Longitarsus serrulatus, Prathapan, K. D., Faizal, M. H. & Anith, And K. N., 2005

Prathapan, K. D., Faizal, M. H. & Anith, And K. N., 2005, A new species of Longitarsus (Coleoptera: Chrysomelidae) feeding on Chinese potato, Plectranthus rotundifolius (Lamiaceae) in southern India, Zootaxa 966, pp. 1-8 : 2-8

Longitarsus serrulatus new species

( Figs 1 –13)

Host plants. Plectranthus rotundifolius (Poir.) Spreng. , P. amboinicus (Lour.) Spreng. and P. scutellarioides (L.) R. Br. ( Lamiaceae ).

Distribution. India (Kerala).

Description. Coloured light chestnut brown. Antennae and all tarsi yellowish brown. Fore­ and mid­legs, hind tibiae lighter than hind femora. Suture narrowly dark brown. Head slightly darker than elytra. In some specimens clypeus, labrum, distal one or two antennomeres darker than rest of head.

Length 1.70–1.92 mm, width 0.82–1.00 mm ( Fig. 1 ). Vertex moderately flat, minutely wrinkled, impunctate. Supraorbital pore surrounded with minute setiferous pores. Inner margin of eyes slightly concave. Antennal callus moderately convex, 2.7 times wider than long, mesally wider than laterally, almost transverse, forming obtuse angle to each other. All sulci delimiting antennal calli moderately developed, not wide. Postcallinal sulcus curved. Orbital sulcus deep, wide. Frontal ridge sharply raised, narrow in middle, wider towards anterofrontal ridge, concave in middle in lateral view. Anterofrontal ridge slightly curved, lower than frontal ridge, moderately raised laterally as well as medially with a denticle in middle. Frontoclypeal suture with four long setae. Labrum with anterior margin convex with indistinct notch in middle, with four long setae arranged in a transverse line, besides a short seta on either side slightly below row of long setae. Mandible with five denticles. Maxillary palp with last palpomere longer than second and third separately. Antenna extends beyond middle of elytron, not reaching apex. Second antennomere slightly longer than half of first; second and third subequal; fourth slightly less than twice length of third; fourth to sixth subequal in length ( Fig. 2 ).

Pronotum wider anteriorly than posteriorly, with maximum width anterior to middle; lateral margin weakly curved, narrow, wider anteriorly than posteriorly, with short setae along margin. Anterolateral callosity slightly longer than one­third of lateral margin including anterolateral callosity, moderately low, reaching middle level of eye, concave, lower anteriorly than posteriorly, forming obtuse denticle at setiferous pore. Pore situated at posterodorsal face of callosity. Posterolateral callosity well developed, longer than width of lateral margin. Seta on anterolateral and posterolateral callosity separately about as long as lateral margin. Disc shiny, punctures indistinct, longitudinal, much weaker than those on elytron. Scutellum wider than long with obtusely angulate apex. Elytron having well developed humeral callus with indistinct depression posteriorly, sides convex, maximum width at middle, apical margin slightly convex, apex obtusely angulate with a long seta. Surface covered with fine punctures, distance between adjacent punctures varied, less than diameter of to slightly more than diameter of a puncture in middle of elytron. Interstices between punctures slightly convex. Punctures tend to form lines along lateral sides. Hind wings polymorphic, being greatly reduced to completely developed.

