Delia antiqua (Meigen, 1826)

Salmane, Ineta, Apenīte, Ilze & Ciematnieks, Rinalds, 2013, Environmentally Friendly Organic Products And Onion Pests In Latvia, Acta Biologica Universitatis Daugavpiliensis 13 (1), pp. 101-108 : 104-106

Delia antiqua

The adult onion flies were found on sticky traps in vegetation season of 2012 ( Fig.1 ), but no damages of onion bulbs by its maggots were stated. Imagoes were found on sticky traps only in the middle of the vegetation season in 2011 (Fig. 3). The average amount of damaged onion plants varied from 3.8-12.8%. No significant difference from the control was observed.

Absence of D. antiqua can be explained by the lower average air temperature and the higher precipitation in vegetation season of 2012. Significant influence of weather conditions on amount of this pest was confirmed by some investigations ( Musa 2005, Tanaka & Watari 2011).

Treatments used in trials were the same in both investigation periods, but the climatic conditions significantly differed between vegetation seasons: the average air temperature was higher and the average amount of precipitation lower in 2011 than in 2012. It is hard to give an eligible explanation why obtained results in current trials varied between vegetation seasons. Whether differences are caused by the influence of weather conditions or the extracts used, or those jointly with climatic conditions have some effect on pests, is not clear. There are some investigations, which confirm the role of environmental conditions in the pest-plant relationships and plant resistance ( Rabinowitch 1997). There is some information on influence of environmental conditions on effects of plant extracts, as well as climatic condition effects on development of pests ( Richter & Hommes 2003, Musa 2005, Skrabule et al 2008, Watari & Tanaka 2010, Tanaka & Watari 2011, etc.). Some studies differ from ours as they were performed in laboratory conditions, where the complete control of all parameters is possible.

Unfortunately, there is limited information on how the above-mentioned extracts affect invertebrates (e.g. pests). In some investigations positive effect of vermicompost in pest control was observed ( Arancon et al. 2005, Arancon 2011). Still the mechanisms, which lead to decrease of pest infestation due to vermicompost, cannot be clearly identified and this has to be developed in the future investigations. There is no available information on how peat and vermicompost extracts affect onion plants

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and their pests. After two years research with the current set of the obtained data we cannot make any reliable conclusions on potential effects of peat and vermicompost extracts in the pest control. More possibly, particular pests on specific crops (onions) are not affected by the above extracts in the given concentration. However, assuming that such effect exists, it is possibly not direct and extracts probably act through improved plant resistance or as chemical repellents.

Figures

Fig. 1. Average number of individuals of D. antiqua, A. assectella and Ph. atricornis recorded on the yellow sticky traps in onion plantations, SSCBI, Dižstende. a) vegetation season 2011, b) vegetation season 2012. (Over a vegetation season, 1 - 6 times sticky traps were exposed).