BIOLOGICAL CONTROL IN ISRAELI AGRICULTURE; USING THE TREE OF KNOWLEDGE
By Hana Charny
Hana Charny has a B.A. in Biology and English Literature from the University of Pennsylvania and is currently studying towards her M.S. in Science Education at the Hebrew University of Jerusalem. She works at the Society for the Protection of Nature and in Hebrew University’s Department for Communications in Education.
Not long ago, jackals roamed the Land of Israel. Their eerie cries vibrated through hills and valleys, piercing the silent night air. Little did they know that troubled waters lay ahead. Jackals eat anything: vegetables, fruit, small mammals, even garbage. By 1955 their vast numbers presented a severe agricultural problem. The Ministry of Agriculture decided to selectively reduce their population by fifty thousand. The ministry placed poisoned chickens around farm lands, while taking precautionary measures to ensure that other animals were not harmed. A net was placed above the chickens to prevent raptors from eating the deadly prey, and poisoned jackals were buried. Unfortunately, individual farmers, impressed by the project’s success, entered the picture as well. Yet, they ignored safety standards. The results of their actions disrupted the ecological web: nature’s finely tuned check and balance system. One hundred thousand jackals were killed, together with numerous raptors, badgers, and weasels. The animals slain fulfilled a key role in the ecological food web, by preying on rodents. Consequently, the rodent population exploded. Snakes, which prey on rodents had a field day, their ranks swelled to epidemic proportions and reported snake bites surged. Some farmers trying to fight rodents with poison pellets, ended up killing song-birds as well. Finally, the Nature Reserves Authority (NRA) stepped in, introducing strict laws which banned the unauthorized use of poisoned livestock and pellets. Today, the jackal is returning. Yet its story joins a long list of scars to nature that serves to question acceptable limits for human control of life on earth. The use of chemical control in agriculture is one such issue.
Dangers of Chemical Control
Israel is well known for its landmark agricultural achievements. Its success was fired by the belief that only by working the soil, could the rebirth of the Jewish nation in Israel strike roots. Extensive scientific research complemented this approach. However, the "greening of the desert" and impressive yields were often secured by an increasing reliance on insecticides and fertilizers.
Shlomo Amitai, an entomologist with the Volcani Institute of Agriculture, describes the sobering lessons of four decades of insecticide use. Pesticides must often be used extensively to generate increased quality and yields. Natural selection evolves "super-pests," that are no longer vulnerable. Most ominous, the insecticides’ deadly content does not discriminate between "pests" and other species, some of which are essential to life on earth. Many insecticides which do not disintegrate, accumulate in environmental resources, and endanger all forms of life.
Pesticides are linked with a variety of diseases. Studies completed by Dr. Elihu Richter of Hebrew University’s Unit of Occupational and Environmental Medicine revealed an association between illness and organophosphate exposure in various occupational and agricultural communities. Symptoms included dizziness, nausea, respiratory problems, neuronal damage, and seasonal neuropsychological changes. Symptomatic patients, including children, were found to excrete significantly higher levels of organophosphate residues in their urine.
Some agents are mutagenic. Their grasp effects the genetic endowment of future generations. The story of "Bromine Industries," a Beer-Sheva based factory, is a case in point. Some workers involved in the production of a nematocide, Dibromochloropropane (DBCP), became infertile. Production was discontinued in 1977. A 1983 follow-up study by Dr. John Goldsmith and colleagues at Ben Gurion University, showed that only some males had recovered. Likewise, following male parental exposure, the percentage of female births significantly exceeded statistical expectations. A mutagenic process may have been at fault. Tests showed high numbers of abnormal Y chromosomes in the sperm of DBCP workers. Another study of agricultural workers exposed to DBCP revealed a significant increase (from 6.6% to 19.8%) in the rate of spontaneous abortions.
There are nearly 780 licensed insecticides in Israel. Their use is monitored by three bodies: the ministries of agriculture, health, and environment. The Ministry of Agriculture’s Plant Protection and Inspection Department is in charge of licensing, labeling and monitoring insecticide usage. Assistant Director Moshe Hofman contends that "compared to other countries, we are well equipped and able to deal with almost every molecule that is released. There is no residue problem."
However, while clear legal standards exist, they are hardly enforced. Hofman says that all instructions and warnings are detailed on the label. Yet, according to Dr. Richter, this is precisely the problem; governmental control only covers the pesticide’s registration and labeling; after which is a no man’s land. Further, Dr. Richter claims that the labels are misleading and withhold information essential to agricultural workers’ right to know and act according to measures imperative to their well- being, such as exposure prevention and emergency care.
