Aims: To develop a natural fungicide against aflatoxigenic fungi, to protect stored rice, using the essential oil of lemongrass. Methods and Results: Aspergillus flavus Link. was isolated from stored rice and identified as an aflatoxigenic strain. Lemongrass oil was tested against A. flavus and the test oil was fungistatic and fungicidal against the test pathogen at 0AE6 and 1AE0 mg ml )1 , respectively. Aflatoxin production was completely inhibited at 0AE1 mg ml )1 . The results obtained from the thin layer chromatographic bioassay and gas chromatography indicated citral a and b as the fungicidal constituents in lemongrass oil. During the fumigant toxicity assay of lemongrass oil, the sporulation and the mycelial growth of the test pathogen were inhibited at the concentrations of 2AE80 and 3AE46 mg ml )1 , respectively. Conclusion: Lemongrass oil could be used to manage aflatoxin formation and fungal growth of A. flavus in stored rice. Significance and Impact of the Study: Currently, fungicides are not used to control fungal pests or mycotoxin production on stored rice. Rice treated with the essential oil of lemongrass could be used to manage fungal pests as well as the insect pests in stored rice. The essential oil is chemically safe and acceptable to consumers, as synthetic chemical fungicides can cause adverse health effects to consumers.

Rice plants, infested with eggs of Nilaparvata lugens (Stal) or Nephotettix spp. in laboratory cultures, were used to trap egg parasitoids in rice fields at two sites over a period of four days in Sri Lanka. Levels of egg parasitism per plant varied from 0 to 54% in N. lugens and 45 to 100% in Nephotettix spp. Egg predation was a minor cause of mortality, but attack by a species of Panstenon (Hymenoptera: Pteromalidae) killed up to 18% Nilaparvata lugens eggs. N. lugens eggs were parasitized by Anagrus sp. nr flaveolus Waterhouse, A. optabilis (Perkins) (Hymenoptera: Mymaridae) and Oligosita sp. (Hymenoptera: Trichogrammatidae). Nephotettix spp. eggs were parasitized by two species of Gonatocerus (Hymenoptera: Mymaridae) and one of Paracentrobia (Hymenoptera: Trichogrammatidae). There was no overlap in field host range between the two parasitoid assemblages. Gonatocerus spp. and Paracentrobia spp. seldom attacked the same Nephotettix sp. egg batch, suggesting the possibility that these species compete in the field. Overall egg parasitism of Nilaparvata lugens was positively related to host egg density at the spatial scale of the rice plant, but unrelated at the tiller or batch scale. Nephotettix spp. egg parasitism showed a negative density dependent relationship at the spatial scales of the tiller and plant and no relationship at the batch level. The potential role of these egg parasitoids in preventing outbreaks of hopper pests in Sri Lanka is discussed.

Amplified fragment length polymorphism (AFLP) analysis was used to assess the biodiversity of one of the most important dipteran pests of cereals, the Asian rice gall midge (Orseolia oryzae Wood Mason). Larvae and pupae were collected at 15 locations in five Asian countries and preserved in 95% ethanol for storage, shipment, and DNA extraction using cetyltrimethylammonium bromide (CTAB). Although only approximately 1 microg of DNA was extracted from a single pupa or larva, the use of several AFLP primers in various combinations meant that this amount of DNA was sufficient to allow many DNA fingerprints to be made per individual. Fingerprints were sufficiently reproducible, especially during selective amplification, to allow the genetic diversity within a field population to be characterized. Extraction of DNA from a pool of 20 insects yielded AFLP fingerprints in which variation among individuals was sacrificed in favor of detecting differences among populations. For each location, pooled DNA was amplified with three primer pairs. A total of 261 distinct AFLP bands were identified for the 45 fingerprints. Cluster analysis, performed by the unweighted pair-group method (UPGMA), separated the populations into two distinct groups. Group I included two populations from Guangdong province of southern China and one each from Laos and Imphal in northeastern India, while group II was comprised of eleven populations from elsewhere in India (Assam, Orissa, Madhya Pradesh, Andhra Pradesh, and Kerala) and from Nepal and Sri Lanka. AFLP analysis provided insight into the origins of gall midge biotypes. In 1992, the prevailing biotype in Imphal changed from Indian biotype 3 to a new biotype 3M. Our data show that biotype 3M belongs to group I and did not arise by a recent mutation from biotype 3, which belongs to group II. By contrast, Indian biotypes 2 and 4 are likely to have diverged through recent mutation and selection, as are Chinese biotypes 1 and 4. The almost simultaneous emergence of new biotypes in Kerala and Sri Lanka during 1985-1988 was most probably coincidental, because these biotypes are not closely related. AFLP fingerprints were also able to detect sexual dimorphism in the DNA of adult gall midges and to distinguish gall midge from its major parasite Platygaster oryzae.

To obtain basic information needed to develop an efficient rearing procedure for the rice thrips, Stenchaetothrips hi/armis (Bagnall), its life history was studied. The effects of plant age, adult density, and temperature on fecundity and population growth were determined. Adult females had a longevity of 13 days; during that time they laid 27 eggs, primarily in the youngest leaf of the rice plant. An average of 17 days was required to complete the life cycle from egg to preovipositing adult. Fecundity and population growth were influenced by plant age and adult density. A rearing procedure providing between 400 and 500 thrips daily was developed.

The essential oils of the leaves of Cymbopogon citratus, Cymbopogon nardus, Cinnamomum zeylanacum and rhizome ofAlpinia calcarata grown in Sri Lanka were tested for repellent activity, fumigant toxicity and contact toxicity against Sitophilus oryzae. The major components of the essential oils were geraniol in C. nardus, citral a and b in C. citratus, eugenol in C. zeylanicum and 1,s-cine01 in A. calcarata. In a dual choice repellency test, repellency to S. oryzae increased with increasing dose of each oil except C. zeylanicum a t a dose of 1 mg. Cymbopogon citratus was the most toxic oil to S. oryzae during the fumigant toxicity test with an LC,, value of 0:035 gA. Adults ofS. oryzae were equally susceptible to the fumigant toxicity of C. nardus and C. zeylanicum a t 0.1 gll level. Furthermore, S. oryzae adults were tolerant to the contact (0.15 g/m2) and fumigant (0.1 g/l) activities ofA. calcarata oil and the mortality of the test insects was not significantly different from the controls.