Indian Journal of Marine Sciences Vol. 32(3), September 2003, pp. 237-239 Short Communication Insect foliovory in mangroves K. Kathiresan Centre of Advanced Study in Marine Biology, Annamalai University, Parangipettai 608 502, Tamil Nadu, India [ E-mail : [email protected]; cdl [email protected] ] Received 1 October 2002, revised 3 April 2003 The insects cause extensive damages to mangrove leaves. The damages are visibly seen as holes, galls, necrotic spots, and incursions occurring along leaf margins. The predominant insect species are leaf-mining moth (Phyllocnistis sp.), leaf gall species (Stephaniella falcaria, Monolepta sp.), caterpillars (Dasychira sp., Capua endocypha and Odites spp.) and scale insects (Aspidiotus destructor). Avicennia species suffer more leaf damage than do Rhizophora species. This correlates negatively with tannin concentration in the leaves. [ Key words : Insect, Mangroves, Rhizophora, Avicennia, foliovory, herbivory] Insects inflict an extensive damage to mangrove January to December 2002, on the insects that existed leaves, and in extreme cases even kill the mangrove in the forests. Insects were identified following the trees1. Very little information on this aspect is keys given by Murphy6. available in India2-4. The insect-induced damage needs The common damages encountered in mangrove to be assessed in the mangroves that are ecologically leaves are holes, galls and miner attack in Avicennia very sensitive systems. In the absence of such data, it spp., necrotic spots in Ceriops decandra and is difficult to manage health of the systems, and Rhizophora spp., and incursions occurring along leaf hence, is this study. margins of Bruguiera cylindrica. In general, the Fifty leaves from each of ten species (Avicennia incidence of insects was found to be abundant during officinalis L., Avicennia marina (Forsk.) Vierh., postmonsoon months. Murphy7 described 102 insect Lumnitzera racemosa Willd., Rhizophora mucronata herbivores that attack 21 mangrove species in Poir., Rhizophora apiculata Blume, Aegiceras Singapore. Veenakumari et al.4 listed l97 species of corniculatum (L.) Blanco, Bruguiera cylindrica (L.) Bl., herbivores on the Andaman and Nicobar Islands; Rhizophora annamalayana Kathir., Excoecaria some of the insect herbivores are serious crop pests agallocha L., Ceriops decandra (Griff.) Ding Hou,) that simply use mangroves as alternative hosts. A few were randomly collected as monthly samples for three dominant species of insects observed in the present months during the postmonsoon period from January study are briefed here. to March 2002 from Pichavaram mangrove forest (lat. 11°27′N; long. 79°47′E), southeast coast of India. The scale insect that often attacks seedlings of Outline of leaves was drawn on graph sheet. When Rhizophora mucronata Poir. was identified as edges of a leaf were missing, leaf margins were Aspidiotus destructor (Hemiptera, Diaspidiae). The visually reconstructed by extrapolating from the intact scale insect affects leaves first and shows a yellow margins. Necrotic spots and holes enclosed within the discolouration around areas of the sucking activity leaf were also marked on the graph sheet. Then the followed by brown necrosis. In extreme cases, the number of squares occupied by the leaf and by each leaves dry up, drop off, and the whole seedlings die. damage type was counted. The per cent damage The scales of the female are circular, flat, transparent, caused by insects was calculated as leaf area damaged whitish to grey white and about 1.8 mm in diameter. divided by total leaf areas multiplied by 100. The The scales of male are oval and much smaller than leaves of the same samples were washed thoroughly that of the female. The female insects deposit about and estimated for the content of total tannins 20-25 yellow, tiny eggs under her scale. After a week, following the method of Hagerman & Butler5. A field the eggs hatch, and the crawlers start feeding on the observation was made for a period of one year from leaf. 238 Indian J. Mar. Sci., Vol. 32, No. 3, September 2003 The caterpillar, 'tussock-moth' larvae with most Rhizophoraceae. These reports did not show any distinct median dorsal tufts (Dasychira sp. specific relation between a particular chemical and Lepidoptera, Lymantriidae), is very common and intensity of insect damage in the mangrove foliage. causes severe damage to leaves of Rhizophora spp. To fill this gap, the present study shows a specific Larva pupates among foliage in a loose cocoon. Male negative correlation (r=0.91) between tannin content insects have a wingspan of 22 mm and the females are of mangrove leaves and damage inflicted by much larger, paler and perhaps are more foliovores. Avicennia species that have lower content conspicuously