| Alligatorweed Alternanthera philoxeroides (Mart.) Griseb natived in South America, belonging to Amaranthaceae Alternanthera, has now spread to North America, Europe and Southeast Asia and China. Alligatorweed was listed as one of important invasive weed, now the alligatorweed has been distributed in 28 provinces and cities in China. Alligatorweed threatened the industrial, agricultural production and people’s life and also caused considerable effects on the ecological environment, biodiversity due to its high reproductive and strong tolerance. Practice has proved that using the alligatorweed flea beetle Agasicles hygrophila Selman & Vogt to biocontrol A.philoxeroides is one of effective and economic methods. Good control effect were meet in southern China and currently the alligatorweed flea is still one of the most effective natural enemy of alligatorweed.Early studies showed that high temperatures and low temperatures significantly limited the survival and fecudity, different biotypes A.philoxeroides also limited pupation ability. But the environmental factors were diverse and also not constant in nature which potentially affect the insects’ survive and dynamic, such as temperature factor, etc., showed a certain periodicity and regularity of changing. Therefore, this paper by setting different photoperiod, thermoperiods, food resources, mating resources and to investigate the effects of these factors on the alligatorweed flea beetle reproductive and survival ablity. The main results are as follows:Effect of photoperiod on alligatorweed flea beetle:In this study, we set the different photoperiods and found the different effects on alligator weed with the different instars.1) Different photoperiodic conditions had no effect on egg hatchability.2) When the light of the photoperiod was 2-16h, which obviously impacted the 1,2-instar larvae, their developmental period increased with the increasing of light photoperiod time, the larvae sensitive critical photoperiod point located in L:D=8:16, but the larval favorable survival condition was the long photoperiod.3) Different photoperiodic conditions has no effects on alligatorweed flea beetle pupation ability.4) Long photoperiod conditions was conducive to adult survival and the adults’ optimum photoperiod conditions was L:D=16:8. studies showed adults fecundity, spawning duration, single female fecundity presented different changes in the set photoperiods, the optimum mainly located in the 4～8h and 20h light photoperiods, but the adult survival was relatively low.5) Adults did not pass the photoperiods impacts to the offspring, their offspring’s growth and development were not affected. To sum up, long photoperiods were fit for survivaling and reproducing, due to the seasons photoperiods condition in china, the photoperiod duration increases in spring and decreases in autumn, which indicate why the alligatorweed flea beetle population changed with the seasons.Effects of thermalperiods on alligatorweed flea beetle:In this study we tested the effects of different thermalperiods on alligator weed flea beetle.1) The results showed that alligatorweed flea beetle eggs hatching duration increased with the experienced duration of cryphase, the changing meet with the function y= 3.5982e00658x (y:hatching period, x:periods of cryphase, there was a significant delay in the cryphase conditions, but short duration cryphase were favorable for the development of the egg. Egg hatchability showed no significant differences with the control. Low temperatures not only disturbed the whole egg hatchability and incubation duration but also affected the larvae development duration and survival.2) The long duration cryphase thermalperiods significantly delayed the 1,2 instar larvae development duration and has little effect on the third instar larvae. Alligatorweed flea beetle larvae accumulated development temperperature with cryphase duration relationship was y= 0.131x2-1.8686x+ 15.967, (y larval development of effective temperature, x is the duration of the cryphase), when the thermperiod was C:T= 3:21 promoted the development of larvae and is conducive to the survival of larvae.3) Alligatorweed flea beetle preoviposition duration increased with the cryphase duration and the pre-oviposition duration was 29d under the whole cryphase condition, the relationship met the function y= 0.0123x2+0.0262 x+3.5366, when the cryphase duration> 12h the preoviposition duration were obviously increased. The highest life span was C:T=11:13 and C:T=18:6 and C:T= 21:3, and lowest was C:T=3:21, C:T=13:11. The highest fecundity was C:T=11:13 and lowest was the whole cryphase condition. The longest spawning duration appeared in the C:T=11:13, C:T=18:6 and C:T=21:3 treatments. Alligator weed flea beetle survival ability was increased with the duration of the cryphase in the thermalperiod, they exhibited a relative increasing in life expectancy and survival ability, but fertility declined. Adults did not pass the thermalperiods signal to the offspring. To get conclude, the short cryphase were suit for the alligatorweed fleabeetle growth and development, the thermophase were the necessarly factor for the flea beetle’s development. The day-and-night temperature difference as well as of the cryphase were increased in the autuman which would significantly affect the alligator weed fleabeetle development and reproductive ability, hence the population number decreased.Effects of food resources on alligator weed flea beetle:1) in this study, we set the same food and space conditions and changed the population density found alligatorweed flea beetle elderly larvae survival rate decreased with increasing population density and their developmental period extended.2) High density significantly affected the adults’s oviposition and survival ablity.3) Pupate under limited resources, along with its increasing number of mature larvae, pupation rate gradually decreased, but some larvae pupate in A.philoxeroides stalk away.4) By feeding on different season A. philoxeroides and found their developmental duration, survival rate was less affected.5) Comparison of different plants under different selection pressures with different given plant specices, the alligatorweed flea beetle only feed on A.philoxeroides and showed normal development, A.sessils can be used as an alternative food resources, but can not be host plant. To sum up, the food resources played a very important role in alligator weed flea beetle development and survival, especially, while the population number increased at the limited condition.Effects of mating resources on alligatorweed flea beetle:1) Compared different photoperiodic efffect on the alligator weed flea beetle mating behavior and found under short photoperiod conditions, the mating time reduced, but did not change the mating rhythm. Under the full dark conditions, the flea beetle fecundity decreased.2) Alligator weed flea beetle female and male adult belong to polygamy type insects can mate several times in their lifetime, the number of mating times and spouse number benefieted reproduce ability and the female fecundity significantly increased.3) By setting different densities of food resources in the flea beetle mating platform and found adults invested on mating hehavior under less food condition was significantly higher than plentifuly food conditions, and the higher investment were on courtship and mating behavior guardian behavior when under high-density food conditions. Adults investments on mating behavior, mating guarding behavior, courtship behavior time was quite., adults mating times per day showed no significant difference under different Male and female ratio conditions, the highest fecundity was polygynous conditions.4) In polygynous conditions, the peak of mating located from 14:00 to 16:00, in the multi-male and one female, one male and one female condition, the peak of their mating located around 19:00. Under the multi-male female condition, the mating behavior investment was larger than the single female single male condition, under the single female single male conditions, the adult investment to mating guard behavior was large than the multi-male condition.5) By testing the mated and unmated males spouse choice, found that both were inclind to select for unmated female, the courtship and mating probability significantly higher than mated females. Due to the adults’ tolerance difference, the mate conditions were asymmetrical, which significantly affected the flea beetle reproductive ability.Through this study showed that different photoperiod, thermoperiodic, food resources and mating resourses cann’t induce the diapause of alligatorweed flea beetle, alligatorweed flea beetle were sensitive to these factors and the survival and reproduction were all affected, in which the thermalperiods played a very important role than the other factors. Based on our study, we learn the biological characters and potential control ability which will do well to the releasing and artificial preserving this natural enemy. |
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