C A N
C A N H
G I A C
v d i C A C
•ThS. Tran Van Hien
L
oai nhap noi hay la loai ngoai lai la loai dtfdc mang den mot viing nam ngoai viing phan h6' tif nhien ciia chiing do vo tinh hay co muc dich ciia con ngtfdi. Sau khi xam nhap vao moi trifdng mdi, cac loai ngoai lai nay md rong pham vi phan hd' vao viing dia ly mdi va trd thanh loai xam lan (Usher, 1991). Phan ldn cac loai xam lan difdc con ngtfdi nhap ndi, mdt sd' loai khac dtfde nhap ndi mdt each vd tinh ciing vdi hang hda. Ddng vat. thifc vat lam canh, cd ldi hoac lam mau thirdng dtfdc nh;ip ndi. (1 nifdc ta, trong nhifng nam qua da xuat hien nhieu ddng thifc vat ngoai lai theo hirdng tren nhif cay mai difdng, d'e btfdu vang, ho canh ctfng hai dtfa, ca chim trSng, chudt hid ly. torn hiim do.ca lau kieng, riia tai do... Mdt vai loai trong sd do da trd thanh nhu'ng mdi hiem hoa cho san xuat ndng nghiep va he sinh thai nhtf cay mai dtfdng. dc btfdu vang, bo canh ctfng hai dtfa. riia tai do. Xin gidi thieu mdt vai dac diem va tac hai ciia nhtfng loai nay.
1. Rua tai do
Trong thdi gian qua, riia tai do da cd mat trong mdi trtfdng ttf nhien d nhieu dia phtfdng trong cii ntfdc. Dau tien, riia tai do dtfdc mdt so'cdng ty xuat nhap khau thiiy san nhap ve nudi thtf nghiem va da de chiing thoat ra sdng rach ben ngoai. Nhieu ngtfdi di le chua ciing phdng sinh riia tai tai do nen pham vi phan bd'ciia chiing lan ra rat nhanh.
Riia tai do (Trachemys scripta elegans), tudi tho ttf 50 -70 nam, phan bd' ttf nhien d cac viing ntfdc ndi dia Bac M y . Co ciia loai rua nay thtfdng cd mang do, tren mai riia ed nhtfng soc vang cam, phia tren mat cd vanh mau do nen dtfdc goi la rua tai do. Riia cai cd the de tdi ba d trtfng mdt nam, mdi 6 cd ttf 4 - 23 trtfng. Theo cac nha khoa hoc, riia tai dd cd the mang vi khuan salmonella, loai vi khuan gay benh thtfdng han dd'i vdi ngtfdi. Day cung la mdt nguy cd cho ngtfdi dan sd'ng trong viing sdng ntfdc. Rua tai dd la mdt loai ddng vat an tap hung dtf, chiing an tat ca loai ca be hdn nd cung nhtf cac dong vat thiiy sinh khac. Chinh vi the' ma To chtfc Bao tdn thien nhien qudc te' (IUCN) xep loai nay dtfng dau trong 100 loai xam hai nguy hiem nhat the' gidi. Khi thoat ra ttf nhien, riia tai dd se canh tranh thtfc an, giao phd'i vdi rua ban dia, dan de'n lan ap, tfc che' hoac tieu diet cac loai sinh vat ban dia, dtfa de'n pha vd can bang sinh thai. V d i kha nang thich nghi cao, dac biet la vdi dieu kien khi hau am ap, nhieu ao hd, dam lay, sdng sud'i nhtf d ntfdc la, khi thoat vao thien nhien thi chiing se nhanh chdng phat trien va hinh thanh quan the tan pha cac quan the khac. Chinh vi the', cac nha nghien ctfu mdi trtfdng cho rang, riia tai dd pha huy sinh thai khdng kem cay mai dtfdng.
2. Tom hum dd
Sau d'e btfdu vang va riia tai do. trong thdi gian nay, gidi nudi trdng thiiy san d Dong bang sdng Ctfu Long (DBSCL) dang rat lo lang vdi mdt loai gid'ng torn mdi vtfa nhap khau tif M y ve, dd la torn hiim do.
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Tom hum do co ten khoa hoc la procambarus clarkia, con dtfdc goi la torn hum ntfdc ngot, co nguon gd'c tu" Bac My. Tom hum do co mau sac la lung la toan than mau do rtfc, an tap, thu'c an chinh la mun ba hiru cd. Ngoai ra, chiing con an nhieu loai thu'c an nhtf ngii cdc, kho dau, rau qua, co non, xac dong vat. Theo cac nha chuyen mon, torn hum do co vo ctfng, cap cang to, khdi ltfdng thit thap (khoang 15 den 20% trong ltfdng cd the). Loai torn nay dung cang de dao hang de trtfng, tni ddng, tranh gianh thtfc an va cd kha nang canh tranh rat manh de sinh tdn.
