Environmental Effects of Insect-Resistant GM Crops!
Plant-eating insects can cause great damage to crops; the European corn borer, for example, can destroy up to 20 per cent of maize yields. Over the past half-century, insecticides have become the main weapon of choice against insect pests. In the 1960s, concerns about their adverse health and environmental effects led to the prohibition or restriction of the most powerful broad spectrum contact poisons such as DDT.
Alternative insecticides have been developed which attack selectively instead of indiscriminately and which break down into non-toxic substances in the environment. Though these are subject to stringent testing, concerns about their effects persist, particularly about residues in food and water and their effects on non-target insects. The development of transgenic crops to enhance resistance to insect pests has been a focus of the agricultural biotechnology sector since the 1980s.
Genes expressing toxins from the soil bacterium Bacillus thuringiensis (Bt) were first engineered into tobacco in the middle of the decade. Bt toxins are highly specific to, and highly effective against, particular groups of insects but are not harmful to other organisms. They are also biodegradable and have been used as commercial insecticides in spray formulations since the 1950s. Though environmentally benign, their utility in spray form has been limited by high production costs and variable operational persistence.
Several varieties of Bt maize, cotton, and potatoes have received regulatory approval in the United States. Bt maize and cotton are estimated to have accounted for 25-30 per cent of the total US acreage of these crops in 1999.A variety of Bt maize which also incorporates a gene for herbicide tolerance has received marketing approval in the EU, but the acreage under cultivation in member states is negligible. Other transgenic crops incorporating Bt toxin genes are currently in development, as are genetically modified plants incorporating other proteins with insecticidal properties such as lections and protease inhibitors.
Crops genetically modified to incorporate Bt genes, and thus to produce the Bt insecticide inside the plant tissues, offer growers a number of advantages over other insect pest control methods. Unlike insecticide sprays, their utility is not dependent on weather conditions; plant parts difficult to reach by spraying are also protected. Particularly in the case of crops which require heavy applications of insecticide, there are significant potential savings to growers in pesticide, labour and equipment costs.
It has also been claimed that crops modified for insect resistance offer environmental advantages compared with conventional insecticide spraying. Spraying, especially from the air or in windy conditions, tends to be indiscriminate in its impact and often affects non-target plants in the vicinity. Bt toxin produced within the plant by genetic modification only kills insects which eat the plant tissue, and only certain kinds of insects at that because of its specificity.
Contamination of ground water around farmland should also be reduced as the Bt toxin is a natural protein which is readily biodegradable into non-toxic substances. Critically, the use of Bt crops should mean that less insecticide is needed as the insecticidal material is contained in the plant tissue.
There are possible risks associated with the modification of crop plants for insect resistance. Concerns have been expressed, first, that insects will evolve resistance to GM plants. This has been a long-standing problem with conventional insecticide treatments. The main counter-measure at present against the threat of enhanced resistance consists of the provision of ‘refuges’, that is areas of non-GM crops, which can support pest populations that are not resistant to Bt toxins.
The Environmental Protection Agency in the United States insists that, when farmers grow Bt cotton, 4 per cent of the crop must consist of unmodified cotton that has not been treated with any pesticide; if growers wish to spray with other pesticides, 20 per cent of the crop must be non-Bt cotton. In the case of Bt maize, the Agency’s new regulations announced in January 2000 provide that unmodified maize must account for at least 20 per cent – and in some cases up to 50 per cent – of the total crop.
While such provisions may help to address the problem, some recent research findings have raised questions about the effectiveness of refuges. This underlines the need for continued careful monitoring of the risk of enhanced resistance to Bt crops among target insects.
Effects on Non-Target Insects:
The other main concern about insect-resistant crops concerns their possible impact on non-target insects, some of which play an important role in the control of insect pests. On the one hand, the impact of such crops might be expected to prove beneficial because, unlike sprays which may affect all susceptible insects in the field, they should directly affect only insects which attack the plant.
On the other hand, GM crops may adversely affect non- target insects by depleting the supply of prey on which they feed. This problem also arises with non-GM pest control measures and gives cause for concern only to the extent that Bt crops are more effective in killing insect pests.