Hofman claims that enforcing department policy is an extensive task which requires additional manpower. Likewise, it is often difficult to prove legal transgressions since most chemicals break down by the time of analysis. Yet, Dr. Richter notes that while most of the organophosphates do break down quite rapidly, many of their intermediaries remain. Some intermediaries are even more toxic than the original materials. Further, as happens with parathions, a conversion from less to more toxic intermediates often takes place inside the body.
Recent data collected by Richter and co-workers has shown that cotton yields per hectare have actually increased despite, or perhaps because of, a huge drop in use of organophosphates in Israeli cotton fields, dictated by the toxicity of chemicals used. This may imply an important breakthrough for chemical control tactics. In some cases, more (chemicals) may mean less (yield).
While the department performed around 5000 crop analyses last year, nearly all of them were on crops designed for export; local produce is monitored by the Health Ministry. A clear double standard exists. Foreign agricultural regulations are different than Israeli ones. Ironically, produce that doesn’t comply with foreign standards is often sold in Israel. A phone call during the interview with Shlomo Amitai drove the issue home. A farmer rang asking for application instructions of chlorobenzilate. Amitai noted that America doesn’t allow the import of produce treated with chlorobenzilate. "In other words, in Israel we eat vegetables that are considered inedible in other parts of the world," said Amitai. Fortunately, the situation may soon improve. Dr. Shlomo Capua, Director of the Ministry of Environment’s Agro-Ecology Department, notes that last year only a few hundred tests on local produce were completed. However, this year the ministries of environment and health have joined forces to improve inspection measures. For the first time, Environment Ministry inspectors will conduct spontaneous spot checks in agricultural fields, before the produce arrives at the marketplace, and the Ministry of Health will test the samples in its laboratories. Most significantly, test results will be discussed by a joint committee of representatives of the two ministries. When violations of the standard are discovered, the committee will decide on appropriate measures, whether publicity in the media, warning or confiscation of the contaminated produce.
The Story of Biological Control
Despite the dangers of chemical control, it is still applied to roughly 95% of Israeli crops. However, Israeli scientists are increasingly pursuing less harmful agricultural control methods; replacing chemical with biological and other measures.
Biological controls work together with, rather than harness natural forces. They utilize the continuous scientific unravelling of long-held secrets governing the world of nature. Research of the insect’s chemical world is in full gear. Successful identification of chemical components will enable laboratory synthesis of highly specialized signals, painstakingly designed by evolution. These artificial compounds can easily deceive unsuspecting insects. A dirty trick? Perhaps, but it works.
One example involves the isolation and synthesis of pheromones; substances secreted by insects to communicate a variety of social messages, including trail marking, battle orders, and sexual states. Fertile female insects often secrete pheromones that are carried by the wind, attracting males downstream. Initially, natural pheromones, extracted from females, were used to trap males. Later, a laborious process which monitored the response of male antennae, enabled scientists to chemically synthesize the compounds. Moshe Streinlicht, of the Volcani Institute, used this method to combat the citrus moth whose larvae prevent fruit development by destroying the flower’s ovary. The researchers managed to isolate the pheromone secreted by the female citrus moth. The pheromone was then chemically synthesized, and used to attract love-hungry males into a deadly trap. Each synthetic trap captured 500 males. The pheromone was also released in wide quantities throughout the field, saturating the air. Males had difficulty finding the females and so less females were fertilized. The project’s success reduced the need for chemical control in citrus groves.
Pheromone traps also help farmers plan integrative control strategies. This is particularly significant in crops that are plagued by a variety of insects. Traps enable farmers to monitor the number of males present as well as the egg-laying period, thereby reducing chemical usage by pinpointing the ideal time for spraying. Another form of biological control utilizes knowledge of insect predator-prey interactions. "Natural enemies," such as predatory and parasitic insects, are introduced to the fields to combat agricultural pests. The first commercial application in Israel, began in 1950. Professor Rivnay of the Volcani Institute went to China, hoping that the corner of the world that had given rise to citrus trees, also harbored the secret to controlling citrus pests, like the Egyptian black scale. His journey paid off. He returned armed with a parasitic wasp (Aphytis) that was bred and released in mass throughout the coastal area. A year later, the pests had largely disappeared.
