ANNALS <IF ARID ZONEVo•• II, Nos. 3 & 4, September & December, 1972

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OBSERV ATIONS ON THE INCIDENCE AND SEASONALAI:iUNDANC~ .OF WHITE GRUB LAOHN08PERN ACON8ANGUINEA BLANCH INFESTING SESAMUM

IN RAJASTHAN

J.P. VERMA AND Y.K. MATHUR

ALL INDIA CCORDINATED RESEARCH PROJECT ON OILSEEDS-SESAMUM

ACRICULRURAL RESEARCH STATION

V ALLABHNAGAR ( UDAIPUR)

White grub, Lachnosterna (Rolotrichia) consanguine a Blanch( Coleoptera: Scarabidae ) is a most noxious pest of a variety of kharifcrops in Bihar, Gujarllt and Rajasthan. Published information indicatesthe occurence and damages to sugarcane by grubs of L. cOllslJnguineafrom Bihar (Gupta and Avasthy, 1957; Prasad and Thakur, 1959; Kalra andKulshreshtha, 1961 );to sorghum,groundnut, :maizo, .~bajTfJ and chilliesby R%trichia sp. near consanguinea in Gujarat (Desai and. Patel, 1965;Patel et ai, 1967). In Rajasthan the pest has been recorded infestingroots of groundnut. jowar, bajra, maize and sugarcane (Ritcher, 1961;Kalra /lnd Kumar, 1967; Joshi et ai, 1969; Rai el a/, 1969). But for thefirst time in July 1970 Lachno,~terna consanguillea Blanch has been observedin damaging proportion on sesamum at Agricultural Research Station,Vallabhnagar. However, a casual report on another species of white grub,R. insularis on se.•amum is on record from arid tracts of the state (Paland Doval, 1970). Since little is known regarding the incidence andseasonal abundance of this pest on sesamum intensive investigations weremade to fill in the existing gap in our knowledge.

Larval behaviour •. Like other white grubs this species feed under-ground part of the roots of sesamum (Fig. I AB). They have been found toattack young as well as older plants. Grubs start feeding on roots, a fewhours after hatching. As they grow old they become voracious feedercausing enormous losses to the crop. In the seedling stage the root of

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22J J. P. VERMA AND Y. K. MATHUR

Big. 1 A. Grub feeding the root of sesamum

Fig. 1 B. 1. Healthy roots of sesamum2. Roots damaged by the grub

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INCIDENCE OF WHIT~ GRUB IN.SESAMUM. IN RAJASTHAN· 221..

the plant is cut and completely devoured resulting in drying up of theplant. Such attacked plants either fall on the ground or can easily be pulledout from the soil. In heavy infestation field show patchy appearance dueto wilting of plants (Fig 2).

Population Densities: Random samples were taken by digging thesoil (1m x 1m x 0.3m). 25-30 such samples.w,ere. taken per hactare . andt.he population of larvae in each sample \yas ·recorded. During crop se~sonweekly observations were also recorded OD: the percentage of. plants affected.During kharif, 1971 the population of grubs. was so much so that at .peaki. e. in first weak of september it varied from 2-5 grubs per cubic met~r,the average being 3.5 ( Table 1 ).

Table}; Incidence of' wbite grubs on /sesamtim at Vallabhnagar farm inthe year 1970-71

S.No . Month Mean grub population .Mean percentage ofIhact in thousands . p1ant infestation

1970 1971. 1970 1971

I. July S· 7. 30.4

2. August 8.5 12.2 42.2 51.7

3. September 11.5 14 47.8 61.4

4. October 12 16 49.6 63.0

5. November 0 0 Crop .. harvested

The presence of grubs in sesamum crop (feeds) were observedfrom July to October. Further attempts were also continued by theaUlhors to find out the presence of grubs throughout the year. Duringthe period from November to June when crop did not exist in the field,no grubs could be collected. However. beetles were available in soilfrom November onwards. It was further observed that for want ofmoisture in upper layer of soil, grubs go as deep as 90 ems for pupa-tion.

222 J.Il. VERMA AND Y. K. MATHUR

Fig. 2 Plant affected by the grub damage

INCIDENCE OF WHITE GRUB,IN SESAMUM IN RAJASTHAN 223

The pest hibernates in the pupal stage in soil. With tbe onsetof premonsoon rains adult beetles come out from the soil and congregateon tbe trees. After copulation tbey lay eggs in the fields and thus thelife cycle is repeated. There is only one generation in a year.

Incidence of pest wa~ observed to be markedly effected by sowingdate variations. Crop sown on 20th June, 1971 was found free from thepest attack while the crop sown late i. e. 15tb August was most severelyeffected (55 per cent plant~ damaged). The percentege of plants damaged on2nd and 3rd date of sowing i. e. 5tb and 20th July respectively, was 11.6and 19.3 respectively.

ACKNOWLEOGEMENTS

The authors wish to record their sincere thanks to the Director,Agricultural Experiment Station, Udaipur and to Sbri K. B. Trehan, PlantBreeder (Sesamum), Vallabhnagar for providing the facilities during thecourse of this work.

REFERENCES

D.:sai, M T. and Patel, R.M. 1965. Some observations on the biologyand control of white grubs in soil ( H%trichia near consangui~eaBlanch. affecting groundnut and cereal in Gujarat. Indian J. Ent.27 (1) : 89-94.

Gupta, B. D. and Avasthy, P. N, 1957. First record of white grub;Lachnos!prnn con,~anguinea Blanch. in India. Ourr. Sci. 26 (1) : 114-115.

Joshi, R. K., Kaul, C. L. and Srivastava, B. P. 1969. Studies on chemicalcontrol of white grubs, Holotrichia consanguinea Blanch. (Melol-onthidae: Coleoptera). Indian J. Ent. 31 (2) : 143-146.

Kalra, A. N. and Kulshreshtha, J. P. 1961~ Studies on the biology andcontrol of Lachnosterna consanguinea Blanch. A pest of sugarcane

. in Bihar (India). Bull. Ent. Res. 52: 577.

Kalra, A. N. and Kumar Sunil, 1967. Record of beetle grub attack insugarcane in Rajasthan. Indian sug. 17 (5) ; 417·425.

Pal, S. K. and Doval, S. L. 1970. Some observations on the whitegrub llolotrichia insularis Brenske (Melolonthidae: Coleoptera)and its control in Jodhpur division of Rajasthan. Anna/s of AridZone 9 (2): 151-156.

224 J. P. VERMA AND Y. K. MATHUR

Patel, R. M., Patel, G. G. and Vyas, H. N. 1967. Further observationson the biology and control of white grub, (H%trirhia sp. nearconsanguinea Blanch) in soil, affecting groundnut in Gujarat.Indian J. Ent. 29 (2): 170-176.

Prasad, S. K. and Thakur, C. 1959. White grub Lachnosterna con,qanguineaBlanch. a new menace to sugarcane. Indian. J. Ent. 21 (3) : 184-189.

Rai, B. K.• Joshi. H. C., Rathore, Y. K., Dutta, S. M. and Shinde.V. K. R. 1969. Studies on tbe bionomics and control of wbitegrub. H olotrichia consonguinea Blanch in Lalsot, dis trict J,aipurRajasthan. Indian. J. Ent. 31 (2): 132-142.

Ritcher, P. O. 1961. Description of some common North Indian scarabaeidlarvae (Coleoptera). lndian. J. Ent. 23 tl): 13-19.