Natural enemies

Despite the use of 2.5 million tons of pesticide worldwide, approximately 35% of potential crop production is lost to pests. An additional 20% is lost to pests that attack the food post-harvest. Thus, nearly one-half of all potential world food supply is lost to pests despite human efforts to prevent this loss. Pesticides, in addition to saving about 10% of world food supply, cause serious environmental and public health problems. These problems include human pesticide poisonings fish and bird kills destruction of beneficial natural enemies pesticide resistance contamination of food and water with pesticide residues and inadvertent destruction of some crops. 

Insect and plant pathogen attacks are reduced because 1) natural enemies of the pests are increased in the polyculture ecosystem because the array of hosts for the natural enemies is increased, 2) and the movement of pests from one host plant to another is interrupted by the presence of a different host plant growing nearby (36). In this way overall pest damage is substantially reduced. 

However, not all natural enemies are fully effective. For example, the gypsy moth has approximately 100 parasites and predators attacking it but the pest reaches outbreak levels periodically (35). Nearly 40 biological control agents were introduced from Europe and Asia to control the moth and 11 of these became established (44). Yet not one of the 11 blocontrol agents is providing fully effective control, although each contributes to some limitation of this pest. 

When pesticides are applied to crops, many natural enemies that help control pests are destroyed (37). This causes pest outbreaks that subsequently are controlled with additional pesticide applications. The control of such pest outbreaks is estimated to cost at least 520 million each year. 

Species targeted by pesticides usually make up only several tenths of a percent of the total number of species in an agricultural environment. Natural enemies and parasites usually decrease a species mass reproduction reliably. Destroying, or sharply decreasing the number of, such enemies through pesticide use often leads to a population explosion in the suppressed species chemical protection thus creates a greater threat to the protected cultivars [1]. 

Different from the use of ordinal insecticides, this disruption method has high target selectivity and, as would be desired, ensures the survival of natural enemies. The sex pheromone, which shows no toxicity to mammals, is an ideal insect-behavior regulator (IBR). Table 8 shows the application areas of main mating disruptants for lepidopteran insects. In addition to the use of the synthetic pheromone of P. gossypiella in large cotton fields, many disruptants are... 

Increased density and diversity of natural enemies and antagonists... 

Webb, R.E., M. Shapiro, J.D. Podgwaite, R.C. Reardon, K.M. Taffnan, I. Venables, and D.M. Kolodny-Hirsch. 1989. Effect of aerial spraying with dimilin, dipel, or gypchek on two natural enemies of the gypsy moth (lepidoptera lymantriidae). Jour. Econ. Entomol. 82 1695-1701. 

OEPP/EPPO (1994) Decision making scheme for the environmental risk assessment of plant protection products. Chap. 9 Arthropod natural enemies. OEPP/EPPO Bull 24(1) 17—35... 

In sustainable agricultural systems, biodiversity has fundamental importance by providing a range of biological services including natural enemies. In conventional farming systems, these services are effectively substituted by external inputs. 

The first indication of the active role of plants in producing volatile chemicals to attract the natural enemies of their herbivorous attackers was found by Dicke, Sabelis, and coworkers (7, 24) in their studies of predatory mites that prey on plant-feeding mites. They found that when herbivorous spider mites feed on lima bean leaves, the plant releases a blend of volatiles that attracts predatory mites. The blend produced differs between plant species and varies depending on the species of spider mite that is attacking the plant. The blends even differ between plant cultivars infested with the same spider mite species, and the predatory mites can detect these differences (25,26). Artificially damaged leaves are not attractive to the predatory mites. 

We also found that the response of the plant to the caterpillar spit is systemic (31). Thus, not only the damaged leaves but the entire plant produces and releases volatile compounds when one or more leaves are attacked by caterpillars. Dicke et al. (7) had earlier found a similar effect in that undamaged leaves of a spider mite-injured plant attracted predatory mites. This systemic effect could be very significant in terms of enabling the natural enemies to locate their victims. It makes the plant under attack stand out from its neighbors and act as a beacon to foraging natural enemies. 

Parasitoid wasps are the most widely studied group of insect parasites. Female wasps lay an egg(s) on or in an insect and the progeny develop utilizing that insect as their sole food source, eventually killing the host. Female parasitoids tend to be host specific and typically exploit a specific host immature life stage (e.g., egg, larvae, or pupae). Most parasitoid wasps are relatively small. Females actively seek out multiple hosts and can find and parasitize host insects in cryptic habitats. There is a wide range of species that attack stored-product insects and a considerable body of research on these natural enemies, only some of which are covered here [see Godfray (1994) for more information on parasitoids and Brower et al. (1995) and Scholler and Flinn (2000) for reviews of information specifically on stored product parasitoids]. 

Natural enemy preservation, in integrated pest management, 14 351 Natural extracts, as food additives, 12 46 Natural fibers, 11 164, 285 24 613, 615-616... 

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