One of the world’s most serious citrus pests, the California red scale (Aonidiella aurantii) was also controlled by parasitism. Scales are parasitized by a wasp that is attracted to a pheromone secreted by virgin females. By laying its eggs in young females, the wasp is assured that the host will not die off before its progeny complete their development. An increase in the number of virgin scales, brings about enhanced parasitic activity and a subsequent decline in the scale population. Pheromone traps were used to seduce male scales, leaving numerous lonely females. The parasites partied away, and the day ended with an overall reduction in the red scale population.
The founding of "Biological Control Industries" (B.C.I.), in 1983, marked a pivotal development of the field in Israel. Located in Kibbutz Sde Eliyahu, at the feet of Mt. Gilboa, B.C.I. is a natural outcome of the path the kibbutz embarked on earlier for ideological reasons. Led by kibbutz members, Mario Levi and Yaakov Nakash, the kibbutz pioneered the field of organic agriculture in Israel. The beginning was modest. For many years Levi and Nakash researched and bred "natural enemies" in their homes and refrigerators! Ideology was quickly supported by economic motives; the kibbutz created a special niche, marketing its produce as pesticide-free.
B.C.I. is committed to developing innovative, environmentally- responsible solutions to agricultural problems. Its philosophy is that of Integrated Pest Management" (IPM), in which a pest control strategy is designed for each crop, with the objective of maximizing crop yields, quality, and environmental safety.
B.C.I.’s Director of Research and Development, entomologist Dr. Shimon Steinberg, enthusiastically describes natural enemies like a general presenting his troops. IPM strategies sound like battle plans. The "problem insect" is followed by a description of "the solution." As effective warfare requires knowledge of one’s enemy, the biology of both predator and prey is extensively examined. Number of eggs laid by prey versus number eaten by predator, optimal growth and "attack" conditions; all are considered.
For example, long white tunnels in home-grown vegetable leaves or unattractive flowering Chrysanthemums and Gerbera may be the result of leafminers; flies from the genus Liriomyza. Each female lays 100 eggs that hatch within a week into larvae that tunnel through the leaf tissue. Once mature, the larvae exit and pupate on the ground. When adult flies emerge, the cycle begins anew. The worst news is that the leafminer is a virulent pest, capable of breeding throughout the year. However, help is nearby in the form of Diglyphus isaea, a small parasitic black and green wasp. Leafminer larvae are helpless against the wasp’s clever battle plan. Paralyzed by the female wasp, they await the day when the numerous wasp eggs deposited throughout the leaf hatch and begin to consume them.
What if one natural enemy is not sufficient? Simply integrate forces. The predator (Cryptolaemus montrouzieri) and parasitic wasp (Leptomastix dactylopii) are simultaneously introduced to combat the citrus mealybug (Planococcus citri), because the predator is most effective in cases of heavy mealybug infestation, while the parasite prefers low host densities. Prior to IPM application, any ants present must be destroyed, since they protect the mealybugs, receiving honeydew in exchange for services rendered.
Aren’t there risks to human intervention in nature? Can the predator itself become a pest? Steinberg believes not: "we have to realize that modern agriculture, the intensive cultivation of crops in concentrated regions, is a vulgar disruption of nature’s balance… Biological control merely attempts to turn back the wheel through planned intervention. Further, records from the past 103 years, since biological control began, fail to indicate cases in which the introduction of natural enemies led to unbalanced forces." The reason being that most parasites and predators are obligatory upon their hosts. Presently B.C.I. exports around 90% of its products to the more receptive European and American markets. It hopes however to soon introduce a product that will orchestrate a crucial turning point in the conventional Israeli market: an improved way to pollinate greenhouse tomato plants. Presently, each plant has to be manually pollinated 2-3 times a week by a device called an electric bee. B.C.I. hopes to put the "electric bee" out of business through mass introduction of bumblebees. The process is strikingly different to the mass rearing of other natural enemies, because the bee is a social insect. Breeding conditions must comply with the "social etiquette" inherent to bee societies. A typical hive, consisting of one queen and 50-60 workers is applied to 2.5 dunams of tomatoes for 6-7 weeks.
Tomato crops are currently sprayed up to 3 times a week. The chemicals are primarily needed to combat the white fly, which transmits a severe viral disease. The catch is that bumblebees cannot be applied together with insecticides. Farmers must choose; either make a complete shift in the concept of greenhouse pest control by reducing chemical applications, or give up the bumblebee idea. Since tomatoes are a major Israeli crop, B.C.I. hopes this new package will be a driving force of biological control in Israeli agriculture.
Steinberg believes that the proper attitude, together with government support, can promote biological control as a competitive alternative. "The European experience demonstrates that governments, together with citizen support can and should induce farmers to turn to healthier alternatives… The turning point will undoubtedly come only when the Israeli consumer starts to demand alternatives to pesticide-laden produce," says Steinberg.
