廣食性幼蟲若把老葉新葉混著吃比較頭好壯壯

圖片來源：SwampThings文獻來源：R Johns, DT Quiring, R Lapointe, CJ Lucatotti. 2009. Foliage-age mixing within balsam fir increases the fitness of a generalist caterpillar. Ecological Entomology 34(5): 624-631. DOI: 10.1111/j.1365-2311.2009.01110.x

1. 作者利用野外操作實驗評估一種極度廣食性的植食性幼蟲-白斑毒蛾(Orygia leucostigma Smith)對植物-膠樅(Abies balsamea (L.) Mill)枝葉年齡的偏好表現情形。
2. 田野調查指出早齡幼蟲幾乎只取食年輕的枝葉（近一年生長者），而熟齡幼蟲則同時取食年輕和成熟的枝葉（如一年、兩年）。
3. 實驗中發現早齡幼蟲中取食幼嫩（近期或一年）枝葉者具有最高的存活率，但在取時老熟枝葉的組別中存活率則顯下降。相反地，熟齡幼蟲具有最高存活率的組別出現在能夠取食到所有年紀的枝葉者，而在熟齡幼蟲時期取食年輕枝葉者卻具有最高的生殖潛力。
4. 整體而言，能夠取食到所有年紀階層植物的幼蟲，其適應度比僅能取得一個年齡層枝葉的幼蟲高出 32–65% 。
5. 以上結果同時支持“互補飲食假說”和“個體發生學假說”。前者說明混合不同年齡層枝葉的食物能增加養分的攝取且/或稀釋掉有害的植物次級代謝物，而後者則歸因於昆蟲幼期在成長發育過程中隊營養需求之改變與/或對植物防禦的容忍度。

Abstract.

1. Manipulative field studies were carried out to evaluate the foliage age preference–performance relationship for an extreme generalist herbivore, the whitemarked tussock moth (Orygia leucostigma Smith) (Lepidoptera: Lymantriidae), within balsam fir [Abies balsamea (L.) Mill].
2. Field surveys indicated that early instar caterpillars fed almost exclusively on young (i.e. current-year) foliage, whereas late instars caterpillars fed on both young and mature (i.e. 1- and 2-year-old) foliage.
3. Survival of early instar caterpillars was highest in treatments where current-year and/or 1-year old foliage were available, but decreased significantly on older foliage. In contrast, late instar caterpillars had the highest survival when allowed to feed on all age classes of foliage, whereas potential fecundity was highest for late instars that fed on young foliage.
4. Overall, caterpillars had 32–65% higher fitness when able to feed on all rather than just one age class of foliage.
5. These results support both the ‘complementary diet’ hypothesis, which states that dietary mixing of different-aged foliage can increase nutrient uptake and/or dilute harmful secondary plant chemicals, and the ‘ontogeny’ hypothesis, which attributes changes in diet to changes in the nutritional needs and/or tolerance to plant defences of juvenile insects as they develop.

Key words. Foliage quality, foraging behaviour, intra-tree heterogeneity, polyphagy, whitemarked tussock moth.