Interfacial forces and permeation of the codling moth cocoon silk.

STADLER, T.; FORNES, A.; BUTELER, M.

Bulletin of Insectology

Department of Agroenvironmental Sciences and Technologies

Lugar: Bologna; Año: 2005 vol. 58 p. 57 - 64

Abstract The silk from Cydia pomonella (L.) (Lepidoptera Tortricidae) cocoon was considered as a key factor affecting the effectiveness of control practices on over-wintering codling moth populations. The interaction energy between the silk cocoon surface and different products -Diphenilamine, sprayoils (winter and summer) and vegetable oils (castor-, soy-, jojoba- and peanut oil) - was determined. Dynamic viscosity, surface tension, and silk permeation (L²) of these products were also determined. To establish whether the silk cocoon may act as a barrier to chemical treatments, the effectiveness of these products when applied to fifth instar codling moth larvae in contact bioassays was compared to their toxicity when applied to cocooned fifth instar larvae. The highest codling moth silk permeation activity was shown by summer sprayoils, followed by winter mineral sprayoils and vegetable oils. No strong correlation was found between measured silk permeation and oil viscosity (R = -0.06685) or oil surface tension (R = -0.51074). Hence, the behaviour of a substance on the silk surface cannot be predicted by analyzing individual physical characteristics. However, the calculated permeation (L²) is shown as a useful tool to recognize silk wettability because measured permeation correlates with L² (R = 0.97354). Some products presented a reduced effectiveness when they were applied to cocooned larvae, even though they caused high mortality to codling moth larvae when exposing them directly. Interestingly there was no difference in mortality between contact application to larvae and spray application to cocooned larvae for products with L² values between 13 and 22 cm. These results suggest that the lack of efficacy of certain products is linked to the presence of the silk cocoon and that calculated L² values can provide valuable information to identify a product that penetrates actively the codling moth silk cocoon. control practices on over-wintering codling moth populations. The interaction energy between the silk cocoon surface and different products -Diphenilamine, sprayoils (winter and summer) and vegetable oils (castor-, soy-, jojoba- and peanut oil) - was determined. Dynamic viscosity, surface tension, and silk permeation (L²) of these products were also determined. To establish whether the silk cocoon may act as a barrier to chemical treatments, the effectiveness of these products when applied to fifth instar codling moth larvae in contact bioassays was compared to their toxicity when applied to cocooned fifth instar larvae. The highest codling moth silk permeation activity was shown by summer sprayoils, followed by winter mineral sprayoils and vegetable oils. No strong correlation was found between measured silk permeation and oil viscosity (R = -0.06685) or oil surface tension (R = -0.51074). Hence, the behaviour of a substance on the silk surface cannot be predicted by analyzing individual physical characteristics. However, the calculated permeation (L²) is shown as a useful tool to recognize silk wettability because measured permeation correlates with L² (R = 0.97354). Some products presented a reduced effectiveness when they were applied to cocooned larvae, even though they caused high mortality to codling moth larvae when exposing them directly. Interestingly there was no difference in mortality between contact application to larvae and spray application to cocooned larvae for products with L² values between 13 and 22 cm. These results suggest that the lack of efficacy of certain products is linked to the presence of the silk cocoon and that calculated L² values can provide valuable information to identify a product that penetrates actively the codling moth silk cocoon. Cydia pomonella (L.) (Lepidoptera Tortricidae) cocoon was considered as a key factor affecting the effectiveness of control practices on over-wintering codling moth populations. The interaction energy between the silk cocoon surface and different products -Diphenilamine, sprayoils (winter and summer) and vegetable oils (castor-, soy-, jojoba- and peanut oil) - was determined. Dynamic viscosity, surface tension, and silk permeation (L²) of these products were also determined. To establish whether the silk cocoon may act as a barrier to chemical treatments, the effectiveness of these products when applied to fifth instar codling moth larvae in contact bioassays was compared to their toxicity when applied to cocooned fifth instar larvae. The highest codling moth silk permeation activity was shown by summer sprayoils, followed by winter mineral sprayoils and vegetable oils. No strong correlation was found between measured silk permeation and oil viscosity (R = -0.06685) or oil surface tension (R = -0.51074). Hence, the behaviour of a substance on the silk surface cannot be predicted by analyzing individual physical characteristics. However, the calculated permeation (L²) is shown as a useful tool to recognize silk wettability because measured permeation correlates with L² (R = 0.97354). Some products presented a reduced effectiveness when they were applied to cocooned larvae, even though they caused high mortality to codling moth larvae when exposing them directly. Interestingly there was no difference in mortality between contact application to larvae and spray application to cocooned larvae for products with L² values between 13 and 22 cm. These results suggest that the lack of efficacy of certain products is linked to the presence of the silk cocoon and that calculated L² values can provide valuable information to identify a product that penetrates actively the codling moth silk cocoon.