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Late Pliocene and Quaternary Eurasian locust infestations in the Canary Archipelago JOAQUIŃ MECO, DANIEL R. MUHS, MICHEL FONTUGNE, ANTONIO J.G. RAMOS, ALEJANDRO LOMOSCHITZ AND DEANNA PATTERSON

Meco, J., Muhs, D.R., Fontugne, M., Ramos, A.J.G., Lomoschitz, A. & Patterson, D. 2011: Late Pliocene and Quaternary Eurasian locust infestations in the Canary Archipelago. Lethaia, Vol. 44, pp. 440–454. The Canary Archipelago has long been a sensitive location to record climate changes of the past. Interbedded with its basalt lavas are marine deposits from the principal Pleistocene interglacials, as well as aeolian sands with intercalated palaeosols. The palaeosols contain African dust and innumerable relict egg pods of a temperate-region locust (cf. Dociostaurus maroccanus Thunberg 1815). New ecological and stratigraphical information reveals the geological history of locust plagues (or infestations) and their palaeoclimatic significance. Here, we show that the first arrival of the plagues to the Canary Islands from Africa took place near the end of the Pliocene, ca. 3 Ma, and reappeared with immense strength during the middle Late Pleistocene preceding MIS (marine isotope stage) 11 (ca. 420 ka), MIS 5.5 (ca. 125 ka) and probably during other warm interglacials of the late Middle Pleistocene and the Late Pleistocene. During the Early Holocene, locust plagues may have coincided with a brief cool period in the current interglacial. Climatically, locust plagues on the Canaries are a link in the chain of full-glacial arid–cold climate (calcareous dunes), early interglacial arid–sub-humid climate (African dust inputs and locust plagues), peak interglacial warm–humid climate (marine deposits with Senegalese fauna), transitional arid–temperate climate (pedogenic calcretes), and again full-glacial arid–cold climate (calcareous dunes) oscillations. During the principal interglacials of the Pleistocene, the Canary Islands recorded the migrations of warm Senegalese marine faunas to the north, crossing latitudes in the Euro-African Atlantic. However, this northward marine faunal migration was preceded in the terrestrial realm by interglacial infestations of locusts. h Locust plagues, Canary Islands, Late Pliocene, Pleistocene, Holocene, palaeoclimatology. Joaquıń Meco [[email protected]], Departamento de Biologıá, ULPGC, 35017 Las Palmas, Canary Islands, Spain; Daniel R. Muhs [[email protected]], US Geological Survey, MS 980, Box 25046, Federal Center, Denver, 80225 Colorado USA; Michel Fontugne [[email protected]], Laboratoire des Sciences du Climat et de l’Environnement, LSCE-CNRS, 91198 Gif sur Yvette, France; Antonio J.G. Ramos [[email protected]. ulpgc.es], Estacioń Espacial SEAS Canarias. ULPGC, 35017 Las Palmas, Canary Islands, Spain; Alejandro Lomoschitz [[email protected]], Departamento de Ingenierıá Civil, ULPGC, 35017 Las Palmas, Canary Islands, Spain; DeAnna Patterson [dpatterson@ usgs.gov], ATA Services, Inc., 165 South Union Blvd., Suite 350, Denver, 80228 Colorado, USA; manuscript received on 30 ⁄ 08 ⁄ 10; manuscript accepted on 06 ⁄ 10 ⁄ 10.

The Canary Islands (Fig. 1) have long been a place of importance for the study of past climate changes (Meco et al. 2003) because of their location in the North Atlantic Ocean. This ocean exercises a dominant control in the variations of Earth’s climate through its role in global ocean circulation. The Canary Islands are bathed by the Canary Current, the cold, southward-returning arm of the warm, northwardflowing Gulf Stream, both part of the north sub-tropical gyre. Since its inception after the formation of the Isthmus of Panama (Early Pliocene), this sub-tropical gyre has influenced the climate of the islands during the Late Pliocene and the Quaternary. The latitude of the islands (28N to 30N), midway between Arctic and tropical waters and on the Atlantic border along the Saharan coast, has resulted in geological records of

