Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Development of a management strategy for a sustainable crop rotation system for suppressing the WCR (Western Corn Rootworm) population level over time and space

Evidence for immigration of WCR (Western Corn Rootworm) adults in non-maize crop stands Pherocon AM traps did demonstrate WCR adult presence and activity near the ground surface in winter wheat, soybean, and sunflower. The WCR population in the project trial (mainly in 2001 and 2002), measured by catching adults on Pherocon AM traps, approached the threshold level established for economic larval damage in next year’s maize in USA. In each year, significantly higher numbers of WCR adults were trapped in maize compared to any other crop in the rotation system. Pherocon AM traps (that visually attractant WCR adults) were covered by dense sunflower foliage in July and August or by soybean foliage. Therefore, adults caught by the traps in these crop stands were actively flying into these plots. In the case of winter wheat, one cannot speak about plant stand from mid-July under our conditions. Since winter wheat was harvested around mid-July, the traps were visible from a distance that may have contributed to increase adult numbers on traps on harvested winter wheat plots.

At the population density in the project trial, there was no distinguishable adult density shift from maize to non-maize crops in the growing period of maize or after silking of maize. Certainly, observations showed that WCR adult numbers increased in harvested winter wheat plots on traps and on volunteer wheat plants (feeding adults). This phenomena raises the important question of the possibility that harvested winter wheat fields could be potential egg laying places for WCR females in Europe. However, the proportion of egg-laying WCR females within the population after harvesting winter wheat is still a question. Since harvest time and WCR phenology vary from one region to another in Europe, this phenomena should be considered and checked on a regional basis in the future.

Evidence for WCR female egg laying in non-maize crops:

Although we have not sampled WCR eggs in non-maize plots (and few eggs in continuous maize plots), sampling of larvae and adult emergence in maize after non-maize crops in our trial justifies, that egg laying did happen in non-maize crops. It is expected that at higher WCR population density or with improved sampling techniques WCR egg could be sampled from non-maize crops. This method, however, is labour and time intensive therefore cannot be suggested for purposes under regular farming conditions.

WCR larval development happens in maize after non-maize crops Sampling in 2002 resulted in 4 larvae (one after winter wheat and sunflower, while two after soybean). Again as in the case of egg population, this density was rather low. One should note that the L1 stage practically cannot be found with the sampling method used due to their small size or being in the root, and the same applies for the early developmental period of L2. Therefore, the small number of larvae found was not unexpected. The efficacy of this larval sampling method was effective at higher population densities in continuous maize resulting in 51 and 147 larvae, respectively. Larval activity (root damage) in maize after different non-maize pre-crops varied by year. At observed population densities, no reliable evidence can be demonstrated for the effect of pre-crop on the next year’s maize root damage by WCR larvae.

WCR adults emerge from the soil of maize after non-maize crops:

In the 2001 and 2002 growing seasons, a total of 98WCR adults emerged in maize after non-maize crops the previous year within a total of 54 emergence cages. Due to relatively high adult population in 2001, the number of emerged adults was higher in 2002 when compared to 2001. Continuous maize always maintained significantly higher adult emergence numbers compared to maize after non-maize pre-crops. For the effect of pre-crop on next year’s adult population, there was no difference between winter wheat and soybean, while sunflower resulted in significantly fewer adults compared to soybean.

All of the above points to the fact that part of the WCR population immigrates to non-maize crop stands and lays eggs, and the subsequent maize, the larvae develop (thus damaging maize roots), and adults emerge. Various pre-crops may have different impact on the various stages of WCR. Sunflower blossoms are likely to be attractive for adults. We have also observed this type of attractiveness for adults by volunteer winter wheat.

Based on correlation equations WCR adults highly prefer maize plots. In all cases, there was a strong correlation between the catches on Pherocon AM traps in pre-crops and between the catches in emergence cages in the subsequent year’s maize. From the standpoint of maintaining the WCR population, cereals (oat and winter wheat) and sunflower were similar, while a few WCR adults in soybean plots resulted in the highest population in the next year’s maize. To produce the same number of WCR adults in maize, soybean plots as the pre-crop “needed” the fewest number of adults.

Reported by

Szent Istvan University Godollo
Pater Karoly 1
2103 Goedoelloe