Agresivitatea rizotrofică, filotrofică şi stigmatrofică a noului dăunător al porumbului Diabrotica virgifera virgifera le Conte, în funcţie de factorii climatici

Abstract

We have supervised, in dynamics, the rhizotrophic action exerted by Diabrotica larvae (15 June, 3 July, 1 August) and philotrophic (15 June, 3 July, 1 August, 14 August) and stigmatrophic activity (1 – 14 August) exerted by adults, stages connected to the patosystems Zea mays – Helminthosporium turcicum, Zea mays – Fusarium roseum, Zea mays – Ustilago zeae, present in 2006, in a comparative crop of Pioneer maize hybrid, from different maturity groups (PR39D81 – extra-early, PR38R92 –early, PR38A24, PR37D25, PR37M34, PR37W05 – half-early and PR35P12, PR36K67 – half lattes). Successive to the research of the relationship between the new pest and the climatic factors from Arad region, where we have performed our experiments in 2006, we may conclude: the climatic factors favoring the insect Diabrotica virgifera virgifera Le Conte are: temperatures of 23-25ºC, medium rainfall and air relative humidity of 70-75%. Thermal and hydric requirements of this insect are similar to those of the pathogens from the maize patosystems (Helminthosporium, Fusarium, Ustilago – with some differences for the blight Ustilago). There is a positive correlation between temperature, rainfall, atmospheric humidity and rhizospheric, philotrophic and stigmatrophic aggression; the bigger the climatic values are, concordant to the trophic optimal values, the bigger the attack aggression will be: 6.3 13.8%, 7.5-47.7%, respectively 46.4-51.0%. The rhizotrophic larvae action has a reduced aggression compared to the nutrition on a single leaf epidermis and on the stigmas of the future maize cobs; the specified activity gets emphasized within the phenophasic interval “7-8 leaves” – “milk ripeness”, when maize sensibility to pathogens is increased.