Sex on Six Legs_ Lessons on Life, Love, and Language From the Insect World - Marlene Zuk [11]
Even more impressive than the ability of these wasps is that of another species of wasp that exploits the provisioning kind. These parasites do not care about the wasp larvae waiting for their paralyzed meal, but about the caterpillars that are brought to the larder. Instead of going out and hunting down their own prey, the parasitic wasps capitalize on the food brought in by the hunters and lay their own eggs on the item. The problem is that only a very narrow window of opportunity to lay an egg on the caterpillar exists, which is during the time that the caterpillar is being dragged into the nest by the wasp that first captured it. So instead of trusting to luck to find a host at exactly the right moment, the parasitic wasp performs a reconnaissance mission, flying around areas where the provisioning wasps are likely to be digging their nests, an activity that takes quite a long time and is much more apparent than the brief provisioning period. Once a nest-building wasp is detected, the parasitic wasp remembers where the nest is located and keeps that nest site under surveillance, so that she can spot when provisioning occurs, often many days later. Then she slips in and hurriedly lays her own eggs on the caterpillar.
Yet another species of parasitic wasp lays its eggs on clusters of checkerspot butterfly eggs. The catch here is that the eggs can be successfully parasitized only for the few hours when the checkerspot babies have developed into first-stage larvae but have not yet broken out of the egg. The wasp circumvents this difficulty by learning where the eggs are ahead of time and then monitoring their progress until they are ready, with some individual wasps finding an egg cluster and then revisiting it for up to three weeks, a substantial portion of the wasp's lifetime.
The wasps and their relatives among the other social insects are not the only ones that can learn new things. The caterpillars and butterflies the wasps use as prey are also capable of learning, and they can also develop preferences for particular foods, depending on the type of plant on which their mother laid her eggs. Such food snobbery is of more than academic interest, since some pest caterpillars that eat crops, for example, the young of the familiar cabbage white butterfly, can learn to eat new varieties of cruciferous vegetables; planting broccoli in hopes of evading butterflies that grew up eating cauliflower is futile. Interestingly, not all kinds of butterflies can learn to go to one kind of plant rather than another; checkerspots, eastern swallowtails, and a species of Heliconius butterfly all seem to be relative dullards. You can rear them on one kind of plant, but if you try to train them to visit another kind when it's time to lay eggs, the mother butterflies just won't make the switch. Perhaps it's not stupidity so much as brand loyalty, like refusing to accept Pepsi instead of Coke even if the former is on sale.
Parents often swear that their children are born picky eaters, and that they cannot be taught to prefer healthy snacks. But grasshoppers and their relatives the locusts can be taught to determine the nutritional content of different plants and feed preferentially on the most nourishing ones. In the laboratory, grasshoppers can be fed little cubes of synthetic diet, kind of like the power gels consumed by marathon runners, and the contents of the cubes varied according to the experiment. In one study, groups of locusts were given food lacking either protein or digestible carbohydrates. The experimenters gave one food in a yellow tube and one in a green tube, alternating the association between subjects, and then let the insects feed on a balanced diet for a few days to make sure they didn't become malnourished. Then, the locusts were deprived of food for four hours, a rather long time between meals for the insects, which usually eat more or less nonstop. When the locusts were placed in