The so-called Norway Rat didn’t come from Norway, and this so-called norwegicus bug has no known relationship to Norway, either. According to CABI, the Invasive Species Compendium, this bug is not even found in the Scandinavian countries. It originated in the Mediterranean region, feeding primarily on wildflowers. It spread throughout temperate Europe as a minor pest on a variety of crops. Humans carried it to North America and New Zealand. In New Zealand it developed a taste for clover and for young potato plants, which probably accounts for its currently most common name, “Potato capsid.” In 1997, scientists transferred it from the Calocoris genus to Closterotomus. When it was Calocoris, it also bore the common name “Strawberry bug,” although it showed no special affinity for that crop over any other. One source suggests naming it the Two-point Meadow Bug, because of the two black dots on its neck carapace (pronotum), just visible in the photo above. However, that name doesn’t really work either, because other species have the same two dots and some individuals in this species lack them. If a name contest were held today in California, it would be called the Pistachio borer, because some members of the species make their living by piercing young pistachio nuts, causing significant economic damage to pistachio orchards in the northern areas of the Central Valley.
This bug, by whatever name, is one of the Miridae, a vast insect family with more than 10,000 known species and new ones being found all the time. Like other mirids, it possesses a sharp and hard needle-like mouth that’s capable of penetrating tough tissue and suctioning nutrients. This is what it does to pistachio nuts before their protective membrane hardens. This causes the outside of the nut to discolor and the inside to rot and shrivel. Scientists speculated that C. norwegicus injected one or another toxic protein into the nut, causing the damage. An interesting experiment showed that mere mechanical penetration of the nut by a sterile steel needle had the same effect. The nut did not tolerate penetration and shut itself down by way of response to the injury.
American pistachios originated from a bagful of mixed nuts obtained in 1930 in Persia, today’s Iran, where the pistachio is an ancient native. Ironically, the C. norwegicus bug is not listed as a pest that troubles Iranian pistachio production currently.
The mirid‘s needle is thought to be the reason why it is able to feed on cannabis. The surface of cannabis leaves contains a potent insecticide. The leaves have been used for centuries to protect stored grains and other crops from insects, or laid under mattresses to kill bedbugs. Sprays made from cannabis leaves kill many insect pests. Some untutored insects, such as Tiger Moth caterpillars, feed on high-THC cannabis leaves to their doom. The mirid avoids the surface poison by driving its needle into the stem and sucking the benign juices.
C. norwegicus females prefer to lay their eggs on native or introduced legumes such as purple vetch, clovers, and alfalfa, or weeds such as wild mustard, wild radish, thistles, nettles, daisies, and curly dock, most of which we have in abundance in Cesar Chavez Park. Pistachio growers have learned that they can drastically reduce this bug’s harm to their nuts by clearing these weeds from the vicinity of their orchards.
Efforts to identify parasites that specialize in preying on this bug for purposes of biological control in agriculture have so far been unsuccessful. Efforts to attack it with standard pesticides have run into the problem that the pesticides also kill assets used for successful biocontrol of other bugs that attack the same crop. Once biocontrols are used for any purpose, use of chemical insecticides in the same habitat becomes problematic or prohibitive. Thus C. norwegicus has so far avoided becoming a target of modern agropharmatoxicology.
Tomorrow: Black-tailed Bumblebee
P.S. Peter Rauch sent this excerpt from Gmelin’s 13th edition of Linnaeus’ Systema Naturae (1788-1793) to show the possible source of the norwegicus epithet in the scientific name. For details, see Peter’s Comment below.