Mukarugwiro J A, Newete S W, Nsanganwimana F, Byrne M J
School of Animal, Plant and Environmental Sciences (APES), University of the Witwatersrand, Private Bag X3, Johannesburg, 2050, South Africa; Centre for Invasion Biology (CIB), South Africa.
School of Animal, Plant and Environmental Sciences (APES), University of the Witwatersrand, Private Bag X3, Johannesburg, 2050, South Africa; Agricultural Research Council-Natural Resource and Engineering (ARC-NRE), Geo-Information Science Division, Arcadia, Private Bag X79, Pretoria, 0008, South Africa.
Environ Res. 2023 Nov 15;237(Pt 1):116946. doi: 10.1016/j.envres.2023.116946. Epub 2023 Aug 23.
Water hyacinth is the target of nine biological control agents in South Africa including Neochetina eichhorniae (Warner) and Neochetina bruchi (Hustache) (Coleoptera: Curculionidae). These two weevils have also been released against water hyacinth in Rwanda, but failed to control the weed invasion, possibly due to high turbidity in the country's water bodies. This study therefore aimed to investigate the effect of water turbidity on the establishment and performance of N. eichhorniae in Rwanda. Turbidity levels were measured over two seasons in four Rwandan rivers and two lakes. The results were then used to benchmark laboratory trials to test the effect of turbidity on the weevils' development. Water hyacinth plants were maintained at four turbidity levels: Clear water (2 Nephelometric Turbidity Units (NTU): low (85 NTU), medium (600 NTU) and high (1500 NTU). Each treatment plant was inoculated with three N. eichhorniae larvae, while control plants were free of larvae. Plant growth was measured weekly for three months, while adult weevil emergence was recorded from the 56th day of the experiment. The number of adults emerging from the treatment plants grown in the clear water, low, medium and high turbidity levels were 24, 21, 12 and 0, respectively. Larval feeding was greater on plants growing in clear water and the low turbidity, compared to the medium and high turbidity treatments. These results indicate that N. eichhorniae may not establish or perform well in water bodies with high levels of turbidity, which in turn enhances the growth of water hyacinth, allowing compensatory growth for weevil feeding.
凤眼莲是南非9种生物防治剂的防治对象，其中包括水葫芦象甲（Neochetina eichhorniae (Warner)）和布鲁氏水葫芦象甲（Neochetina bruchi (Hustache)）（鞘翅目：象甲科）。这两种象甲也已在卢旺达投放用于防治凤眼莲，但未能控制杂草入侵，可能是由于该国水体浊度较高。因此，本研究旨在调查水体浊度对卢旺达水葫芦象甲定殖和性能的影响。在卢旺达的4条河流和2个湖泊中，对两个季节的浊度水平进行了测量。然后将结果用于基准实验室试验，以测试浊度对象甲发育的影响。凤眼莲植株维持在4种浊度水平：清水（2散射浊度单位（NTU））、低（85 NTU）、中（600 NTU）和高（1500 NTU）。每个处理植株接种3只水葫芦象甲幼虫，而对照植株不接幼虫。连续三个月每周测量植株生长情况，同时从实验第56天开始记录成虫象甲羽化情况。在清水、低、中、高浊度水平下生长的处理植株羽化出的成虫数量分别为24、21、12和0。与中、高浊度处理相比，幼虫在清水和低浊度环境中生长的植株上取食更多。这些结果表明，水葫芦象甲可能无法在高浊度水体中定殖或良好生长，这反过来会促进凤眼莲生长，使象甲取食后的补偿生长得以实现。
