Observations on an Irruption Event of the Moth Achaea Catocaloides (Lepidoptera: Erebidae) at Kakamega Forest, Kenya
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Journal of East African Natural History 103(1): 31–38 (2014) OBSERVATIONS ON AN IRRUPTION EVENT OF THE MOTH ACHAEA CATOCALOIDES (LEPIDOPTERA: EREBIDAE) AT KAKAMEGA FOREST, KENYA Dino J. Martins Turkana Basin Institute, Stony Brook University N507 Social & Behavioural Sciences, Stony Brook NY 11794, USA Insect Committee of Nature Kenya National Museums of Kenya, Museum Hill, Nairobi P O Box 44486, Nairobi GPO 00100 Kenya [email protected] Scott E. Miller National Museum of Natural History, Smithsonian Institution Washington, DC 20013-7012, USA [email protected] Marina Cords Department of Ecology, Evolution and Environmental Biology, Columbia University 1200 Amsterdam Avenue, New York 10027, USA [email protected] Margaret T. Hirschauer, C. Barret Goodale Kakamega Monkey Project PO Box 2579, Kakamega, Kakamega, Kenya [email protected], [email protected] ABSTRACT The moth Achaea catocaloides Guenee (Lepidoptera: Erebidae, formerly Noctuidae) experiences periodic population irruptions in tropical Africa. Large numbers of adult moths were observed in the Kakamega Forest, Western Kenya in March 2012. Estimated densities of adult moths flying in surveyed forest areas were 6.8 individuals per square metre. Roosting moth density was estimated at 12.7 individuals per 50 cm long branch on two common forest tree species: Croton megalocarpus and Bridelia micrantha. Based on scaled-up data from transect counts we conservatively estimate that this irruption contained 800 million – 1.5 billion moths. The Achaea moths were common throughout the indigenous forest and were being preyed on by birds and monkeys. These population irruptions occur periodically in African forests, but the underlying causes and factors driving them remain undetermined. DNA barcodes of Achaea catocaloides, Achaea catella and Achaea lienardi are provided to facilitate identification of future irruption events. Keywords: irruption, caterpillar outbreak, defoliation by insects, DNA Barcoding, croton 32 D.J. Martins, S.E. Miller, M. Cords, M.T. Hirschauer & C.B. Goodale INTRODUCTION Drastic changes in abundance and population dynamics of tropical Lepidoptera are an interesting phenomenon of seasonal wet-dry environments such as those typical of Eastern Africa (Larsen, 1991). Short generation times and opportunistic behaviour can help insects increase rapidly in numbers and produce observed ‘outbreaks’ when they swarm or migrate locally (Holland et al., 2006). The moth genus Achaea Hubner (Lepidoptera: Erebidae) is well-known for periodic irruptions in tropical Africa, and reports of this phenomenon come from several countries in East and West Africa. Achaea catocaloides Guenee is the species most commonly recorded in this phenomenon. An early record of an A. catocaloides irruption was made by Pitman (1931), at Entebbe in Uganda. This moth was also observed as part of a fruit piercing feeding guild in Sierra Leone (Hargreaves, 1936). This phenomenon was also reported as an annual invasion of Accra, Ghana (Leston, 1979). A ‘moth plague’ was observed in Ghana in 1969, 1972 and 1973 that involved A. catocaloides and the related species A. liernardi (Boisduval) (Grubb, 1980). Achaea catocaloides has also been reported undergoing population explosions in Nigeria, including feeding on cultivated crops (maize Zea mays L. and cassava Manihot esculenta L.) (Eluwa, 1977). A study of defoliation in cocoa (Theobroma cacao L.) plantations in Cameroon found that ants were able to limit the effects of this moth (Dejean et al., 1991). Achaea catocaloides was documented defoliating a rainforest tree (Paraberlinea bifoliolata Pellegr.) in Gabon where large number of caterpillars were observed feeding on the trees and leaving trees by means of silken threads to pupate in the leaf litter below (Maisels, 2004). In late 2008 and early 2009, a very large irruption of Achaea catocaloides occurred in Liberia and Guinea. The 2009 event was so large that a national emergency was declared in Liberia because of crop damage and contamination of water supplies, capturing considerable attention from international news media (CABI 2009; G. Goergen, pers. comm., 2009). We describe some observations of an irruption event in the Kakamega Forest, Kenya. The Kakamega Forest is a relict tropical rainforest fragment situated in western Kenya (0°19’N 34°52’E; ~1580 m). It is the last large area remaining in Kenya of the Guinea-Congolian rainforest that was once connected to the rainforests of the Congo Basin and Central Africa. The main block of forest (23 777 ha in 2003) includes two nature reserves and a national reserve, and comprises mixed vegetation types including near-natural and secondary forest, bushland, grassland and agricultural land. Natural forest covers 50% of this area (Mitchell et al., 2009). We base our estimates of natural/indigenous forest on these data as ~11 000 ha. Annual rainfall averages 1915 mm. Rain falls seasonally, typically with two annual peaks and a pronounced dry season from December through