Biorational methods have currently emerged as viable alternatives to monitor and suppress pest populations. The estimated annual production of semiochemicals for monitoring and mass trapping is to the tune of tens of millions, covering at least 10 million ha.
Insect pest populations are controlled by air permeation and attract-and-kill techniques on at least one million ha. Besides the problems that have occurred in the practical application of biorationals, there are a number of examples of their large scale use in pest management.
1. Role of Allelochemicals:
Although a number of kairomones have been isolated and identified from plants and animals, only a few of them have been exploited for pest suppression.
Corn Rootworms:
Three species of corn rootworms, viz., the western corn rootworm, Diabrotica virgifera Le Conte; the southern corn rootworm, D. undecimpunctata howardi Barber, and the northern corn rootworm, D. barberi Smith & Lawrence, are known to attack corn. Two features of diabroticite chemical ecology are helpful in manipulation of their behaviour.
Firstly, the association between these beetles and cucurbitacin, a potent arrestant and feeding stimulant, may be so strong that other behaviours such as sex attraction are masked. Secondly, several plant-derived volatile attractants appear to mediate host selection by Diabrotica beetles.
Powdered gourd roots and squash fruits have been evaluated for improving the capture of beetles in monitoring programmes. In addition, palatable baits containing cucurbitacins and an insecticide have been employed for short-term suppression of rootworm populations.
The addition of a volatile plant-derived attractant also enhanced the suppression of D. undecimpunctata liowardi. The first insecticide-laced bait was registered for use against corn rootworms in 1993 and it was applied to 12,000 ha in 1994. This approach reduced the insecticide use in corn by 90-95 per cent.
However, three factors may limit further adoption of this approach:
(i) Adult management requires more intensive scouting and better timing than conventional approaches;
(ii) Adult management is feasible in only corn-corn rotations; and
(iii) In view of difficulties in extracting cucurbitacin from the buffalo gourd, Cucurbita foetidissima Kunth, this approach is costly.
Tse-Tse Flies:
Traditionally, tsetse flies, Glossina spp., have been managed by clearing suitable habitat and by area-wide insecticide applications. Early experimentation with semiochemicals made use of livestock treated with toxicants to attract and kill flies. Specific attractants, such as 1-octen-3-ol, isolated from cattle, when combined with acetone and carbon dioxide, were similar to ox odour in attracting the flies.
The addition of cattle urine further enhanced the attraction. The commonly used bait to attract the flies is a combination of acetone, 1-octen-3-ol, 4-methylphenol and 3-propylphenol. Baited traps have been used to monitor the presence of tse-tse fly.
Baited targets have also been used in combination .with insecticides and a setrilant for pest suppression. This approach has resulted in eradication of tse-tse fly from a number of areas, but continual reintroductions of flies demand that a yearly trapping programme be maintained.
Recently, the introduction of artificial cow that attracted tsetse flies saved thousands of cattle from nagana infection (caused by tse-tse flies) in Zimbabwe. The kairomones mimic the smell of real cattle and attract the tse-tse flies to fake cow, which is loaded with pesticide.
Blow Flies:
The Australian sheep blow fly, Lucilia cuprina (Wiedeman) and related species are potentially controlled by a rather selective synthetic kairomone attractant, traditionally, blow fly traps have been baited with liver and sodium sulfide. However, a synthetic kairomone, consisting of 2-mercaptoethanol, indole, butanoic acid, and a sodium sufide solution is far more effective and selective for L. cuprina, than the standard liver attractant.
More importantly, the synthetic mix can be packaged in controlled-release dispensers to generate constant, prolonged release of the attractant. Field studies have confirmed that kariomone traps are a useful component of a blow fly control programme.
2. Role of Pheromones:
Considerable progress has been made in the use of pheromones for pest control in agriculture, forestry, stored products and households. It has been estimated that about 20 million pheromone lures are produced for monitoring or mass trapping every year. The worldwide area treated with pheromones for mating disruption has surpassed 770,000 ha.
Pink Bollworm:
Pink bollworm, Pectinophora gossypiella (Saunders), a key pest of cotton, has been successfully managed in a number of countries including USA, Egypt, India and Pakistan by using controlled release formulations of its female sex pheromone, a 1:1 mixture of (Z, E) and (Z, Z)-7, 11-hexadecadienyl acetate known as gossyplure.
