35°C, and varied in a linear manner with temperature. Threshold temperatures and thermal unit requirements were obtained for eggs, each instar, the total nymphal stage, and overall development. Photoperiod also affected the development of N. huttoni. At 20°C, development from egg to adult was significantly faster under a 12-h photoperiod (57.7 days) than under 16-h (63.1 days) or 8-h photoperiods (65 days). At 27.5°C, however, the influence of photoperiod was less clear. In the field, N. huttoni had three overlapping generations a year and three peaks in abundance. Developmental duration and period of occurrence of each generation and life stage were recorded. Adults of the third generation overwintered from mid-April - early May, and emerged from hibernation in late August or early September. Three copulation peaks and three oviposition peaks occurred each year. Third-generation adults underwent reproductive diapause from late summer to early spring and the diapause was terminated within about two weeks in early spring. Naturally-induced diapause of adults collected from the field in autumn was also broken within about two weeks at 25°C/12L:12D in the laboratory. Adults entered diapause in about one month under 20°C/8L:16D conditions and terminated diapause in about one week when transferred to 25°C/16L:8D. Sex ratios of laboratory-reared populations were 1:0.90-1:1.31 (♀:♂) at six experimental temperatures and 1:0.69-1:1.86 under three photoperiods. Mean annual sex ratios of field-collected insects ranged from 1:1.05 to 1:1.23. Experiments showed that a single copulation could not fertilise a female for life, although sperm remained viable for one to three months. Parthenogenesis was not found. Laboratory experiments on the tolerance of adults to starvation indicated that starvation-longevity of first-generation adults (mean 4.2 days) was about twice that of second- and third-generation adults (mean 2.2 and 2.5 days). Water prolonged longevity (mean 8.4 days), while glucose in concentrations of 2-40% increased longevity substantially (means 27.6-51.6 days). Three wing-length morphs were identified in both sexes of N. huttoni: macropters (M), sub-brachypters (Sb), and brachypters (B). In the field, the M-form was numerically predominant (94.1%). M x M was the predominant mating combination (up to 80.9%), while ♂M x ♀Sb was the second most common combination (13.7%). Temperature and photoperiod affected wing development with low (≤ 15°C) and high (≥ 30°C) temperatures and a short photoperiod (8-h photophase) tending to favour the production of Sb- and B- forms. Temperature was a major factor inducing flight. Four species of insects in 4 families and two orders, and five species of spiders belonging to 4 families in one order all attacked N. huttoni under laboratory conditions. However, their significance as predators in the field is unknown since no encounters were seen.