Oct
30
Filed Under (SW10) by Lindsay Gaskins on 30-10-2010

Weed Science Vol. 51(3): pp. 449-455.

The purple loosestrife is the cause of a lot of destruction to the habitat around it, and it has been shown that two particular species of beetles, Galerucella calmariensis and G. puscilla, are very effective at controlling the loosestrife.  But with any biocontrol method, they have their downsides, and one of the big ones is their effect on several species of native plants, one of which is the crepe myrtle.  To help assess whether it is more beneficial ecologically to release the beetles to control the loosestrife, Schooler et al. preformed a test to see the relationship between distance from the released beetle colony and damage done to the crepe myrtle.  They found that as you get further away from the colony of beetles, the damage to the crepe myrtle also decreases, and at 50 meters away, the damage is basically zero to the plants.  The plants were actually not too severely damaged, because the beetles couldn’t complete development on the crepe myrtle, so these results suggest that though there was damage, that the beetle’s introduction to control the purple loosestrife would still be more beneficial overall.

Sep
26
Filed Under (SW5) by Manuela Mejia on 26-09-2010

Biological Control 53, 1-8 (2010)

Biological control is a widely used method of controlling invasive species. The melaleuca tree (Melaleuca quinquenervia), an Australian native currently populating the Florida Everglades, has had devastating effects on the ecosystem. Several biological control agents have been used in an attempt to reduce melaleuca populations.

Min Rayamajhi and his colleagues at the USDA investigated the effectiveness of three biological control agents, herbivorous insects Oxyops vitiosa (weevil) and Boreioglycaspis melaleucae (psyllid) as well as rust fungus Puccinia psidii individually and together. 120 trees were felled, harvested and measured for damage, height, branching, mortality, and biomass for each of the groups. The team found that when used in conjunction, these three control agents caused more damage to the melaleuca than when used separately. Because of their interspecies competition, the insects and fungi each feed on different parts of the tree, resulting in more widespread control. The authors concluded that these species have great potential to suppress melaleuca growth in the Everglades.

Sep
25
Filed Under (SW5) by Lindsay Gaskins on 25-09-2010

The purple loosestrife have gotten out of control in the continental US, and are taking over and choking out native species and altering the habitats.  Blossey et al. argues that the impacts of the purple loosestrife upon the environment are of great enough magnitude where it would be worth it to release another nonnative species, an insect, as a biocontrol method to attempt to reduce the population of the loosestrife and keep it under control.  The loosestrife have risen in both number and extent to which they alter the habitat they live in, and though it might seem that they would only impact other competing native plant species, they also have become enough of a problem where they also are hurting animal species, especially specialized wetland birds.  Though the introduction of other nonnative species may have unforeseen negative impacts, with so much potential in danger as a result of the loosestrife, the prospective benefits would outweigh the possible dangers.

Blossey, Bernd, Luke C. Skinner, and Janith Taylor. “Impact and Management of
Purple Loosestrife.” Biodiversity and Conservation 10 (2001): 1787 – 1807.
Web of Science. Web. 25 Sept. 2010.

Sep
21
Filed Under (SW3, Uncategorized) by Albert Chen on 21-09-2010

The Water Hyacinth is an invasive species that has proliferated since its introduction to Lake Victoria in the 1980’s. The lack of natural predators has allowed the plant to form dense mats over the lake, stagnating surface waters.  Lentic water provides breeding grounds for mosquitos and other disease causing organisms. The plant also robs sunlight, nutrients, and oxygen from the native species, hinders boating, and interrupts subsistence fishing. One of the more recent cleanup efforts involves the use of Neochetina, a weevil that predates on the Water Hyacinth. This form of biocontrol’s degree of effectiveness is a subject being debated.

El Nino weather patterns in 1997/1998 Lake Victoria were stormy, and water hyacinth numbers dipped around same time. Wilson et al. (2007) concluded that the incidental weather was only supplemental to the pressure imposed by the weevils. Low sunlight levels, they argue, present little trouble to the flourishing hyacinths in West Africa and Papua New Guinea and is not a major threat to the plants’ survival.  The study also points out that Lake Victoria’s time frame between weevil introduction and hyacinth decline is consistent with the maximum four years shown in other countries. Being the only control method implemented across the whole lake, weevil biocontrol is likely the main source of the drop. Wilson et al. however acknowledges that the wind and wave action can be major stressors to the perforated, weevil-ravaged plants.

