Pertanika 6(1),67 -70 (1983)

Field Evaluation of Four Insecticides for the Control of theMango Leaf-cutting Weevil, Deporaus marginatus Pasco

P.G. SOH and K.C. KHOODepartment ofPlant Protection, Faculty ofAgriculture,

Universiti Pertanian Malaysia, Serdang, Selangor, Malaysia.

Key words: Deporaus marginatus; mango; deltamethrin; etrimfos; acephate; dicrotophos.

RINGKASAN

Di dalam percubaan mengawal serangga pengerat daun mangga, Deporaus marginatus Pasc., didapatideltamethrin memberikan kawalan Paling berkesan diikuti dengan etrimfos, acephate dan akhir sekalidicro toph os.

Kajian mengenai kekekalan deltamethrin diladang menunjukkan bahawa racun tersebut berkesansehingga dua minggu.

SUMMARY

In an insecticidal trial for the control of the leaf-cutting weevil of mango, Deporaus marginatusPasc., deltamethrin was the most effective insecticide followed by etrimfos, acephate and dicrotophosin that order.

A persistency study of deltamethrin in the field showed that the insecticide was effective for up totwo weeks.

INTRODUCTION

The mango leaf-cutting weevil, Deporausmarginatus Pasc., has been recorded as a pest ofmango in India (Fletcher, 1914), Burma (Fletcher,1917), Sri Lanka (Hutson and Alwis, 1934) andMalaysia (Ahmad and Ho, 1970).

Two kinds of damage are inflicted on newflushes of leaves by the adult insect. Feedingdamage is caused by both male and female adults.More serious damage is caused by the female whenshe neatly cuts the leaf blade near the petioleafter laying one or more eggs on the leaf laminawhich then falls to the ground.

The eggs soon hatch and development of thelarva proceeds in the severed leaf. When theprepupal stage is reached the insect burrows intothe soil to pupate. Further details concerning thebiology and ecology of D. marginatus can befound in Ooi (1976) and Chuah (1980).

1 Active ingredient is maneb., N:P:K values are 15:30:15; also included are trace elements.

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Deporaus is one of the major insect pests ofmango in Malaysia and the control of this andother insects is an important aspect of mangocultivation. DicH)tophos came into widespreaduse on mango trees when Singh (1980) foundthat the insecticide, when combined with thefungicide Manzate Dl and a foliar fertilizer WelgroStandard', gave good control of insect pestsincluding D. marginatus.

Dicrotophos with an acute oral LDso valueof 22mgjkg for rats (Martin and Worthing, 1977)is rated as highly hazardous under the WHOclassification (Anon, 1975). The high mammaliantoxicity of this insecticide makes it an unsuitableone for use in the home garden on a tree crop.Safety precautions observed by home gardenersare minimal and the danger of spray drift whenapplying pesticides to trees is great. Furthermore,at the time this paper was written, dicrotophoshas not been registered by the Pesticides Board ofMalaysia which means its sale and use in thecountry are prohibited.

P.G. SOH AND K.C. KHOO

The main aim of our investigations was toevaluate insecticides of moderate mammaliantoxicity for the control of D. marginatus. At thesame time we deemed it useful to evaluate theimpact of these insecticides on non-target pestsbecause one of the well-known undesirable side-effects of insecticides is that they cause outbreaksof secondary pests. After the most effectiveinsecticide was selected we determined its residualeffect and hence the frequency of application ofthe insecticide.

MATERIALS AND METHODS

The experimental areaThe experiments were carried out on the

Universiti Pertanian Malaysia farm planted withthe Bombay Green variety of Mangiferd. indica.This variety puts out new shoots throughoutthe year under local conditions and, like otherexotic varieties of mango, is prone to attacks byD. marginatus.

The insecticidal trialThe treatments consisted of four insecticides

and an untreated control. The common andcommercial names of the insecticides are listedin Table 1 together with their respective acute oralLDso values for rats and the rates of application.

The insecticides were applied at weeklyintervals for 20 weeks between July to December1981. Treatment trees were sprayed to the pointof run-off using knapsack sprayers each fittedwith a lance of 126 em length.

The experimental design used was a RCBDconsisting of four treatments and the untreatedcontrol replicated eight times. Each plot consistedof a single tree.

Evaluation was done at fortnightly intervalsby taking 10 new shoots at random and examiningthese for leaf-cutting damage. New shoots were

scarce at certain times so that on some trees therewere less than 10 shoots. When this occurred allthe available shoots were evaluated.

