Evaluation and implications of Andean potato weevil infestation sources for its management in the Andean region

Abstract

The Andean potato weevil Premnotrypes suturicallus Kuschel (Coleoptera: Curculionidae) is one of the most damaging potato (Solanum spp.) pests in the Andes. The objective of this study was to get a better understanding of weevil infestation sources and its distribution in potato fields as well as on the effect of potato cropping intensity and farmers’ harvest practices on weevil infestation to provide better clues for its management. For this purpose, a methodology was developed to assess weevil field densities in potato. A Taylor’s power law indicated that 177 and 69 samples are necessary to assess low (0.5 weevils/m2) and high (5 weevils/m2) weevil densities for a moderate reliability or precision level (D = 0.5). In potato fields, overwintering weevil densities were highest at field borders with 3.5 weevils/m2 at a distance of <2.5 m compared to 0.7 weevils/m2 at distances >10 m from the field border. No effects of time of harvest could be detected on soil overwintering weevil densities. The quantification of the larval density per potato plant after harvest showed that fields after 2‐year potato rotations had eight times more overwintering weevils compared to 1‐year rotations. Weevil infestation sources were mainly potato fields with the highest infestation (89%) followed by olluco (Ullucus tuberosus) and oat (Avena sativa) fields having volunteer potato plants (35%). The results confirm and support previous assumptions about the importance of the cropping systems for Andean potato weevil infestation and management. The confirmation that weevils do not occur or only in neglected numbers on fallow fields supports the use of plastic barriers to effectively exclude migrating flightless adult weevils to potato fields cultivated after fallow. The distribution of overwintering weevils indicates that farmers could concentrate efforts to control adult weevils mainly to the first meters of potato fields.

Explaining Andean Potato Weevils in Relation to Local and Landscape Features: A Facilitated Ecoinformatics Approach

“…aFarmers apply a layer of ash directly below the potato seed at the time of planting; this practice is intended to kill potato weevils.bFertilization can influence crop defenses against herbivores [17].cMany agronomists recommend hilling the plants (piling dirt up around the stem of the plant) higher to lengthen the distance weevil larvae must travel to find tubers.dEarly harvest shortens the exposure of tubers to neonate larvae [18].eLarger fields have lower perimeter to area ratios and have been suggested to have lower infestations [19].fEarly emerging plants may experience greater infestations [20].gPlanting density may influence the abundance of many insect pests [21].hPlanting potatoes following a potato planting should lead to very high infestations [19], but implementing a single host free period should eliminate this risk. Rotation 2007 indicates if potatoes were sown in the field the previous season while Rotation 2006 indicates if potatoes were sown there two seasons before the study.…”

“… d Early harvest shortens the exposure of tubers to neonate larvae [18] . e Larger fields have lower perimeter to area ratios and have been suggested to have lower infestations [19] . f Early emerging plants may experience greater infestations [20] .…”

“… g Planting density may influence the abundance of many insect pests [21] . h Planting potatoes following a potato planting should lead to very high infestations [19] , but implementing a single host free period should eliminate this risk. Rotation 2007 indicates if potatoes were sown in the field the previous season while Rotation 2006 indicates if potatoes were sown there two seasons before the study.…”

“… e Larger fields have lower perimeter to area ratios and have been suggested to have lower infestations [19] . …”

Pest categorisation of Amathynetoides nitidiventris

“…oca, maize, mashua) or which are part of the same crop rotation (e.g. barley, broad beans, maize, mashua, oats, oca, quinoa) (Fries and Tapia, 2007 ; Ríos and Kroschel, 2011 ). Indeed, López and Herman ( 2004 ) reported that no oviposition could be found on stems of barley, oats, and stover, contrary to closely related potato and oca weevils ( Premnotrypes spp.…”