patterned. Other common caterpillars of tannins, exhibit higher damage by foliovores on Rhizophoracean members are Capua endocypha (Table 1). The reverse is true with Ceriops decandra, (Lepidoptera, Tortricidae) and Odites spp. Excoecaria agallocha and Rhizophora annamalayana (Lepidoptera, Lethicoceridae). Capua endocypha wherein the content of tannins is higher and the leaf usually attacks the leaf buds before opening and then damage is lower. extends attack to newly expanding leaves, which are Besides tannin, high leaf toughness, measured as webbed together. Mature leaves are grazed by leaf the ratio of protein to fiber, may reduce palatability webbing caterpillars of Odites spp. A leaf-mining and digestibility of insects10. Differences in salt moth Phyllocnistis species (Lepidoptera, content of leaf may also restrict foliovores. Newbery11 Gracillariidae) attacks all the species of Avicennia. suggested that the exudates of concentrated salt The moth makes silvery mines on the upper surface of solution on the leaf surface of Avicennia marina young expanded leaves. Larvae are without legs and discouraged establishment of coccoids on leaves. non-feeding instar. Avicennia spp. show leafy galls of However, in the present observation, Avicennia Stephaniella falcaria (Diptera, Cecidomyiidae). species that excrete salts on the leaf surface do not The leaf damage was found maximum in Avicennia discourage the establishment of herbivores. A similar spp. and minimum in Ceriops decandra, Excoecaria result was obtained with phylloplane fungi, which agallocha and Rhizophora annamalayana (Table 1). were higher in Avicennia species than in other This differential leaf damage has been attributed to mangrove species12. leaf chemistry. Lacerda et al.8 found that leaves of Avicennia schaueriana differed significantly from The caterpillar Nephpterix syntaractis completely defoliates Avicennia marina, severely reducing the Rhizophora mangle in several chemical features like Na, N, phenols, ash, carbohydrates and fibers, and reproductive output of the trees during summer in Hong Kong13. Kandelia candel in the same region that A. schaueriana exhibited significantly higher 14 levels of herbivory than R. mangle. Ghose et al.9 also experiences 35% defoliation . In Belize, Central found interfamilial differences in the levels of lipid, America, an outbreak of the lepidopteran Phocides sterol and triterpene between Avicenniaceae and pigmalion increased leaf abscission rates and reduced above-ground net production by 5-20 % on Rhizophora mangle15. This damage from feeding Table 1 — Damage caused by foliovores and tannin content of mangrove leaves (Critical difference at 1% level is 0.15 for herbivores could also invite further attack. leaf damage and 1.3 for tannin) In the present study, insects cause about 1 to 12 % Mangrove species Leaf area Total soluble of leaf damage (Table 1). The leaf damage caused by damage (%) tannin herbivores could substantially influence growth and (mg.g-1 dry wt.) productivity of the mangroves. However, this is a Avicennia officinalis 12.04 5.56 natural process and is of ecological significance in a A. marina 9.28 5.54 detritus-based mangrove ecosystem. In general, a Lumnitzera racemosa 3.13 8.56 quick recovery after insect damage is also observed. It Rhizophora mucronata 2.69 11.06 is not clear that whether controlling the insects in the R. apiculata 2.64 12.84 natural system is necessary, and that up to what level Aegiceras corniculatum 2.37 12.88 the natural infection of insects can be allowed to Bruguiera cylindrica 2.31 12.96 manage the health of mangroves. Above all, studies Rhizophora annamalayana 0.83 15.80 pertaining to biology and taxonomy of many insects Excoecaria agallocha 0.75 15.98 in mangroves are very poor, and the insect species Ceriops decandra 0.74 16.78 have not been mostly identified properly. Hence a Critical difference at 1% level 0.15 1.30 special attention on these issues is highly warranted. Short communication 239 References 8 Lacerda L D De, De Rezzende C E, Francisco M C R, 1 Kathiresan K & Bingham B L, Biology of mangroves and Wasserman J C & Martins J C, Leaf chemical characteristics mangrove ecosystem, Adv Mar Biol, 40 (2001) 81-251. affecting herbivory in a New World mangrove forest, Biotropica, 18 (1985) 350-355. 2 Kathiresan K, Foliovory in Pichavaram mangroves, Environ 9 Ghose A, Misra S, Dutta A K & Choudhury A, Pentacyclic Ecol, 10 (1992) 988-989. triterpenoids and sterols from seven species of mangroves, 3 Santhakumaran L N, Remadevi O K & Sivaramakrishnan V Phytochemistry, 24 (1985) 1725-1727. R, A new record of the insect defoliator, Pteroma 10 Choong M F, Lucas P W, Ong J S Y, Pereira B, Tan H T W plagiophleps Hamp. (Lepidoptera: Psychidae) from & Turner I M,