I have been pondering some aspects of gardening that are perhaps more esoteric lately. Last month I discussed the Biodynamic Movement, and how the Steiner philosophy and Biodynamic Preparations may impact the energetics of plants. Another field of study has been the subtle chemical changes that are just recently being analyzed and measured by plant chemists. You may have seen some of these changes in your own garden.
The relationship between plants and their chemical aromas and insects goes beyond the delightful fragrances some flowers use to attract pollinators. Some chemical interactions are so subtle that we humans cannot detect them, but insects pick up on them right away. Plants can apparently direct these chemicals to different parts of the plant and use them to their advantage. I have read, for instance, that fruit trees will use hormone-like substances, called “semiochemicals”, to attract pollinators, but also to repel predators. And sometimes, they will vary the chemical release on different parts of the plant, sacrificing some parts of the plant to protect other parts, or to attract the invading insect’s predators.
I saw this demonstrated vividly on a neighbor’s peach tree. While three-fourths of the major branches of the young tree were growing vigorously and putting on small peaches, one major section of branches was covered with aphids and shriveled leaves and had no fruit. The owner said that happens most years. I could see no other damage on the branches to explain the difference. Ladybugs soon arrived to begin aphid harvesting.
The interplay of insect and plant can be fascinating! I recently discovered that some overwintering spinach was beginning to flower. Shortly thereafter, I saw some Ash Gray Blister Beetles, especially on the male plants.
Did you know spinach has male and female plants? The males tend to have more pointed leaves, and a plume of tiny flowers at the end of short stems. Females also have tiny flowers, but they are usually under a leaf. After pollination occurs, the females form small round seeds at the leaf nodule, which ripen into a cluster of hard tan balls. Eventually, they will fall off and start new plants if they are not collected and saved by the gardener.
The blister beetles seemed happy supping on stems and flowers. They like to congregate in groups, and their behavior is surprisingly sophisticated. If threatened, they will “play dead” and drop to the ground and be very still until the predator (the human)
leaves the area. However, if you try to pick it up, it will run quickly away and hide under debris. They vary in size from less than a quarter inch to about an inch and can easily disappear. If you do catch one, do not squash it. Its body contains a chemical, Cantharidin, that can cause blisters on the skin.
An invasion of blister beetles can defoliate a group of plants quickly if not controlled. If you see a group on a stem, put your hand under it and gently shake the stem. The beetles will fall off of the stem and you can put them in a jar of water where they will eventually drown. You can pick them off individually as long as you don’t squash them. While cruel, it is a better choice than chemicals.
The balance in nature is interesting. While I do not feel I can ignore an invasion of blister beetles, their larvae feed on grasshopper eggs, and help provide control of this other plant predator.
So, I am bending over my spinach plants, patiently collecting blister beetles and putting them in water, while contemplating the interactions and communications be– tween plants. Do the blister beetles prefer male flowers because they are more exposed? Because they have more attractive “semiochemicals”? Because the spinach plants are sacrificing the male plants to protect the females? Or did the blister beetle clan just decide that they are eating male flowers today? The wonders of nature!