Small Pests, Large Losses: Nematodes, Mites, Planthoppers and Swarms

Root Knot Nematode opens the trail because it shows how much damage an animal too small to see can do. The genus Meloidogyne invades roots and induces swollen galls that disrupt water and nutrient uptake across an extremely broad range of crops, and the entity page notes that it is considered among the most economically damaging plant parasitic nematodes worldwide.

Soybean Cyst Nematode shows the damage can be hidden. Infested plants are stunted and lose yield, often with no visible above ground symptoms until infestations are severe. The atlas records it as the single most economically damaging pest of soybean in North America, and it is listed on the EPPO A2 list of pests recommended for regulation as quarantine pests.

Potato Cyst Nematode adds persistence. Its cysts can stay in soil for a decade or more without a host, so in most potato producing countries infested fields fall under strict quarantine and rotation requirements and can be forced out of potato production for years.

Twospotted Spider Mite moves the trail above ground. It feeds on the sap of hundreds of crop and ornamental species and leaves stippled, bronzed foliage. The entity page ties its short generation time and high reproductive rate to pesticide resistance that evolves faster than in almost any other agricultural pest.

Cassava Green Mite is a story of an accidental introduction and a deliberate answer. A South American mite reached Africa in the early 1970s, where cassava had no natural resistance, and losses at times exceeded 80 percent in heavily infested fields. The classical biological control program that used South American predatory mites is described as one of agriculture's larger successful biocontrol efforts.

Brown Planthopper is the most damaging insect pest of rice across South, Southeast and East Asia. It causes hopperburn, the rapid browning and collapse of rice hills, and transmits rice ragged stunt and grassy stunt viruses. The entity page links its outbreaks to insecticide overuse that kills the natural predators which normally hold its numbers down.

Desert Locust shows what happens when a pest shifts from a solitary to a gregarious phase under crowding. Swarms range across North Africa, the Arabian Peninsula, the Sahel and southwest Asia, and the entity page describes a single large swarm stripping crops across an area the size of a small country in a day. The 2019 to 2021 upsurge threatened the food security of tens of millions of people.

Migratory Locust has the widest range of the locusts, found across Africa, Asia, Australia and parts of Europe, and is second only to the Desert Locust in the damage its swarms do to cereals and pasture. Its regional subspecies have driven major outbreaks in China, where locust plagues have been recorded and combated since antiquity, and more recently in Madagascar and parts of Southeast Asia.

Japanese Beetle closes the trail with a pest that is harmless at home and costly abroad. Native to Japan, it was first found in the United States in New Jersey in 1916 and has since spread across most eastern and midwestern states and into parts of Europe. Adults skeletonize the leaves of several hundred plant species while the grubs damage turf and pasture roots, and EPPO lists it as a quarantine pest.