In Egypt, 1,50,000 ha of cotton (about 36% of the country cotton acreage) were treated with pheromones against P. gossypiella in 1994. Mating disruption has been successfully employed in San Joaquin Valley, Imperial Valley of California and Parker Valley of Arizona of USA. Continual immigration of pink bollworms into the Imperial Valley and severe outbreaks of whiteflies, have reduced cotton production and adoption of mating disruption in this region.
The growers in Parker Valley formed an informal pest control district in 1990 and adopted the use of mating disruption over 1,20,000 ha of cotton. The programme has been very successful, but problem of whiteflies has increased and a more expensive pheromone-insecticide strategy is required.
Sex pheromones of cotton bollworms have been extremely useful for monitoring, survey and surveillance, and assessing damage to cotton in India. Gossyplure is commonly used for monitoring the pink bollworm throughout the cotton belt. In Punjab, pheromone traps used for monitoring the activity of cotton bollworms on hirsutum cotton indicate that the maximum activity of P. gossypiella, Helicoverpa armigera (Hubner) and Earias spp. was in July, September and mid October to the end of season, respectively.
Monitoring the population of bollworms can help in their early detection and build up, and a need-based control measure can be adopted depending upon the severity of a particular species of bollworms. The pheromone trap catches of H. armigera moths have been successfully used to predict the egg and larval populations of this insect and damage to cotton plant reproductive bodies.
In Pakistan, a single twist-tie formulation containing pheromones of both pink and spotted bollworms has been successfully used to obtain season long control of bollworm complex. A single application of the pheromone either alone or in combination with a conventional insecticide provided effective control, while the conventional spray programme required 4-5 sprays per season to achieve a similar level of control.
Gypsy Moth:
The identification of a female produced sex pheromone, disparlure, has led to spectacular advances in the management of gypsy moth, Lymantria dispar (Linnaeus). Mating disruption programmes were established on about 7000 ha from 1979 to 1987 in the eastern United States. In 1993, a federal programme ‘Slow the Spread’ was launched to slow the rate of gypsy moth expansion by following IPM strategies over an area of 3,000,000 ha spread in four states.
About 13,000 ha are treated each year and mating disruption is used on 15 per cent of this area. The greatest use of disparlure has been in surveys to determine the need for management tactics. In the western United States, incipient infestations of gypsy moth were detected in mid 1970s. In Washington State, gypsy moth adults were trapped only in a few sites, but by early nineties, 13-35 new outbreak sites were located each year.
The standard protocol for monitoring gypsy moth in Washington State each year is to place about 10,000 traps at a density of one trap per square mile in all high-risk areas. When a moth is captured, a grid of traps is placed within a 3-mile radius around each site. If additional moths are caught and other life stages are also found, three sprays of Bacillus thuringiensis Berliner are applied. This strategy has prevented the establishment of gypsy moth in western Unites States and British Columbia.
Codling Moth:
Codlemone, the major sex pheromone component of codling moth, Cydia pomonella (Linnaeus), has been used extensively for monitoring and timing of pesticide applications. It was also used for mass trapping in some of the earliest evaluations. Mating disruption with codlemone has been tested in several apple-growing regions, including Australia, USA and parts of Europe.
The effectiveness of mating disruption in these trials was determined by moth density, moth immigration, amount of pheromone released, and the number and positioning of dispensers used per area. A three-component blend housed in a polyethylene dispenser was registered in USA in 1991 and was applied to treat about 10,000 ha in 1994.
A fully integrated attract-and-kill product, containing 0.16 per cent pheromone and 6 per cent permethrin, has provided control of codling moth at economic levels of less than 1 per cent harvest infestation in apple orchards in Switzerland, Based on reduction in trap catch and mating frequency of tethered moths, efficiency of the attract and kill droplets lasted 5-7 weeks, requiring two seasonal applications. Subsequent experiments replaced permethrin with an insect growth regulator, fenoxycarb, which has a sterilizing effect.
