The weevil is an insect of the Coleoptera order. The family of weevils is one of the largest among beetles (about 40,000 species). Most weevils have long, clearly articulated antennae that can fold into special depressions on the snout. Many members of the species do not have wings, while others are excellent fliers.
Origin of the species and description
The weevil was first described by Thomas Say in 1831 as a weevil from specimens taken in Louisiana. The first economic report on this insect was that of Asa Fitch of New York, who received infected beans from Providence, Rhode Island in 1860. In 1891, J. A. Lintner, New York State, proved that the bean weevil bred continuously in stored beans, which distinguished it from the well-known European pea weevil.
Interesting Fact: Weevils are actually bugs. There are more species in this family than in any other beetle group. Scientists estimate that there are over 1,000 species of weevils in North America.
There are 3 main types of weevils:
- Rice weevils are small beetles only 1mm long. The adult is greyish-brown to black in color and has four reddish-yellow spots on its back. The larvae are white and soft, without paws. Weevil pupae look like adults in their long snouts, but they are white. An adult is able to fly and live up to five months. The female of this weevil lays up to 400 eggs during her lifetime;
- Corn weevil was previously considered only a large variety of rice weevil due to their superficial similarity. It is slightly larger, up to 3 mm long, and like the rice weevil, it is reddish-brown to black in color and has four reddish-yellow spots on its back. But its color is slightly darker than that of rice. The development rate of the corn weevil is slightly less than that of the rice weevil. Its larvae are white and soft, without paws. The pupae also look like adults in their long snouts, and they are also white. The corn weevil is also capable of flight;
- Garn weevils are more cylindrical than others and are about 5 mm long. Their color is reddish brown to black. The body is approximately 3 mm long and the muzzle extends downward from the head. Its larvae are white and soft, without legs, and the white pupae are similar to those of other weevils. This weevil is not able to fly, so it can be found near places it has infested. Adults can live up to 8 weeks, during which time the female lays up to 200 eggs.
Appearance and Features
Different types of weevils occur in a wide range of colors and body shapes:
- size: length of weevils varies from 3 to 10 mm; many are oval insects;
- color: usually dark (brown to black);
- head: adult weevil has an elongated head forming a snout. The mouth is at the end of the snout. In some weevils, the snout is the same length as the body. Another family of beetles, grains, has a different appearance. They do not have the elongated snout found in other weevils.
The survival of the adult weevil depends in part on its exoskeleton, or cuticle. The cuticle is composed of a mixture of chitin and proteins, which are organized into three layers: epicuticle, exocuticle, and endocuticle. The cuticle undergoes a hardening process known as sclerotization and melanization, which requires the presence of the compound dihydroxyphenylalanine (DOPA).
The weevil's midgut contains small sacs that increase the surface area of the intestine, improving digestion and nutrient absorption. At the tip of each caecum is a bacteriome, a specialized organ made up of cells called bacteriocytes that protect endosymbiotic bacteria from attacking the host's immune system. Bacteriocytes not only contain endosymbionts in their cytoplasm, but also provide the nutrients needed to support bacterial growth.
Where does the weevil live?
outdoor weevils eat the leaves of trees, shrubs and plants. However, in the autumn of this, these plant-eating weevils begin to look for a place to winter.
Some species, such as the Asian oak weevil, are attracted to light. They gather around the doors and windows of houses. Homeowners sometimes notice hundreds of weevils clustered outside the home. When weevils detect cracks or holes around windows, they move inside the house. They also enter through broken screens on vents or vents. They can also crawl under doors that have been damaged by the weather.
Fun Fact: Many of the weevils that invade a home spend the winter behind insulation inside the walls. The attic and garage are also common winter shelters for weevils. These beetles can spend the winter without being seen by the homeowner.
However, some weevils make their way into the living space of the home. They can go through a crack in the wall or in the space next to the pipe. They can crawl out through the gap under the plinth. They can even use the light hole to crawl out of the attic.
In winter, the living space of the house is warmer than the attic or garage. This can confuse weevils. When they get into a warm home environment, the weevils start behaving as if spring has arrived and are trying to find a way to get outside.
Weevils that come to shelter indoors can infect every room in the house. They are often grouped in rooms with windows. Beetles gather at the windows, trying to get outside. Homeowners are finding these weevils crawling up walls, window sills and ceilings.
What does a weevil eat?
Like other pests pantry, weevils feed on grains and rice, as well as nuts, beans, cereals, seeds, corn and other foods.
Most weevils feed exclusively on plants. The fleshy, legless larvae of most species feed only on a specific part of the plant — i.e. flower head, seeds, fleshy fruits, stems or roots. Many larvae feed on either individual plant species or closely related ones. Adult weevils tend to be less specialized in their feeding habits.
Weevils live and feed inside the grains they eat. The female gnaws a hole in a seed or grain and lays an egg in it, then closes the hole, leaving the egg inside the grain or seed. When the egg hatches, the larva will feed on what's inside until it's fully grown. When an adult weevil grows up, it will eat all the grain.
Fun fact: Because female weevil emit pheromones, males will expect them to emerge from the grain and will immediately seek to connect with them to multiply.
Homeowners may not see weevils when they gather around the house. But if the weevils manage to find a hole and get into the house, the owner often finds hundreds of insects crawling along the windowsills and walls.