Williams et al. (2007) address the arguments presented by Wilson et al. (2007) by clarifying that though poor lighting may not kill the plants, it is a stressor that compounds with other weather related factors such as water level, wave action, water quality, temperature and humidity. The study also calls attention to the 1998 “crash” that came prior to the larger hyacinth drop. Williams et al. (2007) believe that early deterioration of plant quality led to instability and weevil decline; plants sink, “taking with them weevil eggs, larvae, and pupae.” Williams et al. (2007) agrees that weevils are integral to the reduction of the water hyacinth, but notes that weevil densities remained low up to 2002 and likely did not play the largest role in hyacinth damage.

The authors of both studies seek to better monitor the hyacinth and weevil populations.

Hyacinth populations have rebounded since the two studies were written; nutrient laden runoff is suspected (NASA Earth Observatory, 2007).

I think the studies complement each other very well because each presents new scenarios and variables to be considered. I believe Williams et al. (2007) explanation regarding unstable bug populations is correct because weevils are very weak swimmers and heavily dependent on their hosts.

References

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 20 Jan 2010.

Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline across Lake Victoria – Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87:94-96.

Wilson, J. R. U., O. Ajuonu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenschwander, S. W. Njoka, J. Ogwang, R. H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp. Aquatic Botany 87:90-93.

Sep
21
Filed Under (Uncategorized) by Brandon Braxton on 21-09-2010

Lake Victoria in Africa has been overrun with an invasive plant called the water hyacinth. The plant has affected the local drinking water, which has caused more sicknesses that were not previously prevalent. Water hyacinth has also affected fishing, a major income and food source. Insects called weevils have been introduced as a biocontrol method to eliminate the water hyacinth. Biologist Adrien Williams believes that although weevils did play an important role in the reduction of water hyacinth the largest destruction of water hyacinth was due to the 1997/1998 El Nino. Biologist John Wilson states that the use of weevils in destruction of water hyacinth is the main reason why the plants masses were decreasing. However, the El Nino might have propelled that process.
I agree with Wilson in that the weevils played an important part in the removal of water hyacinth from Lake Victoria and without them the plant would still be a problem. The El Nino alone would not be able to destroy the plants in the massive amount in such little time. The El Nino acted as a positive unexpected factor in the hyacinth’s removal. The change in weather also had a negative affect. Because weevils only feed and affect the water hyacinth, once its numbers lowered due to the destruction of their habitat and food there would be less weevils. Now that we know that the water hyacinth has restored itself we can say that the population decrease of the weevils after the El Nino played a huge role in its resurgence so we cannot rely on nature to come to our rescue. An El Nino only occurs every two to seven years so there needs to be something in place to control the water hyacinth.
This being said biocontrol is not a quick fix all. Recently, due to heavy rains and floods that “swept agricultural run-off and nutrient rich sediment” into the lake, there has been a rebound of water hyacinth. There aren’t going to be drastic changes within a few years but with time the weevils will help deplete the hyacinth to a manageable amount.
References:
NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 20 Jan 2010.
Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline across Lake Victoria – Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87:94-96.
Wilson, J. R. U., O. Ajuonu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenschwander, S. W. Njoka, J. Ogwang, R. H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp. Aquatic Botany 87:90-93.

Sep
14
Filed Under (SW3) by Michael Di Nunzio on 14-09-2010

Michael Di Nunzio

09/13/2010

Water hyacinth has posed a problem for Lake Victoria since first being reported there in 1989. The plant forms dense mats of vegetation that inhibit the movements of fishermen, block sunlight to native plants, and obstruct irrigation systems.  The invasive weeds can also deplete the water’s oxygen levels, suffocating the indigenous flora and fauna of the lake and in turn disrupting the local ecosystem. To control the hyacinth populations, invasive weevils (Neochetina spp.) were introduced with the intention of suppressing the noxious weed.

