Feeding Potential of Cassida Circumdata Herbst (Chrysomelidae: Coleoptera) on Ipomoea Reptans (Linn.) (Convolvulaceae)

5 Pages·2000·3.3 MB·

by  M John George

:
FEEDINGPOTENTIALOF CASSIDA CIRCUMDATA HERBST(CHRYSOMELIDAE
COLEOPTERA)ONIPOMOEAREPTANS(LINN.)(CONVOLVULACEAE
)1
M. John George3 and Ipe M. Ipe2
(With one text-figure)
Key words: Cassida circumdata Coleoptera, Ipomoea reptans, Convolvulaceae
,
ThetortoisebeetleCassidacircumdataHerbstfeedsontheaquaticplantIpomoeareptans(Linn.)
(Family: Convolvulaceae), which grows profusely in the tropical wetlands. This plant species
was found invading the open water area and changing the proportion ofhabitats available for
aquaticbirdsand fishes. Thedifferentlarval instarsand adultsofthetortoisebeetlewerenoticed
feedingontheleavesandtenderstemsofIpomoeareptans, oneoftheabundantaquaticplantsin
Keoladeo National Park, Bharatpur, Rajasthan, which is among the majorprotected wetlands in
India.
Toassessthe impactofCassidacircumdataon itsmain hostplantI. reptans,consumption ofthe
leaves in terms of area fed by different larval and adult stages were studied under laboratory
conditions (30 ±2 °C and 50-70% relative humidity). The first to fifth instar larvae and adult
differedwidelyintheirconsumptionofhostplantleaves.Theareaconsumedwasintheorder 1st
<2nd<3rd<4th<5thinstars>adult. Significantcorrelationcouldbeobtainedbetweenthegrowth
ofthe larvae and their food consumption. The different rates offood consumption indicate the
varying energy requirements ofthe various larval stages ofthe beetle.
Introduction Keoladeo National Park of which the most
dominantspeciesisagrass,Paspalumdistichum
,
Recently, much attention has been given that covers amajorpart ofthe aquatic area. The
to the herbivore-plant relationship, with restis mostly covered withIpomoea reptans an
,
reference to its ecological and evolutionary important amphibious herb. Ipomoea reptans
impacts (Denno and McClure 1983). Such floats inwater, usuallyappears as atrailingherb
studies demand a knowledge of the actual and changes the proportion of the habitat
consumption of the host plant parts by the available for aquatic birds and fishes (Ali and
herbivore and its growth rate. The quantitative Vijayan 1986). In the Park, I. reptans remains
assessment ofconsumption ofhostplants by its in a dormant stage during winter (December-
pestmayhelp us to assess the impact ofthepest February).
on the growth of the plant and thereby the Insummer(April-June), as thewaterlevel
possibleuseofthatpestasanagentofbiological drops and the stem makes contact with the
control. ground, it produces leaves in large numbers.
The tortoise beetle Cassida circumdata Aftermonsoonandwhenthelevelofwaterrises,
Herbst feeds on the aquatic plant Ipomoea I. reptans spreads andattains maximumgrowth.
reptans (Linn.), which grows profusely in Thispaperreports the resultofthe study carried
tropical wetlands. About 91 species ofwetland outin the field andunder laboratory conditions,
macrophytes have been identified from the to determine the feeding potential of
'AcceptedJuly,1999 C. circumdata.
2SchoolofEntomology,St.John’sCollege, The life-cycle of C. circumdata includes
Agra282002,UttarPradesh,India. 5 larval stages and apupal stage. The eggs were
?PPerreusmenbtavAododrre,sEs:maMkaurlTahmo6m8a3C5o4l2l,egKeerfaolraW,oImndeina., laidontheventralsideofI. reptansleaves.Under
370 JOURNAL, BOMBAYNATURAL HISTORYSOCIETY, 97(3), DEC. 2000
FEEDINGPOTENTIALOFCASSIDACIRCUMDATA
laboratory conditions (30 ±2 °C), the eggs food consumed by the adult and grub ofLema
hatched within 4 days. The duration of the 5 lacordairei (Chrysomelidae), Visalakshi and
larval instars was 2, 1-2, 2, 2 and 4 days Nair (1987) used similar methods.
respectively. The pupal stage lasted for4 days. Alongwiththeexperimental studies inthe
laboratory, an attemptwas made to quantify the
Study area feeding impact ofdifferent instars ofthe beetle
on the host plant. This was carried out by
The present study was carried out in the collecting the plant and different stages of the
well-known protected wetland, the Keoladeo beetles fromrandomlyplacedquadrats of100 x
National Park, Bharatpur (27° 7.6' to 27° 12.2' 100 sq. cm. Collectionsweremade from6 study
N and77°29.5' to 77°33.9' E), Rajasthan, India. plots. Oncethequadratwasplaced, alltheleaves
above water were plucked and transferred into
Methodology plastic bags (harvest method). The adults that
flew offon being disturbed were also counted.
