Preference Bioassays Research Articles

Effect of coffee alkaloids and phenolics on egg-laying by the coffee leaf miner Leucoptera coffeella

The recognized importance of coffee alkaloids and phenolics mediating insect-plant interactions led to the present investigation aiming to test the hypothesis that the phenolics chlorogenic and caffeic acids and the alkaloid caffeine and some of its derivatives present in coffee leaves affect egg-laying by the coffee leaf miner Leucoptera (=Perileucoptera) coffeella (Guérin-Méneville & Perrottet) (Lepidoptera: Lyonetiidae), one of the main coffee pests in the Neotropical region. These phytochemicals were, therefore, quantified in leaves from 12 coffee genotypes and their effect on the egg-laying preference by the coffee leaf miner was assessed. Canonical variate analysis and partial canonical correlation provided evidence that increased leaf levels of caffeine favour egg-laying by the coffee leaf miner. An egg-laying preference bioassay was, therefore, carried out to specifically test this hypothesis using increasing caffeine concentrations sprayed on leaves of one of the coffee genotypes with the lowest level of this compound (i.e. Hybrid UFV 557-04 generated from a cross between Coffea racemosa Lour. and C. arabica L.). The results obtained allowed the recognition of a significant concentration-response relationship, providing support for the hypothesis that caffeine stimulates egg-laying by the coffee leaf miner in coffee leaves.

Inducible resistance to herbivory in Fucus vesiculosus—duration, spreading and variation with nutrient availability

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 273:109-120 (2004) - doi:10.3354/meps273109 Inducible resistance to herbivory in Fucus vesiculosus–duration, spreading and variation with nutrient availability Anne Hemmi*, Tuija Honkanen, Veijo Jormalainen Section of Ecology, Department of Biology, University of Turku, 20014 Turku, Finland *Email: anne.hemmi@utu.fi ABSTRACT: Inducible resistance in plants is a defense strategy for avoiding the negative consequences of herbivory on plant fitness. Since resistance is costly, the induction of resistance may depend on resource availability. Resource-based plant-herbivore hypotheses predict that the cost of producing carbon-based defensive metabolites will be higher when an excess of nutrients is available for growth. We tested experimentally the effect of nutrient availability on the occurrence, duration and within-alga spread of inducible resistance in the brown alga Fucus vesiculosus L. Based on feeding preference bioassays using the herbivore Idotea baltica (Pallas), simulated grazing of F. vesiculosus caused a clear, rapid, induced resistance that disappeared after 10 to 38 d. Furthermore, the induction of resistance does not spread to neighboring fronds or to growing tips above the point of simulated grazing. Induced resistance against isopod grazing, however, was not explained by increased production of phlorotannins, despite their putative role in the defense against herbivory. Phlorotannin production responded most strongly to nutrient enhancement, which reduced the phlorotannin concentration of the alga. Nutrient enhancement, however, did not affect the induction of resistance. The occurrence of induced resistance together with the lack of correlation between the phlorotannin concentration and the food preferences of herbivores imply that I. baltica is not deterred by the total quantity of phlorotannins; there may, however, be other, as yet unknown, rapidly inducing substances in F. vesiculosus that are capable of functioning as feeding deterrents to isopod grazers. Resistance may also arise as a side-effect of substances with a functional role, for instance in wound-healing processes. The localized nature and short duration of such deterrence imply that it may be inefficient as a general defense against herbivory, but may benefit the alga by dispersing future damage within the individual and avoiding the breakage of whole fronds. KEY WORDS: Fucus vesiculosus · Inducible resistance · Nutrients · Eutrophication · Herbivory · Chemical defense · Phlorotannins · Plant-herbivore interactions Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 273. Online publication date: June 08, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

Responses of the sweetpotato whitefly, Bemisia tabaci, to the chinaberry tree (Melia azedarach L.) and its extracts

SummaryHost preference bioassays for adults of the sweetpotato whitefly were performed with leaves of the chinaberry tree Melia azedarach L., tomato, cucumber and bean. Fruit and leaf extracts of the chinaberry tree were tested against adults of the sweetpotato whitefly. Fruit extracts were tested against eggs, first and second instar nymphs, and pupae of the insect. Treatments included aqueous, methanol, and acetone fruit extracts of 200 mg ml−1 and serial dilutions of 20.0 and 2.00 mg ml−1, ether extract, the botanical insecticides Azatin® and Margosan® ‐O and the control, water or water with Triton®. Mortality data was collected at 6, 7, and 8 days after treatment of the eggs, nymphs and pupae, respectively. Results of the host preference bioassays indicated a significantly lower number of live insects on leaves of the chinaberry tree vs leaves of bean, cucumber, and tomato after 24 h. This indicates that M. azedarach is not a good host for the sweetpotato whitefly. Adults of the insect were significantly more repelled from tomato plants treated with the undiluted extracts when compared to the control after 72 h. There were significant differences in percent mortality of nymphal instars when exposed to the undiluted extracts compared to other extracts and the control. However, there was no significant effect of the fruit extracts on the egg and pupa instars. Thus M. azedarach extracts were found to be repellent to the whitefly adults, while the fruit extracts have shown a significant detrimental effect against early nymphal instars. In general, the methanol extracts were more active against B. tabaci than extracts with other solvents.

Preference and performance responses of California grape phylloxera to different Vitis rootstocks

Laboratory experiments on host preference and performance were simultaneously conducted with Cabernet Sauvignon, AXR#1, and 5C Vitis rootstocks for the California biotypes A and B grape phylloxera. Preference bioassays recorded over a 3‐day period indicated that phylloxera exhibit differential host choice. AXR#1 is antixenotic to biotype A, and 5C is antixenotic to both phylloxera biotypes. Preferences observed with biotype B for Cabernet Sauvignon and AXR#1 were not statistically different, whereas biotype A had shown a significant preference for Cabernet Sauvignon. On 5C the preferences scored were significantly lower than on either of the other two rootstocks, and there was no significant difference beetween biotypes. Performance bioassays recorded over a 29‐day period indicated that survival, development, and reproduction of both biotypes were affected by Vitis rootstock. Both biotypes were unable to survive or develop on 5C suggesting the presence of antibiotic resistance in 5C against these phylloxera biotypes. The antibiotic effects observed with AXR#1 against biotype A were expressed as significant reductions in survival, development, and reproduction. Performance of biotype B on AXR#1 was similar to its performance on Cabernet Sauvignon. For both AXR#1 and 5C rootstocks and both phylloxera biotypes A and B the antibiotic mechanism was considerably stronger than the antixenotic mechanism. This research indicated that host preference and performance are positively correlated in grape phylloxera with the rootstocks and phylloxera biotypes tested.

A Feeding Preference Bioassay for Neodiprion Sawflies on Jack Pine, Pinus banksiana1

A feeding preference bioassay was developed that provides consistent qualitative and quantitative evaluation of antifeedant activity of a candidate compound to larvae of several Neodiprion sawflies. The bioassay utilizes twigs of mature jack pine, Pinus banksiana, foliage; one-half is treated with the antifeedant deet and one-half nontreated. Neodiprion sawflies exhibit natural behavioral characteristics in this bioassay, and upon detection of the antifeedant they migrate to untreated foliage to feed.