Field tests showed that autosterilization, i.e. transfer of insect growth regulator from a contaminated male to the female moth at mating, contributes to the control effect. World wide annual production of codlemore is about 25,000 kg for codling moth control on about 21,000 ha and the price of codlemone is now well below US$ 1000 per kg.
Brinjal Fruit and Shoot Borer:
Eggplant is an important vegetable in South Asia and brinjal fruit and shoot borer, Leucinodes orbonalis Guenee, is a key pest of the crop which causes enormous loss. A pheromone-based mass trapping strategy has been developed, from optimization of the pheromone blend and dose, trap design, and placement to field implementation.
Mass trapping, without the use of insecticides, has led to a 50 per cent and higher increase in marketable fruit, which has been attributed to the combined effects of mass trapping and enhanced impact of natural enemies. Additionally, secondary pests, such as mites and whitefly, were reduced in the pheromone plots. The yield increase translate to earnings of $1,000 US$ per ha and year for resource-poor families.
Tomato Pinworm:
The tomato pinworm, Keiferia lycopersicella (Walsingham) has been amenable to control with mating disruption due to several features of the pest:
(i) The host range of the tomato pinworm is restricted to plants in the family Solanaceae.
(ii) As the pest feeds inside the calyx of the fruit, the insecticides have not proved to be highly effective in its control.
(iii) The pest has developed high levels of resistance due to the overuse of pesticides.
The sex pheromone of the tomato pinworm was identified in 1979 and the first large scale trials (500 ha) were conducted in Culican, Mexico, in 1981. The results of this trial demonstrated that the programme reduced fruit injury with less use of insecticide and was economical as compared to conventional insecticide programmes. These results gave impetus to adoption of an IPM programme for tomatoes using pheromones, biological control, B. thuringiensis and cultural control.
Rice Stem Borers:
Two species of rice stem borers, viz. Chilo suppressalis (Walker) and Scirpophaga incertulas (Walker) have been effectively controlled with sex pheromones in large scale field trials. In Spain, C. suppressalis has been successfully controlled for upto 100 days in 1500 ha of rice in both the Ebro Delta and Valencia rice-growing areas.
Deployed at the rate of 2500 polymer dispensers ha-1 (8 mg active pheromone each) translating into 20 g ha-1, they performed as well as conventional insecticide (fenitrothion) by controlling stem borers down to a damage level of 0.2 per cent. Confusion efficacy rates were approaching 100 per cent.
Similarly, high rates and control levels were achieved by reducing the point sources to 500 or 100 ha-1, depending on infestation history and using, respectively 1.6 or 8.0 g pieces of polymer to give a total dosage of 40 g ha-1, a system which is now recommended commercially in Spain.
Similarly, a single application of a polymer formulation of the pheromone of yellow stem borer, S. incertulas of rice provided effective, season-long control of the pest in Andhra Pradesh, India in large scale field trials. Under normal pest pressure, the control was at least as good as achieved with several applications of conventional insecticides, but under high pest pressure both approaches failed to provide adequate control. Field trials on 20 ha of rice in West Bengal showed pheromone control to be equal to that achieved with insecticide regimes against yellow stem borer, S. incertulas.
In Uttarakhand, mass trapping resulted in 5.78 per cent white ears due to S. incertulas, 70 days after installation of the pheromone traps, as compared to 17.90 per cent white ears in plots treated with insecticides, suggesting that sex pheromone mediated male annihilation technique is self-sufficient to keep pest under control. The use of pheromones for mating disruption of rice stem borers has also been made in Indonesia, China, Korea and Thailand.
Cotton Boll Weevil:
The cotton boll weevil, Anthonomus grandis Boheman, is a major pest of cotton in the Americas. Males produce an aggregation pheromone, grandlure that has been successfully incorporated into a pheromone-baited killing station known as “Boll Weevil Attract and Control Tubes.”
These tubes are produced in large numbers every year. A density of 14 traps per ha achieves a strong reduction in weevil population, at minimal crop damage. After successful control and eradication programmes in the USA, boll weevil trapping is now also used in South America on at least 250,000 ha.
