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Vol. 55, 2016
(update: 2016.5.31)
Population Dynamics and the Effects of Temperature on the Eggs of the Seawater-dispersed Stick Insect Megacrania tsudai (Phasmida: Phasmatidae)
doi:10.6620/ZS.2016.55-20
Shun Kobayashi1,2,*, Ryota Usui3,
Kouta Nomoto4, Mineyuki Ushirokita5, Tetsuo Denda66,
and Masako Izawa6
1Graduate School
of Engineering and Science, University of the Ryukyus, Senbaru 1,
Nishihara, Okinawa, 903-0213 Japan
2Research Fellow of Japan Society for the
Promotion of Science
3Graduate School of Agriculture,
University of the Ryukyus, Senbaru 1, Nishihara, Okinawa, 903-0213 Japan
4Itami City Museum of Insects, Koyaike
3-1, Itami, Hyogo, 664-0015 Japan.
5ECO-PLANNING RESEARCH co. Ltd.,
Sakaemachi 2-28-5, Higashimurayama, Tokyo, 189-0013, Japan
6Faculty of Science, University of the
Ryukyus, Senbaru 1, Nishihara, Okinawa, 903-0213 Japan
(Received 2 June 2015; Accepted 4 January 2016)
Shun Kobayashi, Ryota
Usui, Kouta Nomoto, Mineyuki Ushirokita, Tetsuo Denda,
and Masako Izawa (2016) Although
the stick insect Megacrania tsudai
cannot fly, its eggs are dispersed by seawater, which allows the
species to distribute itself widely via the ocean. The life history of
this non-volant insect that establishes settlements by egg dispersal
remains poorly understood. We aimed to clarify the population dynamics
and effects of temperature on the eggs of M. tsudai through
field observation in near the northern limits of the distribution and
laboratory experiments. In the wild, all instars appeared over a period
of several months, with a larger proportion of first instars emerging
from December to March, and a greater number of adults being observed
from June to August. Laboratory experiments showed that the hatching
rate of M. tsudai was not different between conditions of 25
and 30°C, whereas it was significantly lower at 20°C. The
egg-development period was shorter when eggs were maintained under high
temperature conditions, and longer for eggs kept at 20°C. The effective
cumulative temperature was estimated as 1561.5-2000.0°C, and the
developmental zero was estimated as 12.2-13.9°C. The peak appearance of
the first instar in the laboratory, which was used to obtain an
estimate for the effective cumulative temperature and peak appearance
of adults in the wild, was not entirely accurate because the peak
appearance of the first instars in the wild was not consistently
observed when the estimation indicated that they should appear. Megacrania
tsudai
is a univoltine in near the northern limit of its distribution, and
temperature has a strong effect on its egg development. Our estimation
of population dynamics by laboratory experiments did not exactly
predict what was observed in the field and it may be controlled by
other factors. However, our findings indicate that the limiting factor
of the distribution of this species is likely the effect of temperature
on egg hatching.
Key words:
Developmental zero, Hatching rate, Megacrania tsudai,
Non-volant, Northern limit, Population dynamics, Seawater dispersal,
Temperature.
*Correspondence: E-mail: cheirotonus.jambar@gmail.com
Citation: Kobayashi S, Usui R, Nomoto K, Ushirokita M,
Denda T, Izawa M. 2016. Population dynamics and the effects of
temperature on the eggs of the seawater-dispersed stick insect Megacrania tsudai (Phasmida: Phasmatidae). Zool Stud 55:20. doi:10.6620/ZS.2016.55-20.
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