Carlos Cruz and Alejandro Segarra
Crop Protection Department
College of Agricultural Sciences
University of Puerto Rico, Mayagüez
Mayagüez, Puerto Rico 00681
Biocontrol of plant pests in the Caribbean was almost completely neglected with the advent of pesticides which appeared to be the solution to all pest problems. However, due to the development of resistance in some major pests, as well as to public awareness of hazards posed to human health and the environment searches are being made for seemingly old alternatives.
The tropical environment in the Caribbean facilitates year round growing season and supports continuous generations of both pests and beneficial organisms. Agriculture is characterized by small subsistence farms, multiple crops and pests, pesticide problems and other problems common to production and marketing.
Biocontrol is now being acknowledged as a area for further research and is a component of a USDA initiative in sustainable agriculture. The ARS, the Entomology Department Administrators (1988) in U.S. Universities and the Experiment Stations have proposed working groups to prepare national biocontrol research programs. This has evolved as an effective alternative to the pesticide dilemma.
Biocontrol is one of the most thoroughly studied methods against insects, nematodes, diseases and weeds. Scientists are now increasing efforts and emphasis on pest control methods not aimed at wholesale eradication, but rather at maintaining pest populations below economic thresholds.
This has already started in the Caribbean, where efforts of national and international institutions have begun to emphasize and implement biocontrol programs. These efforts are directed at identification of research priorities and possible areas for cooperation within the region. At present, there are several institutions conducting individual research with little or no regional coordination. Biocontrol efforts and findings remain little known even between neighboring countries. This is due in large measure to inadequate communication between research and development organizations in the region. There are limited means to disseminate and exchange findings (scientific congresses, journals, meetings, seminars, etc.). Lack of funds for research and for attending local or international meetings is by far the greatest constraint to the development of biocontrol in the region. A workshop should serve to identify research needs and to promote interchange of knowledge within the Caribbean community.
There is evidence of the effective biocontrol successes worldwide and in the Caribbean (Cock, 1985). Bennet (1990) and Alam et al. (1990) summarized the most important cases of successful biocontrol in the Caribbean. The recent introduction of the citrus blackfly Aleurocanthus woglumi in Puerto Rico and its outstanding effective control with the subsequent introduction of the parasitioids Encarsia opulenta and Amitus hesperidum are a pertinent example (Medina et al. 1991). Chemical control of this pest has been impossible in most places; only biocontrol has been effective.
In Puerto Rico, as in many other Caribbean countries, biocontrol has been used for decades. Table 1 presents information regarding the introduction of parasites and predators into Puerto Rico in the 1900's. Most introductions were made during the 1930's, up to 1940, just before the pesticide era. As often occurs, data on many of these introductions are not available since relevant studies were never conducted.
Table 1: Parasites and predators of insect pests of Puerto Rico introduced in the 1990's.
Some exotic natural enemies have been recently introduced for the control of certain insect pests, such as citrus blackfly, the lima bean pod-borer, and the sugarcane borer and others such as nematodes, diseases and weeds (Cruz & Segarra, 1990). Also, several species of entomophilic nematodes for the control of root weevils were introduced and tested.
Some recent biocontrol attempts have been successful in Caribbean countries, i.e. the sugarcane borer, the citrus blackfly, the diamondback moth (to a certain level). On-going projects are devoted to control the coffee berry borer, Hipothenemus hampei (Baker, 1990). Two potential parasitoid candidates have been identified: Prorops nasuta and Cephalonomia stephanoderes. These parasitoids will be reared and increased for distribution in the areas where the pest has been identified: Colombia. Jamaica, Mexico, etc. Very positive results are expected from this initiative.
Important Crops and Insect Pests in the Caribbean
Several lists of important pests in the Caribbean have been compiled elsewhere. However, a partial list of crops and pests which are considered important in the Caribbean are presented in Table 2 and potential biocontrol agents are presented in Table 3. These are based mostly on experience and the literature. Among the most important crops grown in the Caribbean are coffee, sugarcane, bananas, plantains, root crops (sweet potato, yams, taniers, cassava), tomato, peppers, cabbage, cucurbits, citrus, pineapple, avocado, mango, pigeonpea and beans. There are important insect pests attacking these crops, some of them with a high potential for biocontrol.
Table 2: Some important crops and their main insect pests in the Caribbean.
| Crops | Main Insect Pests |
|---|---|
|
Sugarcane |
Diatraea, Diaprepes, Phyllophaga |
|
Coffee |
Hypothenemus hampei, Leucoptera coffeella |
|
Banana and plantains |
Cosmopolites sordidus |
|
Sweet potato |
Cylas formicarius, Euscepes postfasciatus |
|
Yams |
Diaprepes |
|
Cassava |
Silva spp. (Stem shoot fly), mites |
|
Citrus |
Aleurocanthus woglumii, Diaprepes, scales |
|
Pineapple |
Batrachedra comosae (gomosis) |
|
Beans |
Leafhoppers, whiteflies, pod borers |
|
Pigeonpea |
Pod borers, leafhoppers |
|
Tomato |
Heliothis, Liriomyza, Keiferia lycopersicella |
|
Pepper |
Anthonomus eugenii, Myzus persicae, Thrips palmi mites, etc. |
|
Cabbage |
Plutella xylostella |
|
Cucurbits |
Diaphania spp. |
Table 3: Some important insect pests and their potential for biological control in the Caribbean.
