Abstract
The exoskeleton lipids of three dangerous pests, Sitobion avenae, Hyalopterus pruni and Brevicoryne brassicae were identified by GC/MS studies. The main components found were triacylglycerols with one hexanoyl group. Fatty acid composition and position of triacylglycerols were determined from mass spectra. There was a trace of triacylglycerol with the E,E-2,4- hexadienoyl group in the extract of Brevicoryne brassicae. A series of hydrocarbons and free fatty acids were identified. Single components of straight chain aldehyde (C30) and alcohol (C32) were detected in the lipids of H. pruni, B. brassicae. Free fatty acids, including these found in the aphid lipids, were subjected to fungi-insect ecological studies. A homologous series of acids were added individually into media used to evaluate the mycelia growth and sporulation tests of the fungi, Beauveria bassiana and Paecilomyces fumosoroseus. The tests were performed in vitro and linear mycelial growth and sporulation of fungi after 14 days were measured. For both fungi, complete inhibition was observed with pentanoic and sorbic (E,E-2,4-hexadienoic) acids at a concentration as low as 0.02% w/v in both tests. Growth stimulation effects were only observed for B. bassiana with tetradecanoic and eicosanoic acid. Inhibitions were noticed for both fungi and the strongest effects were for dodecanoic (B. b.) and eicosanoic acid (P. f.). Beside free fatty acids, no other group of chemical compounds was found in the lipids which could be involved in aphids resistance to entomopathogenic fungi.
Highlights
Chemical pesticides continue to be the main pest control agents, interest in biopesticides is growing, as they show promise in the protection of agriculture crops
The aphid species chosen for this study, Sitobion avenae (F.), Hyalopterus pruni (Geoff.) and Brevicoryne brassicae (L.), feed on cereals, plum trees and cabbages, respectively
Juveniles and adults of aphids: S. avenae, H. pruni and B. brassicae were collected from host plants
Summary
Chemical pesticides continue to be the main pest control agents, interest in biopesticides is growing, as they show promise in the protection of agriculture crops. Aphids are major pests of temperate agriculture and horticulture, causing damage either directly by feeding on the plants or by serving as vectors for plant viruses. Paecilomyces fumosoroseus (Wize) Brown et Smith were determined earlier to be very efficacious biopesticides against thrips and whiteflies, but ineffective against some aphids.[1,2,3] B. bassiana is an effective mycoinsecticide which virulence capability against Galleria mellonella and Trichoplusia ni have been studied.[4] Aphids are subject to predation, parasitism or competition from other organisms, and it may be feasible to use all or some of these ecological interactions to control the population of these insects.
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