Peculiarities of character and lifestyle
Outdoors, weevils can destroy garden plants. Indoors, these bugs are more of a nuisance than a threat. Weevils contaminate food with feces and skins, causing more damage than they can eat. At home, weevils can be seen on packaged foods, they can also come from outside. Once inside, the population can grow and reproduce on nearby food if not checked.
Some weevils can become structural pests. These are weevils that frustrate homeowners because they often invade homes in large numbers. Some of them invade in autumn. They hide in the winter and leave in the spring. Others invade in the summer when the weather begins to warm up.
Adult weevils are nocturnal and tend to hide under plant debris during the day. This behavior is used for monitoring and control purposes. Weevils can be tracked using traps and insecticides applied when adult weevils are first caught. However, the most widely used method of capturing — these are “hideouts” that contain insecticide-flavored potato foliage. Cover traps are especially effective just before the emergence of potato plants in new fields.
Social Structure and Reproduction
The life cycles of the weevil are highly dependent on the species. Some adults lay their eggs on the ground near their host plants in spring. When the eggs hatch, the larvae burrow into the ground and feed on the roots. Since the larvae are underground, people rarely see them.
Adults chew grain from the outside and also lay eggs. Females can lay 300 to 400 eggs, usually one per cavity. Larvae develop through several stages (ages) inside the grains, and also pupate in the nucleus. They can complete a generation in a month in warm conditions. Adults often live 7 to 8 months, but some can live more than 2 years.
The egg, larva, and pupa stages of weevils are rarely found in grains. Feeding is done inside the grain, and adults cut holes to exit. The exit holes of the grain weevil are larger than those of the rice weevil and tend to be more ragged than smooth and round.
The females drill a tiny hole in the grain, place the egg in the cavity, then seal the hole with a gelatinous secretion. The egg hatches into a young larva, which spreads to the center of the nucleus, feeds, grows and pupates there. New adults have holes to emerge from the inside, then go into mating and begin a new generation.
Female granary weevils lay between 36 and 254 eggs. At a temperature of 23 to 26 degrees Celsius, a relative humidity of 75 to 90%, eggs are hatched in wheat with a moisture content of 13.5 to 19.6% for 3 days. Larvae mature in 18 days, and pupae — after 6 days. The life cycle is 30 to 40 days in summer and 123 to 148 days in winter, depending on temperature. It takes about 32 days to complete the life cycle. Both barn weevils and rice weevils feign death by bringing their paws close to their body and pretending to fall.
Many larvae spend the winter in the ground and become adults the next spring. However, adults that appear in summer or autumn may enter houses for shelter. Some, such as the Asian oak weevil, are attracted to light and are drawn into houses at night. Others may be attracted by warmth from home.
Natural enemies of weevils
Weevils have many natural enemies.
Insect predators include:
- ground beetles;
- predatory nematodes.
Animal predators include:
- wrens and other birds.
Red fire ants are efficient predators of the cotton weevil in eastern Texas. For 11 years, weevils have not suffered economic losses due to mortality, mainly due to ants. The removal of the ants has resulted in increased crop damage from the weevil. Insecticides used on cotton pests significantly reduce ant populations. To benefit from this efficient ant predation, unnecessary insecticide applications must be eliminated.
The main enemies of weevils are people who are trying to get rid of them. The simplest and most effective measure — find the source of infection and quickly get rid of it. Use a flashlight or other light source to carefully inspect all food storage areas and food items. If possible, dispose of heavily contaminated food in wrapped, heavy plastic bags or sealed containers for waste disposal, or bury deep in the soil. If you detect an infestation at an early stage, only disposal can solve the problem.
Population and species status
The weevil is considered a pest species against which disposal measures are applied. The cotton weevil, a historically destructive pest of cotton, was first recorded in the US (Texas) in 1894. Over the next 30 years, about 87% of the cultivated area was infected and the cotton industry was destroyed. Early weevil-targeting insecticides were only effective until 1960. The next phase of the weevil management program began in 1962 when the Weevil Research Laboratory was established at Mississippi State University.
A major breakthrough in the fight against weevils came with the release of its synthetic aggregating pheromone, which has proven to be an effective monitoring tool that can play a significant role in the control and eradication program against the weevil. A pilot eradication trial was started in 1971 and included the use of pheromone traps, sterile males and insecticides.
A second eradication trial was subsequently conducted using pheromone traps. In 1983, an eradication program was started in the Southeast Cotton Belt (North and South Carolina), which was later extended to parts of Georgia, Alabama, and all of Florida. The main focus of the program was the prevention of diapause and reproduction of the weevil, combined with control during the growing season. In 1985, the program was extended to the southwestern United States, and by 1993 California, Arizona, and northwestern Mexico had achieved eradication of the weevil.
The pheromone-based weevil eradication program uses traps to detect, population assessment, mass capture and decision-making on the use of insecticides. In addition, insecticide-impregnated protective strips can also be incorporated into pheromone traps to induce mortality and thereby prevent escape. /p>
The weevil probably became successful because of their development of a snout, which is used not only for penetration and feeding, but also for making holes in which eggs can be laid. This family includes some extremely destructive pests such as grain, barn and rice weevils.