Variation in the number of nymphal instars inNysius huttoniWhite (Hemiptera: Lygaeidae)

Abstract

The number of nymphal instars of Nysius huttoni White was investigated at five constant temperatures (15, 20, 25, 30 and 3590.58C), one fluctuating (laboratory room conditions) temperature and three photoperiods (16-h, 12-h, and 8-h photophases) in the laboratory. Nymphs passed through four to six instars before they emerged as adults, individuals with five instars formed over 90% of the population, whereas those with four or six instars formed 4.2Á5.8 and 1.6Á2.9% respectively. Two nymphs were each recorded to pass through three and seven instars before emergence as adults. Both temperature and photoperiod affect the number of nymphal instars. Insects with four instars were more frequent at lower temperatures and those with six instars tended to be most frequent at higher temperatures. An 8-h short-day photoperiod resulted in more 4-and 6-instar types than other photoperiods. There was no obvious difference in the duration of nymphal stages of individuals with a maximum four, five, or six instars (P!0.05, t-test). This is the first report to show variation in the number of instars in a species of Lygaeidae. The results indicate a potential increase in survival of this adult-overwintering species, as more autumn generation nymphs in the field could reach the adult stage.

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“…There may be differences in life history patterns between species or even geographically within a species. The usual number of nymphal instars is 5, as in other lygaeoid bugs, but Millikin (1918) reported 4 to 6 nymphal instars and this is supported by Wei (2010), who observed similar variation in the New Zealand species, N. huttoni White. Wei found the number of instars was positively correlated to rearing temperature.…”

The evolutionary ecology of the Lygaeidae

“…In the laboratory, variation in the number of instars is affected by both temperature and photoperiod, with lower numbers of instars more frequent at lower temperatures (Wei 2010). This suggests that flexibility in the number of larval instars may aid survival under changing environmental conditions (Wei 2010). N. huttoni normally have three generations per year in their natural range and overwinter as adults; therefore, a shorter nymphal stage could potentially be Phelan and Frumhoff (1991), Root and Chaplin (1976) Oncopeltus fasciatus Typical clutch size is approximately 30 eggs though this appears to be highly variable (recorded clutch sizes range from 5 to more than 50).…”

“…In this species, the number of larval instars ranges from three to seven, though individuals with five instars still form the majority. In the laboratory, variation in the number of instars is affected by both temperature and photoperiod, with lower numbers of instars more frequent at lower temperatures (Wei ). This suggests that flexibility in the number of larval instars may aid survival under changing environmental conditions (Wei ).…”

Evaluating responses to temperature during pre-metamorphosis and carry-over effects at post-metamorphosis in the wood tiger moth ( Arctia plantaginis )

“…It has been shown that moulting is a period of high activity and regulation of several processes such as digestion, transport, proteolysis and cell death [6][7][8][9]. Likewise, larval moults can vary in number and frequency in response to environmental conditions such as temperature and diet [10,11]. Thus, the larval stage is highly responsive at many functional levels.…”