Athari za Mazingira za Mazao ya GM Yenye Uvumilivu kwa Wadudu! Wanyama wanaokula mimea wanaweza kuharibu mazao kwa kiasi kikubwa, kwa mfano, mnyama anayeitwa European corn borer anaweza kuharibu hadi asilimia 20 ya mazao ya mahindi. Katika miaka ya hivi karibuni, dawa za kuua wadudu zimekuwa silaha ya kwanza ya kupambana na wadudu. Katika miaka ya 1960, wasiwasi juu ya athari zao mbaya kwa afya na mazingira ulisababisha marufuku au vizuizi vya sumu zenye nguvu zaidi za mawasiliano ya wigo pana kama vile DDT. Dawa mbadala za kuua wadudu zimetengenezwa ambazo huua kwa njia ya kuchagua badala ya bila ubaguzi na ambazo huvunjika kuwa vitu visivyo na sumu katika mazingira. Ingawa hizi ni chini ya majaribio kali, wasiwasi kuhusu athari zao kubaki, hasa kuhusu mabaki katika chakula na maji na athari zao juu ya wadudu wasio lengo. Maendeleo ya mazao ya transgenic ili kuongeza upinzani kwa wadudu wadudu imekuwa lengo la sekta ya biotechnology ya kilimo tangu miaka ya 1980. "Kama vile kuna ""toxin"" inayotokana na bakteria ya Bacillus thuringiensis (Bt) ambayo ilitengenezwa kwa njia ya mbinu ya uhandisi ili kuingiza sumu katika tumbaku." Bt sumu ni maalum sana kwa, na ufanisi sana dhidi ya, makundi maalum ya wadudu lakini si hatari kwa viumbe wengine. Pia, ni biodegradable na imekuwa kutumika kama kinga ya wadudu katika dawa za kunyunyizia tangu miaka ya 1950. Ingawa ni salama kwa mazingira, matumizi yao katika fomu ya kunyunyizia yamepunguzwa na gharama za juu za uzalishaji na uvumilivu wa uendeshaji tofauti. Aina kadhaa za mahindi, pamba, na viazi vya Bt zimepokea idhini ya kisheria nchini Marekani. Bt mahindi na pamba ni takriban asilimia 25 hadi 30 ya jumla ya ardhi ya Marekani ya mazao hayo katika 1999. aina ya Bt mahindi ambayo pia inajumuisha jeni kwa ajili ya uvumilivu wa dawa za kuua magugu imepokea idhini ya masoko katika EU, lakini eneo chini ya kilimo katika nchi wanachama ni negligible. Mimea mingine ya transgenic inayojumuisha jeni la sumu ya Bt sasa iko katika maendeleo, kama vile mimea iliyobadilishwa kijeni inayojumuisha protini zingine na mali ya kuua wadudu kama vile lections na protease inhibitors. Mimea iliyobadilishwa chembe za urithi ili kuingiza jeni za Bt, na hivyo kutengeneza dawa ya kuua wadudu ya Bt ndani ya tishu za mmea, huwapa wakulima faida kadhaa juu ya mbinu nyingine za kudhibiti wadudu. Tofauti na dawa za kuua wadudu, matumizi yao hayategemei hali ya hewa; sehemu za mimea ambazo ni vigumu kuzifikia kwa kunyunyizia pia zinalindwa. Kwa mfano, kwa mazao ambayo yanahitaji matumizi makubwa ya dawa za kuua wadudu, kuna uwezekano mkubwa wa kuokoa kwa wakulima katika gharama za dawa za kuua wadudu, kazi na vifaa. Pia imedaiwa kwamba mazao yaliyobadilishwa ili yasiweze kuambukizwa wadudu hutoa faida za kimazingira ikilinganishwa na kunyunyizia wadudu kwa njia ya kawaida. Spraying, hasa kutoka hewa au katika hali ya upepo, huwa na kuwa indiscriminate katika athari yake na mara nyingi huathiri mimea yasiyo ya lengo katika ujirani. Toxin ya Bt, inayotokezwa ndani ya mmea kwa mabadiliko ya maumbile, huua wadudu tu ambao hula tishu ya mmea, na aina fulani tu za wadudu kwa sababu ya upendeleo wake. Uchafuzi wa maji ya chini ya ardhi karibu na mashamba pia inapaswa kupunguzwa kwa sababu sumu ya Bt ni protini ya asili ambayo ni biodegradable kwa urahisi katika vitu visivyo na sumu. Kwa kweli, matumizi ya mazao ya Bt yanamaanisha kwamba dawa ndogo ya kuua wadudu inahitajika kwani nyenzo ya kuua wadudu iko katika tishu ya mmea. Kuna hatari zinazowezekana zinazohusiana na marekebisho ya mimea ya mazao kwa ajili ya upinzani wa wadudu. Wengine wana wasiwasi kwamba wadudu wanaweza kuwa na uwezo wa kuzuia mimea ya GM. Hilo limekuwa tatizo la muda mrefu kwa matibabu ya kawaida ya dawa za kuua wadudu. Hatua kuu ya kukabiliana na tishio la upinzani ulioimarishwa kwa sasa ni utoaji wa "mahali pa kukimbilia", ambayo ni maeneo ya mazao yasiyo ya GM, ambayo yanaweza kuunga mkono idadi ya wadudu ambao hawawezi kukimbilia sumu za Bt. Shirika la Ulinzi wa Mazingira la Marekani linadai kwamba wakulima wa pamba ya Bt lazima wawe na asilimia 4 ya pamba isiyo na kemikali yoyote; wakulima wa pamba wa Bt wanapaswa kuwa na asilimia 20 ya pamba isiyo na kemikali yoyote. Kwa mahindi ya Bt, kanuni mpya za Wakala zilizotangazwa mnamo Januari 2000 zinatoa kwamba mahindi yasiyo na mabadiliko lazima yawe angalau 20% na katika hali zingine hadi 50% ya mazao yote. Ingawa huenda sheria hizo zikasaidia kutatua tatizo hilo, utafiti fulani wa hivi karibuni umeonyesha kwamba kuna shaka kuhusu ufanisi wa makazi hayo. Hii inasisitiza haja ya kuendelea kufuatilia kwa uangalifu hatari ya kuongezeka kwa upinzani kwa mazao ya Bt kati ya wadudu wa lengo. Matokeo ya mimea isiyo na wadudu: Madhara ya mimea inayopinga wadudu ni hatari kwa wadudu wasio na wadudu, ambao wanaweza kuwa na athari kubwa kwa wadudu. Kwa upande mmoja, athari za mazao hayo zinaweza kutarajiwa kuthibitika kuwa na faida kwa sababu, tofauti na dawa za kunyunyizia ambazo zinaweza kuathiri wadudu wote walio na uwezekano katika shamba, zinapaswa kuathiri moja kwa moja wadudu ambao huvamia mmea. Kwa upande mwingine, mazao ya GM yanaweza kuathiri vibaya wadudu wasio lengo kwa kupunguza ugavi wa mawindo ambayo wao hula. Tatizo hili pia hutokea na hatua za kudhibiti wadudu zisizo za GM na hutoa sababu ya wasiwasi tu kwa kiwango ambacho mazao ya Bt ni ufanisi zaidi katika kuua wadudu wadudu.