Using satellite image samples, Wilson et al. (2007) estimated the proliferation of water hyacinth over Lake Victoria and fluctuations in the plant’s presence over time. However, Williams et al. (2007) warns that this method of gathering data is oversimplified for such a complex environment. Regardless, the results indicated that hyacinth levels dropped after the 1998 El Niño disturbed the lake. Following the initial drop in 1998 came a steady rise until 1999 when hyacinth levels again began to decline dramatically. Hyacinth levels stayed at close to zero from 2000 until 2002.

Wilson et al. (2007) reasoned that the drop in 1999 was a result of the control weevils introduced in 1995 becoming effective after four years. They also note that the weevils used indirectly lower plant buoyancy as a means of sinking and controlling the weed, and that wind and wave action from El Niño could have facilitated this process. Because El Niño would inevitably blow some hyacinth into new areas, Wilson et al. (2007) suspected that local reports of hyacinth resurgences might have actually been false. Valid reports of resurgence may have resulted if weevils died due to a lack of buoyant hyacinth leaving the plant temporarily uncontrolled. According to Wilson et al. (2007), there is no substantive evidence to link low light levels with any of the withdrawals of hyacinth.

Williams et al. (2007) places less emphasis on the importance of the weevils in regards to water hyacinth control. Rather than weevils controlling the plants, El Niño more likely pulled hyacinth from the shoreline along with native plants and destroyed them in the lake with wave action. This would account for the decline in 1998. Furthermore, the current nadir in hyacinth is thought to be a fleeting byproduct of the weevils efficacy after 1999 and “suboptimal light.” Williams et al. (2007) points to the River Kagera as a source for resurgence, as hyacinth from this region is untainted with weevils and can float freely into the lake. This means that there is a delay before the biomass control can take effect.

While Wilson et al. (2007) offers the more optimistic outlook on the data set, Williams et al. (2007) is unfortunately the most realistic. Williams et al. (2007) provides the most coherent argument, and reasonably parallels the situation in Lake Victoria with that of sub-tropical climates plagued by water hyacinth. They assume that the current lack of hyacinth is a part of a cyclic process involving a balance between weevils and weeds that will invariably lead to hyacinth resurgences. Wilson et al. (2007) seems to make convenient excuses for all reported instances of resurgence, rather than offering any real insight into their possible validity. The satellite images from MODIS vindicate the argument of Williams et. Al (2007), as resurgence obviously took place by 2006. Thus the relationship between adequate light, the presence of weevils, and the predominance of hyacinth must be a continued subject of study at Lake Victoria if definite conclusions about the hyacinth resurgence cycle are to be drawn.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nas/IOTD/view.php?id=7426. Viewed 12 Sep 2010.

Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline across Lake Victoria – Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87:94-96.

Wilson, J. R. U., O. Ajuonu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenschwander, S. W. Njoka, J. Ogwang, R. H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria

Sep
13
Filed Under (SW3) by Cecile Diaz on 13-09-2010

Scholars debate the main factor of the significant decrease of water hyacinth on Lake Victoria around 1999-2000 in Wilson et al. (2007) and Williams et al. (2007). First, Wilson et al. (2007) replies to a previously published article by Williams et al. (2005) which claims that although weevils played a role in the eventual decrease of water hyacinth on Lake Victoria, the invasive species’ population was ultimately and predominately the result of the 1997/1998 El Nino. Williams et al. (2005) cites the condition of “low light availability” from El Nino and its subsequent effect on water hyacinth’s growth as the main contributor to the weed’s destruction.

Wilson et al. (2007) counters the referenced article by stating first, Neochetina bruchi and Neochetina eichhorniae (collectively Neochetina spp.) were the primary destructive agents to water hyacinth; second, El Nino caused waves and strong currents on Lake Victoria which dispersed its water hyacinth and made the weed easier to destroy by weevils; and third, water hyacinth will not reemerge in Lake Victoria unless its Neochetina spp. populations are disturbed. The authors reevaluated the light conditions around the time of El Nino, but found that by mid-1998, water hyacinth was already rebounding on Lake Victoria. Wilson et al. (2007) acknowledged that weevils took nearly four years to take effect against the invasive species in 1999 (weevils were released into the lake in 1994), but this timetable was expected and is congruent with weevil versus water hyacinth time frames from other countries with similar climates.

