RESUMO
The diamondback moth (DBM), Plutella xylostella (L.) (Lep.: Plutellidae), is an important pest of broccoli (Brassica oleracea L. var. italica Plenck). Few studies have focused on the real DBM impact on broccoli yield. We performed greenhouse studies to assess the effect of DBM densities and infestation timing (at pre-heading, heading, or during the entire cycle) on broccoli head weight. Polynomial trend analysis revealed a downward linear response of head weight to DBM densities, indicating that broccoli is susceptible to DBM attack. As for the infestation timing, infestations during the pre-heading stage significantly impacted head weight, whereas the same did not occur for infestations during the heading stage. DBM density did not affect plant height or total leaves but was upward-related to plant defoliation, and head weight correlated negatively with plant defoliation. These findings indicate that pre-heading is the determining stage for head weight loss of plants under DBM attack. In order to prevent quantitative losses, efforts for DBM management should be focused on this particular stage.
Assuntos
Brassica , Herbivoria , Mariposas , Animais , Brassica/crescimento & desenvolvimento , Larva , Folhas de PlantaRESUMO
The demand for effective insecticides in pest control with low toxicity to the non-target organisms, such as natural enemies and pollinators, is increasing steadily. A good alternative for synthetic insecticides is natural compounds, including essential oils (EO). This work assessed toxicity of essential oils extracted from Artemisia annua, A. absinthium, A. camphorata, A. dracunculus and A. vulgaris against the melonworm Diaphania hyalinata (Linnaeus, 1758) (Lepidoptera: Crambidae) larvae, a pest of Cucurbitaceae, and their selectivity for fire ant Solenopsis saevissima (Smith) (Hymenoptera: Formicidae) and jataí bee Tetragonisca angustula (Latreille) (Meliponinae). The plants were grown in a greenhouse with mineral fertilization and were used for EO extraction. The insects in the bioassay belonged to the second instar of D. hyalinata and adult forms of S. saevissima and T. angustula. Essential oil from A. annua induced a high mortality rate in D. hyalinata (96 %) over a 48 h period. The same essential oil was selective for predator S. saevissima (42 % mortality) and pollinator T. angustula (74 % mortality), while causing high mortality in D. hyalinata. The insecticidal activity of A. annua oil was attributed to the synergism of its constituents viz., camphor and 1,8-cineole. Therefore, this essential oil contains constituents that are promising for effective use as insecticide due to its high toxicity and rapid action against D. hyalinata as well as low toxicity for predator and pollinator.(AU)
Assuntos
Animais , Óleos Voláteis/toxicidade , Inseticidas , Himenópteros , Cucumis melo , 24444RESUMO
Deltamethrin, a member of the pyrethroids, one of the safest classes of pesticides, is among some of the most popular and widely used insecticides in the World. Our objective was to synthesize an oxabicyclolactone 6 and five novel pyrethroids 8–12 from readily available furfural and D-mannitol, respectively, and evaluate their biological activity against four insect species of economic importance namely A. obtectus, S. zeamais, A. monuste orseis, and P. americana. A concise and novel synthesis of 6,6-dimethyl-3-oxabicyclo[3.1.0]hexan-2-one (6) from furfural is described. Photochemical addition of isopropyl alcohol to furan-2(5H)-one afforded 4-(1'-hydroxy-1'-methylethyl)tetrahydro-furan-2-one (3). The alcohol 3 was directly converted into 4-(1'-bromo-1'-methylethyl)-tetrahydrofuran-2-one (5) in 50% yield by reaction with PBr(3) and SiO(2). The final step was performed by cyclization of 5 with potassium tert-butoxide in 40% yield. The novel pyrethroids 8–12 were prepared from methyl (1S,3S)-3-formyl-2,2-dimethylcyclopropane-1-carboxylate (7a) by reaction with five different aromatic phosphorous ylides. Compounds 6–12 presented high insecticidal activity, with 6 and 11 being the most active. Compound 6 killed 90% of S. zeamais and 100% of all the other insects evaluated. Compound 11 killed 100% of all insects tested.