The paper describes the impact of two different plant protection products on silkworm ( Bombyx mori L.) development. These products are commonly used in agrotechnical treatments and are officially allowed to use in ecological agriculture. They are also fungicides, which suggests lower negative impact on other groups of organisms. The two used products were Biosept Active Spray (grapefruit extract) and Miedzian 350 SC (copper oxychloride) which were sprayed on mulberry leaves used to feed silkworms from the beginning of the 4th instar. As to measure the level of impact, the mortality of larvae (percentage of dead specimens) and cocoon shell ratio (percentage of shell weight in whole cocoon) were checked. The highest mortality was recorded in the group treated with 0,7% Miedzian solution (92,5%) as well as the lowest shell ratio (12,06) comparing to the control group (mortality 7,5% and shell ratio 17,43). In the Biosept group, no significant mortality was recorded (comparing to the control group) but mean shell ratio showed a significant decrease in the cocoon quality. The study shows that one of the pesticides is highly effective against a non-target organism.