8342937073

Pertamk. 14(1). 7-13(1991)

The Effects of S0₂ and NO,, Singly or in Combination on the Growth Performance of Cocoa Mirids (Helopelńs theobromae Miller).

MUHAMMAD AWANG, RITA MUHAMAD¹ and SYED AZELAN S.A. HASSAN

Department ofFnnironmen tal Sciences, Faculty ofScience and Enuironmental Studies

¹ Department of Plant Protection, Faculty of Agńcullure 43400 U PM, Serdang, Selangor DarulEhsan, Malaysia.

Key words: air pollutants, S0₂, NC>₂, cocoa mirids, growth performance.

ABSTRAK

Nimfa instarkeliga mińd koko (Helopeltis theobromae Miller) yang menghisap pucuk muda koko terdedah kepada SO_?dan NO ₍secara berasingan atau gabungan telah digunakan untuk menilai kadar tumbesarannya. Nimfa yang terdedah secara serentak kepada SO_? semasa menghisap daun telah menghasilkan kadar tumhesaran yanglebih haik di mana rangsangan min kadar tumbesarannya mencapai 18.9%. Keadaan yang sama fuga berlaku pada nimfa yang terdedah kepada SO₇ da n NO^ (secara gabungan) iaitu 34.3%, manakala nimfa yang terdedah kepada N()₇ m em perli haik an kadar yang berlainan. Nimfa yang tidak terdedah tetapi menghisap pucuk selepas fumigasi menunjukkan 20.0 % lebih haik kadarnya apabila mencapai umurdewasa. Hasilkajianjuga menunjukkan bahawa kesan gas pencemaran terhadap perlaksanaan tumhesaran mińd berlaku tidak secara langsung dan terkendali menenisi perubahan biokimia tanaman perumah.

ABSTRACT

Third instar nymphs were used to assess the growth performance of cocoa mińd ('Helopeltis theobromae Miller) while suckingon young cocoa shoots which had been exposed with or without nymphs to S0₇ and N0₇ either singly or in combination. Nymphs exposed simultaneously to SO_? while suckingon leaues produced bettergrowth performance with mean growth ratę beingstimulated by 18.9%. Similarperformance was obseroed on nymphs exposed to S0₇ and NO₀ (in combination) i.e. by 34.3 % while insects exposed to NO ₇ performed differenlly. Nonfumigated 7iymphs fed on post fumigated leaues showed 20.0 % better performa nce when they emerged as adu Its. The results also prom de euiden ce that the effects ofihese pollutants on the cocoa mińd s performance are indirect and mediated via changes in the biochemistry of the host plant.

INTRODUCTION

The significance of Iow concentrations of atmospheric pollutantsasan environmental factor in influencing the growth of phytophagous insect populations has been recognised for many years, particularlyin theforestenvironment (Weinstein et al. 1973). Interactionsbetween pollutants, plants and insects could have a major impact on the growth oł insect populations and subsequent!y plant damage and yield reduction (Hughes et al. 1985). Recent studies by Chappelka et al. (1988) revealed that changes in plant metabolism grown underlow pollutantstressaffected the insect feeding preference. In addition, lowconcentrationofgases applied to insects did not affect their growth performance but altered their behaviour and enhanced theirsurvival (Hughesetal. 1981). Since plantsprovide insects with nutrition and Chemical cues, relatively smali biochemical changes in the plant could greatly affect the source of food for insects (van Emden 1973; Lewis 1979; Wbite 1984).

Concentrations of SO,, and NO_t) less than 25 ppb and 30 ppb respectively are considered suffi-ciently Iow sińce fumigation toplantsat these levels generally does not produce any morphological injury but has been reported to affect certain physio-logical (Darrall 1989) and biochemical processes