The control of pests and diseases affecting cultivable plants is made mainly by the use of chemical compounds. The use of agrochemicals to control insects and plant pathogens represents, however, a high risk to field workers, consumers and environment. They are responsible, for eliminating important species of insects that control other pests, and microorganisms that are performing a critical role in the environment, inhibiting growth and multiplication of useful microbes. The natural and biological control is an alternative way that may contribute to reduce or even eliminate the use of chemical products in agriculture. The natural and biological control of agricultural pests gained more attention during the past decades. Latin America, having vast agricultural areas, most of them located in the tropics, is severely affected by pests and diseases. Ways to control them, are important to reduce costs and protect the environment.

One group of useful microbes that are affected by man modifications is the endophytes. Endophytic microorganisms are those that inhabit at least for one part of their life cycle, the interior of plants. Although already described during the XIX Century, they did not received considerable attention.

Only in the last twenty years they were recognized with capacity to protect the host-plants against insect-pests and diseases. Also they could confer to plants, other important characteristics like greater resistance to some stress conditions as, for instance, hydric stress. On the other hand, they can produce phytohormones and other substances of biotechnological interest as enzymes and pharmaceutical drugs including antibiotics and anti-tumour drugs.

In the early 80's researchers started to show that endophytic fungi and bacteria could give to their host-plants, protection against insects and phytopathogenic microorganisms. Several reports correlated decrease in attack frequency of insect-pests and presence of endophytic fungi. Mainly in grasses, certain genera of endophytic fungi were shown to be able to control insect-pests. On the other hand they can be also responsible for intoxication, weight loss, decrease of milk production and other effects in cattle and other herbivores fed on these plants.

Nowadays, many examples of reduced host-damage provoked by insect attack, due to the presence of endophytes, are known. The examples are mainly derived from temperate hosts as grasses and woody plants.

The mechanisms of insect control displayed by endophytic fungi are quite well studied. Some were based in the capacity to render the plant unpalatable to several types of pests as grasshoppers, aphids, beetles and other insects. Endophytes may also produce several toxins as ergot alkaloids and neurotoxines, which cause death, decreased of development rate and other effects against insects.

The expression of insect resistance by the host-plants may be affected by several factors as soil fertility, hydric stress, temperature, soil pH, plant and endophyte genotypes among others. So, there is a complex interaction among plant-endophyte-pests related to the environment. Some endophytes are entomopathogenic fungi, that is, are able to infect insects and kill them.

Other indirect effect of endophytes is the control of ectoparasites in domestic animals. Insects, as for instance the horn fly, a cattle ectoparasite, feed on manure derived from animals fed with grasses infected with endophytes are killed or have reduced development.

More recently, Recombinant DNA techniques, commonly known as Genetic Engineering, have been applied as a tool to improve endophytic microorganisms, aiming to the introduction of new characteristics of agronomic interests as biological control of pests. Genetic modified endophytic bacteria able to secrete toxin against insect-pests, inoculated inside plants protect them against attacks of target insects. There are several advantages of using endophytic inoculated plants with genetic engineered microorganisms when compared to the use of transgenic plants or chemical products to control pests. Plant inoculation of valuable strains of endophytic microbes used for biological control is starting to be used with success in agriculture. These techniques are expected to become popular as it is nowadays the inoculation of nitrogen fixing bacteria in leguminosae plants, already largely used in agriculture.

Most of the research with endophytes has been carried out using plants from temperate regions. The data from tropical regions are scarce but preliminary results are shown that tropical plant hosts contain a great diversity of endophytic microorganisms, many of them not yet classified and possibly belonging to new genera and species. Potentially they are of biotechnological importance. New pharmaceutical compounds, secondary metabolites, agents for biological control of insect-pests and plant diseases besides other useful characteristics could be found, by further exploration of tropical endophytic microorganisms. These microorganisms, mainly bacteria and fungi have been isolated from few plants as Araceae , Bromeliaceae and Orchidaceae from several Latin America countries including Brazil, Colombia, French Guyana, Costa Rica among others. Studies are been carried out by isolating and characterizing endophytes from tropical palm trees, some fruit trees as citrus, bananas, mango and cashew-trees. Brazilian Amazon species as guarana (Paullinia cupana), cupuaçu (Theobroma grandiflorum), copaíba (Copaifera multijuga) and several other plants of economic interest have been also studied in relation to their endophytic microbiota. This is a broad field of investigation that is almost entirely open to new findings. It is expected that new ways of interactions between endophytes and their hosts will be found. It is expected also that new drugs of biotechnological importance, produced by endophytes will be described, with the increasing of studies focusing these tropical microorganisms.