by
M.M. Escalada, Visayas State University, Baybay, Leyte, Philippines,
J.L.A. Catindig and K.L Heong, International Rice Research Institute, Los Baños, Philippines
Three common planthopper parasitoids. A = Oligosita B = Anagrus C= Gonatocerus
The most important functional group to enhance biological control ecosystem services in rice production is the parasitoid. These are tiny (~ 0.01 mm) wasp like insects whose adult females lay their eggs into the eggs of planthoppers which are inserted into the rice stem tissues. Although tiny they have ovipositors strong and long enough to pierce through the tissues that seal the planthopper eggs. The inserted egg parasitoid then hatches into a tiny larva in the planthopper egg and grow by feeding on the egg tissues. And after a week, the larvae turn into pupae and eventually into the adult wasps which emerge. As a result the planthopper eggs that are parasitized die. Thus when high parasitism rates, expressed in percent eggs parasitized, are recorded entomologists know that planthopper populations would not develop exponentially to outbreak proportions.
Life cycle of parasitoid of hopper eggs
To an entomologist the concept of parasitism seems simple and the obvious strategy is thus to conserve the parasitoids as natural resources. Since planthoppers “hide and protect” their eggs by inserting them into the stem tissues, normal predators or pesticide cannot get at them. In the field the tiny parasitoids (about a hundredth that of a bee) have to wander around searching for eggs and thus in an insecticide sprayed crop, the tiny drops of chemicals on the stem and leaf surfaces are like “land mines” to the searching parasitoids. This phenomenon is fundamental to ecological engineering techniques and for farmers who are the primary managers of rice ecosystems to understand, appreciate, value and develop innovative means to conserve parasitoids.
However, parasitism although obvious to entomologists may be alien to laymen and farmers. First, most farmers do not know that planthopper keep their eggs into rice stems. They are too tiny to observe with the naked eye. The very concept of parasitism may also need explanation and parasitoids are too tiny to be observed. The challenge now is to develop a communication intervention to facilitate some understanding so as to motivate farmers to adopt ecological engineering techniques to conserve parasitoids.
Challenges in communicating less visible concepts
Communication specialists need to convey ecological engineering and biodiversity conservation concepts in ways that farmers can understand and take action, but there are challenges involved. For abstract concepts, experts advocate visual and experiential communication. Mediated learning experiences progress from most concrete experiences to most abstract. Dale (1946) visualized this in his Cone of Experience to classify the varied types of learning experiences. The cone, which makes a connection between concrete and abstract ideas, suggests that the more senses are involved, the better the chance for learning to occur.
Dale's Cone of Experience
The cone suggests that the more appropriate instructional methods can be selected by considering concreteness of learning experiences. At the middle level are audio-visual materials, substituting visual images for the real thing, leading to iconic learning. Printed materials are more abstract since these rely on verbal symbols. Not all teaching and learning should move from direct purposeful experience to verbal symbols. Teaching starts with the kind of experience most appropriate to the needs and abilities of the learner. Dale argued that learners could make use of more abstract instructional activities only when they have had concrete experiences that will give meaning to the more abstract representations of reality.
Applying Learning Theory to Communicate Ecological Engineering
Parasitoids belong to the order Hymenoptera. From the human’s standpoint, this order is probably the most beneficial in the entire insect order (Borror et al, 1976). It contains not only the wasps but also the bees that are involved in the pollination of plants and honey production. Bees are bigger, easier to observe and also well known. One strategy is use bees as surrogates to help communicate to farmers.
Guided by Dale’s cone of experience and Kolb’s Experiential Learning Theory (Kolb, Boyatzis, and Mainemelis, 1999) which emphasizes the central role that experience plays in the learning process, we employed farmer participatory research to teach farmers to observe bees. A simple field experiment is developed for farmers to conduct in their own field experiments. Farmers are then invited to perform the “experiments”. In the Cai Be farming community in Tien Giang, farmers were trained on two ecological engineering practices, synchronized planting using light trap catches and populating bunds with nectar- producing flowers to attract parasitoids and avoid using insecticide in the early crop season (first 40 days after sowing). About 5,000 meters of bunds were populated with a variety of nectar-producing flower plants.
Communication campaign “bee” poster designed in Vietnam to communicate ecological engineering to farmers
Farmers are taught to observe the bee populations as indicators of parasitism since parasitoids are too microscopic to be seen and the concept of parasitism difficult to explain. The community experiments in Cai Be district showed that rice farms with ecological engineering modifications had significantly higher predators and parasitoids and lower pests.
Beyond the farmer experiments, motivational campaign materials are also developed to scale up the dissemination of ecological engineering. Messages were positioned in “gain” frames. The 3 benefits of using ecological engineering that are communicated are: 1) Flowers in rice environments will bring in bees and their relatives (parasitoids) to protect your rice from invading hoppers, 2) Insecticide use is reduced since they kill the bees and relatives, and 3) Profits are increased. These are presented as a cluster of simple rules as follows:
Simple rule cluster
Flowers on the bunds provide food to attract bees and relatives.
The bees and relatives will help me control the hopper invading my fields, so I don’t need insecticides.
If I apply insecticides, it will kill the bees and relatives.
References
Borror DJ, DeLong DW, Triplehorn CA. 1976. An introduction to the study of insects. Holt, Rinehart and Winston, New York, USA. 852 p.
Dale E. 1946. The cone of experience. In Audio-visual methods in teaching. (pp. 37-51). Dryden Press, New York.
Kolb, D.A., Boyatzis, R.E. and Mainemelis. C. 2000. In: Sternberg, R.J. and Zhang, L.F. (Eds.) Perspectives on cognitive, learning, and thinking styles. Larence Erlbaum, New Jersey.
