Anthonomus eugenii
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Anthonomus eugenii |
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| Cano , 1894 |
Anthonomus eugenii (also known as bell pepper weevil ) is a beetle from the family of weevils (Curculionidae). In the southern states of the USA, in Mexico, Central America, on some islands in the Caribbean and in Hawaii, it is one of the economically most important pests on paprika ( Capsicum ).
features
The beetles have an oval body and reach a length of 2 to 3.5 millimeters and a width of 1.5 to 1.8 millimeters. They have a gray to dark red-brown or almost black body color. Pronotum , wing wings and also the legs are covered with light-colored scales. The upper wings have longitudinal rows with fine dots. The proboscis characteristic of the family are slightly longer than the head and pronotum combined. The anterior two thirds of the tibia are colored yellow-orange. The long and thin antennae have an elongated club at the end. The femora have a small sharp spine.
Apart from a genital examination, which, as with almost all insects, gives clear results, the males can be clearly identified by means of an appendage at the end of the tibiae of the middle pair of legs. Both sexes have such processes on all pairs of legs, but when viewed at about 80 times the magnification one can see that those of the male mesotibiae are significantly larger and thicker than those of the females and are also slightly arched. In addition, the females differ from the males in that they have a slightly narrower and less punctured rostrum , and the distance from the antennae to the mouthparts is slightly larger. These last-mentioned characteristics are clearly confirmed as sexual dimorphisms , but it is not easy to carry out a clear sex determination using these characteristics alone without comparing several specimens.
The larvae are long after hatching 0.8 to 1.5, on average 1.0 millimeters. They reach a length of 2.2 to 5, on average 3.3 millimeters and have a glossy white to grayish body color.
The mandibles , which are initially brown in color and have a black tip, darken to a dark brown or black in the second larval stage. The head capsule is initially cream-colored, later light yellow to brown. The larvae have no developed thoracic legs and have a few long bristles.
Way of life
Anthonomus eugenii can be found in the warm regions of its distribution all year round in all stages. In comparatively cooler Florida, it is most common between March and June and is absent in December and January. The species only overwinters where its food plants grow all year round, as they do not go into diapause and are therefore dependent on food all year round. Mating takes place two days after hatching, which is usually repeated several times, although the female is fertilized for the rest of her life after the first. Presumably depending on the temperature, the eggs are laid two to eight days after mating. Male beetles secrete an aggregation pheromone that attracts individuals of both sexes. The animals can fly well, but they spread over greater distances, especially when agricultural products are transported.
Food crops
The larvae of Anthonomus eugenii develop exclusively on the nightshade family (Solanaceae) of the genera paprika ( Capsicum ) and nightshade ( Solanum ). The adults also feed on other nightshade plants such as bladder cherries ( Physalis ), thorn apples ( Datura ), petunias ( Petunia ) or tobacco ( Nicotiana ). In agriculture, all types and varieties of paprika in particular are infested, with tomatillos ( Physalis philadelphica ) as well as eggplants ( Solanum melongena ), which grow near paprika, the infestation is only moderate.
development
The females usually lay their eggs one by one near a bud or an unripe fruit on the food plant. To do this, they dig a slight hollow in the tissue, which later contains the egg and is closed with a brown, hardening secretion. On average, 341 eggs are laid within 72 days, usually five to seven per day. A female can lay a maximum of 600 eggs. The eggs are slightly oval and measure 0.53 by 0.39 millimeters. They have a shiny, soft, but robust shell that is initially pearly white and later yellow. The larvae hatch after three to five days. The species has three larval stages. The development from hatching to adult imago takes between 16 and 23 days in summer, on average 20.9 days. In spring and autumn the development is a little slower and also depends on the weather. On average, three to five generations can develop per year, in some regions, such as California , under good conditions it can be up to eight.
The larvae either feed on the still immature stamens or on the young ovules within the flower bud, whereby the buds and young fruits are pierced to suck up sap. If there are no more such leaves, the leaves of the plants are pierced. The larvae are very aggressive towards other species, so that only a single one survives within a flower or fruit. Several larvae can only appear in larger fruits. The first moult takes place after about two days, the second after another two days. Pupation takes place after another 3.5 days. For this purpose, the larva forms a cavity within the fruit within one to eight (average 4.9) days, which is closed with feces. This is where pupation takes place. The pupa is initially white, later yellowish and then has brown eyes. As a free pupa (pupa libera) it looks very similar to the later adult animal. The adult beetles hatch after three to six days. Immediately after hatching from the pupa, the plants are eaten, but the beetles remain inside the fruit for three to four days and then cut through a smooth, circular hole to the outside. Their lifespan is approximately three to four months.
distribution
The original occurrence of the species extended over Central America , such as Guatemala and El Salvador . It gradually spread across Mexico across the entire southern United States . There are also reports from New Jersey , North Carolina and Hawaii . But they also occur in the Caribbean and South America . The occurrence of the species is limited to areas in which their food plants grow all year round.