Both sexes were almost alike, the male In the laboratory, all the leaves were carefully
being slightly smaller than the female. To study examined and the different instars and adults
the feeding and oviposition, experiments were counted. The leafarea was measured using the
earned out in plastic containers (height = 8 cm same method as above. The leaf biomass was
anddiameter=3 cm)withscrewtophavingholes quantified using an electrical monopan balance
forventilation. Discs offilterpaperwereplaced of sensitivity 0.1 mg. The samples were taken
at the bottom ofthe containers to absorb excess once in seven days and monthly averages were
moisture and facilitate cleaning. Mating pairs calculated.
were collected from the field and kept in these
containers. The leaf-area fed by the adult and Resultsand discussion
the eggs laid after 24 hrs were recorded. The
adults, when kept in containers laid eggs on the Labexperiment: The average leafarea of
leavesofI. reptans, andtheeggshatchedwithin Ipomoea reptans consumed and the average
4 days. growth (length and breadth) of the larvae of
Newly emerged larvae wereplacedone in Cassidacircumdataforeachdayaresummarized
eachcontainerandprovidedwithfreshleaves of in Table 1. The maximum leaf area was
I. reptans daily. The body length and breadth consumed on the eighth day by the 5th instar
were measured every 24 hrs using a compound larva (59.33 sq. mm). The maximum increase
microscopewithacalibratedocularmicrometer. in the larval stage was noted on the seventh and
When fresh leaves were freely available, the eighth day. On the ninth day, the larvae slowly
larvae and adults fed upon the fresh area. The decreased their rate of feeding and entered
leafareaconsumedandremovedatonemeal(leaf pupation. The 5th instar larva fed about
mm
area fed at a stretch) was measured by placing 101.16 sq. leaf area within 3 days. The
the leafon graphpaper and tracing the leafarea maximumarea was feduponby the two day old
fed, and then counting the squares of the leaf 5th instar larva. This study showed that the 5th
area fed, as suggested by Simmonds (1949). As instar larvae can consume almost 4 times more
theearlyinstars fedvery little andmade circular than the 4th instar and about 100 times more
holes, the radius of the circular path fed was than the 1st instar (Table 1).
measured with graph paper and by a calibrated, A single larva from the 1st through the
mm
ocular micrometer. To estimate the quantity of 5th instar consumed about 145.95 sq. leaf
JOURNAL, BOMBAYNATURAL HISTORYSOCIETY, 97(3), DEC. 2000 371
FEEDINGPOTENTIALOFCASSIDACIRCUMDATA
Table
1
FOODCONSUMPTIONANDGROWTHOFTHELARVAEOFC. CIRCUMDATAREAREDON/.REPTANS
INTHELABORATORY(30±2°C)
Days 1 2 3 4 5 6 7 8 9 10 11
Stage(instar) 1st 2nd 3rd 3rd 4th 4th 5th 5th 5th Pupa Pupa
Increaseinlength(mm) 0.15 0.28 0.3 0.2 0.45 0.45 0.75 0.58 0.18 -0.08 0
Increaseinbreadth(mm) 0.08 0.17 0.15 0.13 0.37 0.17 0.38 0.55 0 0 0
Areafed(sq.mm) 1.86 5.01 4.68 9.83 9.65 16.79 30.25 59.33 11.58 0 0
area ofI. reptans within 9 days (Table 1). The Table2
average leafarea collected during July-October LEAFTAHREELAAORFVAI.EREAPNTDAANDSUCLOTNSC.UCMIERDCU(MSQD.AMTMA)BY
was 17.55 sq. cm. The study showed that two AT30±2°C(N=80)
larvae from the 1st instar through 5th instar can
completely eat and skeletonise a single leaf. 1stinstar 0.21 ±0.13
To study the feeding behaviour of the 2ndinstar 0.35 ±0.19
3rdinstar 0.80 ±0.37
beetle, thehostplantleaveswereobservedwhen 4thinstar 1.86 ±0.82
there was less attack. Ofthe total holes fed and 5thinstar 5.32 ±3.41
made by the larvae and the adult (N 1 5,265 Adult 3.77 ±1.72
holes) 95.5% of the holes indicated only one
feeding. This indicatesthatthe larvae andadults was noted on the 16th day. In Aspidomorpha
preferredtofeedonfreshareawhenthehostplant miliaris, the adult consumed seven times more
leaves were plentiful. leaf area than the 5th instar (Manjunatha et al.
The leafareafedandremovedatonemeal 1987). BombyxmoriandProtoparcesexta, both
(in a stretch) by each instar larva and adult are lepidopterousleaffeeders,eatabout97%oftheir
summarized in Table 2. The result showed that total intake during the lasttwo instars andabout
the 5th instar larvae consumed greater leafarea 99% duringthe lastthree instarsrespectively. In
at a single meal and the first instar the least. Bombyx mori it was noticed that the efficiency
,
The adult C. circumdata pair under ofstorageofmetabolizableenergyincreaseswith
mm
captivity (N=15) fed on 56.81 ±12.53 sq. age, reachingitspeakinthe 5thinstar. The large
leaves and laid 12.6 ±6.1 eggs within 24 hrs. amount ofenergy stored during 5th instar is, of
The mating pairs fed 17.1 ±4.8 times within course, needed to support the non-feeding pupa
24 hrs. The area fed upon by the mating pairs and adult (Waldbauer, 1968).
waslesscomparedtothe5thinstarlarva, asmore Field experiments: Field observations
time was utilized for mating and laying eggs. revealedthatthebeetle appears inthe study area
No significant correlation was noticed between during March (mean min. temp. = 19 °C). The
the area fed and the number ofeggs laid. host plant was available only along the dykes.
