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 (C 30 ) and alcohol (C 32 ) 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.
Bird cherry-oat aphid (Rhopalosiphum padi L.) is the most abundant aphid species on cereals in Poland. It represents approximately 80% of all cereal aphids. Its anholocyclic forms are the most important vectors of Barley yellow dwarf virus (BYDV). These forms are new among the Polish population of R. padi. Their changes in development are the result of higher temperatures. High spring and summer temperatures initiate a change in the run of R. padi's life cycle, which begins to reproduce by means of permanent parthenogenesis. In autumn, this aphid does not fly back to the primary host but inhabits wild grasses. It is in autumn that winter cereals emerge. This results in what appears to be a new problem because this viral infection spreads in warmer environmental conditions.
So far in Poland 7 aphid species developing only holocyclically have been observed on maize. Observations which were carried out in the Wielkopolska region in 2004-2012 revealed an occurrence of 5 aphid species. For the first time, in 2012, anholocyclic development of all the observed aphid species was recorded. Among them, new host races of Rhopalosiphum padi and Sipha maydis were isolated, as strict monophagous on maize. Their distinction was found in the studies conducted in environmental chamber conditions.
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