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 76 eggs and colony odor DHJanzen100158.jpg high resolution
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The eggs are immediately attacked by the ants, but they are very hard (like hard plastic), curved and slippery, and of such large diameter that the ants cannot open their mandibles wide enough to get around them (this large size and shape is, again, the normal size and shape for moths of this body size in the Saturniidae). The eggs hatch 6 days later. In the meantime, the attack by the ants has subsided, presumably because the eggs have acquired the colony odors by being bathed continually in it (and being continually trod on by the ants as well). Of greater importance, the young first instar caterpillars have also acquired the colony odor so that when they chew their way out of their eggs, they are not attacked by the ants. The young first instar larvae are also quite densely spiny, not a soft caterpillar easily grabbed by an excited/upset ant. As the caterpillars grow, they continue to have the colony odor and pass through larval development in about a month (pupation is in the soil below the acacia). The amount of foliage on a healthy large occupied ant-acacia is enough to feed 4-6 Syssphinx mexicana caterpillars through their development. In other words, the flight response by the ovipositing female creates the right amount of oviposition, and requires an aggressive ant colony for its completion. When the ant colony had been experimentally removed, and 3-5 times as many eggs were therefore laid on an unoccupied ant-acacia, all of the caterpillars starved to death after eating all the foliage off the plant long before completing their development. In summary, Syssphinx mexicana has evolved a number of traits as part of its obligatory use of ant-acacias (its larvae develop poorly or not at all on other species of Fabaceae, presumably because of the defensive chemicals in the foliage of these other plants), but there is no indication that the ants have evolved any trait (either repulsive or facilitatory) in response to the presence and activities of Syssphinx mexicana eggs, caterpillars and adults. |
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