Silver Medal HP

Mexico’s agricultural situation

Agriculture is one of the main economic activities in Mexico, and sweet citrus plantations occupy a large portion of the national production. At a time where most of our alimentary goods are imported, sweet citrus production is still mainly destined for national consumption, generating income for families across the country. Mexico’s citrus production industry covers 520 thousand hectares across 23 states, for an annual production of 6.7 million tons and profits reaching 8050 million pesos. Sweet citrus plantations are the main source of income for more than 69 thousand families (SENASICA, 2010).

A day trip to INIFAP: current plague control methods

During the month of May, the whole team conducted a visit to INIFAP, the National Institute of Forest, Agricultural and Livestock Investigation, located in the state of Morelos. Here, we met with Aaron Lugo, an agricultural engineer. We were shown an experimental citrus field, where several conditions, such as HLB disease, are tested and investigated. During this visit we were able to learn insightful information about current plague control methods. Most producers in Mexico rely on synthetic pesticides for control, although other alternatives are also used, such as covering citrus trees with mineral oil that causes insects to burn under the sun at plantations, where temperatures can reach 38 ºC (100 ºF). Pesticides pose several risks for the environment: while laws on the type and quantity of pesticides allowed on plantations have been established in Mexico, corruption is common and laws aren’t always followed. Many farmers which opt for cheaper, although harmful, pesticide alternatives, may cause their produce to contain residues which will later be consumed by humans, or might pollute nearby bodies of water. Other hazards related to pesticides include the decrease in the quality of the soil, as well as increased health risks for agricultural workers, who might be directly exposed to solvents and other compounds. Dr. Lugo mentioned an important problem in plantations is the lack of training that most workers possess. Government-sponsored workshops and lectures on agriculture are not uncommon, but most workers are uninterested, and often opt for the cheaper routes. Additionally, flowering plants such as the ones that rear citrus fruits are home to bees and other insects, which get killed alongside pests. This is the case for the mineral oil use in plants too, which is also a cruel method of killing animals. We were especially interested in this aspect of pest control: how can we develop a product that is able to effectively and humanely kill a pest without affecting other insects, the produce, and the environment?

A visit to Mérida: biological controls

Later in the summer, we visited the Regional massive reproduction laboratory of Tamarixia Radiata (Laboratorio Regional de reproducción masiva de Tamarixia Radiata), to learn more about the handling of the Asian citrus psyllid Diaphorina citri for its study and manipulation for further experiments in our project. Because none of us had experience with the rearing of animals for laboratory testing, it was vital for us to learn the methods used by an established laboratory. Their laboratory uses a biological control as a possible solution to HLB plagues, through the introduction of Tamarixia radiata specimens, a species of wasp which is a natural parasitoid of the Asian citrus psyllid. While this method may be effective in specific regions such as the Yucatán peninsula, where the laboratory is located, it is not ideal for worldwide application, due to the presence of hyperparasites that attack the wasps, greatly reducing its population. Additionally, the use of insecticides renders these methods ineffective (Gottwald et al., 2007). We had previously learned that Murraya paniculata was a good candidate for propagation (Skelley & Hoy, 2003). During the visit, this fact was confirmed, and we were told that D. citri has a higher preference for this plant than for other citrus species such as orange or lemon trees. We were shown the whole propagation process, from the seeding of the plant, the maintenance requirements and the way it must be cut in order to produce new shoots that would allow the psyllids to reproduce. In addition, she mentioned that it was fundamental to eliminate presence of other insects in order to prevent other species from ovipositing, which may compete with the psyllids for nutrition from the plant. Among the most dangerous insect species for D. citri are spiders, ants, ladybugs and any other beetle from the Coccinellidae family, since they are natural predators of the psyllid, in both adult and nymphal forms. Overall, the information given to us during this visit allowed us to prepare optimal rearing conditions for our psyllids.

Handling our specimens safely

Since our project involved the use of live insects, it was important for us to determine the methods for their handling and their correct manipulation for the primary cultures. We were able to talk to Dr. Javier Arturo Sánchez, an entomologist from Israel. While his experience focused on Drosophila melanogaster, he had experience creating primary cultures from insect cells and was familiarized with Diaphorina citri. He provided us with a protocol to dissect the insects and collect their cells, which involved opening the psyllid’s abdomen to extract the hemolymph and tissues. This protocol was later tested and proven ineffective, and it was modified with the help of Carlos Cruz, an investigator at CINVESTAV, who advised us to use the whole body of the psyllid.

References

Gottwald, T. R., Graça, J. V. & Bassanezi, R. B. (2007). Citrus Huanglongbing: The Pathogen and Its Impact. (Plant Health Progress. doi:10.1094/PHP-2007-0906-01-RV.
Skelley, L. & Hoy, M. A synchronous rearing method for the Asian citrus psyllid and its parasitoids in quarantine. Biological Control 29 (2004) 14–23
SENASICA (2010) HLB de los Cítricos, parte 01. Retrieved from https://www.youtube.com/watch?v=XeSZC9jOk-0&t=149s