Simmonds (1949) assessed the leaf area The population of C. circumdata remained
consumed each day by the larvae ofPhysonota almostconstantduringthepeaksummermonths.
alutacea(Cassidinae).Theleafareaconsumption With the onset of monsoon and the release of
wasseentoincreasewiththegrowthofthelarvae water from Ajanbund, an inundation reservoir
eachday, themaximumconsumptionofleafarea situated0.5kmsouthofthePark,theplantspread
372 JOURNAL, BOMBAYNATURAL HISTORYSOCIETY, 97(3), DEC 2000
FEEDINGPOTENTIALOFCASSIDACIRCUMDATA
over the area by vegetative reproduction. There be observed due to low population ofthe beetle
is spatialvariation inthe abundance ofthisplant (George 1988). The maximumpopulation (468/
in the Park. By this time, the beetle had settled sq. m) and leafarea (17.8 sq. mm) during 1986,
indifferentareas.Theadultsmainlyconcentrated was noticed in September.
in certain areas, fed and laid eggs. There was Kolodny-Hirsch and Harrison (1982)
wide fluctuation in the population of different conductedfieldandfieldcagestudiestocompare
stages of the beetle among the different study larvalinjurybythetobaccobudworm,Heliothis
plots. Afterlayingeggs, the adultsmovetoother virescens and corn ear worm, Heliothis zea
less infected areas. The adult beetles prefer to (Lepidoptera: Noctuidae). Their observations
lay eggs on the underside offreshyoung leaves. showedthattheplantcompensatedforleaflessby
Eggs were never laid on skeletonised leaves, to increasingthelaminalareaofthedamagedleaves.
ensure enough food for the emerging larva. The population of C. circumdata in the
,
Theaveragemaximumnumberofdifferent Park,reachedapeakinSeptember,andasaresult
stages ofthebeetlewasnotedduring September the leafarea and biomass declined. In the end,
(Fig. 1). Theleafareaofthehostplantwasfound onlyleafskeletonsremainedintheinfestedareas.
following the same trend as that ofthe beetle. Thus, leaf biomass became zero towards the
Thus, a significant positive correlation was onset ofwinter. In winter, both the plant and its
obtained between biomass and leaf area ofthe pest remained dormant. The beetles were found
plantwiththepopulationofthebeetle(r=0.821, hibernating, in the Park, on terrestrial plants,
p - 0.001; r - 0.8472, p = 0.0001, n= 60). namely Salvadora persica, albeit in small
It was observed that the host plant numbers(George 1988).Thisformedthebreeding
compensated for the leaf area fed upon by the stock for the next population during February-
larval and adult C. circumdata by producing March, and by this time the hostplant also starts
larger leaves. Leaves with greater surface area producing smaller leaves. Thus, the interrelated
were noticed in August and September during life-cycles ofthehostandpest continue.
1985, when the population ofthe beetle was at The study unravels a unique relationship
itspeak(Fig. 1). Butinalaterstudyduring 1986- between the plant and the beetle. Though the
87, asimilarresponse ofthehostplantcouldnot beetle controls the biomass ofthe host plant, it
POPULATION/AREA
10000 §
LEAFAREA
TOTAL
1000 POPULATION
100 =
Fig. 1: Leafarea(sq. mm) ofI. reptans and population ofC. circumdata
JOURNAL, BOMBAYNATURAL HISTORYSOCIETY, 97(3), DEC. 2000 373
FEEDINGPOTENTIALOFCASSIDACIRCUMDATA
does not completely destroy them, thereby sponsored by the US Fish and Wildlife Service
ensuring its own survival. The most important through the Ministry of Environment and
barrierswhichpreventthebeetlefromdestroying Forests,Govt,ofIndia. Encouragementreceived
the plant entirely are the ability ofthe plant to fromMr.J.C.Daniel,Hon. Secretary,BNHSand
survive under water and low ambient tempera- Dr. V.S.Vijayan,Director,SACON,Coimbatore
tures (average minimum temp, in December- is acknowledged. We also thank Dr. N.K.
February 8 °C). Ramachandran, Wildlife Institute of India, for
criticism and suggestions, and Dr. C.R.
Acknowledgements Ajithkumar, PrincipalInvestigator, Mr. K. Raju
Thomas and Mr. C.R. Biju, Research Scholars,
Thispaper is an outcome ofthe Keoladeo BNHS Research Station, Kalady, Kerala, for
National Park Ecology Project of the BNHS, their help.
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NaturalHistorySociety,Bombay,pp54. miliarisF.(Cassididae:Coleoptera)onthreespecies
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AcademicPress,Inc.,London,pp717. 84(3):704-708.
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