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Toxicity to other above-ground organisms

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Five study abstracts were available for review that are describing the chemosterilizing effects of thiourea on beetles and flies. The terrestrial invertebrates examined in the studies are all living above-ground and are therefore out of the scope of the effects assessment for the terrestrial environment under REACH (see ECHA Guidance Document R.7c, p. 105). This information is provided for information purposes only.
Shanker at al. (1990), Pandey & Pandey (1991), and Bhide (1991) determined the chemosterilant effects of thiourea on above ground living beetles. Shanker et al. (1990) could demonstrate a significant reduction of laid eggs of Epilachna dodecastigma with increasing thiourea concentration. Complete sterility was achieved when 0.05 per cent of thiourea was applied. Topically applied thiourea lead to a maximum reproduction control of 88.37 % at a dose of 3.5 µg and at a population density of 0.05 for Callosobruchus chinensis (L.) (Coleoptera: Bruchidae) (Pandey & Pandey, 1991).
In addition, Bhide (1991) describes the effects on mortality, behaviour and metamorphosis and on histopathological and cytological changes in the developing ovaries of the red cotton-bug Dysdercus similis. Thiourea concentrations tested were not reported.
In 1976, Chaudhry & Tripathi determined the histopathological effect of thiourea on the ovarian tissues of the fly Sarcophaga ruficornis. Thiourea treatment leads to subnormal, non-viable eggs. Besides thiourea induces sterility in the fly Chrysomya megacephala (Deepak % Chaudhry, 1979).

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Shanker at al. (1990) determined the effects of thiourea on the longevity of the above ground living beetle Epilachna dodecastigma. 0.005 to 0.05 per cent of thiourea did not show significant effect on the longevity of the beetle, but when the concentration of thiourea was increased from 0.05 to 0.10 per cent (t = 7.72, P < 0.001) and from 0.10 to 0.20 per cent (t = 1.90, P < 0.20), the longevity of the beetles was significantly reduced. In addition, the authors could observe decreasing numbers of eggs laid by the beetle with increasing thiourea concentration. Complete sterility was achieved when 0.05 per cent of thiourea was applied. Therefore, the authors conclude that 0.05 per cent of thiourea concentration is the most suitable dose for the sterilization of E. dodecastigma.

In another study conducted by Pandey & Pandey (1991), the effects of topically applied thiourea on the adaptability by Callosobruchus chinensis (L.) (Coleoptera: Bruchidae) to its own population density was assessed. The study was conducted at 28 ± 2 °C temperature, 75 per cent relative humidity and 16 h photoperiod. Effects of thiourea could be observed when only females were exposed (topical application) to different doses of thiourea. At a population density of 0.05 and a dose of 3.5 µg a maximum reproduction control of 88.37 % was observed.

Bhide (1991) determined the effects of thiourea on mortality, behaviour and metamorphosis and on histopathological and cytological changes in the developing ovaries of the red cotton-bug Dysdercus similis. Thiourea was applied topically in different concentration to the eggs and all the nymphal instars. Adults were exposed by feeding.

The eggs were severely affected (i.e. high mortality). Nymphal instars displayed an adverse effect on ecdysis, while adults which emerged from the treated last nymphal instar were characterized by high mortality, abnormal behaviour and reduced fecundity and viability. These adults were differently coloured, morphologically abnormal, and also smaller and weaker compared to the controls. In addition, they were unable to reproduce due to atrophy of the gonads. The ovaries contained a high number of immature, pathological oocytes with degenerating follicular epithelium, which was thin with a regular outline in the early stages, but later became multilayered, with pyknotic nuclei, and displayed active destruction of glycoproteins and lipoproteins. Fibrogenesis and thickening of the tunica propria were clearly pronounced. Treated females were held together with untreated males. However, neither males nor females were attracted to one another and displayed no mating behaviour, although some females showed a very low degree of ovulation. Although being kept under normal laboratory conditions only a few survived the 1st nymphal instar and none survived up to adult emergence.

In 1976, Chaudhry & Tripathi determined the histopathological effect of thiourea on the ovarian tissues of the fly Sarcophaga ruficornis. They discovered that the follicles in the ovarioles are the primary target of thiourea in female Sarcophaga. As a result the follicle cells turn syncytial and their nuclei get pycnotic, which inhibit the transport of nutrient material into the nurse cells and of yolk into the oocytes, leading to subnormal, non-viable eggs.

In addition, Deepak & Chaudhry determined in 1979 the thiourea-induced sterility in the fly Chrysomya megacephala (Diptera: Calliphoridae) by pupal (dipping) and adult (feeding) treatments with thiourea solutions of varying concentrations for different time intervals. The dipping treatment of pupae caused in some cases a high percentage of sterility, however also pupal mortality was very high. Feeding exposure of adults for 48 h produced 100% sterility with practically no mortality. Males were more susceptible to sterilization compared to females.