Prosternal intercoxal process widened posteriorly, very narrow at middle, being half as wide as distance between anterior margin of prosternum to procoxal cavity, narrowly raised along margin, depressed along middle. Mesosternal intercoxal process wider than apex of prosternal intercoxal process. First protarsomere in male slightly wider than third protarsomere, ventrally flat, without setae ( Fig. 3 ). First protarsomere in female much narrower than third protarsomere, rounded, with setae on ventral side ( Fig. 4 ). Metatibia slightly curved in dorsal view, nearly straight in lateral view. Lateral margin of dorsal surface with a regular row of long, sharp spinules in distal four­fifth preceded by short spinules arranged in two rows, spinules absent in proximal one­fifth; lateral margin much higher than medial margin. First metatarsomere 0.6 times as long as metatibia. Claw with small denticle at base. Metatibial spur longer and wider than claw, peculiar in having serrulations on either side dorsally ( Fig. 5 ). Last abdominal sternite in male with posterior margin bisinuate forming a lobe in middle; in macerated specimens a circular internal flange with anterior extension near posteromedial region evident; lobe in middle of posterior region with a row of short setae along margin; short setae present near posterior margin of internal flange; short peg­like sensilla present in middle, sparse long setae on rest of surface ( Fig. 6 ).

Median lobe of aedeagus nearly parallel­sided in ventral view, ventral side transparent, concave ( Fig. 7 ); in lateral view slightly curved with acute, gently recurved apex ( Fig. 8 ); dorsal opening as long as half of median lobe of aedeagus, partially covered by a lamina not reaching apex ( Fig. 9 ). Arms of tegmen shorter than stem ( Fig. 10 ). Spermatheca with receptacle oblong­shaped, inner and outer sides almost parallel, about three times longer than wide; pump curved, horizontal part longer than vertical; duct forming S­shaped curve proximally, distally straight pointing towards receptacle ( Fig. 11 ). Vaginal palpi wider proximally than distally; medial margin forming angle with lateral margin distally; lateral margin concave preapically; proximal and distal sclerotisation subequal, separately shorter than unsclerotised area in middle (Fig. 12). Tignum slightly curved, proximally as wide as distal arrowhead­shaped sclerotisation (Fig. 13).

Sexual dimorphism. Female (1.84–1.92mm) is distinctly larger than male (1.70– 1.73mm). Posterior margin of last abdominal sternite in male bisinuate ( Fig. 6 ) (entire in female) as is the case in the genus Longitarsus . An internal, circular, chitinised flange with anterior extension, evident in macerated specimens, present near middle of posterior margin of last abdominal sternite in male ( Fig. 6 ). Such modification absent in female. First protarsomere in male slightly wider than third protarsomere, ventrally flat and devoid of setae ( Fig. 3 ). First protarsomere in female much narrower than third protarsomere, rounded with setae on ventral side ( Fig. 4 ).

Measurements (all values in mm; n=10). Length 1.70–1.92 (1.81), width 0.82–1.00 (0.91), length of pronotum 0.41–0.49 (0.46), width of pronotum 0.57–0.69 (0.61), width across eyes 0.50–0.57 (0.54), transverse diameter of eye 0.17–0.22 (0.19), distance between eye and antennal socket 0.04–0.08 (0.06), distance between eyes 0.23–0.29 (0.27), length of aedeagus 0.66, length of receptacle 0.15, length of vaginal palpi 0.35.

Types. Holotype ♂. Labels 1) India: Kerala Vellayani 7.x.2002 Prathapan Coll. ex. Coleus 2) Longitarsus serrulatus sp. nov. Prathapan, Faizal & Anith, 2004 3) Holotype (BMNH).

Paratypes. 11 ♂, 10 Ψ, same data as for holotype (2 BMNH, 2 UASB, 7 NPC, 10 KDPC); 11 ♂,10 Ψ, same data as for holotype except dating 17.i.2004 and lack “ ex. Coleus ” (All KDPC); 17 ♂, 46 Ψ, same data as for holotype except dating 6.vi.2004 (2 USNM, 2 MCZ, 5 NPC, 54 KDPC).

Etymology. The species name serrulatus refers to the serrulate metatibial spine.

Diagnosis. L. serrulatus sp. nov. resembles L. sari Maulik (1926) and L. puncti Maulik (1926) . But it can be distinguished from these by the unique structure of metatibial spine which is serrulate on its either side dorsally in the new species. The metatibial spine is not serrulate in any other species of south Indian Longitarsus . The dorsal opening, which is as long as half of the median lobe of the aedeagus, is another diagnostic feature of this new species.

