WEEVILS (COLEOPTERA, CURCULIONIDAE) ASSOCIATED WITH PISTACHIO TREE (PISTACIA VERA L.) CROPS IN CASTILLA – LA MANCHA (CENTRAL SPAIN)

Introduction[Up]

Pistachio crops were first introduced into Spain in the 1980s. Since then, the area devoted to the cultivation of pistachios has increased, particularly in recent years, and currently comprises around 55 000 ha (‍MAPA, 2021a). Spain has led pistachio cultivation in Europe since 2014, followed by Greece and Italy. The majority of the area devoted to this cultivation in Spain is located in the region of Castilla-La Mancha (around 75% of the total national surface area), and is essentially rain fed. Most of this area is concentrated in the province of Ciudad Real, with over 10 000 ha, followed by the provinces of Toledo, Albacete and Cuenca (‍MAPA, 2021b).

Many pests affect pistachio trees in the zones traditionally devoted to this crop, although its recent introduction and the agri-environmental conditions of Castilla-La Mancha limit their natural enemies in this area. The only defoliator beetle recorded as a pest in this region is the chrysomelid Labidostomis lusitanica (Germar, 1824), which can cause substantial damage to young plantations and the fresh green leaves of adult trees (‍Couceiro et al., 2017; ‍MAPA, 2018; ‍Rodrigo-Gómez et al., 2022).

Several Curculionidae species are considered pistachio pests. They include Chaetoptelius vestitus (Mulsant & Rey, 1861) (Scolytinae), that damages branches and buds in Turkey and Iran (‍Ghrissi et al., 2019; ‍Mehrnejad, 2020), and Polydrusus davatchii Hoffmann, 1956 (‍Hoffmann, 1956; ‍Sadeghi & Zare, 2006), which damages leaves in Central and Southern Iran (‍Mehrnejad et al., 2017). Two other Polydrusus species are potentially harmful, P. nadaii Meleshko & Korotyaev, 2005 for Iran’s pistachio crops (‍Velázquez de Castro et al., 2014), and Polydrusus roseiceps Pesarini, 1975 in Diyarbakir Province, Turkey (‍Şimşek & Bolu, 2017). Recently, Açikgöz et al. (‍2022) reported Strophomorphus sublaevigatus Desbrochers, 1875 to cause damage on UCB1 pistachio rootstock leaves and bark, in Turkey.

Material and methods[Up]

This work has been carried out at several pistachio plantations located in Castilla – La Mancha Region, and specifically in several municipalities in the provinces of Ciudad Real, Cuenca and Toledo (Fig. 1). In order to identify the presence of weevils in pistachio plants and their still-ungrafted rootstock (Pistacia terebinthus or UCB1-Pistacia integerrima × Pistacia atlantica), 12 young pistachio crop plots were monitored, most of them aged between 1 and 7 years and all of which were of the Kerman variety (Table 1).

Two perpendicular transects were carried out, starting from the center of each plot and using the beating tray sampling method and direct observations on the basis of visible damage (‍Speight, 2005). Transects were conducted weekly from spring to autumn 2020. All the specimens collected were placed in tubes and transferred to “El Chaparrillo” research center in Ciudad Real Province for their mounting, labeling and subsequent identification. This material was divided between the research Centre’s reference collection and some of the authors’ private collections.

Results[Up]

The sampling attained a total of 328 individuals belonging to eight species and five genera of Curculionidae. The species collected, ranked in order of abundance (individuals and percentage), are: Polydrusus subglaber (111 individuals, 34%), Otiorrinchus cribricollis (97, 29.6%), Lixus acicularis (40, 12.2%), B. pubescens (27, 8.2%), P. pilosulus (25, 7.6%), B. marginellus (12, 3.6%), Sitona lineatus (10, 3%), and S. discoideus (6, 1,8 %).

ENTIMINAE Schoenherr, 1823

Brachyderes (Brachyderes) pubescens Boheman, 1883.

This species is widely distributed in the Western Mediterranean: the South of France, the Iberian Peninsula, the Balearic Islands and North Africa (‍Viedma, 1967) and it is also found in Italy (‍Alonso-Zarazaga et al., 2017).

It has been recorded on several perennial Quercus, especially Quercus ilex L. (‍Cardona, 1872; ‍Hoffmann, 1950; ‍Wagner, 1928), Q. ilex subsp. ballota (Desf.) Samp. (‍Compte Sart, 1982), Pinus sp. (‍Cardona, 1872), Pinus halepensis Miller (‍Breit, 1909), and generally in oak and pine trees (‍Moragues, 1888). It has also been found wintering in oaks in the Moroccan Atlas Mountains, and on Quercus suber L., Quercus pyrenaica Willd., Castanea sativa Miller, or even Cistus ladanifer L. in the region of Extremadura in the Iberian Peninsula (‍Sáez-Bolaño et al., 2010).

In Castilla – La Mancha, it has previously been captured in Ciudad Real Province, in the municipality of Alcoba (Cabañeros National Park), on Quercus faginea Lam., Q. ilex subsp. ballota, Q. pyrenaica and Betula alba L. (‍Fernández-Carrillo, 2013). In this study, it has been found on Pistacia vera in the municipality of Villamayor de Santiago (Cuenca) (Fig. 2A), and again in Ciudad Real, in May and June. This is, to the best of the authors’ knowledge, the first record of this species feeding on Pistacia vera.