Late Pliocene and Pleistocene oscillations of the Arctic polar front (marine and aeolian deposits: Meco et al. 1992, 1997, 2002) and the intertropical convergence zone (ITCZ) of Africa (humid-climate palaeosols: Petit-Maire et al. 1986). The Canary Islands are situated in a zone where there are collisions of Atlanticgenerated and African-generated winds, governed by the oscillations of the sub-tropical Azores anticyclone and the African monsoons. In addition, ongoing Canary Islands volcanism, active since the Miocene (Carracedo et al. 2002), produces lavas intercalated with climatically generated marine and aeolian deposits, allowing extensive age control that few other localities have. Evidence for past locust plagues (infestations) recorded on the Canary Islands provides a new

DOI 10.1111/j.1502-3931.2010.00255.x 2010 The Authors, Lethaia 2010 The Lethaia Foundation

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Fig. 1. Geographical location of the Canary Islands. A, the Islands as viewed from OrbView-2 SeaWiFS satellite and the ODP (Ocean Drilling Programme) 658 core (Rimbu et al. 2004) off the African coast. Brown colouration represents high concentrations of suspended African dust. Note the boundary between dust (African influence) and clouds (Atlantic influence) observed in the image. B, location of key palaeoclimatic sites marked by black dots.

Tertiary and Quaternary palaeoclimatic indicator (Meco et al. 2010) in addition to the classical proxies of glacial deposits, loess, pollen, foraminifera, and tropical corals. Here, we present new data on the geological records of locust plagues and elucidate a new palaeoclimate interpretation. In the Canary Islands, plagues of locusts are repeatedly recorded in the Holocene and Pleistocene, even reaching as far back as the Pliocene.

Ecology The trace fossils we identify as locust egg pods on the Canary Islands are durable but hollow, ellipsoidal features composed of materials that appear to be

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identical to the surrounding soil or sediment. Typically, these features are ca. 1 cm wide and usually 2– 3 cm long, open at one end and closed at the other end. On the Canary Islands, they occur in astonishing numbers in surficial deposits and have intrigued researchers for more than a century. Previous workers have identified them as having been formed by bees (Hymenoptera; see Aranda Millań 1909; HernańdezPacheco 1909; Edwards & Meco 2000; Von Suchodoletz et al. 2009), or more specifically Ichneumonidae (Ellis & Ellis-Adam 1993; Alonso-Zarza & Silva 2002). Other workers proposed that the features formed from Coleoptera (Genisse & Edwards 2003) or both Hymenoptera and Coleoptera (Ortiz et al. 2006). In a departure from previous interpretations, Meco et al. (2010) proposed that these remarkable features are more likely the egg pods of a species of Acrididae. Comparison of the ellipsoidal features, both of Pliocene and Pleistocene age, with modern features indicates that they are most likely egg pods of the temperate-zone Moroccan locust, Dociostaurus maroccanus Thunberg 1815 (Fig. 2). At present, D. maroccanus lives in a wide latitudinal band centring on 30N in northern Africa, southern Europe, the Middle East, and central Asia (Uvarov 1948; Latchininsky 1998), including the Canary Islands and Madeira (Fig. 3). Female locusts from temperate regions, such as D. maroccanus lay eggs in pods in soils that have sufficient quantities of fine-grained particles (silts and clays). Secretions from accessory glands and oviduct of the female locust provide the cement for soil particles that constitute the ‘shell’ of the egg pod (Latchininsky 2010). Fossil egg pods that we have examined contain secondary carbonates, derived from local bioclastic dune sand that, in addition to African dust, constitutes the soil and palaeosol parent material. Although the size and shape of the fossil egg pods are very similar to modern egg pods of D. maroccanus (Meco et al. 2010), the fossil egg pod morphology is quite unlike those of other locusts, such as Schistocerca gregaria, a resident of the Sahel region of Africa (although this is a species that can travel significant distances). D. marocanus has only one generation per year and its embryos spend about 9 months of the year in the soil-hosted egg pod (Latchininsky 1998). We hypothesize that soil clays and carbonates aid in forming the shell of the egg pod, forming a durable, protective soil sheath, a survival strategy for eggs that must endure a long period in the soil environment. Although the Canary Islands are composed dominantly of basalt overlain by carbonate-rich aeolian sands or marine deposits, fine-grained materials are periodically added to soils of the islands during dust storms that originate in Africa (see review in Muhs

