Arthropods are characterised by the presence of an exoskeleton and articulated legs. The phylum Arthropoda includes more than 80% of the known species with many of these being important agricultural pests. Arthropods, such as insects and mites, inflict billions of dollars in damage worldwide every year. Tons of pesticides are sprayed in efforts to reduce their populations and damage to crops. However, pesticides are not considered sustainable means to manage economically important arthropod mainly because of the development of resistance. In addition, pesticides are highly toxic to beneficial arthropods especially natural enemies of arthropod pests. This induces a continuous dependence on the use of pesticides because the elimination of natural enemies favors exponential growth of pest populations. In addition, pesticide resistance forces the development of new, potentially more toxic chemicals, which can accumulate in the environment generating a new set of problems.
Biological control, defined as the use of these natural enemies to reduce and manage pest populations, can be an alternative to pesticides for reducing agricultural losses due to arthropod pests. Arthropod natural enemies include predators, which prey on other arthropods, and parasitoids, which differ from true parasites in that they kill the host at the end of their development. Predators and parasitoids exist naturally in the environment and normally maintain the population of their prey or host at low levels preventing them from becoming pests. An arthropod becomes a pest when population outbreaks reach a level sufficiently high to cause economic damage. Outbreaks occur when the damaging species escape their natural enemy complex of parasitoids and predators. Current agricultural strategies mainly use a monoculture system which favours the escape of herbivore arthropods from their natural enemy complex by providing them with abundant new habitat with almost unlimited resources. It takes time for the natural enemies to find their host or prey in the new environment and multiply in sufficient numbers to regulate pest populations. By the time this occurs, economic damage has already been done to the crop and the pesticide spray cycle commences.
Pest outbreaks can be prevented by preserving a more diverse environment that favours natural enemy conservation. However, monoculture is the preferred method to produce crops in developed countries because it is conducive to mechanisation. To apply biological control in a monoculture environment, natural enemies must be mass produced and released at the appropriate time to prevent pest outbreaks. Producing large numbers of arthropod natural enemies economically and competitively has been a continuous challenge. The use of arthropod natural enemies in propagation and release efforts have been most successful in greenhouse crops.
Scientist at the USDA-ARS Biological Control Laboratory develops new strategies to produce natural enemies at low cost and associated methods for packing, transporting and releasing these natural enemies in the field.
Insects Used for the Management of Invasive Aquatic and Wetland Plants
Dr. Michael Grodowitz
Invasive aquatic and wetland plants cause manifold problems across the world. Overall impacts, while dependent on plant species, can include hindrance of water delivery systems; adverse changes in water quality; decreases in native flora and fauna; increased damage to bridges; weirs and other structures due to increased plant biomass during flood events; impacts to navigation, transportation and recreation; as well as increases in human health hazards due to expansion of mosquito breeding habitats. A variety of traditional management methods are employed and include both chemical and mechanical technologies through these often only provide short-term control. More long-term and sustainable management occur through the application of biological control technologies mainly through the introduction of host-specific insect agents from the home range of the target plant species. Over 15 aquatic and wetland plant species have been targeted for biological control activities with 48 agents introduced in various parts of the world. New targets are continually being studied worldwide and include such species as Lagarosiphon major (African waterweed) and Butomus umbellatus (flowering rush). Highly successful introductions have been noted for Melaleuca quinquenervia (paperbark tea trees) and Salvinia molesta (giant salvinia). One of the most successful suites of biological control agents includes four insect species introduced for the control of Alternanthera philoxeroides (alligatorweed); an invasive emergent plant species native to South America.
These include Agasicles hygrophila (alligatorweed flea beetle), Arcola malloi (alligatorweed stem borer), Amynothrips andersoni (alligatorweed thrips), and Disonycha argentinensis. The combination of the first two species can be devastating to alligatorweed infestations with almost complete suppression occurring in as little as six months. Lythrum salicaria (purple loosestrife), a problematic species introduced from Europe and possibly Asia in the early 1800s in ship ballast and as an ornamental or medicinal herb, has also been managed to a large extent by the introduction of host-specific insect agents. Five agents have been released for its control and include two leaf-feeding beetles (Galerucella pusilla and G. calmariensis), a root-boring weevil (Hylobius transversovittatus), the flower feeding weevil (Nanophyes marmoratus), and the aphid
(Myzus lythri). The use of biological control technologies for aquatic and wetland plant management continues to show great promise in suppressing damaging infestations across the world.
Additional resources:
http://www.ars.usda.gov/main/main.htm
http://www.biocontrol.entomology.cornell.edu/index.php
Dr. M Guadalupe Rojas
Dr. Juan A. Morales-Ramos
Biological Control of Pests Research
Tel: +1 662 686 3070
guadalupe.rojas@ars.usda.gov
