ENTOMOLOG!E, 73: 177-180, 2003 SCIENCES NATURELLES DE BELGIQUE BULLETIN DE L'INSTITUT ROYAL DES ENTOMOLOGIE, 73: 177-180, 2003 BULLETIN VAN HET KONINKLIJK BELGISCH INSTITUUT VOOR NATUURWETENSCHAPPEN

Alcedo Population decline of Galapagos endemic Lepidoptera on Volcan (Isabela Island, Galapagos Islands, Ecuador): An effect of the introduction of the cottony cushion scale? by Lazaro ROQUE-ALBELO

preventing both respiration and photosynthesis (JoHNSON Summary et al. in prep. ). f, loss from the impact of By eliminating its food plant, Darwiniothamnus tenuifolius (HooK. Nutrient and plant resource (In­ Asteraceae), the cottony cushion scale, Jcerya purchasi MASKELL I. purchasi may also have a direct effect on other insect may have extirpated three Lepidop­ secta, Homoptera, Margarodidae), species, in particular those that have a narrow host range the east slope of Volcan Alcedo, Isabela Island, tera species from to plants that are heavily infested by Galapagos Archipelago, Ecuador. that are restricted this introduced scale insect. However, no studies have local extinction. Key words: Lepidoptera, exotic species, competition, been published on the impact of I. purchasi on others insect populations in the Galapagos archipelago. In this paper I present data showing the decline of three is the Resume species of endemic Lepidoptera whose host plant endemic composite Darwiniothamnus tenuifolius (HooK. f, En eliminant sa plante bote, Darwiniothamnus tenuifolius (HOOK. by I. purchasi. KELL (In­ f) a species highly affected Asteraceae), Ia cochenille australienne, Icerya purchasi MAS de trois secta, Homoptera, Margarodidae), a cause Ia disparition ile especes de Lepidopteres de Ia pente ouest du volcan Alcedo, d'Isabela, archipel des Galapagos, Equateur. Material and methods : Lepidoptera, especes introduites, competition interspecifi­ Mots-clefs on the east slope of V olean que, extinction locale. The study was conducted Alcedo on Isabela Island from October 1998 to April 2001. Sampling was carried out in the wet (April) and dry seasons (October) at three localities in three different Introduction vegetation zones: Arid Zone (300 m) (dry season decid­ uous forest), Transition Zone (500 m) (evergreen steppe Exotic species introduced into habitats with suitable scrub) and Humid Zone (900 m) (evergreen forest). resources and few native competitors often find condi­ In each altitudinal zone, ultraviolet light traps were tions conducive to rapid population growth. A dramatic used for 3 hours (1900 h to 2200 h). Moths attracted to example of an exotic phytophagous insect which has the light were collected or counted. Reference speci­ invaded and impacted native ecosystems is Icerya pur­ mens are deposited in the Invertebrate collection of the chasi MASKELL (Homoptera: Margarodidae) on the Gala­ Charles Darwin Research Station, Santa Cruz Island, pagos Islands. Commonly known as the cottony cushion Galapagos. scale, I. purchasi is native to Australia but has been Following the arrival of I. purchasi to this area, the introduced accidentally to many parts of the world percentage of infested plants was recorded. (CALTAGIRONE & DoUTT, 1989). Since its introduction To evaluate the occurrence of I. purchasi on D. tenui­ to the Galapagos archipelago in 1982, this species has folius qualitative measures were taken using a value scale invaded at least 15 islands causing damage to at least from 0 (no occurrence) to 3 (very common and plant 82 plant species (ROQUE-ALBELO & CAUSTON, 2000, mortality observed). CAUSTON, 2001 ). Icerya purchasi causes direct damage to its host plants by sucking phloem sap, which in turn depletes resources Results intended for new plant growth. Damage can include branch deformation and plant death (BLUMBERG et al., A reduction of population numbers of three species of 1992). Icerya purchasi also produces large quantities of Lepidoptera associated with D. tenuifolius was observed honeydew, which encourages the growth of sooty moulds between 1998 and 2001 (Table 1). that often cover the leaves, blocking the stomata and thus 178 Lazaro ROQUE-ALBELO

A B

Fig. 1. - Lepidoptera species afected by Jcerya purchasi. a) Semiothisa cerussata, b) Platyptilia vilema, c) Tebenna galapagoensis.

