Need for growing non-Bt cotton refugia to overcome Bt resistance problem in targeted larvae of the cotton bollworms, Helicoverpa armigera and Pectinophora gossypiella

Background The effectiveness of Bacillus thuringiensis (Bt) cotton against target arthropod larvae is decreasing day by day. The comparative effect of Bt expression among Bt cotton varieties and different plant parts was observed against the cotton bollworms: Helicoverpa armigera and Pectinophora gossypiella larvae. Results In the present study, larval mortality of H. armigera was higher than P. gossypiella among selected Bt cultivars. Median lethal concentration (LC50) values were 8.91, 13.4, 14.0, and 36.4 for P. gossypiella, while 5.91, 4.04, 2.37, and 8.26 for H. armigera of FH-142, MNH-886, IR-3701, and FH-Lalazar, respectively. These values depicted that P. gossypiella had more Bt resistance problem than H. armigera larvae. The host range of both targeted insect larvae was different from each other due to the polyphagous feeding nature of the larvae of H. armigera that feed on different host plants, but P. gossypiella attacked only cotton with monophagous feeding habit. It was also notable from results that Bt expression in reproductive parts where the attacked pink bollworm was lower than the American bollworm, so the former had the maximum chance of resistance due to repeated exposure to Bt. Conclusions It was concluded that farmers be advised to follow the practice of growing non-Bt as a refuge crop to reduce the problem of Bt resistance in the target arthropod species.

COMPARATIVE EFFICACY OF FOUR INSECTICIDES AGAINST AMERICAN BOLLWORM (Helicoverpa armigera) UNDER FIELD CONDITIONS

The tomato, Solanum lycopersicum L., is the 2nd major crop which is widely grown on the large area of Pakistan. This crop is affected by the fruit borer, Helicoverpa armigera (Hubner). Although some predators and parasitoids have been recorded in the field for their natural control, their manipulation to a successful crop management is still awaited. The present study was planned to evaluate the toxic effects of four insecticides, i.e. Coragen 20SI (Chlorantraniliprole), Steward (indoxicarb), Belt 39.4 (Flubendiamide), Proclaim (emamectin benzoate) against tomato fruit borer (H. armigera) under field conditions. The research trial was laid out under randomized complete block design (RCBD) together with control. Findings of the bioassays displayed that Coragen 20SI exhibited noteworthy mortality (75.23%) of H. armigera after exposure of 6 days, among the four tested insecticides. Whilst Proclaim and Chlorantraniliprole exhibited relatively lower mortalities of 70.90% and 65.41%, respectively. While relatively lower mortality values i.e. 61.10, 55.41, 52.76 and 48.19% were recorded after 4 days and 57.80, 50.12, 46.09 and 39.24% after 2 days. Overall, results disclosed that all four tested insecticides gave enhanced control under controlled experimental conditions. Hence, Coragen 20SI and Steward can be used in integrated pest management (IPM) of H. armigera.

PENGARUH UKURAN BRAKTEA BEBERAPA AKSESI KAPAS TERHADAP TINGKAT SERANGAN HAMA PENGGEREK BUAH Helicoverpa armigera (HUBNER)

