|Crop Knowledge Master|
Anthomonus emigratella (Busck)
Ronald F.L. Mau, Extension Entomologist
Jayma L. Martin Kessing, Educational Specialist
Department of Entomology
The pepper weevil attacks solanaceous plants that belong to the genera Capsicum (peppers) and Solanum (nightshades) (Elmore, J. C., et. al., 1934). Hosts include C. baccatum, common varieties of the pepper Capsicum annuum L. (pimiento, tabasco, chili, and bell pepper), and Black nightshade, Solanum nigrum L.. Thinner walled pepper varieties receive more damage than thicker walled varieties. They may also be found on S. xanti A. Gray, S. umbelliferum Esch., and S. villosum Mill growing near pepper fields.
The pepper weevil are also known to attack eggplant fruits and popolo (S. nodiflorum) (Fullaway and Krauss, 1945). Other potential hosts are two ornamental nightshade species, S. glaucum Dunal and S. aviculare Forst, where adults were found during the winter.
The pepper weevil is native to Central America (Bartlett, et. al., 1978). It has spread to Mexico and parts of the southern United States including California, Arizona, New Mexico, Texas, and Florida (Elmore, J. C., et. al., 1934). According to records, the pepper weevil is also found in South America, Guatemala, El Salvador, Louisiana, Georgia, New Jersey, and North Carolina (Burke and Woodruff, 1980; Fullaway and Krauss, 1945).
The pepper weevil was first discovered in Hawaii on February 24, 1933 in the Kaimuki district of Oahu (Fullaway and Krauss, 1945). The pepper weevil has since spread to other parts of Oahu and the other islands.
The pepper weevil is a destructive pest of peppers. An infestation that is severe and early can wipe out an entire crop. Primary damage is caused by the development of the larvae in flower buds and immature fruits (Burke and Woodruff, 1980). Early signs of an infested fruit are yellow stems and calyces (Elmore, J. C., et. al., 1934). The stems will begin to wither at the point of connection with the plant. Eventually, the fruit will turn yellow or red, and the fruit will fall from the plant. Infested fruits are usually malformed. In many cases, by the time a grower notices that fruits have fallen, there may already be serious damage to the pepper crop. Larvae also feed on buds causing them to fall.
Infested fruits that do not fall will have blackened seeds and cores, a result of the feeding grubs. These fruits may also have weevil exit holes (holes where the developed adult weevil exited the fruit). Weevils may also inflict feeding punctures on buds and immature fruits. These feeding punctures may not adversely affect the quality of dried peppers, but they may lower the quality of canned or fresh peppers. Mature fruits are not susceptible to weevil attack because of the properties of the mature fruit epidermis. Holes made on the fruit by oviposition, adult emergence, or feeding may also open up the fruit to microbial infection. In one observation (Bruton, et. al., 1989), there was evidence of a direct relationship between pepper weevil damage and internal mold caused by Alternaria alternata (Fr.) Keissler.
The pepper weevil lives for about 3 or 4 months under natural conditions (Elmore, et. al.., 1934). They mate in about 2 days after emergence. Mating may occur several times, but a female needs to mate just once to remain fertile for her entire life. The interval between mating and oviposition ranges from about 2 days in midsummer to 8 days in early spring or fall.
Temperature may play a major role in controlling oviposition (Elmore, et. al., 1934). Oviposition and ovulation seem to be seasonal in areas with winters like Orange and Los Angeles Counties. In most females, ovulation stops in winter and resumes in the spring. The presence of pepper buds and nightshade berries in the spring provides a place for oviposition. The presence of male weevils has an inhibitory effect on oviposition. In San Diego County, a warmer climate than Orange and Los Angeles County, development is continuous, all stages can be found in all seasons.
Pepper weevils undergo complete metamorphosis. The estimated total development time from egg to adult during the summer ranged from 16 to 23 days and averaged 20.9 days (Elmore, et. al., 1934). If the period between emergence and oviposition is included, then the average development time is 25 days. Over a period between the middle of April to the end of October (active season), the average generation time from egg to first egg was 32.1 days.
Eggs are an average of 0.53 mm in length and 0.39 mm in diameter (Elmore, et. al., 1934). The eggs are usually oblong-oval but may take the shape of the cavity it lies in. The shell is smooth, shiny, flexible, tough, and pearly white in color at first but later turns yellow.
The female usually oviposits single eggs beneath the surface of a bud or immature fruit. In a laboratory experiment conducted (Elmore, et. al., 1934) with 25 females, the average oviposition period is around 72 days, and the average number of eggs deposited was 341 eggs (Burke and Woodruff, 1980). It takes about 3 to 5 days or an average of 4 days for the eggs to hatch.
The newly hatched larvae range from 0.8 to 1.5 mm in length and average 1 mm. The larvae have large, off-white heads with black-tipped, brown mandibles (Elmore, et. al., 1934). The body is a shiny white. The larvae feed in about 1 to 4 hours after hatching, depending on the temperature. Larva in immature fruit will work its way into the young seed mass. Larva in flower buds will feed on the immature pollen. The first molt occurs in an average of almost 2 days.
After molting, the larva ranges from 1.3 to 2.6 mm in length and averages 1.9 mm. The large head is light yellow and the mandibles are dark brown or black. The larva feeds for an average of 2 days before the second molt.
The third larval stage is from 2.2 to 5 mm in length and averages 3.3 mm. The larva continues to feed for an average of 3.5 days and then prepares to pupate. Pupation begins when the larva makes an oval cavity inside the fruit. The cavity is lined with excrement to make a cell. When the cell is finished, the larva rests in the cell, and its body becomes shorter and wider. At this point, its color is shining, white. This stage lasts from 1 to 8 days and averages 4.9 days. During this period, the pupal cell is kept closed.