Brachyderes (Gastraspis) marginellus Graells, 1858

This endemic species has been recorded in Southern Portugal and in some provinces from Central and Southern Spain (‍Alonso-Zarazaga, 2018).

Previously recorded from Ciudad Real Province by Viedma (1967), it has been also found in Alcoba, (Cabañeros National Park environment), on Q. ilex subsp. ballota (‍Fernández-Carrillo, 2013). It has also been recorded on Arbutus sp. (‍Gurrea Sanz et al., 1989), Cistus sp. (‍Uhagón, 1887), C. monspeliensis L. and C. ladanifer (‍Sáez-Bolaño et al., 2010), and on Q. ilex subsp. ballota (‍Compte Sart, 1982; ‍Viedma, 1967).

In this study, B. marginellus was found on cultivated Pistacia vera in the municipality of Los Navalucillos (Toledo Province), in June and July (Fig. 2B–C). This is the first record of this species feeding on cultivated pistachio trees, although wild Pistacia species could be possible host plants for this beetle, since P. terebinthus L. and P. lentiscus L. can be found in the same distribution area.

Otiorhynchus (Arammichnus) cribricollis Gyllenhal, 1834

This is a ubiquitous, invasive, thermophilic species that is native to the Eastern Mediterranean (‍Alonso-Zarazaga, 2013). It is broadly distributed throughout Albania, France, Hungary, Italy, Portugal, North Africa and Spain, and has colonized the United States, Australia and New Zealand (‍Di Marco & Osella, 2001). Despite being widely distributed in Spain, it had not previously been recorded in Ciudad Real Province (‍Alonso-Zarazaga, 2018).

Otiorhynchus cribicollis is parthenogenetic and its larvae thrive in the roots of Artemisia gallica Willd., Medicago sativa L. and other annual herbaceous plants (‍Hoffmann, 1963). The adults show a strong preference for members of the Oleaceae family (Ligustrum, Siringa, Phillyrea and Olea), although they also attack dozens of wild and cultivated plants (Citrus, Eucalyptus, Prunus, Pyracantha, Pyrus, Rosa, Vitis, etc.) (‍Di Marco & Osella, 2001).

In Spain, O. cribicollis has been described as a secondary pest in olive trees, although it can cause severe damage locally, especially in young trees in late spring (‍Alvarado et al., 1998). Despite its polyphagy, it is the first record on Pistacia. Specimens were found on P. vera in the municipality of Ciudad Real (Fig. 2D), in September, and had devoured the leaves (Fig. 3A) to such an extent that the plot owner sprayed it using the pyrethroid insecticide lambda-cihalotrin.

Polydrusus (Eurodrusus) pilosulus Chevrolat, 1865

This species is endemic to the Iberian Peninsula, where it has been recorded haphazardly but extensively (‍Gurrea & Sanz, 2000). In Castilla – La Mancha, P. pilosulus has been recorded in the provinces of Albacete (‍Gurrea Sanz et al., 1989) and Ciudad Real (‍Iglesias, 1922).

It has been recorded on Q. pyrenaica (‍Sanz & Gurrea, 1995) and Populus sp. trees (‍Ceballos & Dafauce, 1960; ‍Silva et al., 1968). It has also been recorded on Acer monspessulanum L., Cistus ladanifer, C. salviifolius L., Erica scoparia L., Phillyrea angustifolia L., Q. faginea, Q. ilex subsp. ballota, Q. pyrenaica, Q. suber and P. lentiscus in Alcoba (Ciudad Real Province), both in the Cabañeros National Park and in its surrounding areas (‍Fernández-Carrillo, 2013).

In the present study, we encountered P. pilosulus on P. vera in the municipalities of Ciudad Real (Fig. 2E–F) and Pozuelo de Calatrava in Ciudad Real Province, as well as in Villamayor de Santiago in Cuenca Province from April to the end of June.

Polydrusus (Eurodrusus) subglaber Desbrochers des Loges, 1870

This is another native Iberian species, first described from Sierra Nevada, and distributed throughout the southern half of the Iberian Peninsula. Gurrea & Sanz (‍2000) summarized the Iberian records from the Spanish provinces of Albacete, Almería, Granada, Jaén and Málaga, and from the Portuguese province of Beira Litoral. Alonso-Zarazaga (‍2013) reported a similar distribution, in Sierra Nevada and other Baetic and Penibaetic-System mountains. This author also indicates that P. subglaber attacks Q. ilex subsp. ballota. In Extremadura, it has, together with other Curculionidae species, caused damage to the fruit and leaves of plum and peach trees on the Plains of the River Guadiana during spring (‍CADRMAE-Ex, 2015).

