The pinacates (Eleodes) are a genus of beetles belonging to the Tenebrionidae family characterized by the fact that most of them expel a substance with an unpleasant odor when threatened. Due to this property they are also known as bombers. They are dark in color, with the elytra generally semi fused.
It is a highly diverse genus of beetles with more than 200 validly described species, most of them endemic to North America. They are mainly found in Mexico and the midwest of the United States, although some species can be found in Canada and others can even be found in Colombia (Eleodes pos. omissoids).
They are nocturnal, spending the daytime hours in relatively humid environments (under stones, bark or among the litter), although they can also bury themselves in the ground. Some species feed on humus and other organic remains, while others (mainly larvae) can feed on plants, becoming pests.
The control of pinacate species that attack crops is based mainly on cultural practices such as adequate cleaning of the land before planting. Although these species have natural enemies, researchers have not yet developed a specific biological control mechanism for them..
Pinacates are dark-colored beetles, hence their name that comes from the Nahuatl word "pinacatl" and which means black beetle..
They present the elytra partially or totally fused as an adaptation to life in desert areas, which allows them to reduce the loss of water by evaporation.
They have an elongated body, with the pronotum extended laterally and the antennae inserted under the lateral expansions of the forehead and composed of 9-11 joints. The elytra are eroded or striated. Their size exceeds 2 cm in total length.
The abdominal defensive glands are present, which produce a substance with a pungent and nauseating odor that they expel when they feel threatened, which is why they are also known as bombers..
Some indigenous tribes use the pinacate for medicinal purposes, placing the beetle near the nostrils of infants with respiratory problems to use its secretion as an expectorant..
Adults can also be recognized by their particular way of running by lifting the body at odd angles..
As already mentioned, pinacate species possess defensive abdominal glands. These glands secrete complex compounds that can correspond to the group of aldehydes, phenols, ketones or benzoquinones, including toluquinone, ethylquinone and other compounds, which can be presented in different proportions.
When the insect feels threatened it releases these secretions that have a strong, penetrating and nauseating odor. These secretions can also be released when the animal dies and in this case the aroma is more powerful and penetrating than when it is alive..
Despite its unpleasant smell, this secretion is used in traditional medicine in some regions..
Pinacates are insects of the order Coleoptera, taxonomically located in the suborder Polyphaga, infraorder Cucujiformia, superfamily Tenebrionoidea and family Tenebrionidae.
This family was described by Latreille in 1802 and is one of the most diverse within the coleopterans, with about 20 thousand species described to date. It currently includes the families Lagriidae and Alleculidae, which have now been located as subfamilies of the Tenebrionidae..
The gender Eleodes It was erected by a Russian naturalist named Eschscholtz in 1829, to group 12 species of beetles not previously described and collected on an expedition to the western shores of North America..
This researcher, however, did not choose any of these species as the type species for the newly erected genus. It was not until 1840 that Hope designated as such Eleodes dentipes.
Beginning in 1870, when Horn divided Eleodes In three subgenera, the group has undergone a long ordering process and numerous modifications, currently more than 180 species distributed in 14 sections and one subsection are recognized as valid, in addition to 15 species that have not yet been located in any of the these sections.
The pinacates are organisms of sexual reproduction, dioecious, of internal fertilization. Most of the life of these beetles is spent as adults. Its life cycle may vary depending on the species.
These organisms normally live under rocks, leaves, logs or other structures that help retain moisture and protect them from direct sunlight in daylight hours..
They are active at night, which, depending on the species, spend part of their life feeding on decomposing organic material, plants, or their seeds..
For sexual attraction during the mating season, which normally occurs in spring, they release pheromones.
After copulation, the female buries the eggs in loose soil and when the larvae hatch, they can be located at different depths in the soil, depending on the temperature and humidity of the same. Sometimes a second oviposition event can occur in late summer.
The larvae generally feed on newly germinated seeds and seedlings. They are known as false wireworms as they resemble the larvae of beetles of the Elateridae family..
In winter, the larvae can hibernate as adults do. When spring arrives, they become active again and begin to feed until they become pupae, from which they will later emerge as adults..
Although they can have an omnivorous diet as a mechanism of adaptation to dry environments, depending on the species in which they Eleodes Two basic ways of eating can be distinguished. On the one hand, there are the species that are mainly detritivores, which feed on detritus and, on the other, there are the herbivorous species. The latter can feed on seeds, seedlings or more developed plants.
In crops, the larvae can eat the seeds in the place where they were planted, or move them to another deeper place to later eat them, they can also feed on newly germinated plants or on the roots of adult plants.
The adults that feed on seeds extract them from the place where they were sown and deposit them in another area to later devour them. They can also feed on recently germinated plants, such as larvae, or on plants in a higher stage of development..
Due to these eating habits, pinacates cause shortages in the crop, which make replanting necessary, thus increasing costs not only for the labor required for the work but also for the costs of the seeds themselves..
These beetles mainly affect pea, corn, wheat and potato crops, however they can attack a wide variety of other species, including tomato, lettuce and onion. There are no estimates of the economic impact caused by pinacates on the different crops.
To date there is no specific biological control method to counteract Eleodes, However, different species of insects, birds and pathogenic microorganisms attack the species of this genus.
Entomopathogenic fungal species such as Paecilomyces sp., Beauveria bassiana Y Metarhizium anisopliae, that have been used successfully for the control of other species of insects, show poor results in the control of the larvae of Eleodes.
This low efficiency of fungi to attack the insect may be due to the latter having a natural larval tolerance to the infestation process, that is, to the process of penetration of the spores through the cuticle. The enzymes used by the fungus for this activity may not be appropriate for the cuticle of this insect..
Just as there are no specific biological controllers for pinacate to date, there are also no specific chemical agents, and broad-spectrum insecticides must be used that are highly toxic not only for the species to be controlled but also for others that could be beneficial..
Trials carried out in Australia show that compounds containing imidacloprid or thiamethoxam can limit the damage caused by pinacate larvae in crop seeds. Farmers use these compounds to control aphids and other insects but not commonly for pinacates..
Both compounds are used directly on the seed and on the plants, they are systemic insecticides and seem to be the most suitable option to act against Eleodes, but more experiences are necessary to determine their real efficacy on insects of this genus.
Cultural practices to decrease germination time and promote seedling growth help shorten the time in which plants are more susceptible to being attacked by pinacates..
The use of crop rotation with species that are less susceptible to being attacked by Eleodes can also help control populations of these insects.
The work of the land prior to planting can help reduce the number of larvae in the soil, making them more susceptible to being attacked by predators or killing them when exposed to the direct action of the sun's rays..
Additionally, the use of piles of decomposing plant material can serve as a decoy to attract pinacates, making their eradication easier..