Predation of water bug Sphaerodema rusticum Fabricius on the snail Pomaceabridgesi (Reeve), introduced in India

Aditya G; Raut SK

摘要

Being a native of Peru, Bolivia, Brazil and Paraguay, the ampullariid snails Pomacea bridgesi are now thriving well in Florida, Hawaii and in the countries of south-east Asia, including India. They are a serious threat to taro2 and paddy plants, and to gastropod fauna4 of the introduced areas. Also, the fact that they may be involved with the spread of human diseases is of grave concern. Therefore, attempts are being made to prevent their spread furthermore, and to keep the population density in check. Though voracity of P. bridgesi is on record, reports on the organisms devouring them are still wanting, with a view to develop the control strategy. Accordingly, we investigated the same by offering P. bridgesi to the water bug Sphaerodema rusticum, the most effective predator1334 of the endemic freshwater gastropod species experimentally, in the laboratory. The required number of plastic containers (each 135 mm in diameter and 32 mm in depth), containing 250 ml pond water, laboratory-reared P. bridgesi belonging to the size-groups, 2.5-4.5 mm (the newly hatched snails range from 2.3 to 2.7 mm in shell length), 5.0-7.0 mm, 7.5-9.5 mm, 10.0-12.0 mm and 12.5-14.5 mm in shell length, and pond-collected adult S. rusticum were considered for the experiment. In all cases, 15 snails were exposed to a single water bug in a container, for a period of 24 h. Initially, experiments were performed with the snails with regard to their size-group, separately. Since the water bugs failed to capture the snails belonging to 10-12 mm and 12.5-14.5 mm size-groups, we finally supplied individuals belonging to the remaining 3 size-groups together in different combinations, taking at least 2 individuals of a size-group, to the predator to note the preference if any, for the specific sized prey individuals. Observations were continued for 6 consecutive days in the former and 39 days in the later experiments. S. rusticum, essentially a sucker of the visceral mass of P. bridgesi, sometimes consumed it completely (evident from dropping of empty shell from the rostrum) and sometimes, partially (evident from dropping of shell containing a portion of visceral mass). It is to be mentioned that, in cases of complete consumption a small amount of fibre-like material, following dropping of the shell, was seen hanging from the tip of the rostrum of S. rusticum. These fibres were, sometimes consumed or left in the water by the bug. Killing of the snails by such types of feeding was termed as 'destruction'. Data were recorded accordingly, with respect to the feeding types, regularly, at the end of every 24 h. The snails were fed with lettuce and the water of the container was changed daily, adding fresh pond water. In all cases, mean and standard error (SE) were calculated to present the data. One-way analysis of variance (ANOVA)15 was applied to ascertain whether the size of the prey individuals has significant impact on predation.

机译：作为秘鲁，玻利维亚，巴西和巴拉圭的土生土长的蜗牛，Pomacea bridgesi现在在佛罗里达，夏威夷和东南亚国家（包括印度）蓬勃发展。它们对芋头2和水稻植物以及引进地区的腹足动物区系4构成严重威胁。而且，它们可能参与人类疾病的传播这一事实也令人严重关切。因此，正在努力防止其进一步扩散，并控制人口密度。尽管记录了桥螺的种类繁多，但仍需要有关吞噬它们的生物的报告，以期制定防治策略。因此，我们通过在实验室中通过实验为实蝇淡水腹足纲动物最有效的捕食者1334水offering Sphaerodema Rustum提供了P. bridgesi进行了调查。所需数量的塑料容器（每个直径135毫米，深度32毫米），其中装有250毫升池塘水，实验室饲养的桥连小孢子（属于大小组），范围为2.5-4.5毫米（新孵化的蜗牛的范围为2.3 （壳长2.7毫米），壳长5.0-7.0毫米，7.5-9.5毫米，10.0-12.0毫米和12.5-14.5毫米，以及池塘收集的成年链霉菌成虫。在所有情况下，将15只蜗牛暴露在容器中的单个水虫中持续24小时。最初，针对蜗牛的大小组分别进行了实验。由于虫子无法捕捉到属于10-12毫米和12.5-14.5毫米大小群的蜗牛，因此我们最终以不同的组合提供了属于其余3个大小群的个体，并至少采集了2个个体。捕食者注意特定大小的猎物个体的偏好（如果有）。在前一个实验中连续观察6天，在后来的实验中连续观察39天。质朴的沙门氏菌，基本上是桥螺内脏吸盘的吸盘，有时会完全消耗掉（从从讲台上掉下空壳可见），有时则是部分食用（从掉落含有一部分内脏块的壳可见）。要提到的是，在完全食用的情况下，在掉壳后，看到少量的纤维状材料垂在S.rustum的果皮的顶端。这些纤维有时被虫子消耗掉或留在水中。通过这种喂养方式杀死蜗牛被称为“破坏”。因此，每隔24小时定期记录一次有关喂养类型的数据。将生菜喂给蜗牛，每天更换容器的水，并添加新鲜的池塘水。在所有情况下，均值和标准误（SE）都会被计算以显示数据。采用单向方差分析（ANOVA）15来确定猎物个体的大小是否对捕食有重大影响。

Predation of water bug Sphaerodema rusticum Fabricius on the snail Pomaceabridgesi (Reeve), introduced in India

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