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Fig. 2. Modern and fossil egg pods from locusts. A, modern egg pods of the Moroccan locust, Dociostaurus maroccanus, from Uzbekistan (photo courtesy of Alex Latchininsky). B, fossil locust egg pods from a Pleistocene palaeosol at Mala, Lanzarote (Fig. 1). C, detail of fossil locust egg pod from Late Pleistocene palaeosol, Istmo Jandıá locality, Fuerteventura (Fig. 1). D, fossil locust egg pods in the youngest Pleistocene palaeosol, some of which were attacked by predators, also from Istmo Jandıá locality, Fuerteventura.

et al. 2010). In Figure 3, we show many of the important dust sources in Africa and the Middle East (derived from satellite imagery interpretation and maps in Prospero et al. 2002), along with dust-transport trajectories. Canary Islands soils that have developed on aeolian sands (Williamson et al. 2004), alluvium (Von Suchodoletz et al. 2009) and basalt (Muhs et al. 2010) all contain fine-grained, exotic minerals that demonstrate the importance of these dust sources and transport pathways to soil genesis and egg pod formation. We hypothesize that the timing of the locust infestations we document here is related to the alternation of arid climates (deserts and steppes) and maritime climates with dry or sub-humid summers. Climatic oscillations, produced by shifts in the position of the ITCZ, generate changes in vegetation and circulation that apparently affect locust populations.

Stratigraphy Pliocene The oldest marine deposits in the Canary Islands (Fig. 4) date to the beginning of the Pliocene and their fossil fauna, dominated by extralimital southern (tropical) corals, indicates a very warm climate at that time (Meco & Stearns 1981; Meco et al. 2007). During a subsequent marine regression, bioclastic dunes, rich in shell carbonates (Meco et al. 1997), were formed from what are at present offshore sources. Dunes were capped by a palaeosol (Fig. 5) that contains evidence of the first arrival of what we interpret to be African dust inputs and occurrence of locust plagues on the island. Preserved in amazing quantities in this palaeosol are trace fossils of locust egg pods (Figs 6, 7).

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AFRICA Arabian Sea Geographic range of Dociostaurus maroccanus (Latchininsky, 1998)

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Fig. 3. Distribution of modern Dociostaurus maroccanus (red circles; redrawn from Latchininsky 1998), major dust source areas (brown shades; from Prospero et al. 2002) and inferred dust-transport directions (from the present authors), taken from modern satellite (MODIS) imagery, courtesy of NASA.

Fig. 4. The Istmo Jandıá locality, Fuerteventura, Canary islands. A, Miocene basalt. B, marine deposit (4.8 Ma). C, Pliocene dune. D, the oldest Pliocene palaeosol with fossil locust egg pods (>2.9 Ma). E, the last Pliocene palaeosol with fossil locust egg pods. F, Early Pleistocene calcrete.

The relation of the earliest Pliocene palaeosol with dated lavas allows us to place it near the end of the Pliocene, somewhat earlier than 2.7–2.9 Ma at a locality called La Cruz (field no. FUE-76-20: Meco & Stearns 1981; table 1, p. 200) and elsewhere (samples 491-5 and F-11-C: Coello et al. 1992; table 3, p. 260). Stratigraphical data indicate that this palaeosol certainly formed much later than 4.8–5.8 Ma, based on data

from a locality near Ajui (field no. FUE 76-1: Meco & Stearns 1981; table 1, p. 200; sample 488–4: Coello et al. 1992; table 3, p. 260; sample FV-38, Meco et al. 2007; table 1, p. 227) (Figs 4–7). An episode of locust infestations (interpreted as hymenopteran nests) appears in sediments that are preserved between lavas at Los Ma´rmoles (Hausen 1962, p. 245 and fig. 22) and West Arucas, dated at 3 Ma and 2.91 Ma (Field

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Fig. 5. The Istmo Jandıá locality, Fuerteventura, Canary Islands: detail of the section showing the position of the oldest palaeosol (black arrow) between Pliocene dune sands.

