Insects on Vetiver Hedges in China ( II )
\by Chen Shangwen (Institute of forestry of Guangxi University, Nanning)
Vetiveria zizanioides a perennial grass of grass family and paddy subfamily is being paid great attention recently by hundreds of countries and introduced widely. Since the vetiver was introduced from Jiangxi to Nanning, Guangxi, 79 varieties of insect were attracted to the vetiver grass hedgediscoved on March 20, to Nov. 15, 1998. Among those, 14 varieties including Oxya Intricata (Stal) took the leaves of vetiver for feed. There were 30 beneficial varieties of insects as the natural enemy of destructive insects inhabited on the vetiver hedge. Its prospect of controlling destructive insects in agriculture and forestry was described in the first paper written by the author. In another paper the authors advanced that 89 varieties of insects have been found on the grass hedges. A further observation will be reported in this paper.
I. Method and Content
The experimental sites are located on N 22 29; E 108 21; and apart from the Tropic of Cancer about 50 km i.e. on the cut-flower base and Luo San Reservoir of Gao Feng Tree Farm directly under the district of Guangxi, and the campus of forestry institute of Guangxi University.
The atmosphere temperature and relative humidity were record every day with a dic fix temperature meter. Each observation on insects with eyes was conducted and lasted for 30 minutes at a definite time of morning, noon, and evening, and the random observation also conducted at other time. All the emergence of things was recorded. In addition, note was also given to the state of insects during transplanting, fertilizing, pruning and soil loosen etc. processes. The insects collected were appraised under a anatomical glass (lens). The observing contents included: variety and its number, time, times and days of emergence; and the habit of taking food, mating, inhabitation, fly and gathering. The difference of insects between mono-planting in the mountainous area and a compound grass hedge mixed with several kinds of plants in the garden of urban land was also observed.
II. Results and Analysis
Altogether 102 species of insects were found on the vetiver hedge in a period of 211days from Nov. 16, 1998 to July 14, 1999. It belongs to the insect Class Hexpoda, 14 Orders and 63 Families. Among these most is of Order Hymenoptera, 12 families and 19 species were included. Lepidoptera was the next for 11 families and 18 species. Followed by Diptera for 10 families and 14 species; Coleoptera for 8 families and 12 species; Orthoptera for 6 families and 8 species; Odonata, for 3 families and 7 species. There were altogether 50 families and 78 species in the above 6 orders. It accounts for 77.4 % of the total quantity of species. As compared with the former period i.e. from March 20, to Nov.15, 1998 Isoptera order disappeared, while two other orders, Thysanoptera and Neuroptera appeared. That is one order for 10 families and 23 species increased. The reason for this would be that with the increase of settle time of the vetiver as a new plant introduced the succession of insect communities occurred. The species numbers of the rudimentary insects decreased whereas the species number in an order of higher evolution such as Hymenoptera increased. The species number in the order of Orthoptera ranked the second in former period but it dropped to fifth position now.
1. Leaf - eating insects on the leaves
There were 13 species of masticatory insects inhabiting on the leaves. Six species belong to Acridoidea family of Orthoptera order. It was dominated by Oxya Intricata (Stal) in a period of 211 days, similar to the former period. The emergent days of it were the most, 27 days. The days emerged of Catantops sp were ascendant, i.e. 19 days. The emergent days were few and only concentrated in June for Aulacophora fermoralls (Motschllesky) of Coleoptera order. A kind of Longitarsus sp. newly found gathered together on the mountainous land and took the leaves of vetiver transplanted in winter for feed then made the leaves some holes. The destructive insects Chlor ophorus annularis (Fab) of bamboo and Cylas formicaris (Fab) of Yam also emerged on the leaves but only one day.
Sucking insects were less emergence only four species. There were two species in Homoptera. The emergent days of Ricaniidae increased to twelve and it reached to a peak in June. Another species newly emerged was Derbidae. There were two species in Hemiptera, one is Cletus punctiger and another Tessaratoma papillosa Drury which is the famous destructive insect for Logan and litchi. Its adult insect ( imago) inhabited on the leaves (hold the leaves) on the fifth of April. The yearling nymph emerged on the fifteenth of March and the nymph of five length of time emerged on the thirtieth of May and the fifth of June. These species of insects only felt the leaves out of its sucking mouth, except for Ricaniidae which had a slight trace taking leaves for feed. The reason why the species of destructive insects on the leaves decreased from 13 to 4 may be the insects such as Nephotettix cincitceps (Uhler) emerged in the former period only made inroads the annual grass family such as rice. As the growth of vetiver entered to the second year its nutrients component in the leaves has changed.
2. Insects in the spike, stem and root
There were 8 species of insects in the spike. After Nov. the emergent time of aphid was the longest lasting 45days. The other insects were: three species of ant, ladybird, bulb fly, Aphelinidae and Encertidae. Among them the emergent days were more for the bulb fly, it was 15 days.
There were 6 species of insect on the stem. Holes that was moth eaten by Xyleborus sp. were found on the stem burned by fire on a mountainous land in August. It showed that the Xyleborus sp. emerged formerly on the leaves was not accidental. The bore hole of borer could be found under bad hygienic condition and among light-color and weak leaves clumps of vetiver. It may lead to the stem breaking off but it occurred extremely accidentally. The Saccharicoccus sp. newly emerged in Nov. in a compound grass hedge of the garden would destroy the node of stem. The insect body wrapped by cottony matter could be seen. In a serious time more than 10 nymphs on a node of stem were found thus it would result in a sooty mould. Taking food by the sucking mouth of Saccharilcoccus sp. could not result in the stem breaking. The node of stem destroyed by it still developed roots as it soaked in water. Labiduridae of Dermaptera order could emerge on the broken stem and root. In addition, two species of thrips were found on the subtending leaves and node of stems.
