Weeds and flies: a relationship towards biological control by conservation
In the sugarcane fields in the Cauca River Valley there is naturally a great ally for the combat of stem borers Diatraea spp. The tachynid flies of the species Genea Jaynesi They constitute one of the best regulators of these stem borers throughout the region.
In fact, some studies indicate that G. jaynesi may currently be causing between 10% - 39% of the parasitism on the different species of Diatraea present in the Cauca river valley, being one of the most important parasitoids for the management of these pests.
However, unlike other controllers (parasitoids) this tachytin fly only reproduces in its natural environment, which is a challenge for the management of the pest and at the same time an opportunity for the implementation of strategies for biological control by conservation.
Biological conservation control considers the preservation of biodiversity, specifically of the natural enemies of some pests, by stimulating their establishment and proliferation in cultivated fields.
This requires the supplement of food resources such as pollen or nectar, provision of prey or hosts, provision of oviposition or shelter sites, among others.
Precisely in the search to establish conservation practices of low cost and complementary to the biological control carried out from other parasitoids, the behavior of G. jaynesi in alleys of fields of the Risaralda mill with broadleaf weeds was evaluated and compared with fields where Conventional management was done (eradication through the application of chemical herbicides).
With the observations made at the time of study, a total of 17 different species of broadleaf weeds were quantified providing food resources to the fly G. jaynesi, which means a high biodiversity of associated flora in the alleys of the uncultivated cane fields. In addition, the following conclusions were obtained:
- There were a greater number of adults of the taquínida fly in the fields where the broadleaf weeds in their alleys were preserved in comparison with lots where the weeds were eliminated.
- Parasitisms by G. jaynesi they were up to 15 times higher in fields where weeds were preserved than in those where they were eradicated.
- In the fields where weeds were left the damage decreased by 2.5% units of infestation intensity on average; while in the fields where they were removed, crop damage increased 2.8% units of infestation intensity on average.
All these results allow us to see how the conformation of weed vegetation shelters in the uncultivated alleys of the sugar cane fields is a model of biological control by conservation which can become a complementary tool to face the increase in damage by borers in sugarcane crops.
This practice would also favor the presence of other beneficial enemies of potential pests to the cultivation of sugarcane, thus reducing explosions of pests, which may be appearing in the crop without prior notice.
The science of restoring basins
It is no secret to anyone that hydrographic basins are essential to guarantee a permanent water supply, but few know that behind the restoration and conservation of a river system there is more than a tree planting plan and conversion of activities that negatively impact the system.
To begin with, it must be understood that the regulation of a basin seeks to maintain a less changing base flow, so that in rainy seasons the water does not run out of control to river beds and is stored in the soil, and in times of Low rainfall has an adequate supply from that storage both in quality and quantity.
When this operation is affected by factors such as deforestation and erosion, restoration plans are required that provide for the affected areas to return to an equilibrium or sustainable condition.
These efforts focus on maintaining ecosystem services such as water provision, erosion prevention and control, biodiversity conservation and carbon sinks.
For this effort to be effective, the natural process of recovering an ecosystem must be understood; understand the rain-flow relationship in different conditions and know the changes in the patterns of temperature, precipitation and coverage, among others. Currently, pollution and climate change should be considered as decisive factors.
From this knowledge you can select plant species that physiologically tolerate the changes generated in the basin and other special adaptations, as well as define agricultural activities that contribute to ecological restoration.
The above explains why increasing the population of trees in a healthy river system can generate an increase in water consumption due to greater evapotranspiration and, therefore, decrease the water supply of the basin, instead of favoring it.
Measure the micro
The microbasins are territorial units manageable from the hydrographic point of view and with more uniform conditions than those of a basin. In addition, restoration and / or conservation interventions are more concentrated in them. Due to these characteristics, they are ideal for measuring parameters such as water level, sediment concentration, pollution and state of riverine vegetation, among others.
Cenicaña currently carries out hydrological monitoring on four micro-basins and at the sub-basin level in the Aguaclara River, the main contributor of the Bolo river flow, for which information has been available since November 2013.
With this monitoring we want to know the impact of the recovery and conservation actions carried out by the Water for Life and Sustainability Fund Foundation (FFAVS), as a basis for adjusting the restoration plans that are being executed and designing new intervention alternatives that promote regulation and water performance in these basins.
In this way the sugarcane agribusiness contributes to the integral management of the water resource by working on the supply of water from the upper part, with the support of the associations of users of the rivers in the water producing areas, and in the flat area, with the knowledge that leads to precise water requirements by the crop and make efficient use of the resource.
The quantity and quality of surface and groundwater are closely related. In the upper and middle parts of the basins the water is generated that recharges the rivers and aquifers, since they are areas of rainfall concentration.
Germán Vargas, entomologist
Variety Program, Cenicaña
Fanny Hoyos, agricultural engineer
Agronomy Program, Cenicaña
Research carried out by María Alejandra Jiménez, Agronomy student at the University of Caldas, under the auspices of the Risaralda and Cenicaña sugar mill, and published in the XI ATALAC-TECNICAÑA Congress 2018 Memoirs.