Deskripsieng
Larvae. Early instar larvae are green and white (Fig. 3) and may be mistaken for the native Kamehameha butterfly, Vanessa tameamea (Escholtz 1821) (Fig. 4 a) or the endemic moth Udea stellata (Butler 1883) (Lepidoptera: Crambidae) (Fig. 5 a) which also use māmaki as a host plant. We have also found tomato looper, Chrysodeixis chalcites (Esper 1789) (Lepidoptera: Noctuidae) (Fig. 6) feeding on māmaki. However, Arcte coerula can be distinguished from these other Lepidopterans by the presence of black dotted markings on the side of its body, thin white setae or hairs, and its defensive behaviors described in the biology and behavior section below. As they develop, A. coerula larvae become more distinctive, with vibrant yellow and black patterning and bright orange-red spots on their sides. There are two color morphs of A. coerula that develop in response to varying population densities which impact the production of a juvenile hormone (JH) analogue (Ikemoto 1984). The black bands on the larva’s body are narrow under solitary conditions, creating a yellow morph larva (Fig. 7 a), and conspicuously widen under crowded conditions, creating a black morph (Fig. 7 b) (Ikemoto 1984). Most larvae collected in Hawaii are the black morph indicating gregarious larval behavior. First instar A. coerula larvae emerge at about 2 mm in length and grow rapidly through five instars, up to 100 mm before pupating. Although previous studies have indicated six larval instars (Ikemoto 1984, Ide 2006), specimens collected in Hawaii typically had only five instars, with occasional larvae going through six or seven molts. Head capsule size was measured after each molt using a microscope micrometer from captive larvae reared from eggs, reported here as mean head capsule width and range: 1 st instar: x = 0.65 mm, 0.45 – 1.10 mm, (n = 25); 2 nd instar: x = 1.26 mm, 0.75 – 2.00 mm, (n = 19); 3 rd instar: x = 2.00 mm, 1.30 – 2.80 mm, (n = 17); 4 th instar: x = 3.12 mm, 2.25 – 3.85 mm, (n = 15); 5 th instar: x = 5.3 6 mm, 5.00 – 6.00 mm, (n = 9). Larval duration averaged about a month from egg emergence to pupation, but duration was variable. Pupa. Larvae pupate in the soil or at the base of the plant in leaf litter. Pupae are an average of 28 mm, 25 – 39 mm, (n = 20) in length (Fig. 8) and take about 13 to 25 days to emerge. Variation in emergence time is likely due to seasonal temperature changes. Adults. Adults are large moths with a forewing length (FWL) ranging from 22 mm to 36 mm (x = 30 mm; n = 20). They have a dark brown head and dark brown forewings with black markings, speckles of silvery-blue, and scalloped termen or wing edges (Fig. 9). Hindwings have distinctive bright silvery-bluish markings which distinguish them from the similarly large black witch moth Ascalapha odorata (Linnaeus 1758) (Lepidoptera: Erebidae) that is also found in Hawaii. Adults reared in captivity had a short lifespan, living no more than a week and sometimes feeding on decaying fruit and sugar water in the cages. There was approximately a 1: 1 male to female ratio. Sex was determined during the pupal stage based on the genital opening on the ventral side of the abdominal segments (Lin et al. 2020). Biology and behavior. In Southern Japan where ramie plants (Boehmeria nipononivea Koidzumi) are grown, A. coerula is multivoltine with populations appearing in the spring and fall with densities peaking in August and September (Ide 2005). Field surveys on Maui and Hawaii island have also shown A. coerula to be multivoltine; however, populations peaked in the spring, from March to May, and decreased dramatically in the summer. Low-density populations of A. coerula can be found throughout the year in Hawaii. Arcte coerula larvae can be distinguished from endemic species on māmaki by their active movements and aggressive defensive behavior. Early instar larvae were observed defensively dropping from leaves when disturbed and moving quickly between leaves on the plant. Arcte coerula does not produce any protective structures, unlike the leaf folding behavior seen in Vanessa tameamea (Fig. 4 b) and silk coverings made by Udea stellata (Fig. 5 b). In later instars, Arcte coerula displays a distinctive, aggressive, defensive behavior when disturbed or threatened. The larva rears up its head and legs, thrashes around, and regurgitates a green liquid to defend itself. Similar behavior was also reported by Jackson and Mua (2016). Damage. Arcte coerula larvae will feed on both young and mature leaves of host plants. Early instars create small holes on the leaves as they feed (Fig. 10 a). In later larval stages, A. coerula larvae create sizable areas of feeding damage and completely strip leaves, leaving only the major veins (Fig. 10 b). We conducted a simple laboratory experiment using 1 - gallon potted māmaki to quantify the extent of damage A. coerula inflicts. Plants were infested with one or two newly hatched A. coerula larvae. Within two weeks, we observed 100 % defoliation and the eventual death of the potted māmaki plants infested with A. coerula larvae by the second or third instar. Adults do not cause any feeding damage to the host plants. Management. There is very little information available on how to manage this pest. In Australia, botanical insecticides (such as neem, derris powder, pyrethrum), insecticidal soaps, and microbial products such as spinosad and Bacillus thuringiensis kurstaki have been used (Jackson and Mua 2016). However, these products are not labeled for use in Hawaii on māmaki plants and are not recommended in Hawaii as they will also impact the endemic Lepidoptera populations that feed on māmaki and other endemic Urticaceae. Classical biological control is potentially the best management strategy for A. coerula.
Sumber: Ramie Moth, Arcte coerula (Lepidoptera: Noctuidae): A New Invasive Pest in Hawaii on Endemic Plants
