專食性幼蟲無法在3cm距離外分辨前方植物能否下嚥

圖片來源：Paul J. Thompson

文獻來源：P Bierzychudek, KA Warner, A Mchugh, L Thomas. 2009. Testing the host-finding ability of a monophagous caterpillar in the field. Ecological Entomology 34:632–637. DOI: 10.1111/j.1365-2311.2009.01112.x

1.目前關於直接觀察專一植食性昆蟲在未受損的寄主植物與非寄主植物間移動之能力的研究相對較少，然而相關的資訊可提供作為制定保育政策時的重要參考。
2.作者選用瀕危的奧勒岡銀點蝴蝶Speyeria zerene hippolyta (Edwards)置於直徑10cm的透明容器中研究，將幼蟲置於容器中央，周圍擺放三株該幼蟲的寄主植物-鉤距堇菜(Viola adunca)與三株均為不同種類的非寄主植物，中間以裸露地區隔。在第二個試驗中，作者將二齡幼蟲放在間隔3–6 cm的寄主植物與非寄主植物之間，藉此觀察幼蟲選擇走向寄主植物的頻率是否比較高。
3.實驗結果發現幼蟲走向植物的傾向確實顯著高於隨機移動，然而，走向其寄主植物的頻率並沒有顯著高於非寄主植物，而是純粹基於植物的接近程度。
4.綜合以上實驗結果，奧勒岡銀點蝴蝶幼蟲可以在10cm遠處分辨植被與裸露地，但目前沒有證據顯示他們可以在3cm的距離辨認前方植物是否為其寄主植物。

Abstract.
1. Relatively few studies of the host-finding ability of specialised, phytophagous insects involve direct observations of individual insects moving among intact hosts and non-hosts. Information from such studies can inform the design of restoration programmes for species of conservation concern.
2. The movement of caterpillars of the threatened Oregon silverspot butterfly, Speyeria zerene hippolyta (Edwards) (Lepidoptera: Nymphalidae) was studied in the field in cleared arenas with 10 cm radii. Caterpillars were placed in the centre,
surrounded by three individuals of their host, Viola adunca, and three different nonhost individuals, separated by bare ground. In a second experiment, second instars were placed between a host and a non-host, 3–6 cm away. Caterpillars were observed to determine if they walked to their host more often than expected by chance.
3. Caterpillars walked to vegetation significantly more often than expected by chance. They did not, however, reach their hosts more often than expected, based on plant availability.
4. It is concluded that S. z. hippolyta caterpillars can distinguish vegetation from bare ground from 10 cm away. There is no evidence that they can distinguish their host plant from other herbaceous species at distances of 3 cm.

Key words. Conservation, experiment, host plant, Lepidoptera, movement behaviour, reactive distance, Speyeria zerene hippolyta.