Lastly, in Williams et al. (2007)’s rebuttal to Wilson et al. (2007), the authors restate their aforementioned claim that weevils contributed to the reduction of water hyacinth around 1999-2000, but the invasive species would certainly still be growing strong in the absence of the 1997/1998 El Nino. Williams et al. (2007) believe Wilson et al (2007)’s arguments are oversimplified and thus erroneous because Lake Victoria is simply too vast to be considered on an individual graph of experimental results. Williams et al. (2007) maintains the diminution of water hyacinth was a result of El Nino’s flooding because it transpired “synchronously…during the second quarter of 1998”. The authors claim the hyacinth’s first reduction occurred because the floodwaters dislodged the mats that held the weed to the lake floor, and the hyacinth simply washed away into the lake. While Wilson et al. (2007) stated that Williams et al. (2005) believed low light levels caused the reduction, Williams et al. (2007) stressed that the plant mortality was due to prolonged low light, not intermittent glares, which then caused minimal growth in the plants and weak mats.

Ultimately, I believe Wilson et al. (2007) had the soundest argument, which claimed that weevils played the most significant role in reducing the population of water hyacinth on Lake Victoria. While both articles acknowledged the “lesser” cause (whether it was weevils or the effects of El Nino), I felt that Williams et al. (2007) was especially narrow-minded and barely accredited weevils as a destructive force to weevils, when they were clearly a great contributor to the hyacinth’s periodical demise. However, the fact that the water hyacinth continues to make reappearances on Lake Victoria suggests tha solely biocontrol as a method of eradication is insufficient and ultimately non-cost effective. There needs to be a more radical and long-lasting approach to ridding Lake Victoria from the ruthless water hyacinth.

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 10 Sept 2010.

Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline across Lake Victoria – Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87:94-96.

Wilson, J. R. U., O. Ajuonu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenschwander, S. W. Njoka, J. Ogwang, R. H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp. Aquatic Botany 87:90-93.

Sep
13
Filed Under (SW3) by Brandon Braxton on 13-09-2010

Lake Victoria in Africa has been overrun with an invasive plant called the water hyacinth. The plant has affected the local drinking water, which has caused more sicknesses that were not previously prevalent. Water hyacinth has also affected fishing, a major income and food source. Insects called weevils have been introduced as a biocontrol method to eliminate the water hyacinth. Biologist Adrien Williams believes that although weevils did play an important role in the reduction of water hyacinth the largest destruction of water hyacinth was due to the 1997/1998 El Nino. Biologist John Wilson states that the use of weevils in destruction of water hyacinth is the main reason why the plants masses were decreasing. However, the El Nino might have propelled that process.

I agree with Wilson in that the weevils played an important part in the removal of water hyacinth from Lake Victoria and without them the plant would still be a problem. The El Nino alone would not be able to destroy the plants in the massive amount in such little time. The El Nino acted as a positive unexpected factor in the hyacinth’s removal. The change in weather also had a negative affect. Because weevils only feed and affect the water hyacinth, once its numbers lowered due to the destruction of their habitat and food there would be less weevils. Now that we know that the water hyacinth has restored itself we can say that the population decrease of the weevils after the El Nino played a huge role in its resurgence so we cannot rely on nature to come to our rescue.  An El Nino only occurs every two to seven years so there needs to be something in place to control the water hyacinth.

This being said biocontrol is not a quick fix all.  Recently, due to heavy rains and floods that “swept agricultural run-off and nutrient rich sediment” into the lake, there has been a rebound of water hyacinth.  There aren’t going to be drastic changes within a few years but with time the weevils will help deplete the hyacinth to a manageable amount.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 20 Jan 2010.

Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline across Lake Victoria – Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87:94-96.

Wilson, J. R. U., O. Ajuonu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenschwander, S. W. Njoka, J. Ogwang, R. H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp. Aquatic Botany 87:90-93.