<p>ABSTRAK<br />Hingga kini teknik perakitan varietas kapas tahan hama masih<br />dilakukan secara konvensional berdasarkan beberapa karakter morfologi<br />tanaman, seperti: bulu daun, daun okra, braktea berpilin, nektar, dan<br />gosipol tinggi. Karakter-karakter ini diketahui erat hubungannya dengan<br />ketahanan terhadap hama, khususnya H. armigera. Berkaitan dengan<br />serangan H. armigera pada buah, diduga ada bagian-bagian buah kapas<br />yang berkontribusi secara langsung pada serangan hama ini, misalnya<br />braktea buah. Namun demikian, besarnya pengaruh braktea terhadap<br />kerusakan buah kapas perlu dipelajari dalam upaya meminimalkan<br />kerusakan. Penelitian ini bertujuan untuk mengetahui pengaruh ukuran<br />braktea terhadap tingkat kerusakan buah oleh H. armigera pada beberapa<br />aksesi kapas. Penelitian dilaksanakan di Kebun Percobaan Balai Penelitian<br />Tanaman Tembakau dan Serat, di Asembagus, Situbondo, Jawa Timur<br />mulai bulan Januari hingga Desember 2006. Sebanyak 18 aksesi dari 50<br />aksesi kapas dengan berbagai variasi ukuran braktea digunakan sebagai<br />perlakuan. Setiap perlakuan (aksesi) disusun dalam rancangan acak<br />kelompok (RAK), dengan tiga kali ulangan. Lima tanaman kapas dari<br />masing-masing aksesi ditentukan secara acak, dan sebanyak 5 buah kapas<br />muda (diameter ± 4 cm) dipetik dari masing-masing tanaman sampel,<br />kemudian dibawa ke laboratorium untuk diukur luas braktea dan buahnya.<br />Selain itu dilakukan pula pengamatan kerusakan buah dan hasil kapas<br />berbiji di lapang. Hasil penelitian menunjukkan bahwa ukuran braktea<br />berkorelasi positif dengan tingkat kerusakan buah (R 2 = 0,9014), sehingga<br />braktea berukuran besar dan lebar serta menutupi buah secara total<br />berpotensi mengalami kerusakan akibat serangan H. armigera lebih tinggi<br />dibanding braktea berukuran kecil dan sempit. Ukuran panjang dan lebar<br />braktea pada 18 aksesi kapas bervariasi antar aksesi dan masing-masing<br />berkorelasi positif dengan luas (R 2 = 0,876; R 2 = 0,894). Hasil penelitian<br />ini dapat dimanfaatkan dalam merakit varietas tahan hama, dan<br />kombinasinya dengan karakter-karakter morfologi kapas yang sudah ada<br />untuk menghasilkan varietas kapas baru dengan tingkat ketahanan yang<br />lebih tinggi terhadap hama penggerek buah H. armigera.<br />Katakunci : Braktea, Helicoverpa armigera, aksesi kapas, karakter<br />morfologi.</p><p><br />ABSTRACT<br />Effects of bract size of several cotton accessions to<br />American bollworm injury level<br />Conventional method by crossing technique based on<br />morphological characters of plant is now still used in providing resistant<br />varieties of cotton against insect bollworms. A number of genetic<br />characters are now available and have been studying for their assosiation<br />with insect pests resistance such as hairiness, okra leaf, frego bract,<br />nectariless, and high gossypol. Regarding to boll damage by H. armigera,<br />it can be mentioned that there are many other morphological characters of<br />cotton attributable to bollworm damage, such as floral bract. As a part of<br />boll, it is estimated that bracts assosiated with bollworm attacked due to<br />their larger size compared with boll size. Objective of the study was to find<br />out the effect of bract size in relation to bollworm damage on cotton<br />accessions. The study was conducted at Experimental Station of<br />Indonesian Tobacco and Fiber Crops Research Institute in Asembagus,<br />Situbondo, East Java from January to December 2006. Eighteen of fifty<br />cotton accessions were used as treatment and they were arranged in<br />Randomized Block Design (RBD) with three replications. Five randomly<br />cotton plants from each accession and five young bolls were sampled<br />from the selected plant with about 4 cm of diameter were brought in the<br />laboratory to collect information on bract and boll sizes. Bollworm<br />damage was determined by counting the damaged bolls in the field as well<br />as the seed cotton yield. Result showed that bract size was positively<br />correlated with boll damage (R 2 = 0.9014). Higher damaged bolls occured<br />on bolls which is covered completely by bracts. There is variation between<br />length and wide size of bracts among cotton accessions and both showed<br />positive correlation to bract area (R 2 = 0.876; R 2 = 0.894). Based on this<br />study, higher resistance of cotton variety against H. armigera will<br />possiblly be provided through combination between bract size and any<br />other morphological characters of cotton.<br />Key words : Floral bract, Helicoverpa armigera, cotton accession,<br />morphological character</p>