Have you ever seen a "nursery" built by insects on a plant stem or leaf? These insects, which can build all kinds of sea urchin-like raised spines, actually live all around us, but rarely attract our attention, and their mysterious biological properties have always been out of the knowledge of scientists and naturalists.
For 40 years, naturalist Ron Russo has been working on a peculiar plant structure, gall tumors, and of course their builders, gall tumor insects, whose diversity and bizarre biological features fascinate him.
Strange gall tumors
Gall tumors are lump-like structures that grow on the stems and leaves of trees, and their different shapes and colors are enough to make people think. Gall tumors are mostly built by insects, but some are built by bacteria, fungi, and mites. Some of these creatures that inhabit galls can be seen with the naked eye, while others must be seen with the help of observation instruments.
There are about 1 million known insects in the world, and they eat almost everything, with carrion, feces, pollen, fungi, leaves, nectar, sap and blood stains being their favorites. Of these, only about 13,000 species of insects have evolved the ability to induce galls on specific host plants. Unlike the face-to-face ants, bees, mosquitoes, butterflies, and caterpillars that damage crops, gall tumor insects rarely attract our attention, perhaps because they have little impact on the economy and agriculture.
Ron's research focuses on gall wasps. He was intrigued by the fact that each of the more than 1,400 gall bees could create uniquely styled gall tumors, such as sea urchins, stars, flower baskets, bowling balls, bats, antennae and corals, and in a variety of shapes and colors.
The mysterious life course of the gall bee
Gall tumors are actually "nursery rooms" that insects build on trees. Gall bees are mainly based on oak trees, small fig trees and certain rose family plants as their hosts. Most gall bees are small, the smallest being only the size of a comma, and the largest being the size of a housefly. They are both miniature architects and masters of biological secrets – since 2400 years ago, the ancient Greek physician Hippocrates
After describing the medical effects of gall tumors, their mysterious biological properties have always been outside the knowledge of scientists and naturalists.
Soon after the wasp lays eggs, a shell of plant tissue quickly forms around each egg. After the shell is formed, the gall tumor does not begin to grow immediately, but only after the larva breaks out of the shell and begins to eat hungrily. When chewed, gall bee larvae release a complex compound that causes plant tissues to change direction of growth, forming the external protective structure of gall tumors of different shapes. The inside of the gall tumor consists of a larval bedroom and a vegetative lining. All gall bee-built gall tumors are warm and livable without exception. Many organs of plants can form galls, including roots, flowers, and fruits, but most galls are built on young branches and leaves. The external shape, color, and size of gall tumors vary greatly depending on the species of gall bee and the different places they are built in.
Gall bee larvae develop into adults after several months of development in the nursery, and adults generally live for about a week after drilling out of the gall tumor. During this time, they fly between the trees in search of host plants, then lay eggs, and a new cycle of life begins. In many parts of North America, wasps breed their first generation in the spring, galls grow in March to April, and in May-June they mature, after which they begin to breed a second generation, the summer and autumn generations. The gall tumor develops between July and October, when the gall tumor looks completely different from the spring gall tumor. Adults developed from summer-autumn gall tumors sometimes appear in the fall and more often in the early spring of the following year.
Some of the gall bees that create galls on oak and small fig trees have very strange reproductive properties, they will switch back and forth between sexual reproduction and asexual reproduction, often the first generation of gall bees in the spring for sexual reproduction, both male and female, and the second generation of gall wasps in summer and autumn are unisexual reproduction, all females. The second generation of females reproduces as a parthenite, has no male genes, and is essentially "self-cloned.". Some gall bee species can only reproduce as parthen, they produce only one generation per year, and there are no male bees in the population.
Except for some adult wasps that can complete their breeding journey, the rest are eaten by predators, some of which become the mouth food of spiders, lizards, and birds such as daisy birds, Veerio birds,, and five-soned finches almost at birth. Even in a relatively safe place like gall tumors, gall bee larvae can sometimes become a good meal for parasitic bees and hermit animals. Parasitoids
Parasitoids
Living in or on the surface of gall bee larvae, they eventually eat gall bee larvae. Hermits are particularly fond of moths, weevils, beetles, wasps, and other insects that specialize in gall tumor tissue. Since these insects are plant-eaters, the hermits destroy all the larvae they encounter at the same time while foraging. Despite the dangers, many gall bees live to the age of childbearing.
Unsolved mysteries
There are many unsolved mysteries about gall tumors. For example, there is a type of leaf vein gall tumor, and the gall bee lays eggs directly in the leaf veins, usually in the leaf edge part. The veins of the leaves extend out of the leaves and swell at the tip of the leaves, forming galls. Therefore, the "large vein" can directly inject nutrients into the larval bedroom. The gall tumor was described more than 50 years ago, but failed to successfully breed adults. Exactly when and under what circumstances the adult worms appeared, no one has been able to say clearly. Ron hopes to solve the puzzle, and he has collected some specimens of leaf vein gall tumors, but no progress has been made yet.
Another unsolved mystery of Ron's interest is that in the summer it can create hollow gall tumors as thin as paper, a species that no one has fully described since it was first discovered in 1896.
Six years ago, Ron found a previously described gall on a rouge oak, which he called a "pink bow gall tumor." Since then, he has frequented the host tree to monitor the development of the gall. At first, what Ron saw was a pink flat disc. Ron's feeling is that when the larvae eat, the plate is flattened, and as soon as the larva stops eating, the edge of the gall shrinks inward, forming a bow shape in the late summer or early autumn.
Ron has been tracking various wasps in the western United States to collect information on the distribution and population of gall bees. At the same time, he also cultivates gall bee larvae in the laboratory and raises them into bees in order to understand the habits of gall bees and discover new species. The trickiest job of raising gall bees is choosing the right time to collect gall tumors, as it is only possible to grow larvae into adults using gall tumors collected at the right time. If the gall tumor is collected too early and the larvae are not yet mature, it is difficult to grow them into adults; if the gall tumor is collected after the larva has matured, the adult appearance time will be delayed. One year in late April, Ron collected several green melon-shaped leaf galls from an oak tree in the southern Mojave Desert that he had never seen before and therefore could not determine its stage of development. He put the gall in a specimen bottle, but two days later, on his way home, the adults appeared in the warm carriage, and Ron had to wait for them very carefully, lest they die in the car.
Although Ron's research work was arduous, the surprises of new discoveries often made him forget his fatigue, and every slight progress made him feel that his efforts were worth it.