Biology. Longitarsus serrulatus feeds on three different host plants, belonging to Lamiaceae viz. Chinese potato Plectranthus rotundifolius, Indian borage P. amboinicus and painted nettle P. scutellarioides . P. rotundifolius is a small herbaceous bushy annual with succulent stem and aromatic leaves, bearing cluster of dark brown, aromatic, underground tubers. P. amboinicus , a thick succulent herb, is mainly cultivated for its leaves that are used as an ingredient in ethnic medicine and for flavouring food. P. scutellarioides is a perennial herb grown as an ornamental garden plant for its colourful leaves.

On all three host plants, leaf damage was caused by adult beetles which are mainly nocturnal. They scrape the epidermis and soft leaf tissue on the dorsal side, leaving dark patches of feeding scars which later develop into “shot holes”. Numerous discontinuous scars of approximately 1 mm 2 were noticed on leaves. Adjacent scars often coalesce, leaving large areas of leaves damaged. The damage on the host plants was assessed by observing percentage leaf infestation, number of feeding scars per leaf and percentage leaf area damaged. The latter two were measured from one leaf each from the top, middle and bottom strata of a single twig, selected at random. The observations were made on three twigs. The results are given in table 1.

Name of host Leaves Number of feeding scars / leaf Leaf area damaged (%)

infested

Upper Middle Lower Mean Upper Middle Lower Mean (%)

leaf leaf leaf leaf leaf leaf In Chinese potato, all observed leaves of the plant were found scraped and eaten. The number of feeding scars were minimal on upper leaves, progressively increasing on lower leaves in a twig. However the percentage leaf area damage was more on younger leaves compared to older ones, indicating a marked preference for younger leaves by the beetles. In the other two host plants, there was no damage on upper leaves. The number of feeding scars, as well as percentage leaf area damaged, increased with age of leaf, showing preference for older leaves. These observations would suggest that the beetle has close association with secondary metabolites of the host plant. The indication is that the secondary metabolites present in upper leaves of P. rotundifolius act as a phagostimulant for beetles while those in the other two hosts may be acting as deterrents. Immature stages of L. serrulatus were found in the root zone of P. rotundifolius only. Only adult feeding was observed on the other two hosts. Larvae probably feed on the roots of P. rotundifolius and pupation occurs in earthen cells in the soil. As many as nine larvae and 15 pupae could be detected in 100 cm ³ soil drawn from the root zone (top 20 cm of soil) of P. rotundifolius . Thus, P. rotundifolius is the true host plant on which L. serrulatus breeds while P. amboinicus and P. scutellarioides serve as collateral adult food plants. L. serrulatus is likely to become a serious pest of P. rotundifolius due to dual feeding of both larvae and adults on the roots and leaves respectively, affecting transport of nutrients as well as photosynthetic efficiency of the plant, the most important physiological parameters having direct bearing on tuber yield.

Jolivet and Hawkeswood (1995), who reviewed the host plants of the Chrysomelidae of the world, listed 34 genera of Lamiaceae as hosts of Longitarsus species. This appears to be the first report of Longitarsus feeding on Plectranthus . This also is the first report of a chrysomelid feeding on Chinese potato in India.

Figures

FIGURE 1. Longitarsus serrulatus sp. nov., dorsal habitus

FIGURE 11. Longitarsus serrulatus sp. nov. 11. spermatheca; 12. vaginal palpi; 13. tignum.

FIGURES 2 – 10. Longitarsus serrulatus sp. nov. 2. antenna; 3. male protarsus; 4. female protarsus; 5. metatibial spur; 6. last abdominal sternite of male (macerated specimen); 7. median lobe of aedeagus, ventral view; 8. median lobe of aedeagus, lateral view; 9. median lobe of aedeagus, dorsal opening; 10. tegmen.