In contrast, following the discovery of I. purchasi on lected on alcedo in 1999, and none have been collected Volcan Alcedo in October 1999, population numbers and since then. This is a new distribution record. This species D. tenuifolius mortality increased markedly from April had been reported only from the volcanoes Darwin and 2000 onwards. Sierra Negra (Isabela Island) and Pinta in the wet season Semiothisa cerussata HERBULOT, 1970 (Geometridae) (LANDRY, 1993). (Fig. 1 a) was only collected in April 1999 (19 speci­ A marked reduction of Tebenna galapagoensis HEPP­ mens). It was collected at all three altitudes. This is a new NER & LANDRY, 1994 (Choreutidae) (Fig. 1 c) was ob­ distribution record. The larvae were very abundant on served during the sampling period. This species was leaves and young branches of D. tenuifolius in the Arid common until 1998. At that time, adults and immature Zone (300m). Since this date, the species has not been stages were collected from the transition zone (500 m), observed. Previously, this species had been reported only T. galapagoensis, was not collected from 1999 onwards. from Santa Cruz and San Cristobal islands where adults In April 1999, I. purchasi was recorded for the first had been collected only in the wet season (January to time on the east slope ofVolcim Alcedo (from 300m to June) (LANDRY & RINDGE, 1995). 600 m). Several plants such as D. tenuifolius and Rhynch­ The large plume moth Platyptilia vilema LANDRY, osia minima (L.) DC. were observed with a few indivi­ 1993 (Pterophoridae) (Fig. 1 b) was only collected in duals of this scale insect. Between then and April 2001 a small numbers from Volcim Alcedo. In October 1998, progressive increase of infestation was observed. Plant five adults were collected and one larva found on leaves death and high levels of infestation were first observed in of D. tenuifolius was reared. Only two adults were col- April 2000. Population decline of Galapagos endemic Lepidoptera on Volcan Alcedo 179

Table I - Abundance of three species of moth associated (CAUSTON, 2003). However, even if I. purchasi is not with D. tenuifolius and I. purchasi at three altitu­ the sole factor responsible for mortality, its effects can dinal sites from 1998- 2001. Numbers associated be fatal to susceptible plant species that are already with moth species indicate numbers of specimens stressed by feral goat damage and prolonged dry periods collected or observed on plants. Numbers for lce­ such as those found ly a purchasi indicate: 0: Not observed; I: Scarse; on Volcan Alcedo. 2: Common but no Dmwiniothamnus tenuifolius Interspecific interactions such as competition is an mortality observed; 3: very common and Dan-vi­ important factor influencing the distribution and abun­ niothamnus tenuifolius mortality observed. dance ofherbivorous insects (CRAWLEY, 1983; DAMMAN, 1993 ; DENNO et al., 1995). Most studies of competition Family 1998 1999 2000 2001 have concentrated on a small number of closely related taxa on the assumption that in these cases resource over­ Species Oct. Apr. Oct. Apr. Oct. Apr. lap is most likely to occur (McCLURE, 1980; KARBAN, 1986). However competition between herbivorous insects Geometridae 0 19 0 0 0 0 can occur even between distantly unrelated taxa (BLAKEY Semiothisa cerussata & DINGLE, 1978). Our results on Lepidoptera and Icetya purchasi pro­ Pterophoridae 5 I I 0 0 0 vide the first documented example of delayed, plant­ Platyptilia vilema mediated interspecific competition between phytopha­ Choreutidae 17 0 0 0 0 0 gous insects in the Galapagos archipelago. The evaluation Tebenna galapagoensis of the impact of I. purchasi on the flora and fauna is no easy matter. The data obtained during our study can only Margarodidae 0 I 2 3 3 3 give a glimpse into its effect on the biota. More field Jce1ya purchasi sampling is clearly needed before any reasonable predic­ tions can be made about the probable local extinction of the species in the localities investigated. However, evi­ dence from this study suggests that the direct conse­ Discussion quence of this competition is an increase in abundance of I. purchasi and a significant reduction in abundance of This study suggests that the virtual elimination of Lepidoptera species associated with D. tenuifolius. This D. tenuifolius in the study localities may have had a reduction is due to the combined effect of habitat destruc­ drastic effect on S. cerussata, P. vilema, and T galapa­ tion and food availability as well as, probably, food goensis. These three species of endemic Lepidoptera have quality. not been collected in light traps since 1999, coinciding It will be interesting to see if D. tenuifolius and its with the arrival and establishment of I. purchasi in the associated lepidopteran fauna will recover in this area study area. It is postulated that these moths are restricted now that Rodolia cardinalis (MULSANT) (Coleoptera, to feed on D. tenuifolius and therefore, they disappear in Coccinellidae) has been purposefully introduced as a its absence. biological control agent for I. purchasi. Data obtained for some indigenous plants in Galapagos showed that the scale insect infestation appear to influ­ ence the levels of nutrients and the vegetative growth of the plants (CAUSTON, 2001). Acknowledgements Some plants species appear to be less susceptible to This paper is dedicated to Charlotte Causton. Her research in the I. purchasi attack (JOHNSON et al., in prep. ). However, Galapagos Islands greatly enhanced our knowledge of the noxious D. tenuifolius is a highly affected species. The IUCN effect of invasive species. Funding for this research was provided by category for this species has been changed recently from Alcedo Funds CDF Inc. A special thanks to Charlotte Causton, Bernard Landry, Scott Henderson, Alan Tye and Chris Buddenhagen for pro­ non-threatened to vulnerable as a result of damage by viding constructive comments on the manuscript. I thank to V. Cruz, I. purchasi (A. Tye, pers comm.). M. Torres, M. Soria, P. Lincango, N. Castillo, R. Boada, G. Estevez, Studies in the Galapagos have shown that it is vety A. Mieles, D. Rosero, C. Calderon, R. Oquendo, S. Rojas and P. Aycart the field assistants at Voldn Alcedo, and our colleagues at the Gala­ difficult to identify in the field whether I. purchasi in­ pagos National Park Service and the Charl es Darwin Foundation for festations are entirely responsible for plant mortality assistance with various aspects of this project. 180 Lazaro ROQUE-ALBELO

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