Red Palm Weevil:
The red palm weevil, Rhynchophorus ferrugineus (Olivier) is widely distributed in Asia, Africa and Oceania. It infests a range of tropical palms, including date, oil, and coconut palms. Mating in red palm weevil is mediated by an aggregation pheromone produced by the male weevil, composed of the main compound (4S, 5S)-4-methyl-5-nonanol (ferrugineol) and 4-methyl- 5-nonanone.
Traps loaded with ferrugineol, supplemented with ethyl acetate and plant volatiles, and a fermenting mixture of dates and sugarcane molasses, are placed at densities of up to 10 traps per ha for monitoring and mass trapping. Pheromone traps have played a significant role in the suppression of red palm weevil populations, e.g. in date palm plantations in Isreal.
Fruit Flies:
Several species of fruit flies, viz., guava fruit fly, Bactrocera dorsalis (Hendel); peach fruit fly, B. zonata (Saunders) and ber fruit fly, Carpomyia vesuviana Costa, are known to damage fruit crops in Punjab, Fruit flies cause almost 100 per cent damage to rainy season crop of guava, 78 per cent to peach, 84 per cent to pear and 85 per cent to kinnow.
The population of fruit flies starts building up in April and continues up to November on different fruit crops. The Punjab Agricultural University (PAU) has developed a fruit fly trap using methyl eugenol based one litre mineral water bottle. The trap consists of a plywood dispenser, suspended vertically inside the bottle, aligning with four vents that allow entry of fruit flies inside the bottle.
The plywood blocks (5×5×1 cm) are immersed in a solution of ethyl alcohol, methyl eugenol (98%) and malathion in ratios of 6:4:1 (v/v) for 72 hours. The bented bottles are hanged with the trees at equidistant @ 40 traps per ha in the first week of May in peach, first week of June in pear, first week of July in guava and second week of August in kinnow.
A single trap has the capacity to trap about 6000 male fruit flies. In case of rainy season guava, the yield in 40 traps per h was 20 t per ha as against 0.55 t per ha in untreated control. The corresponding yield in peach was 12.75 and 1.05 t per ha. The traps have provided effective control of fruit flies and have been recommended to farmers for use in guava, peach, pear and kinnow orchards.
3. Role of Parapheromones:
Parapheromones have a high potential as alternative material in integrated pest management programmes, particularly when the natural pheromones are expensive to produce, present longevity problems, or are quickly degraded under field conditions.
Three important criteria need to be taken into consideration to include them in synthetic formulations, viz. the efficiency of the blend must be optimized, the specificity must be observed, and the stability must be improved. A number of field experiments have demonstrated that parapheromones meet these prerequisites for their use in insect monitoring or control.
The most extensive application of parapheromones has been the use of lures to attract tephritid fruit flies. Parapheromones and plant volatiles as attractants (methyl eugenol, trimedlure, cuelure, angelica seed oil, enriched ‘ginger oil, raspberry ketone) and hydrolysed protein have been widely used for monitoring and annihilation of several fruit flies, including Oriental fruit fly, Bactrocera dorsalis (Hendel); melon fly, B. cucurbitae (Coquillett); and Mediterranean fruit fly, Ceratis capitata (Wiedemann), for almost 50 years.
Early detection of pest introductions using traps baited with male lures allows quick eradication of incipient populations. New infestations of the Oriental fruit fly, in California have been eradicated 12 times since 1966 using methyl eugenol in insecticide-laced bait.
Another parapheromone, trimedlure, has been developed for monitoring the Mediterranean fruit fly, and has been used in traps to pinpoint the location and size of infestation sites. The flies can then be eradicated through the use of a sprayable formulation of protein hydrolysate and an insecticide.
The standard monitoring programme for C. capitata in California is five traps baited with trimedlure per square mile in urban areas. After flies are detected, additional 1700 traps are baited in a 4.5 mile radius for three generations. In Los Angeles, the release of sterile flies in combination with helicopter spraying of Malathion mixed with protein hydrolysate was successful in eradicating infestations of C. capitata.
However, this programme was not favoured due to perceived environmetal and health risks. The baited traps were first developed in 1970 and are still in use in many countries today. The lure has proven particularly useful for monitoring pest presence within import/export crops at airports and seaports.
