The world is producing more food using fewer pesticides than ever, thanks to modern science. The gap between modern pesticide usage and organic food pesticides needed per calorie of food got so large, up to 600% more organic pesticides used, that California stopped itemizing organic pesticides separately to improve the optics of the organic industry.
Biologists want to cost pesticide companies even more money and a new study of the two-spotted spider mite, _Tetranychus urticae_, may help. exemplifies the limitations of conventional pesticide-based pest management in agriculture and horticulture. _T. urticae_ mites infest a wide range of crops and fruit trees and can reproduce extremely quickly. They can also develop resistance to chemical pesticides. The new [study](https://doi.org/10.1111/tpj.70046) looked at effects of 18 salivary gland proteins on the resistance of common bean leaves to _T. urticae_ and identified two new tetranins — Tet3 and Tet4 — that appear to reduce the reproduction of spider mites on the plants.
_Credit: Gen-ichiro Arimura from Tokyo University of Science, Japan_
Using genetic engineering plus molecular and biochemical methods, the team uncovered the roles of Tet3 and Tet4 in the complex interactions between _T. urticae_ and its host plants. Interestingly, they found that the expression of Tet3 and Tet4 varies greatly depending on which plant the mites fed on. Mites feeding on common beans, their preferred host, had significantly higher levels of Tet3 and Tet4 expression than those on cucumbers, a less preferred option.
Plants exposed to mites with higher expression of Tet3 and Tet4 exhibited stronger defense responses, including increased calcium-ion influx, higher generation of reactive oxygen species, and elevated expression of a defensive gene named PR1. The individual application of Tet3 and Tet4 to plants had different effects on plant defense responses, highlighting the specificity of each elicitor’s role.Tetranins act as crucial links in these complex systems so from an agricultural perspective, tetranins and similar elicitors offer potential for crop improvement.
“Taken together, our findings show that these tetranins respond to variable host cues that may optimize herbivore fitness by altering the anti-mite response of the host plant,” says Professor Gen-ichiro Arimura from Tokyo University of Science.