INSECTS ON VETIVER HEDGES
(Guangxi University, Nanning, China 530001)
Vetiveria zizanioides (L.) Nash is a perennial plant. In order to conserve and also effect better usage of the natural resources of insects, the author carried out an investigation of insects on vetiver hedges, from March to November 1998 in Guangxi Province of China. The results showed as follows:
In 211 days of investigation, 1225 common species of insects were found in Nanning suburb of Guangxi Province, of these there were 79 species on vetiver hedges. These insects were came from 53 families of 13 orders. There were 14 species from Hymenoptera, 11 species from orthoptera, 10 from Diptera, 9 from Homoptera, 9 species from Lepidoptera, 9 from Coleoptera, 5 from Odonata, 4 from Hemiptera, 3 from Mantodea, 2 from Blattaria, 1 from Isoptera, 1 from Dermaptera, and 1 from Collembola.
Defoliation insects on vetiver hedge
There were 27 species on the leaves or stems of vetiver hedges, and 14 species of them were chewing mouthparts insects:
Among them, O.intricata (stal), A.burri I Bolival, C.rufipennis Jin et L., A.cattigarensis Weise, A.fermoralis (M) and tussock moth (Lymantriidae). can eat vetiver leaves. Especially, O. intricata was found on 46 days out of the 211 day survey period.
The other 13 species on vetiver's leaves were sapsucking insects:
As stated above, most of the species accidentaly perched on the leaves, and only used stylet probes to attack the leaves.
Stalk and root insects on vetiver hedges
There were 3 insect species on the stalks of vetiver. Snoutmoths (Pyralidae) fed in stem and discoved excreta. The insect came from Jiangxi Province through the transportation of planting materials.
On mountain land, the vetiver stems were gnawed by a bamboo rat, and an earwig (Labiduridae) was found in the stem. When wrapped leaves were peeled, mealybugs (Pseudococcidae) was found on the stem joint.
But, borer insects such as bark beettle and weevil were found only on vetiver's leaves, possibly because they were not fond of eating vetiver.
There were 6 species of insects found on roots, namelly:
Most of the above species are saprophagous and crumbs insects.
Predator insects on vetiver hedge
There were 25 species of predator insects on vetiver hedges:
The above-mentioned prey insects fed chiefly on locust and aphids.
There were 5 speciesof parasite insects on vetiver hedges:
When vetiver was in its growing stages, most of the insects were predators alongside the growth of locusts. After September, the number of enemy gradually dwindled. Two things accounted for the occurrence. One possibility is that vetiver get intoreproduction period. Another possibility is that preyenemy insects were attracted by the odour of vetiver leaves. Similarly, after October, Cynipencyrtus sp. and antsgraduallyraises along with aphids on vetiver spike.
Perching insects on vetiver hedge
There are 13 species on vetiver hedges and these insects were not found eating vetiver.
Frequently perching insects: 4 species, namelly Muscadomestica Vicina (appeared for 36 days), M.sorbens Wiedemam, Chrysomyia megacephala Fab, Lucilia cuprina (Wiedemam).
Short time perching insects: 9 species. These insects were named as "tourer" by some scholars (as S.R. Southwood et al 1984) because retention period of them on vetiver was short. Most are butterflies and moths, namelly Parnara guttatus Bremer et Grey, Padmona dora confucius Falderman, Ampittia dioscorides Fab, Lampides boeticus L. and deer moths (Amatidae), night moths (Noctuidae). The above 6 species perched on leaves. Euploea mulciber barsine Fruhstorter and Papilio Polytes L only flew across Vetiver hedges. Another 4 species, namelly Crocisa emarginata Lepeletier, Apis florea F (belong to Hymenoptera Apoidae), not named, midges (Chironomidae), mothflies (Psychodidae).
The followings is a summary:
Position Habits Total
Leaf 14 (chewing)13 (sapsucking) 27
Stem and root 3 (stem) 6 (root) 9
Predator 25 (prey 5 (parasitic) 30
Perching 4 (frequent) 9 (short) 13
With regards to insects on vetiver hedges, Smyle, J.W. and Magrath, W.B. pointed out that for several centuries, vetiver grew adjacent to crops in Africa, Asia, and the Caribbean islands and were not found as an intermediary host of pests (1991). Similarly, Guo ting fu (1990), Chenkai (1992), Grimshaw, R.G.(1990) and Auhuixiu(1996) all indicated that growth and green parts of vetiver were not effected by termites.
But some scholars point out that vetiver hosted pests due to a change of environmental conditions in some areas, such as Huili and Pingshang counties in ShiChun Province. In Jiangxi, Guizhou (1990) people found armyworms and rice snoutmoth, and these 2 pests all needed insecticide control. Paul Trung (1996) point out that Monto vetiver of Austria under hot house conditions had been harmed by armyworm larva
Under the environmental conditions of Nanning of Guangxi Province of China vegetables and flowers are widely cultivated. Of 79 species of insects on Vetiver hedges, insects eating vetiver leaf in test tube are locust, snoutmoth, tussockmoth and leaf beetle. Owing to a tiny population density and limited amount eaten these insects did not cause negative effect on vetiver growth. On the contrary, beneficial predators (total 30 species) were attracted to the vetiver hedges, such as mantids, dragonfly, ladybug etc. -- all are important preadtor insects of garden, agriculture, and forestry pests. Therefore, the author suggests that when vetiver is introduced to a new environment it would be appropriate to practice integrated pest management (IPM). Due to the short time of survey, the above conclusion needs verification by further research.
 Smyle.J.W. and Magrath W.B. Vetiver grass - - A Hedge Against Erosion. Paper presented at the American Society of Agronomy Annual Meetings in San Antonip, Texas. October 1990.
Zhang Yong qiang et al. Insect catalogue of Guangxi Presented at the China: Guangxi Science Technology Press. December 1994.