Structural modification of the pheromone generally reduces field activity, but a significant increase in catches has sometimes been reported. More males of Cydia pomonella (Linnaeus) were caught in traps baited with (E, E) – 10, 11-difluro-8, 10-dodecadienol or (E, E)-11-chloro-8, 10-undecadienol than in traps containing codlemone.
In large scale field trials, pheromone communication was disrupted in the navel orangeworm, Amyelois transitella (Walker), by air permeation with (Z, Z)-9, 11-tetradececadien-1-ol formate, the formate analogue of the main pheromone component (Z, Z) -11-13-hexadecadienal. A novel olefin analogue was also found to disrupt mating communication in this insect. Both compounds are more stable than the natural aldehyde pheromone component.
4. Role of Juvenile Hormone Analogues:
The JHAs have been tested in large scale trials for the control of various pests of agriculture, forestry and public health importance. Five different formulations of methoprene are available commercially for the control of mosquitoes, manure breeding flies, cigarette beetle, pharaoh’s ant, fungus gnat and flies.
In house flies, adult emergence may be prevented by earlier treatment with methoprene. When administrated as a feed additive to cattle, methoprene controls horn flies and other veterinary pests that breed in dung. Other uses of methoprene include coleopteran and lepidopteran pests in stored tobacco, sciarid flies in mushrooms, flea larvae indoors, Homoptera on houseplants, pharaoh ants indoors and leaf-mining flies in vegetable and flower crops.
Hydroprene is used indoors against cockroaches and in this case, exposure of nymphs to the material causes them to become sterile adults. Kinoprene is a strong highly selective JHA effective against aphids, whiteflies, scales and mealy bugs. In view of its environmental instability, it has been most successfully used on ornamental plants and vegetable seed crops in greenhouses and shade houses.
Different formulations of fenoxycarb have been developed for different groups of pests and used against number of coleopteran and lepidopteran pests of stored wheat and rice. It has also been found effective against several fruit pests such as grape moths, Lobesia botrana (Denis & Schiffermuller) and Eupoecilia ambiguella (Hubner); plum moth, Cydia funebrana (Treitschke); codling moth, Cydia pomonella (Linnaeus); summerfruit tortix, Adoxophyes orana (Fisher von Roeslerstamm); pear sucker, Cacopsylla pyricola (Forster); fruit tree tortix, Archips podanus (Scopoli); tufted apple bud moth, Platynota idaeusalis (Walker); and a number of leaf rollers, pear psyllids and diaspidid scales. Foliar application of fenoxycarb on cotton provided satisfactory control of Helicoverpa zea (Boddie) and Heliothis virescens (Fabricius). It is also effective for the control of fire ants, fleas, cockroaches and mosquito larvae.
Pyriproxyfen has proved effective against a number of sucking pests including whitefly, Dialeurodes citri (Ashmead); Thrips palmi (Karny); California red scale, Aonidiella aurantii (Maskell); chaff scale, Parlatoria oleae (Colvee); cottony cushion scale, Icerya purchasi Maskell; sweet potato whitefly, Bemisia tabaci (Gennadius); greenhouse whitefly, Trialeurodes vaporariorum (Westwood); green peach aphid, Myzus persicae (Sulzer); and pear psylla, Cacopsylla pyricola (Forster).
It is also active against a number of mosquito species and as a feed-through compound in poultry, cattle and swine for the control of the house fly, Musca domestica (Linnaeus); faces fly, M. autumnalis DeGeer and horn fly, Haematobia irritans (Linnaeus). Pyriproxyfen also disrupts the development of horn fly following direct application to the fly.
Pyroproxyfen has also been found to impair larval activity comprising hatching and leaf mining of tomato leaf miner, Tata absoluta (Meyrick), leading to nearly 50 per cent mortality. This JHA also has an adverse effect on the development and metamorphosis of the citrus swallowtail, Papilio demoleus Linnaeus.
A newer analogue, diofenolan is highly effective for the control of scale insects and lepidopteran pests attacking citrus, pome fruit, stone fruit, grape, mango, olive, nut, tea and ornamental plants. It shows excellent activity at 300 g a.i./ha against A aurantii, Quadraspidiotus perniciosus (Comstock), Saissetia oleae (Olivier), Planococcus citri (Risso), I. purchasi, Aulacapsis tubercularis Newstead, C. pomonella and C. molesta (Busck).