no. GCR-49 and GCR-48: Guillou et al. 2004; table 5, p. 233). Another locust infestation occurred later than 2.8 Ma (sample FVKA 02, lava under calcrete: Meco et al. 2004; table 1, p. 97) but prior to the formation of a younger pedogenic calcrete that marks the beginning of the Pleistocene on the Canary Islands. This locust infestation is constrained to the latest Pliocene to early Pleistocene by a lava dated to 0.83 Ma (sample F-68-AC: Coello et al. 1992, table 3, p. 260) that flowed down a ravine that in turn cut through the calcrete. These earliest estimated ages of locust infestations correspond to the beginning of major Arctic ice buildup (Lunt et al. 2008), the inception of the cold Canary Current, and increased seasonality in latitudes centering on 30N. This time also marks the gradual disappearance of the equatorial climate in the Canary Islands, a cooling trend that had begun with the formation of the Isthmus of Panama (Haung & Tiedemann 1998; Ravelo et al. 2004). The Early Pliocene marine deposit of Fuerteventura contains a warm fauna represented by Strombus

coronatus Defrance, Saccostrea virleti (Deshayes), Nerita emiliana Mayer, all species of the equatorial seas, and species characteristic of the Mio-Pliocene, such as Ancilla glandiformis Lamarck and Hinnites ercolaniana Cocconi (Meco & Stearns 1981; Meco et al. 2007). Above this marine deposit a calcareous dune deposit contains Theba pisanopsis (Servain), a temperate species of land snail (Meco et al. 2004), in turn overlain by the oldest Pliocene palaeosol with fossil locust egg pods, still-younger dune deposits, the youngest Pliocene palaeosol with fossil locust egg pods, all capped by a calcrete. At Istmo Jandıá, a representative section can seen (Figs 4–7). We interpret the succession of marine sediments with a tropical fauna overlain by aeolian sand deposits with temperate-climate land snails as recording gradual cooling in the terminal Pliocene (Fig. 8).

Pleistocene Palaeontological, stratigraphical and chronometric information shows that during the Early Pleistocene

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Fig. 6. The Istmo Jandıá locality, Fuerteventura, Canary Islands: detail of the oldest Pliocene palaeosol showing the great number of fossil locust egg pods.

and the early Middle Pleistocene, there was a period of intense erosion such that locust egg pods do not appear in the geological record of the Canary Islands. An example of this erosive period is seen in the formation of ravines truncating the Pliocene calcrete, described above. Nevertheless, the geological record of fossil egg pods resumes during a major interglacial period in the mid-Pleistocene, when there was an accentuation of Pleistocene climate oscillations. Along the coasts of the Canary Islands, Middle and Late Pleistocene interglacial marine deposits are well characterized by their warm-water faunas and are situated above palaeosols containing fossil locust plagues and probably African dust as seen in inland palaeosols and modern soils. At Arucas on Gran Canaria Island (Fig. 9), a palaeosol with innumerable fossil locust egg pods underlies a marine deposit that is ca. 30 m above present sea level. The marine deposit contains S. cucullata (Born), a species that at present lives in the Gulf of Guinea but no farther north than the Canary Islands. The

deposits also host other species that represent the debut of the modern interglacial marine fauna of the waters around the Canary Islands. Both the marine deposit and palaeosol lie immediately above a lava dated to 0.421 Ma (sample GC-04: Meco et al. 2002; table 1, p. 201) although previous ages of 0.548 Ma and 0.529 Ma (sample P5: Lietz & Schmincke 1975; table 1, p. 215) have also been reported. This 0.421 Ma volcanic flow is a pillow lava, indicating deposition in a submarine environment. Submarine deposition indicates that sea level was already high and that the age of the lava is a very close estimate for the age of the superjacent marine deposits. The marine deposit and palaeosol are stratigraphically beneath a younger lava that is dated to 0.151 Ma (sample GC-03: Meco et al. 2002; table 1, p. 201), although previous ages of 0.297 Ma and 0.326 Ma have also been reported (sample P6: Lietz & Schmincke 1975, table 1, p. 215). Based on the stratigraphy and the constraining ages of the bracketing lavas, we interpret the marine deposit to represent the

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Fig. 7. The Istmo Jandıá locality, Fuerteventura, Canary islands: detail of the oldest Pliocene palaeosol showing fossil locust egg pods.

