Conservation of natural enemy fauna in citrus canopies by horticultural mineral oil： Comparison with effects of carbaryl and methidathion treatments for control of armored scales

The disruptive effects of an nC24 horticultural mineral oil （HMO） and two other insecticides （carbaryl and methidathion） on two armored scale insects and natural enemy fauna were evaluated in two citrus orchards. In the first orchard, all three spray treatments and non-sprayed controls were distributed separately among individual trees in one block, whereas in the second orchard the control, HMO and methidathion treatments were applied at the level of whole blocks. The results in both orchards were similar. All three of the spray treatments had a lethal effect on the red scale insects and the effects of HMO and methidathion tested at the second site lasted for at least 19 weeks and for purple scale, at least 50 weeks. HMO did not have a significant effect on the abundance and species diversity of parasitoids and （for the most part） did not affect coccinellids and predatory mites. Both carbaryl and methidathion caused significant ongoing disruption to the above groups. No treatment resulted in the resurgence of the scale insects or the outbreak ofphytophagous mites, even where whole blocks were sprayed.

Repellent effect of guava leaf volatiles on settlement of adults of citrus psylla, Diaphorina citri Kuwayama, on citrus

The Asiatic citrus psyllid （Diaphorina cirri Kuwayama [Hemiptera： Sternorrhyncha： Psyllidae] is a vector ofhuanglongbing （citrus greening）, a devastating disease of citrus caused by phloem-limited bacteria. Growing guava （Psidium guajava） as an intercrop appears to be a successful means of reducing psyllid numbers within citrus orchards; however, the mechanism by which such a reduction is achieved is unknown. To determine the repellent effect of guava leaf and factors attributed to this activity, responses of adult psyllids to guava leaf and its odor were evaluated in cage tests and Y-tube olfactometer test. The results showed that guava leaf possessed a repellent effect against the adult citrus psyllids. Fewer psyllids were found on citrus leaves in the presence of guava foliage than in its absence. Young and old guava leaf showed equal repellent activity. By covering the guava shoots with net cloth, it was revealed that the repellent effect of guava leaf against adult psyllids on citrus was attributed to the volatile compounds, rather than physical factors. The olfactometer response of adult psyllids to guava leaf odor was dosage-dependent. Between guava odor and control, only 35.00%, 25.00% and 16.25% of the psyllids moved toward guava odor when presented with 5.0, 10.0 and 15.0 g of guava shoots, respectively. The olfactometer experiments also showed that both male and female psyllids responded similarly to the guava leaf odor.

Capacity of Old Trees to Respond to Environmental Change

Atmospheric carbon dioxide [CO2] has increased dramatically within the current life spans of long-lived trees and old forests. Consider that a 500-year-old tree in the early twenty-first century has spent 70% of its life growing under preindustrial levels of [CO2], which were 30% lower than current levels. Here we address the question of whether old trees have already responded to the rapid rise in [CO2] occurring over the past 150 years. In spite of limited data, aging trees have been shown to possess a substantial capacity for increased net growth after a period of post-maturity growth decline. Observations of renewed growth and physiological function in old trees have, in some instances, coincided with Industrial Age increases in key environmental resources, including [CO2], suggesting the potential for continued growth in old trees as a function of continued global climate change.