It is also effective against tea leaf roller, Caloptilia theivora (Walsingham). NC-196, a derivative of benzyl pyridazinone shows good systemic and contact activity against brown planthopper of rice. In Japan, application of NC-196 @ 300-600 g a.i. / ha effectively suppressed brown planthopper populations for nearly one month.
5. Role of Moulting Hormone Analogues:
Both tebufenozide and methoxyfenozide are highly active in the field against a variety of vegetable, fruit and ornamental pests. Tebufenozide has been found to be highly effective against Cydia pomonella (Linnaeus) and miscellaneous leafrollers in apples, various leafrollers in treefruit, Spodoptera exigua (Hubner) in cotton, Choristoneura fumiferana (Clemens) and Lymantria dispar (Linnaeus) in forestry, Lobesia botrana (Denis & Schiffermuller) in grapes, Cnaphalocrocis medinalis (Guenee) and stem borers in rice, Diatraea saccharalis (Fabricius) in sugarcane, S. exigua, Helicoverpa spp. and various other lepidopteran pests in vegetables and ornamentals. The use rates vary from 100 to 300 g a.i. /ha, depending on the target pest and crop.
Halofenozide is highly effective against the soil-dwelling larval stages of scarabaeid beetles such as Popillia japonica Newman, Phyllophaga spp., Cyclocephala spp. and Hyperodes spp. as well as various soil and sod-dwelling caterpillars such as cutworms and web worms.
Halofenozide was effective against all stages of P. japonica, but its effects were stage dependent in case of European chafer, Rhizotrogus majalis (Razoumowsky) and the Oriental beetle, Anomala orientalis (Waterhouse). Generally, the effects were more pronounced when the applications were made in the egg or first larval stages. Methoxyfenozide has exhibited high field efficacy against lepidopteran pests of apple, cotton, grape, maize, rice, fruits and vegetables.
6. Role of Chitin Synthesis Inhibitors:
Chitin synthesis inhibitors belonging to the acyl urea group are also being used commercially for the control of a number of foliage feeders and tissue borers. Satisfactory control of cabbage looper, Trichoplusia ni (Hubner); cotton leaf perforator, Bucculatrix thurbeviella Busck; Egyptian cotton leafworm, Spodoptera littoralis (Boisduval) and boll weevil, Anthonomus grandis Boheman damaging cotton crop has been obtained with diflubenzuron.
Foliar application of diflubenzuron has shown excellent residual activity against eggs of H. armigera and S. litura. In addition to its well known stomach toxicity, it has significant contact activity against some insect species including H. armigera and S. littoralis. Diflubenzuron is promising against a variety of other pests on several crops including soybean, citrus, vegetables and forests, and against nuisance and medical pests like flies, gnats, midges and mosquitoes.
Some new CSIs like XRD-473, IKI-7899 and ICR 1055 have shown excellent larvicidal activity against H. armigera. Teflubenzuron possesses high ovicidal action against the tortricid, C. pomonella on apple. Buprofezin has been found promising against homopteran pests of rice, cotton, citrus, potato and vegetables. Hexaflumuron is used primarily for termite control around houses and other buildings.
Termites feed on hexaflumuron bait and die within 6-8 weeks during moulting. It is also effective against certain Lepidoptera, Coleptera, Homoptera and Diptera on cotton, potatoes and fruit trees. Lufenuron is prescribed by veterinarians for flea control on dogs. When a female flea bites a treated dog, lufenuron enters the flea’s system, and prevents some eggs from hatching and prevents any enclosed larvae from becoming adults.
In India, several CSIs have been evaluated for their efficacy against Helicoverpa armigera (LIubner) infesting chickpea under field conditions. Lufenuron (0.006%) was found to be the most effective which recorded the least pod damage (11.9%) with highest efficacy (97.4%) and grain yield (2064.3 kg/ha). This was followed by flufenoxuron (0.008%), novaluron (0.01%), diflubenzuron (0.05%) and standard insecticide endosulfan (0.07%) with average efficiency of 94.8, 92.8, 89.9 and 65.9 per cent, respectively.