There is something special going on with these female moths. In an earlier blog I wrote about the winter moth (Operophtera brumata). The wingless females of that species sit on the trunks of trees waiting for the males to mate with. Those females don’t get much further than one or two trees away from the place they emerged. Moving farther afield is hardly possible without wings. The females of the gypsy moth, on the other hand, have fully developed wings but barely use them. The reason for this is unknown. Maybe they cannot or barely move their wing muscles? Or does it perhaps costs them too much energy since both the males and the females of this species don’t eat after they have emerged from their pupa and have to live with all the energy they have absorbed in the caterpillar stage? Whatever the cause, the female barely leaves the place where she hatched and does nothing but spread her pheromones. The males immediately pick up those pheromones, as John’s photo shows. Incidentally, the moths fly both in the evening and during the day, so it is both a nocturnal and diurnal moth.
DDT and HCH (better known as lindane). But also more “friendly” substances of natural origin, such as pyrethrum and derris powder, were investigated to tackle this pest.
In the US and Canada on the other hand they have different thoughts on the gypsy moth. There the moth was introduced in the mid-19th century by the French painter and scientist Étienne Léopold Trouvelot. He thought this butterfly could be a good substitute for the finicky silkworm, so that silk could be produced in a cheaper way. Whether that was the case, the story does not tell, but a few moths escaped in 1868 and managed to reproduce in the North American climate. Trouvelot warned the authorities to take measurements, but he wasn’t heard. Things were going well for the moth and the population grew considerably. In the state of Massachusetts it soon became one of the top pests and was fought with might and main (and presumably the necessary amounts of toxins). But in vain. The gypsy moth had finally established itself and today it has spread across much of the northwestern US and Canada. But the central and western part of the US cannot escape it entirely either, Leaving defoliated oaks, but also beeches, poplars and maples behind.
US federal law even states that when you move from an area where the moth has struck (a quarantained area) to an area where there is no moths plague, you are obliged to check all your garden furniture, tools, machines, et cetera for eggs, caterpillars, pupae and moths. But why is the gypsy moth such a huge problem in North America and is it not so bad in Europe? The answer is quite logical. The moth is not part of the native ecosystem over there. As a result, it has no natural enemies, such as ichneumon wasps that parasitize the caterpillars. But factors such as climate also play a role in the multiplication of species. Warmer weather will probably ensure that – prematurely – hatched caterpillars survive in the winter, which will only increase the population.
Invasive species are therefore timeless and occur all over the world. In Europe, for example, we also acquired the Asian ladybeetle (Harmonia axyridis), grey squirrel (Sciurus carolinensis), muskrat (Ondatra zibethicus), black cherry (Prunus serotina), Himalayan balsam (Impatiens glandulifera) and the Japanese knotweed (Reynoutria japonica). All alien species that have been deliberately introduced here by humans. (This is in contrast to, for example, the box tree moth (Cydalima perspectalis) that came here on boxwoods (Buxaceae) imported from China. The boxwood moth itself was not deliberately introduced here.) These exotic animals and plants also lack natural enemies here in Europe, so that they have been able to reproduce unhindered, with all the consequences.
This item was originally published in Dutch on Augus 16th 2020.