Early in the trial it was found that there wasa very low incidence of attack by D. marginatuson all treatments including control. The problemwas resolved by collecting leaf blades freshlyCli t by D. marginatus in another area of the farmand distributing these beneath all trees in theexperiment. A total of 37 cut leaves was placedunder each tree over a four-week period.

For anyone replicate in anyone treatmentthe data from all the evaluations were pooled andthe percentage of cut shoots was calculated.An analysis of variance was carried out on thesepercentages and the differences between individualmeans were tested using Duncan's multiple rangetest.

Shoots being evaluated for cutting damageby D. marginatus were also examined for:

(a) damage by Mictis longicornis Westw.(Hemiptera: Coreidae)

(b) damage by Chlumetia transversa Wlk.(Lepidoptera: Noctuidae)

(c) presence of mealybugs (Hemiptera:Pseudococcidae)

(d) presence of scale insects (Hemiptera:Diaspididae)

and (e) presence of galls caused by Procontariniamatteiana Kieff and C. (Diptera: Cecido-myiidae)

Since mealybugs and scale insects are generallyfound on mature leaves rather than immatureones, the mature leaves behind the flush selectedwere examined down to the next joint.

TABLE 1The acute oral toxicities and rates of application of insecticides evaluated

Insecticide treatments

dicrotophos (Carbicron 24WSC)

etrimfos (Ekamet 50EC)

acephate (Orthene 7SSP)

deltamethrin (Decis 2.5EC)

*Based on LDso for the rat (mg/kg body weight)

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Acute oraltoxicity*

22

1800

945

537

Rate of application(% a.i.)

0.053

0.075

0.082

0.0022

FIELD EVALUAno OF INSECTICIDES FOR CONTROL OF MANGO WEEVIL

gave means which differed significantly from thatof the untreated control.

1 5.3 a

2 12.5 a

3 36.9 b

o(control) 45.8 c

TABLE 3Effectiveness of deltamethrin in controlling D. marginatuswhen applied at 0,1,2 and 3 week intervals. Effectiveness

was measured by the percentage cutting damage

The persistency ofdeltamethrinTable 3 shows the means of shoots cut by

D. marginatus when deltamethrin was applied ato (untreated control), one, two and three weekintervals.

*Mean % cut shoots/replicate

Treatment(weeks between application)

The residual effect of the insecticide wasassessed by counting the number of shoots showingcutting damage. Damage assessment was carriedout in the manner described in the preceding trialat weekly intervals for six weeks (between 22November 1981 to 2 January 1982). The datafor anyone replicate in anyone treatment werepooled and the percentage cut shoots calculated.An analysis of variance was carried out on thesepercentages and the difference between individualmeans were tested using Duncan's multiple rangetest.

The persistency of deltamethrinAs deltamethrin was found to be the most

effective insecticide in the above experiment itspersistency was then determined as follows.

The treatments comprised deltamethrinapplied at one, two and three week intervalsand an untreated control. Each treatment wasreplicated eight times in a RCBD with each plotbeing a single tree.

Rain is an important determinant of theresidual activity of most pesticides. Rainfall datawere therefore obtained from the University'smeteorological station.

RESULTS AND DISCUSSION

The insecticidal trialTable 2 shows the means of the percentage

cutting damage and how the treatments differed.

TABLE 2Effectiveness of the insecticides tested for the control

of D. marginatus as measured by the cut leaves

Treatment *Mean % cut shoots

control 44.9 a

dicrotophos 30.6 ab

acephate 29.1 ab

etrimfos 22.1 b

deltamethrin 4.9 c

*Means not followed by the same letter are significantlydifferent (P < 0.05) by Duncan's multiple range test.

It can be seen that all the four insecticidestested did reduce damage by Deporaus whencompared to the control. Deltamethrin was clearlythe best insecticide followed by etrimfos, acephateand dicrotophos in that order. ,However only twoinsecticides, namely etrimfos and deltamethrin,

*Means not followed by the same letter are significantlydifferent (P < 0.05) by Duncan's multiple range test.

Least damage was noted when the insecti-cide was applied at one week intervals and mostat three. Even at three week intervals deltamethringave better protection than the control. Thedifference between means for the one and twoweek treatments is not significant. Thus it may beconcluded that deltamethrin gave good protectionfrom D. marginatus for at least two weeks.

The following information on rainfall providessome background information on the kind ofconditions under which the trial took place.A total of 281 mm of precipitation was recordedover the trial period of 42 days of which 21 dayswere rain-free.

