Effects of alternating temperatures on development and reproduction of the armyworm,Mythimna separata (Walker)

Effects of cycling and constant temperature on development and reproduction of the armyworm, Mythimna separata (Walker) were investigated by rearing the insects on the artificial diet under temperatures covering low(16-24℃ vs. 20 ℃ ), medial(20-28℃ vs. 24℃ ) and high(24-32 ℃ vs. 28 ℃) regions. In the low region, all the immature stages of the insect developed significantly faster under alternating temperatures than at corresponding constant temperatures. For the medial region, their development was little affected by variable temperatures. For the high region, developmental durations tended to be longer under cycling temperatures except egg stage.Mean fecundities of the adult moths markedly increased under cycling temperatures as compared with those at respective constant temperature in all regions.Possible reasons for effect of alternating temperatures on insect development are discussed in some details.

Larval diet affects development and reproduction of East Asian strain of the fall armyworm,Spodoptera frugiperda

In December 11,2018,the fall armyworm(FAW),Spodoptera frugiperda invaded China and has since impacted local maize,sorghum and other crops.Here,we draw on laboratory experiments to show how different host crops(i.e.,maize,sorghum,wheat and rice)and artificial diet affect larval growth and adult reproduction of one local FAW strain.Larval diet affected development duration,pupation rate,survival and emergence rate of pupae,and S.frugiperda adult fecundity.FAW attained the slowest larval development(19.4 days)on sorghum and the fastest(14.1 days)on artificial diet,with larvae attaining 99.6%survival on the latter food item.On rice,FAW larvae attained survival rate of 0.4%and were unable to pupate successfully.Pupation rate and pupal survival varied substantially between artificial diet and live plantlets at different phenological stages.Pupal weight was the highest(0.26 g)on artificial diet and the lowest(0.14 g)on sorghum,while FAW females reached the highest fecundity(699.7 eggs/female)on 2-leaf stage maize.Egg hatching rate equaled 93.6%on 4-or 5-leaf stage maize and 36.6%on artificial diet.FAW intrinsic rate of natural increase and the finite rate of increase varied between larval diets,reflecting how young maize leaves are the most suitable diet.Our findings can help to refine laboratory rearing protocols,devise population forecasting models or guide the deployment of‘area-wide’integrated pest management(IPM)modules in FAW-invaded areas of China and other Asian countries.

Evaluation of Effects of Tea Saponin on Behavior, Growth and Development of Cylas formicarius (Coleoptera: Brentidae)

[Objectives] This study was conducted to expand the insect resistance spectrum of tea saponin, and its control effect on Cylas formicarius and the potential as an insecticide for pest control were explored. [Methods] The olfactory avoidance rate of C. formicarius to tea saponin aqueous solution was determined by Y-type olfactometer;the feeding avoidance rate of C. formicarius to tea saponin was determined by the selective method;the antifeedant rate of C. formicarius to tea saponin was determined by non-selective method;and the development duration and mortality of C. formicarius under the influence of tea saponin were determined by artificial feeding method. [Results] C. formicarius had no significant olfactory tendency to every concentration of tea saponin, and the olfactory avoidance rate of 20.0% tea saponin aqueous solution was only 9.14%. Tea saponin had a feeding avoidance effect on C. formicarius, and the avoidance rate increased with the increase of tea saponin concentration. At 6 h, the feeding avoidance rates of 0.5%, 1.0%, 5.0%, 10.0% and 20.0% tea saponin on C. formicarius were 58.14%, 77.77%, 88.23%, 95.00% and 97.65 %, respectively;and the feeding avoidance effect at 6 h was significant, and the feeding avoidance rate was higher than that of 1 h. Tea saponin had a significant antifeedant effect on C. formicarius, and the longer the feeding time, the higher the antifeedant rate. At 72 h, the antifeedant rates of 0.5%, 1.0%, 5.0%, 10.0 % and 20.0% tea saponin to C. formicarius were 63.01%, 67.54%, 97.14 %, 96.42% and 98.57%, respectively. The larval development duration of C. formicarius was shortened with the increase of tea saponin concentration, and the larval death occurred. The development duration of larvae under the influence of 1.0% tea saponin was the shortest, which was 4.01 d shorter than that of the control, and the mortality was the highest, which was 26.65%. [Conclusions] Tea saponin had neither olfactory avoidance effect nor olfactory attracting effect to C. formicarius, but had obvious feeding avoidance effect and strong antifeedant effect. Tea saponin can shorten the development duration of the larvae of C. formicarius and cause the death of the larvae.