There were 5species of insects were found on the roots. In addition to earwigs and cricket, the vinegar flies, scarab and Blattella germanica (L) were newly found. The saprophytic insects mycetophilids, Ostomatidae and springtails etc. may be found in the rotten processes of root.
3. Insects of natural enemy
Altogether there were 26 species of predatory insects. Seven species belonged to Odonata. The time emerged of Gomphidae and Pantala flavescens Fab increased, and they usually inhabited on the tip of leaves in the morning. A mating behavior carried on the leaves for a species of Coenagriidae of Zygoptera order. There were 7 species of ant in the Hymenoptera order, of which Camponotus sp. was a newly emergent species. The emergent times of Parapol ybia varia varia Fab of Vespoidea increased. In addition, the newly emergent species were: Ropalidiidae and Delta campaniforme esuriens (Fabricius). Micraspis discolor (Fab), Vibidia duodecimgutata, (Poda), and Nephus sp. in the order of Coleoptera were newlydiscoved. Melanostoma scalare (Fabricius) in the order of Diptera was found. The emergence of Mantodea decreased, only Paratenodera sinensis Saussure was found. The emergent days of Vespa tropica leefmansi Van der Vecht was also decreased. The points for particular attention were the new emergence of Chrysopa carnea Stephens and Grocus sp. in the Neuroptera order. It was interesting that the long-horned katydids possessed a big body ( long to 70mm) was attracted and inhabited in a empty birds nest constructed on the dense vetiver based compound hedges. The emergent times of parasitic natural enemy increased but its species were less, i.e. only 5 species: Larvaevoridae, Ichneumonidae, Aphelinidae, Encertidae and Tetrastichidae which was newly found for catching eggs of borer on the leaves.
4. Inhabiting insects
There were 38 species ltogether. It is especially emerged more in the compound grass hedge. The Musca domestica vicina Macqurt and Chrysomyia megacephala Fab etc. continuously inhabited emerged for 44 days and 40 days or more respectively. They were only next to the Saccharicoccus sp. and aphid. In addition, mating of Musca domestica vicina Macqurt on the leaves of grass was found. The number of species and times of emergence of Nematocera order increased after vetiver pruning in winter such as mosquitoes [Culicidae], midges [Chironomidae], and Psychodidae etc. The inhabitation of Amata sp., Lampides boeticus L. and Pieris rapae L. Changed from original short turned to steady. Their emergent days were 15, 13, and 10 respectively. Especially the Amata sp. was found in both mountainous land and garden, and there were two times of mating on the hedge observed. Lampides boeticus L. could stay on the hedge overnight. Times of stay and inhabiting also increased for Apis cerana Fab.
Among short term inhabiting insects most were the butterflies. Melanitis leda L., Diaphania sp., Tortricidae were newly discoved. PaPilio Polytes L and PaPilio demoleus L fleeted across the hedge or only sucked the flower pollen of composite family in the compound hedges. And Precis almana L. flew around the grass hedge. The small black beetle and Arge pagana ( Panzer) and Athalia rosae japanensis (Rhower) were also newly found. Some insects such as Stephanitis (Stephanitis) typica (Distant) and Coptosoma sp. ( to take the seeds of Gendarussa vulgaris for food) didnt want to stay on the vetiver. It showed that there was selectivity for the attraction of vetiver to insects. Vetiver formed its own insect resistance.
The ecological environment would be changed since vetiver introduced. One of them is the change of insects. As Waloff (1968) indicated that with the change of age of a single host plant its nutrient component and the standing condition changed. Therefore the succession of insects occurred. In this continuous observation of 422 days this point of view was verified. For example, in the former period ( 211 days ) the Macrotermes barneyi Light emerged but it didnt emerge later. The food taking of Oxya Intricata (Stal) in the later period decreased from former 45 days to 19 days. However, the appearance for the Catantops sp. increased to nearly 20 days. That the appearance of sucking insects decreased on the leaves and increased on the stem was more notable. It was distinct that the insects species during vegetative period and reproductive stage was different. For example, the [ Saccharicoccus sp.] and Aphididae became dominant insects only at the period of heading.
Keeping the bio-diversity is a hot topic at present time. A diversity of plant communities always resulted in the diversity of insect communities. The investigation on plants and arthropoda group inhabited on a mono-plant and multiple plants was made by Root (1973). Also Murdoch, Evans and Peterson (1972) et al. have researched the effect of plant species and pattern on plant feeding insects. According to the observation, the effect of mono-vetiver hedges established on the mountainous land and the vetiver based compound hedge in the garden of urban district on the insects was different. More difference was found on the numbers of species. leaf beetles, Amata sp. and Catantops sp. always emerged in the mountainous land with few natural enemy, but on the compound grass hedge not only were found more natural enemies, butterflies and saprophytic flies etc. were also more. It showed that the diversity of plant communities in the compound grass hedge resulted in a diversity of insect communities. This is only a preliminary observation and a further systematic research will be needed.
A stronger insect-resistance of vetiver in many areas was proved by scientists. It is confirmed in Nanning of Guangxi Province. The insect-resistance and diversity are not contradictory. Insect-resistance displays two respects: anti-feeding effect and endurance. The two behaviors appeared gradually with the extension of time of settlement, such as the restraining of food taking for Oxya Intricata (Stal). It shows a good prospect for sustained controlling destructive insects in agroforestry management. However, much remains to be studied, including appearance of Chlorophorus annularis ( Fab ), Saccharicoccus sp., and Tessaratoma papillosa attracted to the hedges.
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