Loai sinh vat ngoai lai nay khi thoat ra ngoai cd the se gay hai cho cac cdng trinh thiiy l d i bdi chiing dao hang rat sau. Day la loai torn an tap nen khi phat tan ra ngoai cd the lam hai cac loai torn ban dia. Cdn nhffng ngffdi dan nudi va bat dffdc torn hum dd ngoai ttf nhien thi nhan xet rang torn hiim dd rat hung dff hdn so vdi torn cang xanh. Chiing cd ddi cang to be nen dao hang rat gidi va sdng trong hang nhtf cua. Cac cay cd, rau beo quanh ao nudi deu bi torn hdm dd diing cang kep gay hay an trui het. Tham chi bi ngtfdi bat, chiing diing cang kep chat khdng chiu budng.
Moi nguy hiem
Nhieu chuyen gia thiiy san lo ngai: V d i vdng ddi ngan, sinh san nhanh lai cd the di chuyen tren can, cdng vdi ban tinh hung hang va an tap, torn hiim dd cdn cd kha nang thich nghi td't vdi mdi trtfdng nen khi chiing phat trien tran lan ra ngoai mdi trtfdng ben ngoai se la mdi nguy hiem cho cac loai thuy san khac.
Ne'u cho nudi loai torn nay dai tra se lam mdi hoa cho cac cdng trinh thiiy l d i , cdng trinh cdng cdng, bd sdng va cd kha nang chiing se tieu diet loai torn ban dia tff viec tranh gianh thtfc an de sinh tdn.
3. Cfiy mai dtftfng
Cay mai dudng (Mimosa pigra L.) la loai thtfc vat ngoai lai xam lan manh. Loai thtfc vat nay la cd ngudn gd'c ttf vffng Trung M y . ChUa cd mdt loai dich hai ttf nhien tai chd nao cd the kiem soat va han che dtfdc stf lay lan ciia loai trinh nff nay. Loai cay bui nhieu gai nay phat trien manh ttf nhffng nam 70 va da trd thanh mdt loai cay ddc hai d nhffng
vung dat ngap nffdc. Chiing anh htfdng nghiem trong den san xuat ndng nghiep va cdng viec bao tdn d hai quo'c gia Australia va Thai Lan. Hdn nffa, chiing con tiem nang xam lan manh d cac qudc gia Ddng Nam A. O nhffng ndi ma cay mai dffdng moc day dac thi khdng mdt loai thffc vat, ddng vat nao sd'ng dffdc dtfdi tan ciia chiing. Chiing canh tranh vdi ddng co, che phu va ngan can ddng chay cua ntfdc, de doa tdi nganh chan nudi gia sue, dac biet la chan nudi trau, bd, de (Miller va ctv, 1981). Chiing cung anh htfdng den nudi trdng thuy san va cac nganh nghe khac.
0 ntfdc ta hien nay, cay mai dtfdng xuat hien d nhieu ndi nhtf Dong Thap, Vtfdn Qudc Gia Tram Chim (Vtfdn QGTC), Vtfdn Quo'c gia U Minh Thtfdng, Dong Nai, L a m Dong, Quang Ngai... va cay mai dtfdng that stf da la mdt mdi hiem hoa cho he sinh thai ndng nghiep ntfdc nha. Theo sd' lieu ciia Vtfdn QGTC thi cay mai dtfdng da lan chiem hdn 2.000ha, chiing dang lam mat dan tham thffc vat ban dia, dan de'n thay dot he ddng, thffc vat ban dia. Chiing dang xam lan nhffng ddng cd nan, nhffng bai cd nan la bai an, bai nghi cua loai chim qui hiem nhff seu dau do. Se'u dau dd la mdt trong nhffng muc tieu chinh ma du khach trong nffdc ciing nhtf ngoai ntfdc mudn de'n tham d Vtfdn QGTC.
Chinh v i the'ma cay mai dtfdng da lam giam gia tri bao tdn ciia viing ddng cd dat ngap ntfdc cdn lai duy nhat cua Dong Thap Mtfdi, lam giam gia tri du lich sinh thai ciia Vtfdn QGTC. 6" nhieu dia phtfdng khac cay mai dtfdng xam lan vao ca dat trdng cay ndng nghiep, bd sdng, bd kenh gay can trd giao thdng va da gay tdn kem rat nhieu cho cac dia phtfdng de tieu diet chiing.
4. Oc btfdu vang
6 c btfdu vang (OBV) dtfdc dtfa vao ntfdc ta bdi mdt sd quan chtfc di cdng tac ntfdc ngoai dem ve nudi lam canh. Btfdc dau chiing dtfdc nudi trong be, sau dd "xong chudng" va lay lan ra ca ntfdc.
