By testing an agrochemical designed to increase resistance on the mulberry plants used to feed silkworms, a research verified a rise in caterpillars’ mortality and reduction in the size of cocoons. Intensive use of pesticides in monoculture systems may be the cause of silkworm crop losses in Brazil.
ZT Research Desk
One of the problems caused by the intensive use of pesticides is their effect on organisms other than those they are designed to combat — the most notorious of which is the global mortality of honeybees.
However, there are other economically beneficial insects than honeybees which are implicated. “The silkworm is another managed insect whose performance may have been impaired by pesticide poisoning,” said Daniel Nicodemo, a professor at São Paulo State University’s School of Agrarian & Technological Sciences (FCAT-UNESP) in Dracena, Brazil.
In a study supported by the São Paulo Research Foundation — FAPESP, Nicodemo partnered with Professor Fábio Ermínio Mingatto and students at FCAT-USP to investigate the effects of pyraclostrobin, a strobilurin fungicide widely used as a crop spray, on the mitochondrial bioenergetics of silkworms (Bombyx mori) and their production of cocoons.
The researchers found that application of the fungicide to mulberry plants — silkworms’ single source of food — increased caterpillar mortality up to threefold and significantly reduced the size of the cocoons spun by surviving caterpillars, causing silk production losses. The study was the subject of an article published in the Journal of Economic Entomology.
Brazilian silk farmers have reported a fall in the production of silkworm cocoons — even in the absence of factors such as disease, malnutrition and inappropriate management, which impact negatively on the development cycle of the mulberry silkworm, in Nicodemo’s assessment.
Brazilian silk farmers are smallholders who grow mulberry plants to provide food for the silkworms. Most Brazilian silk farms are found in northern part of Paraná State, but there are also sericulturists in São Paulo State and Mato Grosso do Sul. They are small isolated concerns surrounded by vast sugarcane, soybean or corn plantations where pesticides are heavily used.
“This is one of the possible causes of the silkworm crop losses,” Nicodemo said. When the big plantations are sprayed with insecticides, herbicides or fungicides, the wind often blows these agrochemicals into neighboring farms, where mulberry plants may be growing.
Materials provided by Fundação de Amparo à Pesquisa do Estado de São Paulo.