Fig. 8. Estimates of Pliocene SST (Sea Surface Temperature) at Equatorial Atlantic (in red from Herbert et al. 2010) modified with the locust plagues in the Canary islands using stratigraphical and chronometric data (in black). Note that locust plagues are not present during the warmest and coldest climates.

high sea stand recorded as marine isotope stage (MIS) 11 (ca. 400 ka), thought to be a major interglacial of the Middle Pleistocene.

At Piedra Alta, along the southwestern coast of Lanzarote (in the eastern Canary Islands), a deposit ca. 20 above the present sea level is attributed to a tsunami (Meco et al. 2006). Evidence for a tsunami-generated deposit comes in the form of a highly diverse mixture of fossils of both terrestrial origin and marine origin. The deposit contains pedogenic calcrete fragments, fossil locust egg pods, shells of land snails, and marine molluscs and corals derived from habitats spanning a wide range of depths. Included in the marine fauna are species such as S. cucculata (Born) and Senegalese (extralimital southern) species such as Purpurellus gambiensis (Reeve), both of which indicate an interglacial period. This marine deposit is positioned between lavas dated to 0.82 Ma (Field no LZ 75-2: Meco & Stearns 1981; table 1, p. 200) and 0.196 Ma (H. Guillou, personal communication, 2006) and above a palaeosol with innumerable fossil locust egg pods. Based on this stratigraphical position, the marine deposits are tentatively interpreted to represent one of the high sea stands in MIS 9 (ca. 300 ka) or MIS 11 (ca. 400 ka). Although the bracketing lava ages would

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Fig. 9. The Arucas locality, Gran Canaria, Canary Islands. A, Mid-Pleistocene palaeosol with fossil locust egg pods. B, marine deposits (marine isotope stage 11, ca. 420 ka) (Meco et al. 2002).

also permit correlation with an older interglacial period, we prefer a correlation to MIS 9 or 11. It is likely that older interglacials were not sufficiently warm for the survival of the Senegalese fauna, based on global records of pre-MIS 11 interglacial periods (EPICA Community members 2004). Marine deposits that probably date to the last interglacial period (ca. 125 ka; equivalent to MIS 5.5) are found on several of the Canary Islands (Meco et al. 1997, 2002, 2006; Zazo et al. 2002). Existing chronological data for these deposits are mostly U-series ages of molluscs (Zazo et al. 2002), which are known to be unreliable materials for this technique (Kaufman et al. 1971). Nevertheless, elevations, stratigraphical position and amino acid ratios in molluscs from these deposits suggest strongly that the deposits correlate to the last interglacial period (Meco et al. 1997; Zazo et al. 2002). The deposits contain Harpa rosea Lamarck, S. bubonius Lamarck, Siderastrea radians (Pallas) and other extralimital southern species found no farther north than the Gulf of Guinea and the Cape Verde Islands (Meco et al. 2002, 2006). On Lanzarote, at Punta de Penedo and on the west coast of the La Graciosa Island, there is a palaeosol with abundant fossil egg pods that occurs stratigraphically below the marine deposits of

probable last interglacial age (Meco et al. 2006). We interpret this palaeosol to represent the earliest part of the last interglacial period, when aeolian sand deposition of the penultimate glacial period (MIS 6) had ceased, but just before sea level rose above present during the peak warmth of the last interglacial (MIS 5.5). In addition to Pleistocene records on the coasts of the Canary Islands, there are detailed records of locust infestations found in landward aeolian sand sections. Unfortunately, age control at these localities is lacking. Inland at Mala, Los Lajares and Istmo Jandıá (Figs 10–12), palaeosols, containing 10–40% fine silts and clays, likely derived from African dust (Williamson et al. 2004; Von Suchodoletz et al. 2009, 2010; Muhs et al. 2010), are intercalated with highly calcareous (80–95% CaCO3) dune sediments. Attempts to date these deposits have given highly divergent results. At the Mala section, luminescence ages reported by Bouab (2001), also given in Meco et al. (2006), suggest that most of the section is no younger than Middle Pleistocene. In contrast, apparent radiocarbon ages reported by Ortiz et al. (2006) suggest that the entire section is Late Pleistocene. Age estimates by both methods are open to question. The

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Fig. 10. Stratigraphy, locust egg pod frequency, and abundance of non-carbonate minerals, mostly fine silts and clays (