| Insect pests | Biocontrol potential |
|---|---|
|
The coffee berry borer |
Prorops nasuta, Sephanoderes cephalonomia |
|
Whiteflies: Aleurocanthus woglumi, |
Encarsia spp., Amitus sp., |
|
Lepidopterous pests: |
|
|
Diatraea spp. |
Cotesia flavipes, |
|
Plutella xylostella |
Cotesia plutellae, |
|
Leucoptera coffeella |
Mirax insularis -augmentation Others - conservation, foreign exploration |
|
Diaphania spp |
Several: Conservation and augmentation |
|
Heliothis spp |
Many: Conservation and augmentation |
|
Others: |
|
|
Liriomyza spp |
Many: Conservation and augmentation |
|
Thrips palmi |
Some: Foreign exploration, conservation and augmentation |
The Sugarcane Borer
The sugarcane borer, Diatraea saccharalis, is under effective biocontrol in some countries, but it remains an important limiting factor in several others. Different natural agents have been successful on some countries, probably indicating the influence of varying habitats. This pest offers a good opportunity for classical biocontrol. Several natural enemies have been reported by Bennet (1990) and others. Currently, Cotesia flavipes, Lixophaga diatraeae, Metagonistylum minense and Trichogramma spp. are the most successful biocontrol agents. Research is needed to continue the improvement of the existing biocontrol agents.
Root Weevils
Historically, the sugarcane rootstalk weevil, Diaprepes abbreviatus, has been among the most difficult pest to control in the Caribbean. One contributing factor is the high reproductive potential (5,000 eggs/female), in a situation where very low egg survivorship is enough for it to be a pest (Armstrong, 1987). Several biological control attempts have failed, except for entomopathogenic nematodes. However, the search for other biocontrol agents continues Castro (1986) studied the ants species feeding on neonate larvae. She found seven feeding on the larvae. Of these, Pheidole subarmata borinquensis and Pheidole fallax demonstrated the greatest efficiency. In Cuba, Castineiras et al. (1990a, 1990b), reported P. megacephala controlling Cosmopolites sordidus and Cylas formicarius. Richman et al. (1983) reported the ants Monomorium floricola and Crematogaster ashmeadi preying on the egg masses of D. abbreviatus in Puerto Rico and Florida, respectively. Colón (1986) found 17 species of fungi associated with the larvae of D. abbreviatus. Pathogenicity tests demonstrated that half of then were able to kill the larvae. Gliocadium sp. and Fusarium sp. caused the highest mortality. Armstrong (1981, 1987) studied the efficiency of the egg parasitoid Tetrastichus haitiensis on D. abbreviatus eggs oviposited on sugarcane. He found a low efficiency of the parasitoid and concluded it was probably due to the difficulty of oviposition through the sugarcane leaves as compared to other hosts.
Several species of entomopathogenic nematodes have been tested for the control of the most important root weevils in Puerto Rico. Román & Figueroa (1985) reported effective control of the larvae of D. abbreviatus with Steinernema feltiae (=Neoaplectana carpocapsae). Figueroa & Román (1990) reported tests with S. glaseri, S. bibioni and Heterorhabditis heliothidis against D. abbreviatus. González (1986) observed some control using H. bacteriophora and H. heliothidis. Figueroa (1990) obtained excellent results with S. feltiae and S. biboni against C. sordidus. A graduate student is currently evaluating S. feltiae and H. heliothidis against C. formicarius. Several local strains or species of entomopathogenic nematodes recently found in Puerto Rico are being evaluated. Natural enemies against other curculionid pests such as Exophthalmus spp. and Pachnaeus spp. are being sought in some Caribbean countries.
The Coffee Berry Borer
The coffee berry borer, H. hampei is threatening coffee production in the Caribbean. Biocontrol research has produced encouraging finding. Besides the two parasitoids mentioned in the introduction, other potentially effective parasitoids are under study. An example is Heterospilus coffeeicola, which has been classified as effective but difficult to rear in the laboratory. Other potential candidates such as: Phymasticus coffea, Aphanognus dictynnu (apparently hyperparasite of Prorops nasuta) and some microbial agents such as Beauveria bassiana, Metarhizium anisopliae and Paecilomyces spp. These are under study at various research centers worldwide (CENICAFE, Colombia).
The Coffee Leafminer
Another pest of coffee with a high potential for biological control is the coffee leafminer, Leucoptera coffeella. Gallardo (1988) and Wolcott (1947) have reported 15 parasitoids from Puerto Rico. Gallardo has proposed a biocontrol program utilizing the augmentation method using the parasitoid, Mirax insularis. This idea has extraordinary merit and should be pursued vigorously. There are many other natural enemies reported that could be considered when their efficacy and mass rearing techniques are determined. Foreign exploration is another potential alternative which has not been attempted for this pest, which supposedly originated in Reunion (Green, 1984).