GENERAL DISCUSSION

The insecticidal trial reported here has shownthat the previously widely used dictophos is oneof the least effective insecticides together withacephate. Singh (1980) mixed dicrotophos withManzate D and Welgro Standard and evaluatedthe mixture for control of insects and diseases. Itwas therefore the mixture rather than dicrotophoswhich was being evaluated for control of insectsof mango in particular, D. marginatus. Synergismbetween dicrotophos and various fungitoxicantshas been suggested (Lim, 1980). A study willhave to be carried au t to compare deltamethrin +Manzate D + Welgro Standard against dicrotophos+ Manzate D + Welgro Standard.

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P.G. SOH AND K.C. KHOO

When used by itself deltamethrin was clearlythe best of the insecticides tested. Besides beingof moderate toxicity, deltamethrin is made evensafer because the normal rate of application isextremely low. For example, the rate of applicationof deltamethrin in this study was 24 times lowerthan that of dicrotophos.

Although deltamethrin appears to be a desira-ble insecticide to use against D. marginatus,due consideration should be given to its effecton non-target insects. With most insecticidesthere is always a degree of deleterious effect onparasites and predators. If the insecticide shoulddisturb the ecosystem to the extent that parasitesand predators are more adversely affected thanthe target pest, pest resurgences and outbreaks ofsecondary pests could result. Under the conditionsof our trial no increase in the incidence of secon-dary pests was noted.

Concerning possible adverse effects on pollina-tors, field experimentations have shown that theinsecticide presents no danger to bees at dosagesup to 12.5 g a.i.jha; it has also been noted thatbees are repelled when the flower is recentlytreated with deltamethrin (Delabarre and Yeh,1981). Mango pollinators are principally dipteransand the above observations mayor may not beapplicable. Nevertheless deltamethrin has beenused against mango hoppers in the Philippinesand at 12.5 and 25.0 g a.i.jha gave best controlof the hoppers and highest yields compared withfenvalerate, carbaryl and the untreated control(Delabarre and Yeh, 1981). Time of applicationwas 4, 11, 18 and 32 days after flower emergence.So it appears that the application of deltamethrineven during the flowering period did not affectmango pollinators to the extent that yield wasreduced relative to the control.

ACKNOWLEDGEMENTSThanks are due to Harrisons and Crosfield

(Malaysia) and Hoescht Malaysia for supplying

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the insecticides. Thanks are also due to EncikYusof Ibrahim for a critical review of the draftcopy.

Mention of a proprietary product does notconstitute a recommendation or an endorsementby the authors.

REFERENCES

AHMAD, Y. and HO, T.H. (1970): Host-Pest List (1920-1970). Part II. Ministry of Agriculture and Coopera-tives Malaysia. 690 pp. (Mimeograph copy).

ANON (1975): Recommended classification of pesticidesby hazard. WHO Chron., 29: 397-401.

CHUAH, C.K. (1980): Ecological Studies on Mango LeafCutter, Deporaus marginatus Pasc., (Curculionidae).B.Sc. (Hons.) Zoology Thesis. University of Malaya.Kuala Lumpur.

DELABARRE, M. and YEH, R. (1982): Ecologicalimpact and utilisation of deltamethrin in South EastAsia. International Conference on Plant Protectionin the Tropics, 1-4 March, 1982, Kuala Lumpur.Preprint No. II - 2.

FLETCHER, B.T. (1914): Some South Indian insects.p. 334. (cited by Hutson and Alwis, 1934).

FLETCHER, B.T. (1917): Proc. Second EntomologicalMeeting, Pusa. p. 219-220.

HUTSON and ALWIS, DE E. (1934): Two weevil pestsof mango leaves. Trop. Agriculturist, 83: 128-135.

LIM, T.K. (1980): Chemical control of mango anthrac-nose in Malaysia. In vitro fungitoxicity of selectedchemicals. Pertanika, 3: 5-9.

001, B.L. (1976): Biology and Life History of Deporausmarginatus Pasco -- a Curculionid Pest of MangoPlant. B.Sc. (Hons.) Zoology Thesis. University ofMalaya, Kuala Lumpur.

SINGH, G. (1980): The use of a pesticide-foliar fertilizermixture in mango cultivation in Malaysia. SeminarNasional Buah-buahan Malaysia, Universiti PertanianMalaysia, 5-7 Nov., 1980. Preprint No. 14.

(Received 30 April 1982)