Use of novel film forming starch complexes to directly and indirectly reduce insect damage to plants

Abstract

Film-forming polymer technologies can contribute to insect-pest control by causing adverse effects directly to insects such as slowing development, causing mortality, and/or indirectly as a spray ingredient that improves pesticide efficacy by resisting environmental degradation such as wash-off by rain. Amylose complexes produced from either fatty acid [amylose sodium palmitate (Na-Palm)] or fatty ammonium salts [amylose-hexadecylammonium chloride complex (Hex-Am)], when blended with polyvinyl alcohol (PVOH), dry to form films that were significantly more water resistant then films formed by their constitutive components and adhered strongly to treated soybean [Glycine max (L.) Merrill] leaves with no impact on photosynthesis or yield in simulated field trials. As an experimental bioinsecticide formulation to resist wash-off, AfMNPV baculovirus was incorporated into both amylose complex formulations and sprayed on soybean. After a simulated rain event, soybean treated with the baculovirus/Na-Palm/PVOH (1:1) retained 93% of the original insecticidal activity against Trichoplusia ni (Hübner) larvae as compared with the baculovirus only treatment, 53% activity retained. Curiously, initial insecticidal efficacy of film-forming treatments was significantly lower against T. ni when compared with unformulated baculovirus treatments, thus prompting further investigations. Both amylose complexes reduced larval feeding when sprayed on soybean, corresponding with reduced insect mortality by the baculovirus, which must be ingested to initiate infection. Hex-Am film coating over artificial diet inhibited the growth and development of T. ni and caused increased T. ni mortality and developmental delay as film thickness of Hex-Am/PVOH increased. These investigations demonstrate the potential of a new modified starch complex formulation to serve as a protective film forming agent and contribute to control of insect pests.