The pupal stage lasts from 3 to 6 days and averages 4.7 days (Elmore, et. al., 1934; Burke and Woodruff, 1980). The pupa casts off its larval skin and undergoes changes in its appearance. The eye spots begin to show a yellow tinge a few hours after pupation. In 2 to 3 days, the eyes darken, the beak becomes a light yellowish brown with a black tip, and parts of the antenna and elytra become gray.
The newly developed adults are light brown (Elmore, et. al., 1934). It takes about 3 to 4 hours before the developed adults emerge from the fruit or bud. When the adult pepper weevil emerges, it cuts a clean round hole in the fruit or bud. The just emerged adults begin to feed on buds and immature fruits immediately after emerging.
The adult pepper weevil has an oval body and ranges from 2 to 3.5 mm in length. Its color ranges from gray to dark reddish-brown to almost black. Two-thirds of the tibiae tips are yellowish orange. The pepper weevil has the characteristic weevil snout. The pepper weevil snout is one-sixth longer than the head and prothorax. The antennae are fairly long, thin, and the club oblong. The elytra have rows of punctures.
Holes in the walls of pepper fruits and buds are caused by ovipositioning females, feeding adults, or emerging adults. To oviposit, females puncture the fruit or the bud with one mandible, then the other mandible, and then inserts her beak to enlarge the cavity. An egg is placed into this hole and sealed with a clear yellow fluid which hardens.
Adults favor buds and immature fruit for food. Feeding holes are similar to oviposition holes but larger in size. Adults will feed upon pepper leaves if no buds or fruits are available. An alternate food source is the buds, berries and foliage of the nightshade (Solanum nigrum). The pepper weevil may overwinter on nightshade in climates with cold winters.
The pepper weevil disseminates by flight. Pepper weevils fly during the active season (mid-April to the end of October) and on warm winter days (Elmore, et. al., 1934). This weevil may also be accidentally transported with the aid of man by way of infested peppers, pepper plants, or picking sacks.
The male pepper weevil produces an airborne female attractant (Coudriet and Kishaba, 1988). This pheromone has the potential for use in traps to capture females.
Clean farming methods including plowing under the pepper plants as soon as the crop is harvested is recommended for pepper weevil control (Lockwood, 1960). The destruction of wild hosts in and around the field is also recommended. Black nightshade plants in and around pepper farms should be destroyed (Patrock and Schusterm, 1987). Black nightshade can serve as a reservoir for the pepper weevil.
The destruction of fallen fruit and the use of pesticides as a control measure was another recommendation (Fullaway and Krauss, 1945; Goff and Wilson, 1937). However, in an experiment in Honduras, Central America, Andrews, et. al., (1986) found that it was not cost effective to collect and destroy fallen fruit when pesticides were used, but it may be of a limited value in the absence of pesticides.
In Hawaii, biological control agents, Eupelmus cushmani
(Crawford) and Heterolaccus hunteri (Crawford), were released and reported to be established (Bartlett, et. al., 1978). On the mainland, 7000 adult Bracon vestiticida (Vier.) were released to control the pepper weevil but no recoveries were made.
An experiment in Honduras, Central America (Andrews, et. al., 1986) resulted in recommendations for an action threshold for control of the pepper weevil over weekly scheduled applications. A twice weekly count of pepper weevils between 0800 and 1100 hours was recommended. The action threshold was set at one or two adults per 100 terminals.
Another experiment (Riley, et. al., 1992) determined that the action threshold recommended by Andrews, et. al. (1986) for a low input pepper production system was not sufficient to prevent significant yield loss in high-input, high-yielding bell pepper. They found that the type of insecticide affected action threshold values. Andrews, et. al. (1986) used toxaphene. Riley, et. al. (1992) used oxamyl and permethrin. Riley, et. al. (1992) found that a more conservative action threshold, one pepper weevil per 400 terminal buds (2 buds per plant) provided adequate control of pepper weevil in a commercial situation and saved on applications of permethrin.
An experiment conducted in 1990 (Cartwright, et. al., 1990) found that a damage-based action threshold based on the proportion of damaged bud clusters is more appropriate than an adult weevil count. They determined that a 5% damage level was feasible as an action threshold. Also adult weevil count and bud cluster damage were strongly correlated.
An experiment conducted by Segarra-Carmona and Pantoja (1988) used direct counts, yellow sticky traps, drop cloths, sweep nets, and detergent-water traps as sampling methods. They found that only yellow sticky traps were significantly correlated with direct counts. The other methods were inefficient in trapping pepper weevils or caused severe damage to the pepper plants. They also tested the attractiveness of different colored sticky boards. The most attractive color was yellow followed by white. They concluded that yellow sticky traps could be an inexpensive pepper weevil monitoring tool that could replace the time, money, and labor of direct counting.
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Elmore, J. C., A. C. Davis, and R. E. Campbell. 1934. The Pepper Weevil. Washington D. C. United States Department of Agriculture, No. 447. 28 pp.
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Lockwood, Stewart. 1960. Pepper Weevil. Anthomonus eugenii. Loose-Leaf Manual of Insect Control.
Patrock, R. J. and D. J. Schuster. 1987. Field Survey for the Pepper Weevil, Anthomonus eugenii, on Nightshade. Florida State Horticultural Society Proceedings Annual Meeting, 100: 217-220.
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Segarra-Carmona, A and A. Pantoja. 1988. Evaluation of Relative Sampling Methods for Population Estimation of the Pepper Weevil, Anthomonus eugenii Cano (Coleoptera: Curculionidae). Journal of Agriculture of the University of Puerto Rico. 72 (3): 387-393.