Title: Distribution and Range Expansion of two Biocontrol Agents Neochetina eichorniae Warner and Neochetina bruchi Hustache (Coleoptera: Curculionidae) and its possible Impact toward local Insect Biodiversity.

Invasive Alien Insect Species

Eichhornia crassipes Martius is an invasive plant species that occupies many water areas.It has a destructive impact on native ecosystems due to biomass accumulation, rapid closure of lake and river surfaces causing the shallowing of rivers and lakes. Thus it became an important element for changes in the landscape. In 1974/1975 and in 1995/1996, two biocontrol agents (Neochtina eichorniae) and Neochetina bruchi (Coleoptera: Curculionidae) from Amazone, Brazil were introduced. Both species had been released in West Java around Bogor and Jakarta, and since that spread out to many other areas in Java, Sumatra, Kalimantan and Irian Jaya. However, data showed that the spread of these insects do not result in the decrease of E. crassipes population and by now no evaluation and monitoring for studying the effectiveness of these species has been conducted. In fact there are some preliminary data which show that the expansive ability of these exotic insects might potentially harm the insect diversity by eliminating local insects through competition and expanding its potential host plants beside the water hyacinth. We perceive the possible features of N. eichorniae and N. bruchi as invasive species. Its impact toward local diversity is an important issue that has to be studied.
Thus our questions are 1) how successful was the introduction of biocontrol agents to decrease the habitat degradation caused by invasive plants? 2) what are the impacts of this introduction toward the native insect population?
By studying the range expansion of Neochetina we try to understand the possible impacts of species introductions toward the health of an ecosystem. Investigation of the potential hazards for native species as well as how to anticipate these negative impacts and finding a possible way to actively involve the local community in the conservation efforts will be done through a comprehensive study. This research is the first of its kind in Indonesia and thus it will offer urgent information for conservation in the tropics. The result will be used to develop a research model that can be applied to evaluate the biological control efforts for Eichhornia crassipes using Neochetina spp in other regions.
The research was developed through meetings and discussions with different experts and by field trials in order to create a framework for the research implementation. Insect sampling and vegetation analyses were conducted at five different regions, Bogor, Jakarta, Purwakarta, Sukabumi and Cilegon. From July 2003 to January 2004 the field work focused on the sampling of beetle populations and vegetation analyses in different locations covering different altitudes and habitats. The sampling was conducted at four different selected locations in West Jawa, Lido Lake-Sukabumi (S:06o44’33,0”; E:106o48’45,8”; 512m a.s.l), Muara Angke-Wetlands (S:06o06’54,7”; E:106o46’2,2”; 28m a.s.l), Karawang (S:06o11’28,7”; E:107o26’56,8”; 37m a.s.l), and Purwakarta (S06o30’18,5”; E:107o23’26,6”; 56m a.s.l.).

Invasive Aliens Insect Species

Neochetina was surveyed by hand collections at selected plots. o far, we found Neochetina in Muara Angke, Lido-Lake, and Purwakarta but not in Karawang. All of the collected beetles were Neochetina eichorniae . N. bruchi has not been found,which indicates that N. eichorniae is the dominating species in those habitats. Even though it is too early to say that, we predict that there is inter-specific competition between those beetles which can lead to a population decrease of N bruchi. The number of beetles in Muara Angke and Purwakarta (lower altitudes) is significantly higher than in Lido Lake (higher altitude). The results from different areas at West Java showed that the number of beetles collected is significantly related to the population size of the water hyacinth. If the beetle doesn’t exist, the abundance of water hyacinth is high. This is also shown by the fact that Neochetina has not been found in Karawang where the water hyacinth is highly abundant. Our analyses proved that Neochetina decreases the water hyacinths population but not enough to control the population under a desired threshold value. The survey showed that the water hyacinth is still covering the freshwater surfaces in many wetland areas, such as in Muara Angke, Jakarta. Based on the vegetation sampling, we found 3-6 plant species colonizing fresh water at selected locations. The analyses showed that the water hyacinth is dominating the space. The index value for water hyacinth was significantly higher than for other aquatic plants living in the same habitats. To date we are still working on sorting, identifying and analyzing the insect data.
Our analyses proved that the weevil could survive in other host plants between 10 to 54 days by consuming leafs and stems of the plants. The weevil also successfully reproduces and lays its eggs on two of the seven tested host plants. Although this species favor to consume water hyacinth, it could cause significant damage on several tested aquatic plants like Ludwigia adscendens and Spirodela sp. This fact demonstrates a potential negative impact on non-target aquatic plants. This supports our hypothesis that the weevil also lives in other aquatic plants and harms those.