engleski

The sugar-beet weevil (Bothynoderes punctiventris Germar 1824., Col.: Curculionidae): life cycle, ecology and area wide control by mass trappingTRAPPING

The sugar beet weevil (SBW) (Bothynoderes punctiventris, Germar 1824, Coleoptera: Curculionidae) is a very important pest of sugar beet. The life cycle and ecology of this pest has been studied in neighboring countries 20 and more years ago, while the data on SBW life cycle and ecology in the conditions of Croatia don’t exist. Due to the specific morphological structure of SBW, their large feeding capacity and the small leaf area of plants at the time of insecticide application, insecticides often give very poor results and require repeated treatment, which is not in accordance with the principles of integrated pest management (IPM) nor with the rational use of pesticides in modern agriculture. Therefore, it is necessary to consider non- pesticide plant protection measures and other available methods that are compatible with all agricultural practices. Knowledge on the life table parameters of pests allows for the successful implementation of control in accordance with the principles of IPM. The area- wide mass trapping of SBW using aggregation pheromones in the previous year’s sugar beet fields within a particular larger area might provide the possibility of reducing the pest population and reduces the need to apply insecticides what is in accordance with IPM. The entomopathogenic nematode (EPN) Heterorhabditis bacteriophora Poinar may have significant potential to reduce SBW population and shall be integrated with other measures into the strategy for SBW control. During the four years (2012- 2015) life table parameters and the population characteristics of SBW have been investigated. Area–wide (AW) mass trapping was implemented within a total area of 6 km2 (in 2014 additional 8.8 km2). The pheromone traps (15/ha) were installed on all previous years sugar beet fields in AW at the beginning of SBW emergence. The efficacy of three different doses of EPNs (3, 5 and 7 million of nematodes/10 m2) on beet weevil larvae in two year field trials has been established. The degree day accumulation (DDA) for SBW emergence can be calculated based on the soil temperature at 10 cm depth by the use the temperature of 5°C as the thermal threshold. The first emergence started when DDA reaches 20°C (first two decades of March). However, the emergence depends on the existing snow layer as well as on the availability of food. Weevils completed emergence when DDA reaches 428°C what usually happen in the first week of May. The largest proportions of specimens (which emerge from overwintering) were established in 14th and 15th week of the year (between 95 and 102 Julian day - JD). Males of SBW emerge first and dominate in the adult population up to 15th week of the year when an equally sex ratio is present. Afterward adult population is dominated by females. SBW development in eastern Croatia is very similar with those in the neighboring countries (Serbia and Hungary). Overwintering adults are present in the fields up to the beginning of July. Newly developed adults emerge from the soil in July. Although the development stage of egg takes 10-15 days, due to expanded time of weevil emergence, in prevailing conditions, eggs were found on average in 102 days (between 112th and 214th JD), larvae development established up to 143 days (between 122th and 265th JD) and pupae development up to 102 days (between 143th and 245th JD). It is established that population growth positively correlate with air (r=0.9409**) and soil temperature (r= 0.9307**) during the vegetation period and negatively correlate with the amount of precipitation in vegetation period (r= -7971**) as well as with the amount of precipitation in May (r= -0.7794**). Population growth rate depends on the ratio between new and old sugar beet fields in marked area (r= 0.7813**). With increasing the share of newly sown sugar beet field, the population growth increases. Overwintering success depends on the air and soil temperature prevailed in the period of overwintering and doesn’t depend on the amount of precipitation. In the conditions of very high population, baited traps were useful in terms of lowering SBW population. Mass trapping of SBW on the “old” sugar beet fields in AW area significantly reduced the number of insecticide applications and the amount of used insecticides with keeping the damage and weevil infestation on the same or even lower level comparing to the fields outside AW. EPN, H. bacteriophora has a potential in suppressing the SBW. EPNs shows dose response in the conditions of moderate intensity attack. In such conditions, the highest dose resulted with the efficacy of 92.46 %. AW mass trapping shall be combined with other non- pesticide measures for control SBW. The EPN might serve as good tool to be implemented into AW programms. The research results significantly contribute to the ability of sugar beet producers to introduce mandatory principles of integrated pest management in their production and enable environmentally acceptable control of SBW which almost became a limiting factor in the production of sugar beet.

aggregation pheromones ; area wide ; entomopathogenic nematodes ; mass trapping ; sugar beet ; sugar beet weevil

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