Tobacco budworm resistance

The multiresistant strains now extant also show a certain cross-tolerance, but not resistance, to the third-generation insecticides such as the juvenile-hormone mimics and other so-called insect growth regulators, as was found in strains of the housefly, flour beetle and tobacco budworm. Resistance to the JH mimic methoprene and Monsanto-585 has been induced by laboratory selection of Culex taxsalis (28) and Culex pipiens (29), and to Monsanto-585 in Culex quinquefasstatus (30). Whatever insect or IGR is chosen, the result of exposure to selective doses in successive generations is usually the development of resistance, repeating our previous experience with chemosterilants, and the... 

Simpson, R., A. Johnson, and R. Severson Leaf surface chemistry of tobacco budworm resistant and susceptible tobacco grown in the field and greenhouse at different fertilization rates Tob. Int. 187 (1985) 89-91. 

The continuing use of pyrethroids in agriculture has led to the emergence of resistant strains of pests. One of the best-studied examples is the tobacco budworm (Heliothis virescens), a very serious pest of cotton in the southern United States (McCaffery... 

Cotton Monsanto/1994 CrylAc protein Bacillus thuringiensis subsp. kurstaki (Btk) Resistance to cotton boUworm, pink boUworm and tobacco budworm... 

Cuticular diterpenes-duvanes and labdanes. Cutler have found that the cuticular diterpenes of green tobacco have both allelopathic and insect-deterrent effects (38). Present in the cuticle are duvane and/or labdane diterpenes (Figure 3) The levels of these specific cuticular components are believed to be responsible for the observed resistance of some types of tobacco to green peach aphids Myzus persicae (Sulzer), tobacco budworm Heliothis virescens (F.), and tobacco hornworm Manduca sexta (L.) (39). 

Hedin, P.A. et al.. Multiple factors in cotton contributing to resistance to the tobacco budworm Heliothis virescens F., in Plant Resistance to Insects, Heden, P.A., Ed., American Chemical Society, Washington, 1983, 347. 

Hedin, P.A., Jenkins, J.N., and Parrott, W.L., Evaluation of flavonoids in Gossypium arboreum (L.) cottons as potential source of resistance to tobacco budworm, J. Chem. Ecol, 18, 105, 1992. 

Multiple Factors in Cotton Contributing to Resistance to the Tobacco Budworm, Heliothis virescens F. 

Different lines, each with Insect resistance, may possess different ratios of antibiotic compounds. Thus, It may be possible to Increase resistance by crossing lines where each contributes genes for biosynthesis of different antibiotic compounds. The tobacco budworm was selected for study In preference to the cotton bollworm because It Is easier to rear and use In the laboratory, Is more resistant to Insecticides In the field, and It Is approximately as susceptible to cotton constituents Incorporated In laboratory diets (14). This present study was carried out to Identify and analyze for cotton constituents that were toxic In laboratory feeding tests, and to determine whether there were positive correlations of their content In leaves and/or other tissue with field resistance. From this Information, the generation of lines with multiple factors for resistance could be Initiated. 

The effect of these resistances has been to drive chemical control from one insecticide to the next. In most parts of the Nile delta the cotton leafworms can still be controlled by some OP compound, such as chlorpyrifos, supplemented where necessary with the insect growth regulator Dimilin. But in southern Texas, Mexico, Nicaragua and Peru the multiple resistances of the tobacco budworm, and to a less extreme degree of H. zea and Spodoptera sunia, have made even 20 insecticide applications a season quite worthless, and indeed there is less damage to the cotton if no chemicals are applied at all. The only materials that can be relied upon to kill these multiresistant H. viresoens are the dichlorovinyl pyrethroid NRDC-143 and the Heliothis nuclear polyhedrosis virus. 

The ability to cleave off the leaving group by a process presumably hydrolytic has been detected in a number of OP-resistant species (Table X). In the tobacco budworm clear evidence for OP-resistance being associated with oxidative cleavage was obtained from the action of microsomes on the phosphorothionate chlorpyrifos... 

Sparks, T.C., Leonard, B.R., and Graves, J.B., Formamidine metabolism and pyrethroid interactions in pyrethroid resistant tobacco budworms, 1989 Proceedings of the Beltwide Cotton Production Research Conference, National Cotton Council of America, 1989, p. 330. 