Another form of insect control utilizes bacteria and fungi. A bacterium from the genus bacillus was widely researched in the U.S. and in Israel, by Navon and Wisoki from the Volcani Institute. Bacillus thuringiensis is a potent killer. It poisons its victims by producing a highly toxic substance that induces rapid paralysis, climaxed by death. In 1976, a variant bacterium, lethal to certain flies and mosquitoes, was discovered in a Negev puddle. Coined Bacillus t. israelensis (BTI), it provided a revolutionary means of controlling water-breeding insects. Commercial production proved vital, particularly in Africa, where israelensis zeroed in on insects transmitting severe tropical diseases including malaria and African sleeping disease.
Once again the question arises. Is there no danger to releasing mass quantities of killer bacteria to the environment? The answer
and beauty of the whole design is no. In contrast to their close relative, B. anthrax, which is fatal to many life forms, most bacillus variants can only affect insects, in particular, agricultural pests. BTI, for example, can only function in a basic environment of 8 pH and above. Insects whose digestive tract is characterized by a pH of between 8-9, are therefore affected, while other life forms are safe.
Jerusalem based Ecogyn Israel Partnership (EIP), specializes in the field of fungi control. It is currently developing three products that collectively target an annual market in excess of one billion dollars. Microbial control currently accounts for nearly 60% of the chemicals applied to Israeli crops.
One fungal product, Ampelomyces quisqualis (AQ), kills other fungi, that cause plant diseases, like powdery mildew (Erysiphe). AQ is a major step forward in the field of biological fungi control. Even after fungi interactions were understood, a major obstacle to commercialization remained. Science had yet to create fungi products that possessed the shelf life-span necessary for effective marketing. This was hardly an easy task; it dealt with the packaging and distribution of live organisms. In fact, EIP views AQ’s 10 month shelf-life as a key to commercial success. Another innovative quality of AQ is its appearance and application method. Based on the belief that farmers are wary of biological control products, EIP set out to develop farmer user-friendly products that emulate conventional chemicals. AQ arrives in a powder and is handled exactly like a chemical. The powder is actually comprised of a carrier substance mixed with spores; live, fungi reproductive units.
Other fungi target post-harvest diseases. Presently, all fruits and vegetables arriving at packing plants are subjected to yet another chemical bath. The treatment protects crops from a wide array of molds that develop on wound sites commonly inflicted during packaging. EIP was originally offered funding for research of organisms capable of producing antibiotic compounds against fungi. However, the controversial aspect of offering fruit laced with antibiotics, motivated it to explore other avenues.
Through an intriguing process of scientific and detective patchwork, EIP then discovered Candida sake, a naturally occurring yeast-like organism, that targets post-harvest diseases. Dr. Raphael Hofstein, EIP’s Scientific Director, described the process. Examination of post-harvest fruit revealed that some had developed various blue and green molds, while some were disease-free. This raised the hypothesis that the disease-free fruit was protected by a natural organism. Experimentation began. Wounds were induced, and sites that did not develop decay were scraped and washed off into a growth-favoring medium. The assumption was that the cocktail contained beneficial fungi that somehow antagonized molds. Sure enough, the medium was found to contain C. sake that competes with pathogens at wound sites for space and nutrients. Once successful, C. sake returns to its normal population level, and the wound heals naturally. Interestingly, once again, a particular aspect of the organism’s biology makes it environmentally safe. Since the yeast is applied in packaging plants, only acute mammalian toxicological testing is required. As the yeast dies if subjected to a temperature above 30C, mammals are not endangered by this organism.
EIP has much in common with other biological control industries. Like B.C.I., generally its products cannot be applied with chemicals. It also believes in the need to provide farmers with comprehensive pest control packages. Recently, EIP and B.C.I. put their philosophy into practice in a successful joint project.
The tree of knowledge has given rise to a diverse array of biological controls. Reason suggests that it’s time to perform a "changing of the guards," opting for an improved integrative agricultural policy. Seeds of environmental consciousness have struck roots and are slowly making their way towards public awareness. Some are solely ideological, while some are dictated by financial interests. All incorporate wisdom, respect for and an understanding of nature to fulfill essential human needs. It seems fitting that environmentally-responsible agriculture be the hallmark of the Land of Israel. Israel is well known for its agricultural expertise, and as the country that made the desert bloom. This wealth of knowledge should now be directed to establish a national policy that addresses the challenge of cultivating produce of superior quality, yield, and health and environmental safety.