Resistance to aphids

Lettuce is the most pest- and disease-prone member of the Asteraceae. Common pests include slugs, cutworm, leaf aphids, and root aphids. Linder cover, downy mildew and gray mold (botrytis) can be a problem, especially in cool, damp conditions. Cultivars with resistance to aphids, downy mildew, and various physiological disorders are available. For more advice and information, see the A-Z of Plant Problems ipp.320-341). 

If you expect a virus problem, you may able to plant a virus-resistant cultivar. For example, many peas and beans have been rred for resistance to bean mosaic, and breeder have developed tomatoes that resist tobacco mosaic virus. In some cases, a cultivar may be susceptible to a virus, but not prone to getting It because it is resistant to insects that transmit the virus. Such is the case with Royalty purple raspberry, which, though prone to mosaic, is resistant to aphids that spread the disease. 

B-caryophyllene, a major component of S. berthaultii trichomes and of S. tuberosum foliage. This effect of B-caryophyllene raises doubts about the claim of Gibson and Pickett (21) that E-B-farnesene of S. berthaultii trichomes is an important factor in resistance to aphids, because we found that trichomes of accessions studied by Gibson and Pickett (21) contain high concentrations of B-caryophyllene (22). 

To-date, over 180 wild, tuber-bearing species of Solarium are known (i) and while many of these have been screened for insect resistance over the past ten years, the first large-scale systematic efforts to examine wild Solarium germplasm for insect resistance were initiated by E. B. Radcliffe at the University of Minnesota and reported in a series of papers first appearing in 1968 (. These studies led to the identification of several excellent sources of resistance to aphids and leafhoppers. Prior to this time, very few species were known to resist attack by... 

Clones selected from these hybrid populations have demonstrated excellent levels of resistance to aphids, leafhoppers, and the Colorado potato beetle in field and laboratory studies. We have demonstrated season-long reduction in aphid populations on hybrid clones of up to 60%, compared with populations on commercial cultivars (17.411. We have also demonstrated population reductions of leafhopper adults and nymphs of over 80% on hybrid clones, compared to those on commercial susceptible potato cultivars (221. This level of resistance eliminates the... 

Dreyer, D. L. and B. C. Campbell, Chemical basis of host-plant resistance to aphids. Plant Cell Environ., 10, 353-361 (1987). 

There are marked species differences in A-esterase activity. Birds have very low, often undetectable, levels of activity in plasma toward paraoxon, diazoxon, pirimi-phos-methyl oxon, and chlorpyrifos oxon (Brealey et al. 1980, Mackness et al. 1987, Walker et al. 1991 Figure 2.10). Mammals have much higher plasma A-esterase activities to all of these substrates. The toxicological implications of this are discussed in Chapter 10. Some species of insects have no measurable A-esterase activity, even in strains that have resistance to OPs (Mackness et al. 1982, Walker 1994). These include the peach potato aphid (Myzus persicae Devonshire 1991) and the... 

In the middle of the 1980s in the USSR, approximately 150 species acquired resistance to one of the various OCPs and OPPs used [3], and now require more complicated means of suppression. For example, until the 1950s, weevils and boll weevils were the main pests damaging cotton. After the widespread use of OCP insecticides - DDT, toxafene, and others - cottonworms, tobacco tortricids, tobacco aphids, spider mites and loopers must now be fought as well. Their number jumped after suppression of the first two target species. 

Carboxylesterases are well-represented in insects and are sometimes important in the development of resistance to insecticides. Thus, a well-characterized carboxylesterase E4 is responsible for resistance to organophosphorus insecticides in the aphid (Myzuspersicae) [107]. In the California Culex mosquito, the esterase B1 is 500-fold more abundant in organophosphate-resistant than in susceptible insects. The increase of esterase levels is the result of gene amplification, i.e., the resistant animals have an increased number of copies of the structural esterase gene [108],... 

Resistance of Cereal Crops to Aphids Role of Allelochemicals... 

In this paper we summarize our work on the role of indole alkaloids and hydroxamic acids on the resistance of cereals to aphids. In addition, we describe the effects of water stress on susceptibility of barley to aphids. 

All these data support the idea that QA may function as chemical defense compounds. We also tested whether this chemical defense is relevant for the survival of a lupin plant. Lupins offer a unique chance to explore this question experimentally plant breeders have selected "sweet" varieties, which have a very low alkaloid content. These varieties can be compared to semi-bitter or bitter ones. We have grown Lupinus albus strains that differ in their alkaloid content in our experimental garden and greenhouse and have monitored their susceptibility to attack by plant pests. As can be seen from Figure 2, "sweet" lupins are preferentially eaten by rabbits (Cuniculus europaeus) or are infested by aphids (Aphidae) or leaf miners (Agromyzidae). Literature data also support the assumption that alkaloid-rich lupins are much more resistant to plant pests than "sweet" varieties (30-32). We conclude therefore, that QA are indeed important for the fitness of a lupin plant and that they constitute a major part of its chemical defense system, in which... 

HVlOl Barria, B. N., S. V. Cpaj, and H. M. HV113 Niemeyer. Occurrence of Diboa in wild Hordeum species and its relation to Aphid resistance. Phytochemistry 1992 31(1) 89-91. 

The mechanisms of resistance fall into two main categories. Many insects produce an increased level of detoxifying enzymes, such as esterases, that modify the insecticides to inactive metabolites very rapidly. Such a system is seen in aphids that are resistant to OP insecticides. In other cases it is the target site that is modified such that the insecticide (the enzyme inhibitor) no longer binds to the target and is, therefore, ineffective. This has recently been shown to occur in some aphids that are resistant to OP insecticides but the classical example is knockdown resistance (kdr) and super-kdr to pyrethroid insecticides shown by many insects but particularly house flies Musca domes tied). This resistance is thought to result from a modification of... 

Aphids are a little more resistant to a simple castiie soap spray, so I recommend using insecticidal soap on them. These soaps contain salts of fatty acids and are quite safe to use, even within days of harvest. The directions say the soap can be left on, but I wash the leaves off the following day after application just to be safe. 

Aphids are a little more resistant to a simple castile soap spray, so I recommend using insecticidal soap on them. 

Feng, R. and Isman, M.B. Selection for resistance to azadiractin in the green peach aphid, Ayzus persicae. Experientia, 51, 831-833, 1995. 

Leszczynski, B. and Dixon, A. F. G. 1990. Resistance of cereals to aphids interaction between hydroxamic acids and the aphid Sitobion avenae (Homoptera Aphididae). Ann. Appi. Biol. 117, 21-30... 

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