Harmful effect
When they eat or develop in the buds and fruits, these begin to rot and turn brown. The infestation by Anthonomus eugenii can be recognized by numerous unripe fruits that have fallen to the ground. Thin-walled fruits are more affected than thick-walled ones. The puncture sites of the adult animals can be seen as brown speckles. Adult animals are significantly less harmful, but occasionally cause deformities or fungal diseases.
In commercial paprika cultivation, about 50% of the fruits can be lost due to early shedding due to an attack by Anthonomus eugenii , in experiments a loss of up to 90% of the harvest has been shown with early attack on the plants and failure to control them. Often even the entire harvest has to be foregone in order not to cause further spread through the sale of infected fruits.
Enemies
Natural enemies
The species' enemies include the bracon wasp Bracon mellitor and the ore wasp Catolaccus hunteri , which develop as parasitoids in Anthonomus eugenii . They attack up to 26% of the beetle population, but they are not exclusively specialized in the species, which is why they do not play an important role in controlling the beetle. Before 1950, two attempts were made to establish several parasitoids in the United States that were supposed to combat A. eugenii , but also A. grandis , but this failed. In the meantime, parasitoids from eleven genera are known, with brackish wasps of the genus Urosigalphus and Triaspis eugenii being suspected to be the most effective at combating the beetles because they specialize in them and are the only known parasitoids that also attack their eggs and such Can prevent damage to the plants. The beetle's eggs are also the most vulnerable stage as they are laid outside the fruit. This is also reflected in the relatively high infestation of these two species; T. eugenii was found in 18 to 40% of the eggs found in the wild, and Urosigalphus species in 30%. Values between 70 and 90% were achieved in the laboratory, which suggests a significantly higher potential.
Combat by humans
In order to prevent an infestation by Anthonomus eugenii , harvested pepper plants are immediately removed from the field in order to deprive the animals of their food source. All other nightshade plants in the field and on the edge of the field must also be removed. However, it is still necessary to check for infestation on a weekly basis and to examine different areas, especially at the edge of the field, as the infestation often only spreads slowly from a place of strong infestation over the entire field.
Permethrin , oxamyl , esfenvalerate and cryolite are approved as insecticides against attack by Anthonomus eugenii in the USA . If the infestation has been determined once, regular use and further thorough monitoring of the development of the infestation is necessary. After using these agents, a rest phase must be observed before harvesting; when using cryolite, washing the fruit after harvesting is sufficient. However, only the adult stages of the beetle can be combated with the help of insecticides, as the larvae are protected within the fruit.
supporting documents
- University of Hawaii College of Tropical Agriculture and Human Resources, and Hawaii Department of Agriculture: Knowledge Master (English)
- John L. Capinera: Pepper weevil. University of Florida, accessed February 22, 2013 .
Individual evidence
- ↑ Bell pepper weevil first discovered in Europe. In: Taspo. August 30, 2012, accessed February 22, 2019 .
- ↑ Monitoring of quarantine pests in horticultural businesses 2017/2018 Plant protection in horticulture January 10, 2019 in Dresden. State Office for Environment, Agriculture and Geology - Free State of Saxony, January 10, 2019, accessed on February 22, 2019 .
- ↑ a b c David G. Riley and Alton N. Sparks, Jr .: The Pepper Weevil and its Management (PDF file; 1.9 MB), Texas Agricultural Extension Service, Texas A&M University, publication L-5069.
- ↑ Fred J. Eller: A previously unknown sexual character for the Pepper Weevil (Coleoptera: Curculionidae) (PDF file; 400 kB). In: Florida Entomologist , Volume 78, Number 1, March 1995, pages 180-185.
- ↑ Esteban Rodríguez-Leyva et al .: Diversity and distribution of parasitoids of Anthonomus eugenii (Coleoptera: Curculionidae) from Mexico and prospects for biological control (PDF file; 182 kB). In: Florida Entomologist , Volume 90, Number 4, Dec. 2007, pp. 693-702.