This study provides new evidence on the food plant of this species in Villamayor de Santiago, Cuenca, where a large number of specimens were found devouring the leaves and even the bark of the tree trunks and young branches of Pistacia vera (Fig. 3B). This is the first record of P. subglaber on P. vera, where it was causing significant damage. Numerous clutches of eggs were found on the lower side of the leaves throughout May. The majority of the individuals observed and trapped from May to the end of June corresponded to the description of P. variegatus Desbrochers, 1870, which is currently synonymous with P. subglaber (‍Alonso-Zarazaga, 2013; ‍Alonso-Zarazaga et al., 2017). Unlike the typical greenish-scale appearance usually observed (Fig. 2G), the variegatus form is brown with some light checkerboard-like spots (Fig. 2H). Only a small number of the individuals had the typical appearance.

Sitona discoideus Gyllenhal, 1834

Sitona species attack herbaceous or shrub legume crops. Sitona discoideus is an Euro-Mediterranean species introduced into Oceania and America (‍Río et al. 2019). It is common and widely distributed throughout the Iberian Peninsula (‍Velázquez de Castro, 1997), where it attacks Medicago and Trifolium (‍Velázquez de Castro et al. 2007).

Only two specimens have been recorded on the plots surveyed in this work, in May and June, both on P. vera in the municipalities of Ciudad Real and Pozuelo de Calatrava (Ciudad Real) (Fig. 2I). Their presence in pistachio crops is probably due to the use of these plants as a shelter.

Sitona lineatus (Linnaeus, 1758)

Sitona lineatus is widely distributed in the Holarctic Region and Australia (‍CABI, 2019). It is the most commonly found species of Sitona and is broadly distributed throughout the Iberian Peninsula (‍Velázquez de Castro, 1997). It feeds on legumes in Trifolieae and Vicieae tribes (‍Velázquez de Castro et al. 2007).

Some specimens were collected in June on P. vera on plots in the municipality of Ciudad Real (Fig. 2J). As in the case of S. discoideus, this crop is probably used as a shelter by S. lineatus.

LIXINAE Schoenherr, 1823

Lixus (Ortholixus) acicularis Germar, 1823

This taxon is distributed in the west Palaearctic region (‍Alonso-Zarazaga et al., 2017). It thrives on Dittrichia viscosa (L.) Greuter (Asteraceae) (‍Hoffmann, 1954), although it has been recorded on other genera such as Crepis (mentioned as Barkhausia), Hedypnois (‍Hoffmann, 1954), and Senecio (‍Compte Sart, 1982).

It has additionally been found in Cabañeros National Park in the municipality of Alcoba, Ciudad Real Province, on Erica scoparia L. and Cistus ladanifer (‍Fernández Carrillo, 2013).

In the sampling described here, it has been found, from the end of June to August, in the municipalities of Ciudad Real, Los Navalucillos (Figs. 2K, 3C), and Villamayor de Santiago (Ciudad Real, Toledo and Cuenca Provinces, respectively), again, for the first time on P. vera.

Discussion[Up]

Of the eight species discussed in this work, Brachyderes marginellus, B. pubescens and Lixus acicularis have been observed feeding on P. vera leaves, yet causing little damage without having a significant injurious effect on the plant. However, Otiorhynchus cribricollis and Polydrusus subglaber damaged the plants to such an extent that plant development was affected, and plant protection products were required or treatment was planned for the next season, respectively.

With regard to the remaining species, the low numbers detected of specimens of Polydrusus pilosulus, Sitona discoideus and S. lineatus indicate that their presence on P. vera is likely accidental.

Although Castilla – La Mancha’s pistachio crops are considered essentially pest-free, our results show that two of the afore mentioned species do behave as significant defoliators, at least in their adult stage. However, the O. cribricollis specimens were close to irrigated alfalfa and olive tree crops, both of which are host plants, which could have been a predisposing factor for the occurrence of attacks. Moreover, P. subglaber specimens have been found feeding on Q. ilex, as previously reported, and it is, therefore, likely that this species has gradually started moving to pistachio crops and feeding on them.

As the contributions of Sadeghi & Zare (‍2006) made clear, most harmful arthropods associated with wild pistachio plants in Iranian forests are commonly found on cultivated trees. In this way, the enormous growth in the cultivation area in Castilla – La Mancha, together with the use of new agronomical techniques to maximize production, such as irrigation or hybrid rootstocks, might lead to the progressive emergence of new pests or the expansion of those already existing, as had previously occurred in California, which was once considered to be virtually pest-free (‍Daane et al., 2005). Another example can be found in Iran, where the population density and colonization areas for P. davatchii have increased during the last decade (‍Mehrnejad, 2020).

As evidenced by the Official Registry for Phytosanitary Products of the Spanish Ministry of Agriculture, Fisheries and Food (‍MAPA, 2022), there is currently a serious shortage of authorized active substances to treat pistachio crops. It is also worth noting that a large proportion of the area devoted to pistachio cultivation in Spain is farmed organically (currently 44%), thus making it the crop with the greatest share of this differentiated-quality production program (‍MAPA, 2021c). Farmers are consequently confronting significant risks that may rapidly increase over the next few years, and they will have little leeway to respond.

Further research into the identification of potential pistachio defoliators, their natural dispersion conditions and factors affecting population dynamics are, therefore, required. Research into their possible natural enemies is also desirable in order to control their populations if needed.