De'n nay thi dc btfdu vang da that stf la mdt trong nhtfng loai dich hai quan trong nhat cho nghe san xuat liia d ntfdc ta. Theo sd lieu ciia Dtf an "Tong hdp dich hai dc btfdu vang tren cay liia Viet Nam"
thi OBV da xuat hien va gay hai d hau het cac tinh thanh trong ca ntfdc va dien tich liia bi hai bdi OBV, dac biet la d khu vtfc DBSCL tfdc tinh hang chuc
ngan ha moi nam. 0" DBSCL sau khi thu hoach liia He Thu, rudng bi ngap nu'dc va mua lu thffdng keo dai vai thang. Trong mua Iu nguon sinh vat phu du va cac thu'c an khac cho OBV rat phong phii nen chiing sinh trffdng, phat trien rat nhanh.
Trung binh sau mua lu, mdi ha rudng sau khi bdm nffdc ra de' lam liia Ddng Xuan bat dffdc ca tan d'e ldn, cdn so d'e con thi nhieu vd ke. Lffdng tiling dc thu dffdc tren bd rudng sud't vu cung phai vai chuc kg. Sau khi sa liia Ddng Xuan, d nhffng chd trung trong rudng, ne'u khdng diet dffdc he't OBV thi chiing se an sach liia. Qua nhieu vu theo ddi chiing tdi nhan thay mdi ha trung binh phai cay dam 1,0 - 1,5 cdng dat, chi phi cho cay dam va thud'c diet chung de'n vai trieu d/ha.
Hien nay tren ddng rudng khdng chi cd OBV hai liia ma trong qua trinh lai tap tff nhien giffa OBV va d'e lac da tao ra mdt loai con lai cd vd day hdn va sffc pha hoai ciia chiing cdn ldn hdn OBV. Tff ngay xuat hien OBV thi loai d'e lac ban dia gan nhff bi tuyet chiing.
5. Bo canh crfng hai difa
Bo canh effng (BCC) hai dffa cd ten khoa hoc la Brontispa longissima, ngoai gay hai tren dffa thi chiing con gay hai cho nhieu loai khac nhff thien tue', cau kieng. Bo canh effng hai dffa xuat hien va gay hai cho tat ca cac nffdc trdng dffa tren the' gidi. Bo canh effng hai dffa dffdc phat hien d nffdc ta (Bdn Tre) vao thang 5/1999 va de'n nay thi chiing da lay lan ra ca nffdc. Gay thiet hai nhieu nhat d cac tinh cd dien tich trdng dffa ldn nhat nhff Ben Tre, Binh Dinh. Cdc tinh cd de'n ca hang tram ngan cay dffa bi ddn bd do BCC hai dffa gay ra. BCC hai dffa cd kha nang gay hai cho dffa d tat ca cac giai doan tudi, nhffng gay hai nang nhat khi cay con nho den 4-5 tudi. O nhffng viing khd han thi cay dffa bi hai nang hdn va mua nang bi thiet hai nhieu hdn miia mffa. Cay dffa bi giam san lffdng rd ret khi 8 tau la ciia cay dffa bi BCC tan cdng.
Ca thanh triing va au trung gay hai tren cay dffa khi la dffa ehffa bung ra, chiing an diep luc tren be mat la tao ra nhffng soc dien hinh song song
v d i mep la. A u trung thffdng pha hai manh hdn thanh triing. BCC la loai cdn triing bie'n thai hoan toan qua 4 giai doan: Trffdng thanh, trffng, au trung, nhdng.
D i e t BCC hai dffa kha khd khan bang cac l o a i thud'c hda hoc vi tan la rdng, cay cao, cay trdng phan tan va quanh nha. Trffdc sff pha hai ciia chiing, chung ta da cho nhap mdt sd loai ong ky sinh tff dao Samoa nhff Haeekeliana brontispae, Asecodes hispinarum, nhieu l o a i thudc ho Eulophidae tan cdng sau non va nhdng bo dffa.
Do mffc dd pha hai nhanh ciia BCC h a i dffa, Bd Ndng nghiep va PTNT da phai thanh lap Ban chi dao Qudc gia diet BCC hai dffa ngay 30/
7/2002. Sau dd tirng tinh ciing da thanh lap Ban chi dao phdng chdng diet BCC hai dffa.
Cac sinh vat ngoai lai cd the' gay ra nhffng hie'm hoa khdn lffdng cho san xuat ndng nghiep, cho he sinh thai, cho sffc khde con ngffdi, chiing cd the phat sinh thanh dich ma con ngffdi khd cd the7 k i e m soat dffdc. Chinh vi the' trffdc khi cho nhap mdt loai sinh vat nao dd chiing ta phai cd che' dd kiem dich that chat che va can phai nudi trdng thff nghiem ky trffdc khi dffa vao san xuat dai tra./.
An triing ciia bo canh ciing hai difa
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