POLARIZED LIGHT AND BODY TEMPERATURE LEVEL AS ORIENTATION FACTORS IN THE LIGHT REACTIONS OF SOME HYMENOPTEROUS AND LEPIDOPTEROUS LARVAE

Abstract

Larvae of the diprionid sawfly, Neodiprion banksianae Roh., the lasiocampid, Malacosoma disstria Hbn., and the tortricid, Choristoneura fumiferana (Clem.), were used to demonstrate the effects of heat and of plane-polarized light upon the photic orientation of immature insects. Photic orientation was shown to be primarily a result of internal temperature level. When larvae were heated sufficiently, they reversed the sign of their orientation. Larvae of the three species were sensitive to variations in the plane of polarization, and they used the polarization pattern of the sky to varying degrees in their orientation. Neodiprion larvae orientated primarily with reference to the polarization pattern when one was available. Malacosoma larvae and photonegative Choristoneura larvae appeared to orientate with reference to the position of the sun, but rotation of the axis of a "Polaroid" screen through 90° could change the direction of their travel by this amount. On the other hand, photonegative Choristoneura larvae subjected to a 90° shift of the axis continued to orientate with reference to the solar compass position when the sun was visible, even when their actions under the "Polaroid" showed that they could detect changes in polarization. The type of eye structure, the number of pairs of eyes, and the position of these on hypognathous and prognathous heads are considered to have some influence upon the different degrees of efficiency in orientation. Smoke and ice crystal cloud affected the orientation of the "Polaroid" axis that would produce a response, notably when the sun was obscured. Water droplet cloud had little effect, except in a complete overcast, under which polarization was disrupted.