The Department of Entomology of the Research Institute for Agriculture at Maros is concerned with insect pests of food crops, and serves the needs of farmers, most of them living near subsistance level, and of extension workers.
South Sulawesi, formerly known as South Celebes, is a major rice-growing province and one of the two provinces of Indonesia that produces a rice surplus. The area planted with rice is about 550,000 hectares, which is more than half of the total arable land. A sketch of the agriculture of South Sulawesi is given.
A justification of the activities is presented by the results that have been obtained while striving for a more up-to-date and varied research programme in order to achieve a better control of rice insects at farmers' level.
The major and minor insects pests of rice and the rice tungro virus are presented and the nature of damage described.
The white stem borer, Tryporyza innotata
is the most important pest. The rice seedbug, Leptocorisa oratorius,
and the rice leaf folder, Cnaphalocrosis medinalis,
come next. Insects of minor significance include the whorl maggot Hydrellia phillippina,
the caseworm Nymphula stagnalis,
spp., the green leafhopper Nephotettix virescens,
the white-backed planthopper Sogatella furcifera,
the pink stem borer Sesamia inferens,
the striped stem borer Chilo suppressalis,
the brown planthopper Nilaparvata lugens,
the green stinkbug Nezara viridula
The brown planthopper is likely to become a major pest in South Sulawesi and it is quite possible that there will be other shifts in the future as well.
Evaluation systems for infestations in insecticide trials, in phenological studies and in varietal screening tests are described for the whorl maggot, caseworm, stem borers, brown planthopper, green leafhopper, leaf folder and seedbug. These systems include rating scales, assessments and direct and indirect counting methods.
Experiments to establish the crop losses inflicted by each individual insect species on its specific plant stages were conducted both in the field and in greenhouses.
It was found that roughly 5 to 10 per cent of the crop is lost by the combined effects of normal, light infestations of Hydrellia, Cnaphalocrosis, Nymphula
and grasshoppers up to four weeks after transplanting.
Yield losses of 10 to 20 per cent caused by stem borers is the rule rather than the exception. There was a poor correlation between dead heart counts and yield loss, but every unit per cent white head consistently caused about one per cent loss in yield.Cnaphalocrosis medinalis
infestations of the later vegetative and generative stages may often inflict losses of 5 to 10 per cent.
Another 5 to 10 per cent is frequently caused by Leptocorisa oratorius,
sucking on the ripening grains. Boiling mature grains in a KOH solution provides an easy and reliable method to assess the percentage of infested grains. This percentage of infested grains proved to be silimar to the yield loss inflicted.
Defoliation experiments, designed to simulate the damage caused by leaffeeding insects, showed that rice does not fully recover after serious defoliations even in very early growing stages. The effect of defoliation is most severe between 7 and 9 weeks after transplanting. Towards maturity of the grains defoliation becomes progressively less damaging.
Every one per cent increase in tungro infection reduces yield by a half or one per cent depending upon the rice variety and the time of infection.
It is concluded that insects alone reduce the potential yield of rice varieties such as Pelita, C4-63, IR5, IR20, IR26, SPR and B462c by 1 to 3 tons per hectare or 30 to 40 per cent in South Sulawesi.
Population densities of most of the pest insects and the rice tungro virus incidence were monitored by rating scales and direct counts from the end of 1974 onwards. A light trap was used to monitor fluctuations of T. innotata, Ch. suppressalis, Noctuidae, Cn. medinalis, N. virescens
and N. nigropictus.
Of course, not many conclusions can be drawn from graphs that represent the data of less than two and a half years. They form, however, a basis for further work.
A great number of insecticide experiments were conducted with insecticides that became available in the late sixties and seventies. Up to about 1973 most of the attention was focussed on conventional applications, later other modes of applications were very successfully investigated.
Insecticides proved to be effective in controlling the pest insects and tungro virus. Carbofuran is an excellent insecticide but chlordimeform, mephosfolan, cartap, diazinon, BPMC, monocrotophos and others are also good.
Granular broadcast applications are superior to spraying. By far the best method is the root-zone application of systemic insecticides. The insecticide is applied between the roots and taken up by the plant. The Maros Research Institute developed and concentrated on the mud ball technique.
If a lump, plucked from a big moist mud ball containing insecticide, is applied soon after transplanting, it often gives protection up to harvest time. The quantity of insecticide required is quite low, there is no equipment needed, it cannot be washed away, one application suffices and the secondary effects are probably negligible. The root-zone application almost invariably gives the highest yields and in many cases doubles even the best spray or granular application. It requires more labour, which is advantageous macro-economically, but is of course disliked by the farmer.
It is envisaged that with the growing concern for the environment and ecosystems and the increasing prices of insecticides, there is a future for this rootzone application technique, in spite of its prophylactic nature. Several methods, such as mud balls and liquid applicator, and time and density of application are discussed.
The total insecticide consumption in South Sulawesi is low, less than one litre per hectare per season. There is a discrepancy between what is available, what should be used and the actual demand. The situation is slowly changing for the better.
The incorporation of insect-resistant genes into high-yielding rice varieties has only recently been given much attention. Because of a coincidence, the search for varietal resistance has been most rewarding for Maros in the case of the leafhopper-transmitted tungro virus. Many thousand varieties and lines have been evaluated and the information has been incorporated into breeding material and varieties of the International Rice Research Institute and other institutions.
From the screening for varietal resistance against the brown planthopper, Nilaparvata lugens,
at least two local Sulawesi varieties were found promising for breeding activities. Biotype 1 is the predominant planthopper in South Sulawesi.
The impact of the release of tungro-resistant varieties in South Sulawesi and brown planthopper resistant varieties elsewhere in Indonesia, has been enormous. In the latter case only temporary, due to the development of new biotypes. Voluntary restraints are suggested with the introduction of resistant material to places where that particular pest is not (yet) a problem, such as the brown planthopper in South Sulawesi.
A detailed account is given of the recent tungro outbreak transmitted by the green leafhopper, Nephotettix virescens,
in South Sulawesi with special reference to some ecological and phenological aspects.
Discouraging the growing of Pelita and increasing the growing of resistant varieties, especially C4-63, IR20 and some local varieties have been the main reason for the decrease in tungro incidence.
Insecticide sprays and broadcast applications are fairly effective in controlling the virus. The root-zone application of carbofuran, BPMC, cartap and mephosfolan proved to be extremely effective. When these insecticides are applied to the root- zone, the green leafhopper is killed before it can transmit sufficient tungro inoculum.
Rice plants are infected by tungro in the field after transplanting and not in the seedbed. Also, direct-seeded rice is less infected than transplanted rice.