A biochemical study indicated that the cuticle of the DDT-resistant strain of tobacco budworm contains more protein and lipid than that from the susceptible strain (Vinson and Law, 1971). Also, there was evidence of increased sclerotization of the cuticle of resistant insects. This suggests an increase in density and hardness of the cuticle that probably decrease its permeability to insecticide molecules. 

Kanga, L.H.B. and Plapp, F.W., Jr., Target-site insensitivity as the mechanism of resistance to organophosphorus, carbamate, and cyclodiene insecticides in tobacco budworm adults, j. Econ. Entomoi, 88,1150,1995. 

Plapp, F.W., Jr., Campandhola, C., Bagwell, R.D., and McCutchen, B.F., Management of pyrethroid-resistant tobacco budworms on cotton in the United States, in Pesticide resistance in arthropods, Roush, R.T. and Tabashnik, B.E., Eds., New York Chapman and Hall, 1990, p. 237. 

Genetically modified, insect resistant cotton expressing the Cry 1 Ac protein provides protection against several of the major insect pests in U.S. cotton the pink bollworm, cotton bollworm, and tobacco budworm. Given their strongly resembling appearance. 

While these results are encouraging, recent studies on the Indian mealmoth, Plodia interpunctella, and tobacco budworm, H. virescens, discussed below, have shown that under certain conditions the risk for resistance remains high. 

The second case of resistance involves larvae of the tobacco budworm selected with a genetically engineered strain of the epiphytic bacterium Pseudomonas fluorescens... 

A case in point is the unraveling of resistance to methyl parathion in the tobacco budworm, Heliothis virescens, which is a major pest of cotton as well as tobacco. In South Carolina, there is very severe, stable resistance. Although pyrethroid insecticides are very effective and there is no resistance to them in South Carolina at this time, it would be very useful to understand the genetic basis of methyl parathion resistance in case resistance to pyrethroids should arise in the future or spread eastward from Texas where it has been detected. Recent investigations with this pest will be described to illustrate certain mechanisms. 

In methyl parathion resistant tobacco budworms, larvae were treated, lots of 10 were homogenized, and methyl parathion was recovered by solid phase extraction and analyzed by reversed phase high performance chromatography with ultraviolet detection. Unexpectedly, the resistant strains lost methyl parathion at a lesser rate than the susceptible Florence 1987 strain (Figure 3). Independently, T. Konno et. al. have found a slower bioactivation of [l4C]-methyl parathion in another resistant strain of this pest (791. 

Hydrolases. Hydrolytic mechanisms are also important in insecticide resistance, despite the apparent low activities in resistant insects when compared to mammalian enzymes (Table III). Some strains of resistant mosquitoes (22), Tribolium beetles (24), and Indianmeal moth (22) have specific resistance for malathion and similar carboxylester insecticides. This is due to increased catalytic hydrolysis, possibly through production of a more efficient enzyme (25.26). Californian tobacco budworms with low level permethrin resistance exhibited twice the normal activity of trans-permethrin carboxylester hydrolase (27). 

In general, resistant acetylcholinesterases are less sensitive as indicated by a smaller bimolecular reaction constant, kj, for phosphorylation of the active site. In our studies of methyl parathion resistant tobacco budworm larvae, lots of ten larval nervous systems were homogenized and kj was determined (22). We observed 25-fold less sensitivity to inhibition to methyl paraoxon in the resistant strain (Table IV). 

Table IV. Reduced Rate of Acetylcholinesterase Phosphorylation in Resistant Tobacco Budworm Larvae, Heliothis virescens...

Recovery of phosphinylated acetylcholinesterase was also greatly enhanced in our studies of methyl parathion-resistant tobacco budworm larvae (Figure 5). Phosphinylated acetylcholinesterase recovery can be measured without the complication of "aging" which occurs with phosphorylated enzyme (Figure 6). Activity was totally inhibited with 4-nitrophenyl methyl(phenyl)phosphinate. Excess inhibitor was removed by solid phase extraction and recovering activity at 30°C was monitored in aliquots. We have confirmed this insensitivity with individual heads of adults from these strains and we are investigating inheritance of this trait. 

Can individual alleles for resistance be detected in the field This will be necessary in order to develop sound resistance management strategies. An example of the complexity of the problem is analysis of methyl parathion resistance, in which we have preliminary evidence for six possible mechanisms in tobacco budworm (Table V). Many important pests have multiple mechanisms toward each group of insecticides. Some are accumulating multiple resistance at an alarming rate. 

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