The Diamondback Moth
The diamondback moth (DBM) Plutella xylostella is a lepidopteran pest of importance to the Caribbean with a significant number of natural enemies. It has outstanding potential for a successful biocontrol program. In Puerto Rico several parasitoids are particularly effective. Diadegma insularis, may have rates of parasitism up to 90% when protected from pesticides. One limitation is the very low economic injury level of the pest. However, the selection of planting dates, use of selective pesticides and the introduction (where not available) of the most effective parasitoids will undoubtedly improve the level of biocontrol.
Alam (1986) reported complete biocontrol with Trichogramma spp., and Cotesia sp. Bennett & Yasseen (1972) reported effectiveness of C. plutellae against DBM in Barbados, Montserrat, St. Vincent and Trinidad.
The Corn Earworm
The corn earworm (CEW) Heliothis zea is the limiting factor for sweet corn and other vegetable crops. Chemical control is very difficult, even with and effective insecticide. However, many natural enemies have been observed attacking the eggs and larval stages of this insect (King & Coleman 1989). The wasp Trichogramma sp. and the predator Orius pumilio are considered by Figueroa (1983) to be the most important natural enemies in Puerto Rico. In the US, CEW infestations are considered more severe in dry than in wet summers because moist conditions favor the development of several fungal and bacterial diseases. Also several species of predators and parasitic wasps attack it. Populations of these natural enemies can significantly reduce or almost eliminate CEW infestations early in the season. Therefore, early season sprays should be delayed in order to allow populations of natural enemies to develop. Frequent sampling and control measures are necessary in vegetables because even minimal damage by this and other pests can render produce unmarketable.
The Melonworm
Usually the melonworm Diaphania hyalinata (L.) is the most important insect pest of cucurbits in the Caribbean. Medina et al. (1989) observed several parasitoids and predators in Puerto Rico. No natural enemies have been studied in detail. In Barbados, Alam (1986) reported melonworm egg parasitized by Trichogramma pretiosum, the larvae by Eiphosoma dentator and by Cotesia sp., and the pupae by Brachymeria sp. There is a great potential for the biocontrol of this pest, particularly with microbial insecticides, which are already being used in some countries like Guatemala (Agrícola El Sol, 30 Calle 11-42, Zona 12, Guatemala).
Scale Insects, Whiteflies, Aphids and Thrips
The potential for biocontrol of small insects is well known. Since the introduction of Rodolia cardinalis in California in 1892 for control of the cottony cushion scale or the biocontrol of the citrus blackfly in the Caribbean, many outstanding examples have occurred. In Florida, a biocontrol project is seeking natural enemies for whiteflies. As a result several natural enemies have been recorded from Florida, California, the Caribbean, and Central and South America.
Some Criteria for Biocontrol Target Selection
Because there are many biocontrol success stories and the many introduced pests in the Caribbean, primary emphasis (or first step) should be given to classical biocontrol. The main task is to identify biocontrol agents (Fry 1989) and introduce them where the target species are present. There are many known effective biocontrol agents that still have not been established in countries where target pests are causing crop losses. It is only recently that many species of important pests have been introduced into Puerto Rico and several other Islands, e.g., the citrus blackfly, A. woglumi, the pepper weevil, Anthonomus eugenii, the beet armyworm Spodoptera exigua, the tomato pinworm, Keiferia lycopersicella, the imported fire ant, Solenopsis invicta, Thrips palmi, the sugarcane thrips, Fulmekiola serrata, and the avocado lace wing bug, Pseudacysta persea. Most recently an apparently new race of the whitefly, Bemicia tabaci has invaded the Caribbean, being more destructive and with a wider range of plant hosts than the common whitefly.
Designating priority to pests should be an important goal of local and regional efforts to establish biocontrol programs. Pests, needs, and goals will vary among Caribbean countries. Therefore, a system to evaluate candidate pests should be developed based primarily on three main components: 1) an assessment of current or potential impact of the pest to the regional economy; 2) a thorough appraisal of institutional policy and logistic capabilities; and 3) an evaluation of prior biocontrol achievements against the pest. When applied within the context of local conditions, these criteria should insure that the initial phases of a biocontrol initiative in the Caribbean will be as risk free as possible.
Pests should be targeted according to crop importance, impact on the crop, and finally a cost and benefit analysis. Those pests which attack a major commodity with highly predictable temporary consistency, where current management methods are no longer effective, and which are not under quarantine regulations are excellent candidates. Similarly, pests with high economic injury levels, that are non-vectors and which are sole 'key' pests ought to be given reference as targets. Finally, if funds are scarce, priority should be given to pests with natural control agents which have proven effective elsewhere in contrast to projects requiring more expensive operations like mass rearing or foreign exploration.
The depth of biocontrol achievements against the pest should be the final component of its assessment as a target. Pests where natural enemy taxonomy is well known as well as those where the study of natural mortality is available should be considered first. Targets where successful programs exist abroad should be favored initially.
References Cited
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