文獻來源: Pimentel C, Ferreira C and Nilsson J-Å. 2010. Latitudinal gradients and the shaping of life-history traits in a gregarious caterpillar. Biological Journal of the Linnean Society 100: 224-236.
此研究以松舟蛾 (pine processionary moth, Thaumetopoea pityocampa) 為例，探討地理因子的影響會如何塑造群居性物種之生活史特性。松舟蛾廣泛分布於地中海地區，其幼蟲為一典型之群聚性物種，一個群落由一雌性成蟲所產的一批卵組成，為地中海地區多種松樹的重要經濟害蟲。此研究回顧了整個地中海地區關於松舟蛾之文獻，特別針對松舟蛾在不同緯度、海拔、溫度及寄主植物的影響下，其生育力(卵之個數)、卵之大小、卵寄生蜂導致之死亡率、成蟲飛行時間、以及幼蟲成長時間之變化進行探討。結果顯示隨著緯度增加，松舟蛾的生育力有增加趨勢，但卵的大小並沒有隨之增加，松舟蛾於高緯度地區擁有較大的群落被認為與造巢策略及熱能調節有關，因此會隨著緯度權衡卵之大小與數目。除此之外，松舟蛾在不同寄主植物下，也會因針葉的堅硬度及氮的含量而影響卵之大小與數量。
The present study aimed to investigate how the impact of several factors linked to geography would shape history traits in a gregarious species, using the pine processionary moth (PPM) Thaumetopoea pityocampa as model system. PPM has a wide geographical distribution over the Mediterranean Basin, and it is a strictly gregarious species throughout larval development, where the total reproductive output of each female forms a colony. We reviewed both published and unpublished data on PPM from all over its distribution in the Mediterranean Basin and extracted data on fecundity, egg size, egg parasitoid mortality, flight period, and development time. These life-history traits were then related to location, expressed as latitude and altitude, local average temperatures, and host tree species. We found that PPM fecundity increaseed with latitude, concomitant with an increase in the length of development and an earlier onset of adult flight. These results are the opposite of that found in other Lepidoptera species with a wide geographical distribution, as well as in insects in general. We propose that a large colony size in PPM is important at higher latitudes because this confers an advantage for thermoregulation and tent building in areas where larvae have to face harsher conditions during the winter, thus shifting the optimal trade-off between the number and size of eggs with latitude. However, host tree species also affected the relationship between egg number and size and the optimal outcome of these traits is likely a compromise between different selection pressures.