Avocado, Persea americana Miller (Lauraceae), is one of the most economically important crops in Mexico. Mexico is the world's largest avocado producer with an established area of 234,270 ha and a production of 2,300,888 tons in 2019; the state of Nayarit produced 67,058 tons (SIAP 2019). It is estimated that more than 54% of the avocados produced in Mexico are exported to the USA, Canada, and Japan; the rest is destined for the local market for fresh consumption and processing (SAGARPA 2017). Avocado seeds are an unconventional alternative source of flour and starch with potential for the agri-food industry (Gomez et al. 2014). Seeds represent approximately 16% of the fruit fresh weight with a starch content up to 29% (Builders et al. 2010; Chel et al. 2016). Nayarit producers use avocado seeds as rootstocks and the demand for seeds has increased considerably.

In the present study, Pagiocerus frontalis (Fabricius) (Coleoptera: Curculionidae) is reported for the first time from fallen avocado fruits of the cultivars Hass and “Criollo” in Nayarit. This insect is not considered a pest in Mexico and it does not restrict the export of avocado fruits to the countries mentioned above. But it limits the procurement of rootstocks used for the production of avocado seedlings in the region. This borer was recently reported from seeds of tropical and subtropical Lauraceae (Persea, Nectandra, Ocotea) trees in Argentina and Chile (Córdoba & Atkinson 2018; Lawrence 2018). This species also has been associated with stored grains, causing losses greater than 44% in corn (Zea mays L.; Poaceae) (Eidt-Wendt & Schulz 1990).

Fig. 1.

Pagiocerus frontalis in avocado fruit. (A) Holes caused by P. frontalis, (B) adult of P. frontalis, (C) presence of seed (embryo) damage indicators, (D) dehydrated seed with external evidence of sawdust.

In Feb 2019, avocado fruit at physiological maturity with hard skin, fresh and ripened pulp, and without damage by pathogens (Fig. 1A–C) were collected from soil in an experimental orchard of the Academic Unit of Agriculture (21.4127778°N, 104.9263889°W; 1,129 masl), located in Xalisco, Nayarit, Mexico. Avocado trees were in the full flowering phenological stage; hence, the fruit corresponded to the previous cycle. External holes (Fig. 1A) were observed in avocado seeds. The holes led to internal galleries (about 1.5 mm in diam) containing P. frontalis larvae and adults. The galleries led to the seeds (Fig. 1B, C) and each seed contained about 30 adults. The weevils continued feeding until completely degrading the seeds in about 18 d (Fig. 1D). The adult specimens were preserved in 70% ethanol for identification, which was confirmed by Armando Burgos Solorio (woodborer specialist, Autonomous University of the State of Morelos, Cuernavaca, Morelos, Mexico). Specimens were deposited in the insect collection of the Agricultural Parasitology Laboratory of the Autonomous University of Nayarit, Xalisco, Nayarit, Mexico. Genomic DNA (gDNA) was extracted using the Pure Link Genomic DNA Mini Kit (Invitrogen, Carlsbad, California, USA) following the manufacturer's protocol. Genomic DNA was used to amplify the cytochrome C oxidase (COI) subunit gene by Polymerase chain reaction (PCR) using the following primers, LCO (5'-GGTCAACAAATCATAAAGATATTGG-3') and HCO (5'-TAAACTTCAGGGTGACCAAAAAATCA-3') (Folmer et al. 1994). Polymerase chain reaction products were visualized by electrophoresis on a 1.0% agarose gel, then sequenced by Macrogen USA (Rock-ville, Maryland, USA). The sequence data of P. frontalis was submitted to GenBank (accession number MN419152.1).

Pagiocerus frontalis was reported previously as an occasional insect in avocado orchards in other states of Mexico such as Chiapas, Federal District, Guanajuato, Guerrero, State of Mexico, Morelos, Nayarit, Nuevo León, Oaxaca, Puebla, San Luis Potosí, Tamaulipas, and Veracruz (Atkinson & Riley 2013; Soto et al. 2013; Atkinson 2019), but not associated with fallen avocado fruit (Fig. 1A). High populations of this coleopteran are uncommon in avocado orchards (Atkinson et al. 1986). Therefore, both occurrences of extraordinarily abundant P. frontalis in avocado orchards and feeding on freshly fallen fruit are reported for the first time in Nayarit, Mexico.

These findings could be the starting point for a better understanding of the behavior and potential damage caused by this insect in fallen avocado seeds. For this reason, we suggest performing studies related to their thermal requirements, host plants, natural enemies, and determine their abundance, distribution, and potential economic impact on avocado regions of Mexico.