This study quantified how different shading levels alter the foliar nutrient, C:N ratio, chlorophyll content and key leaf characters in azalea `Delaware Valley White' Rhododendron mucronatum (Blume) (Ericales: Ericaceae), which influenced, in turn, feeding, oviposition, survival and development of the azalea lace bug, Stephanitis pyrioides (Scott) (Heteroptera: Tingidae). The mean contents of N, Ca, Fe, and Zn increased linearly with increases in the shading level, whereas P, K, B, Mn, and the C:N ratio of leaves were significantly decreased. Although injured leaves contained significantly less chlorophyll than uninjured leaves, the mean relative chlorophyll content of leaves increased linearly with the level of shading. Mean leaf area and moisture content of leaves increased linearly with increased degree of shading, while the mean trichome density decreased. The mean number of oviposited eggs and the percent of nymphs reaching adulthood increased linearly with the degree of shading. Azalea shoots suffered increased feeding injury as the season progressed, yet unshaded plants suffered more feeding injury than shaded plants. While the mean number of eggs laid, and the mean number of reared adults, were significantly and positively correlated with the mean leaf N, the mean feeding injury was negatively correlated with leaf N. Although these dependent variables were not correlated with K nor Ca, the mean number of eggs laid, and the mean number of reared adults were negatively correlated with the mean leaf P and with the mean C:N ratio. Mean feeding injury was positively correlated with leaf P and with the C:N ratio, but negatively correlated with N. This study shows that shaded plants are of better quality as hosts and that these plants can tolerate infestations by the lace bug.
Jo-Ann Bentz and Alden M. Townsend
The suitability of container-grown clones of red maple, Acer rubrum L., as a host to the potato leafhopper, Empoasca fabae Harris (Homoptera: Cicadellidae), under different fertilization regimes was determined, and compared to different freeman maple cultivars (A. ×freemanii E. Murray). Three clonal selections of red maple (USNA numbers 56026, 59904, and 55410), and three freeman maple cultivars (55892 `Indian Summer', 67256 `Jeffersred' [trademark Autumn Blaze], and 55890 `Armstrong') were potted in 7.6-L containers, fertilized with either 0, 3.3, or 6.6 g/pot of calcium nitrate and used in experiments. When given a choice, female leafhoppers laid more eggs on leaves of red maple clone 56026 than on leaves of clone 59904, with oviposition linearly increasing on both clones with increases in the fertilization level applied to the trees. Yet, when female leafhoppers were confined to leaves using organza sleeve cages, oviposition increased linearly as fertilizer level increased, without a significant clonal effect. Oviposition did not differ among freeman maple cultivars, nor was it influenced by the fertilizer level applied to the freeman maple trees. Nymphs had the lowest odds of surviving to adulthood when reared on the freeman maple `Jeffersred', but highest when reared on red maple 59904. Red maple 59904 had the fastest growth rate while red maple 55410 had the slowest. Leaf initiation and expansion in red maple 56026 was significantly slower than in the other selections. Leaf development of these three red maple clones was significantly accelerated by the application of fertilizer, regardless of level. The maple selections differed in their mean amounts of foliar macronutrients and micronutrients, which related to the fertilizer level applied to trees. Unfertilized trees had the highest C to N ratio, which decreased as fertilizer level applied to trees was increased. This study showed that fertilization improved the performance of the potato leafhopper on previously nonpreferred maple selections, and that the foliar nutrient content and C to N ratio could be used as indicators of tree susceptibility to insect attack under different growing conditions.
Yuefang Wang, S. Kristine Braman, Carol D. Robacker, Joyce G. Latimer, and Karl E. Espelie
Epicuticular lipids were extracted from the foliage of six deciduous and one evergreen azalea genotypes (Rhododendron sp.) and identified by gas chromatography-mass spectrometry. The relationship of leaf-surface lipid composition with measures of resistance to azalea lace bug, Stephanitis pyrioides Scott, was evaluated. Each genotype had a distinct epicuticular lipid composition. The major surface lipid components from all test taxa were n-alkanes and triterpenoids. In the most resistant genotypes [R. canescens Michaux and R. periclymenoides (Michaux) Shinners] ursolic acid, n-hentriacontane, and n-nonacosane were the most abundant epicuticular lipids. The lipids present in largest proportion among all susceptible deciduous genotypes tested were α-amyrin, β-amyrin, and n-nonacosane. The proportions of the lipid components from the same plant of each genotype varied between spring and fall samples. Among classes of lipids, n-alkanes, n-1-alkanols, and triterpenoids had significant correlations with azalea lace bug behavior on host plants. Among individual components, heptadecanoic acid, n-hentriacontane, oleanolic acid, ursolic acid and one unknown compound (with major mass spectra 73/179/192/284/311) were significantly negatively correlated with host plant susceptibility to azalea lace bug, as measured by oviposition, leaf area damaged, egg and nymphal development, and nymphal survivorship. Triacontanol, α-amyrin, β-amyrin, and three unknowns were significantly positively correlated with host plant susceptibility. Acceptance or rejection by azalea lace bug to a particular plant may be mediated by a balance of positively and negatively interpreted sensory signals evoked by plant chemicals. This study indicated that the high levels of resistance observed in R. canescens and R. periclymenoides may be due to the lesser amount or the absence of attractants and stimulants for feeding or oviposition.
Carlos R. Quesada, Adam Witte, and Clifford S. Sadof
water relations influence the distribution of an armored scale insect Ecology 74 1081 1091 Hanks, L.M. Sadof, C.S. 1990 The effect of ants on nymphal survivorship of Coccus viridis (Homoptera: Coccidae) Biotropica 22 210 213 Hanson, P.E. Miller, J