February (Bennun & Njoroge, 1999; Mitchell et al., 2009). We do not have comprehensive records of previous irruptions at Kakamega, but we know that one occurred in 2001, with moths emerging in late May. J.M. Wathihi, District Forest Officer, reported (pers. comm. to Miller, 2001) defoliation of Bischofia javanica Blume, Cupressus lusitanica Mill., and pines (Pinus sp.) in Kakamega forest, and provided voucher specimens to National Museums of Kenya and the Smithsonian Institution. These were confirmed as Achaea catocaloides. Achaea is a diverse genus of global distribution. The African taxa were reviewed by Berio (1965), who enumerated 35 species. Until recently, Achaea was placed in the Noctuidae, subfamily Catocalinae. Based on molecular studies that led to the extensive reclassification of the former Noctuidae, Achaea is now placed in the Erebidae, subfamily Erebinae (Holloway & Miller 2003; Holloway 2011). Here we report observations of an Achaea catocaloides irruption that occurred in the Kakamega Forest in western Kenya in March and April 2012. We include estimates of adult Irruption event of Achaea catocaloides 33 A. catocaloides abundance, which have not been made previously. We also report on the predation of the adult moths by birds and mammals in the forest. MATERIALS AND METHODS Observations of the moth Achaea catocaloides were made in March and April 2012 in the Isecheno area of the Kakamega Forest. The peak of the adult moth irruption occurred from approximately 18 March to 3 April 2012. Detailed observations on abundance were made between 25 March 2012 and 1 April 2012. The presence of moths in large numbers was recorded at multiple sites in the forest during the observation period (figure 1). Figure 1. Sites (indicated by closed circles) at Kakamega Forest where abundance of A. catocaloides was quantified between 25 March–3 April. (a) location where large numbers of eggs were observed on March 1, and moths peaked on 18–22 March. (b) Moth abundance peaks here 18–22 March. (c) Moth abundance peaks here 25 March–3 April. Note our assessment of ‘peak abundance’ is based on general observations that were conducted on a daily basis by field teams spending c. 9 hrs per day in the forest. Scale bar is 1 kilometre. Image courtesy of GoogleEarth. KFS = Kenya Forest Service HQ at Isecheno. To estimate the local abundance of moths, we used two counting methods: short transects and beating of tree branches where moths were roosting. Transect estimates consisted of DJM walking slowly for 10 m and counting all moths flying across the transect area (a 1 m band) using a hand-held counter. This was repeated 5 times at each of five different sites (Rondo stream trail, junction to Lirhanda Hill, base of Lirhanda Hill, River Yala trail and along the main road through the forest; figure 1). Beating involved a gentle tap of a ca. 50 cm long branch of each of 2 common tree species in the forest (Bridelia micrantha (Hochst.) Baill. and Croton megalocarpus Hutch. (identified using Beentje [1994]) and counting the number of moths that flew out. Each branch was tapped only once so as to estimate the number of moths on that branch alone and not startle moths roosting in surrounding vegetation. This procedure was repeated 20 times for each plant species. We used transect and beating data to derive estimates of the abundance of A. catocaloides in the forest as a whole. Data were analysed with Microsoft Excel Version 14.2.4. 34 D.J. Martins, S.E. Miller, M. Cords, M.T. Hirschauer & C.B. Goodale We observed predators feeding on the moths at the five counting sites while conducting transects and walking through the forest. Blue monkeys also were observed by three of us (DJM, MTH & CBG) feeding on the moths at other nearby sites (figure 1) that are part of a long-term primate monitoring project in Kakamega Forest (Cords, 2012). Specimens were collected to confirm identification and these have been deposited as vouchers in the collections of the Smithsonian Institution and the National Museums of Kenya. Identity of specimens from the 2001 Kakamega irruption was confirmed by male genitalia (USNM slides 92502 and 125566, figure 2) using Berio (1965). COI (cytochrome oxidase I) sequences were generated at the Biodiversity Institute of Ontario, University of Guelph using standard DNA barcoding protocols (Miller, 2007; Craft et al. 2010). Figure 2. Details of Achaea catocaloides. A. Representative adult specimen of A. catocaloides from West Africa. Scale bar is 10 mm. B. Main part of male genitalia from slide USNM 92502. C. Vesica from slide USNM 125566. D. Group of moths at light photographed at 7 am, 02 April 2012. E. Adult A. catocaloides at rest near a light at Kakamega Forest, Kenya. Scale bar is 10 mm. Irruption event of Achaea catocaloides 35 RESULTS AND DISCUSSION On 1 March 2012, an unusual number of thin white lepidopteran eggs was noted in the forest, attached in large numbers to one side of dead leaves on the forest floor. We assume that these eggs were laid by earlier numbers of Achaea catocaloides moths, but this was not monitored directly as the irruption event had not yet peaked and attracted our attention.