Sep
13
Filed Under (SW3) by Michael Reinsvold on 13-09-2010

The water hyacinth plant is an extremely aggressive aquatic plant.  In 1989 it was spotted in Lake Victoria, the largest lake in Africa.  The plant took over tens of thousands of hectares.  In the past decade there have been multiple efforts to combat the water hyacinth invasion.  In 1995 weevils were introduced as a method of biocontrol,  since they have an appetite for the water hyacinth and not local plants.  Wilson et al.(2007) suggest that the weevil was the primary source of decline during 1998 and early 1999.  However, between 1998 and 1999, the largest El Nino event of the century was recorded.  Wilson et al.(2007) admit that the environmental impact of El Nino contributed to the decline of the water hyacinth as well  but they maintain that the weevils were the primary cause for the decrease in the water hyacinth biomass.  The reason the weevils did not have a major effect before 1998 was because it took them three years to spread and multiply.

Williams et al.(2007) make the flip side of this debate over whether the weevil or El Nino was primarily responsible for the decline of water hyacinth in 1998-1999.  Williams et al.(2007)claim that while the weevils aided the decline of water hyacinth, it was El Nino that accounted for most of the decline.    Lake Victoria is massive and subsequently it is difficult to describe it as a single environment.  While the weevil was able to affect much of the water hyacinth once it expanded,  El Nino was able to impact the entirety of the water hyacinth invasion.  The low amounts of sunlight combined with heavy rain decimated the plant.  Williams et al.(2007) make a stronger case of El Nino.  They make use of multiple data points while Wilson et al.(2007) use only one.

Since 2007, however, the water hyacinth in Lake Victoria has been increasing.  The evidence is provided by recent NASA satellite images.  The resurgence is likely caused by two primary effects.  The first one being that the decline in water hyacinth also decreased the weevil population.  The weevils declined as their primary food source decreased.  It curbed the weevil population boom.  The second reason is likely the lack of El Nino.  The El Nino event had a profound impact on the water hyacinth.  Without it, the plant was able to make a recovery.  It is interesting to see how the water hyacinth population changes over the coming years.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 20 Jan 2010.

Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline across Lake Victoria – Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87:94-96.

Wilson, J. R. U., O. Ajuonu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenschwander, S. W. Njoka, J. Ogwang, R. H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp. Aquatic Botany 87:90-93.

Sep
13
Filed Under (SW3) by Lindsay Gaskins on 13-09-2010

Water Hyacinth

The water hyacinth has been the subject of both much concern and debate over the past years.  It’s dramatic takeover of Lake Victoria in Uganda has sparked a heated discussion on why the invader suddenly receded, though it later came back.  The opposing views were in expressed in Wilson et al, arguing that weevils should be given the most credit for the reduction of the water hyacinth, whereas Williams et. al presented the argument that El Niño should be given the credit.

The Wilson et al. paper presents a strong argument, saying that the weevils introduction to Lake Victoria was the main reason for the water hyacinth’s decline.  Though they acknowledge that El Niño may have had a slight effect on the water hyacinth population, the light levels that got through the cloudy weather as a result of the altered climate pattern would’ve been enough to keep the water hyacinth population alive and growing, so the answer to the question of why the water hyacinth declined muse lie in the biocontrol, or the weevils.  Williams et al. presents essentially the opposite argument,  saying that El Niño’s cloud pattern would’ve blocked out light for the water hyacinth, therefore making it hard from them to photosynthesize and expand throughout the lake.  To back their argument, they cited that this wet and cloudy weather had a detrimental effect upon vegetation throughout other parts of Africa as well, and that the weevils may had a helping hand in the decline, but were in the end, of nominal effect in the larger scheme of things.

I think that Wilson et al.’s argument in favor of the biocontrol makes the most sense, given the dramatic reduction of water hyacinth population after the introduction of the weevils, and the sustained decline even after the passing of El Niño. Though the light levels made have adversely effected the population of the water hyacinth, the light levels despite the cloudy weather wouldn’t have stopped their growth and caused the population reduction.  Though, as MODIS images revealed, the water hyacinth has returned, it just reminds us that when using biocontrol, that constant monitoring is required, and problems with invasive species will be something that our society will have to learn to cope with for many years to come.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 13 Sept 2010.

Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline across Lake Victoria – Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87:94-96.

Wilson, J. R. U., O. Ajuonu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenschwander, S. W. Njoka, J. Ogwang, R. H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp. Aquatic Botany 87:90-93.

Photo from here.