The Andean Potato Weevil complex is a pest that causes serious damage to the potato crop at high altitudes in the Andes of Bolivia, Peru, Ecuador, Colombia and Venezuela, between 2,500 and 4,700 meters above sea level. Most of the species involved in this complex belong to the Premnotrypes (Coleoptera:Curculionidae) species.
Andean Potato Weevil
Synonyms: Trypopremnon (Pierce, 1914), Solanophagus (Hustache 1933), Plastoleptops (Heller, 1935)
Common names: Andean Potato Weevil (English), Gorgojo de los Andes, Gusano blanco de la papa (Spanish)
Host plant: Andean potato larvae can complete their development only on potatoes; adults can occasionally feed on other plants.
Damage from Andean potato weevils is caused by larvae feeding on tubers and by adults feeding on leaves.
Tubers: The larvae produce deep galleries, lowering tuber quality and rendering tubers useless for consumption or use as seed. Larvae live in tubers until they have completed their larval development. On emerging from the tubers, larvae produce characteristic circular holes. Larval development may be completed before harvest; in this case weevil development continues in the field otherwise weevils will complete their life cycle in potato stores.
Leaves: Adults feed on leaf borders causing characteristic half-moon feeding damage; in general this damage is not significant but indicates the presence of weevils in potato fields.
Status of the pest
Andean potato weevils (APW) are the most serious pests of potatoes (Solanum spp.) at high altitudes (between 2,800 and 4,700 m) in the Andean region, where wild and cultivated potato species are their host plants. They are distributed from Argentina to Venezuela, covering a mountain territory of about 5,000 km in length. Without control, tuber damage can be up to 50-80% at harvest. In commercial potato production highly toxic insecticides are usually applied at planting as soil treatment or post-emergence on potato foliage.
Although species of the genus Premnotrypes are the most important and widely distributed Andean potato weevils, the first taxonomic descriptions were made in the year 1824 for the genera Phyrdenus, and in 1906 for the genus Rhigopsidius. All species of both genera attack potato and are native to the Andes. Pierce (1914) established the genus Premnotrypes and described two species from infested tubers in Peru. Today 12 Premnotrypes species have been described: P. solani Pierce, P. latithorax (Pierce), P. vorax (Hustache), P. solanivorax (Heller), P. fractirostris Marshall, P. sanfordi (Pierce), P. clivosus Kuschel, P. zischkai Kuschel, P. pusillus Kuschel, P. solaniperda Kuschel, P. suturicallus Kuschel and P. piercei Alcalá. Since most of the species occur in Peru and Bolivia these countries are considered as the center of origin. Ten of twelve Premnotrypes species have been identified in Peru. The most widespread and damaging species are P. vorax, P. latithorax and P. suturicallus, which all have a similar behaviour.
Life cycle and biology
Adult weevils are dark brown ground beetles of 6.0 – 9.2 mm in length. Most species have tubercles or sculpturing on the elytra and in some the abdomen is squarely truncated posteriorly. Larvae and pupae are typical for Curculionidae of 6.2 – 10 mm in length and whitish. The eggs are 1 – 1.5 mm of length.
Adults, both males and females, remain hidden during the day beneath soil clods, stones, dry leaves, or any other shelter including soil cracks near the potato plant. In the evening weevils climb to the foliage to feed and mate. Females lay eggs inside straw or other plant debris near potato. As thelarvae hatch, they seeking potato tubers. Larvae feed in tubers until leaving them as L 4 for pupation. The larvae prepare pupal cells in the soil, in which they hibernate. Emergence of adults starts with the onset of rains.
In the high Andes of Peru and Bolivia, with one potato crop per year, species of the genus Premnotrypes develop one generation per year. Development is well synchronized with climatic conditions, the cropping system and the phenological development of potato. The following developmental times have been reported: egg (26.5 – 47.7 days), larva (59.2 – 117.9 days), pre-pupa (26 – 46.6 days), pupa (28.5 – 54.4 days), hibernating adult (65.9 – 134.6 days), longevity of active adults (159.2 – 276.8 days) and total life cycle (424 – 499.3 days). In Ecuador and Colombia, P. vorax develops more than one generation per year when potato cropping is year-round. Weevils remain in the field if potato cropping continues in the next seasons, or they migrate to new potato fields. When immigration occurs, infestations are more pronounced at field borders. In Peru, adult emergence lasts from the end of October until the end of February. Weevils migrate into potato fields between December and February. The highest adult populations are observed in February. Larval tuber damage starts at the middle of March and increases until April. Pre-pupa occur from April to September, pupae from May to October, and hibernating adults are found from June to November. Hibernating adults are not active while in the process of citinization, changing color from yellow to dark brown or black.