The two-spotted spider mite, found throughout temperate and subtropical regions, thrives in both greenhouses and fruit trees (much to the chagrin of growers). The typical life cycle of these mites starts when eggs, attached to fine silk webbing, hatch after approximately three days. Under optimum conditions (around 80º F), spider mites complete their development in five to 20 days, so there can be many overlapping generations per year.
All mites have needle-like piercing-sucking mouthparts, according to the University of Florida. Spider mites penetrate plant tissue with their mouthparts to feed and are found primarily on the undersides of leaves. All spider mites spin fine strands of webbing on host plants. (That’s how they earned their name.) Their feeding can cause graying or yellowing of leaves and necrotic spots. The two-spotted spider mite is considered one of the most economically important spider mites, reported to have infested over 200 species of plants, including ornamentals like azaleas, evergreens, ligustrum and rose; maple, elm, redbud and other trees; black-, blue- and strawberries; and tomatoes, squash, eggplants and cucumbers.
Generally, they’re just not welcome guests. Predatory mites, ladybugs and pirate bugs are good biocontrol measures, and for those looking to steer clear of chemical pesticides, an international team of researchers recently discovered how a biopesticide can work against spider mites.
A food-ingredient-based biopesticide called Suffoil made from safflower and cottonseed oils has been shown to be effective against two-spotted spider mites while sparing their natural predators. Food ingredients are used as alternative pesticides against arthropod pests, like insects, ticks and mites, because they tend to be less toxic to mammals and have a smaller impact on the environment. The way biopesticides work also reduces the chance that the targeted pest will develop resistance, which then reduces the need to use greater quantities of the pesticide or develop new ones.
Suffoil has no effect on another species of mite (Neoseiulus californicus) that naturally preys on spider mites.
How does it work? A spider mite normally hatches by cutting its eggshell (“chorion”) with its appendages as it rotates in the egg. The spider mite embryo also uses the silk threads surrounding the eggs to aid this rotation. Researchers dipped spider mite eggs in Suffoil and then examined them under microscopes. (They also dipped eggs in water as a control group.) The Suffoil partly covered the surface of the eggs and the surrounding silk threads, and the researchers observed that the embryonic rotation essential for hatching was absent or stopped in the Suffoil-covered eggs. It looked as if the oil seeped into the eggs through the cut chorion, making the inside too slippery for the embryo to turn.
“The biopesticide works by preventing the spider mite embryo from rotating within its eggshell for hatching,” said Takeshi Suzuki, a bio-engineer at Tokyo University of Agriculture and Technology and senior author of the study. “It may also weaken the toughness of silk threads and reduce the anchoring effect of the egg on the substrate.”
Why does Suffoil have no effect on the spider mites’ natural predators? They don’t use rotation to hatch out of their eggs. That means Suffoil could be used in conjunction with the spider mites’ natural predators.
Alexa, play “Slip Slidin’ Away” by Paul Simon.