Effect Of Cotton Extrafloral Nectar On Predation And Behavior Of Harmonia Axyridis(Pallas)

Plant extrafloral nectar is the nectar secreted on the vegetative organs in addition to flowers. It can be induced by pests injury, mechanical injury and plant volatiles. There were reports that extrafloral nectar(EFN) produced by plants was associated with indirect defenses, so more and more attention have been paid by researchers both domestic and abroad on the relationship of EFN and natural enemy insects. This study chose cotton extrafloral nectar as a representative to explore its influences on predation and behavior of H. axyridis. Results are as follows :(1) A survey about H. axyridis occurrence and extrafloral nectar secreted by cotton in the field showed that H. axyridis is one of dominant species which happened mainly in mid to late June and september to october. Cotton(Hebei cotton 30) planting in field can secrete extrafloral nectar on leaf. While H. axyridis was not directly observed feeding on extrafloral nectar in our investigation, dry extrafloral nectar and H. axyridis were found around extrafloral nectary.(2) Laboratory studies were conducted evaluating prey consumption on aphid(Aphis citricola(von der Goot)) of 1st to 4th instar larvae and adults of different genders in the presence of extrafloral nectarine minic. Results show that equation of predator functional response in different stages of H. axyridis conform to Holling model. The Ⅱinfluence of EFN on 1stto 3rd instar larvae prey was not significant. However, when treated with EFN, instar larvae of 4th predacious number limited to 90.9, female and male adults were respectively 208.3 and 153.8.This study demonstrated that the presence of EFN can reduce the predacious number of 4th instar larvae and adults of H. axyridis. Repeated measures ANOVA and analysis of variance confirmed when dealing with EFN for continuous 7 days under density of 80, H. axyridis prey on aphids decreased significantly.(3) Y-tube olfactometer studies were conducted and effects of EFN on olfaction were evaluated. Primarily cis-Jasmone was proved attractive to H. axyridis. In this study, 37.5% males and 36.7% females chose cis-Jasmone, while in contrast only 25.0% females and 23.3% males chose n-hexane, which demonstrated that cis-Jasmone have a significant attraction for H. axyridis. Researches about the effect of EFN on olfaction were conducted using the same equipment. Results showed whether extrafloral nectary artificial or cotton with extrafloral nectarine, H. axyridis manifested a low selectance. There were only 8.3% males and 6.7% females chose extrafloral nectarine minic, 2% males chose cotton with EFN, while no female chose cotton with EFN, which demonstrated cotton extrafloral nectarine had no significant influences on H. axyridis olfaction.(4) The main composition of EFN are sugars. Study of preference for cotton extrafloral nectarine compositions were conducted. Compared to control with a selectance of 2.5% to 4.5%, the selectance of H. axyridis choosing cotton extrafloral nectarine minic was 55.5% to 57.0%. This suggested cotton extrafloral nectarine minic had significantly greater attraction than distilled water. When compared sucrose, glucose and fructose for the same concentration, H. axyridis like sucrose more than glucose and fructose, especially at a low concentration(5% or 20%), which demonstrated glucose had a significant advantage in attracting H. axyridis than glucose and fructose. H. axyridis showed a randomness for different sugar solutions of equal calorific value and equal energy. In addition, H. axyridis expressed a preference for sugar solutions at high concentration which had higher energy. Preference degree increased with the rising of sugar concentrations.