Population life tables for the invasive fall armyworm,Spodoptera frugiperda fed on major oil crops planted in China

The fall armyworm(FAW),Spodoptera frugiperda,is a newly invasive,widespread agricultural pest in China.Understanding the suitability of the main field crops in Chinese agricultural system as host for this polyphagous herbivore is especially important for making control strategy.Here,after FAWs were fed three important oil-bearing crops(oilseed rape,soybean and sunflower)planted in China and resultant population parameters were compared using the age-stage,two-sex life table method,survival of larvae on soybean was significantly lower than that on oilseed rape and sunflower.Developmental duration of larvae on soybean was also the longest(23.3 days).The highest pupation rate was recorded on sunflower.The highest pupal mass(0.19 g)was attained on oilseed rape,significantly higher than on the other host plants;the lowest mass was on soybean(0.15 g).On soybean,oilseed rape and sunflower,respectively,the average generation period was 42.21,39.10 and 40.44 d;the intrinsic rate of increase(r)was 0.0844,0.1041 and 0.1134;the finite rate of increase(λ)was 1.0881,1.1098 and 1.1202.While the most suitable host plant overall was sunflower,S.frugiperda completed development and increased its population on all three host plants.Thus,soybean,oilseed rape and sunflower were all suitable for FAW,and population monitoring and management of FAW in these crops should be increased.

Effects of intercropping vines with tobacco and root extracts of tobacco on grape phylloxera, Daktulosphaira vitifoliae Fitch

The effects of grape-tobacco intercropping patterns on populations of grape phylloxera, Daktulosphaira vitifoliae Fitch, as well as on the growth and development of the infested vines were evaluated in the field and the impact of an aqueous tobacco root extract on grape phylloxera was evaluated using a laboratory bioassay. The aqueous tobacco root extract exhibited biological activity against this pest. The egg mortality, nymph mortality, development period, life span and female fecundity were significantly affected. In the field trial, grape phylloxera populations were clearly lower as compared to the monoculture pattern. However, the rates of newly developed roots and newly infested grape roots were significantly higher and lower, in intercropping patterns than in the vine monoculture, respectively. The grape phylloxera population number on the grape roots decreased each year, and the vine trees gradually renewed upon continuous intercropping with tobacco over three years. These results confirmed that intercropping grapes with tobacco can effectively control grape phylloxera in an infested vineyard. The results also indicated that additional crops could be intercropped with grapes and are effective against grape phylloxera, which should be explored as an integrated approach for controlling the pest.

Changes of Essential Substance Contents in Exorista civilis Rondani during Diapause Stage

[ Objective ] The paper was to study the occurrence regularity of Lysiphlebus testaceipes Cresson. [ Method ] With Aphis craccivora Koch as the breeding host, developmental duration, development threshold temperature and effective accumulative temperatme of L. testaceipes Cresson were studied at six constant tem- peratures of 12, 16, 20, 24, 28 and 32℃ in the laboratory, respectively. [ Result] The developmental durations of each growth stage of L. testaceipes Cresson were shortened with the increasing temperature ranged from 12 to 32℃, and the growth rate was significantly accelerated with the increasing temperature. However, when the temperature was up to 32℃, the growth and development from mummy to adult was suppressed, and the developmental duration was extended for 0.45 d than that at 28℃. The developmental durations from egg to adult at 12, 16, 20, 24, 28 and 32℃ were 38.50, 21.25, 14.11, 12.17, 10.28 and 9.01 d, respectively. The developmental threshold temperatures of egg-mummy, mummy-adult and egg-adult were estimated to be 6.5, 6.25 and 5.36℃, respectively; and the effective accumulated temperatures were 136.28, 75.74 and 227.23 d·℃, respectively. [ Conclusion] Forecast formula of developmental duration and Logistic models were established according to effective accumulated temperature and developmental threshold temperature.

Effect of photoperiod on slow and fast developing individuals in aphidophagous ladybirds, Menochilus sexmaculatus and Propylea dissecta （Coleoptera： Coccinellidae）

The effects of environmental parameters on insect development have been studied extensively. But the reasons for 2 differential developmental rates within same cohort under varying environmental factors have not been explored. For the purpose, in this study the existence and stability of slow and fast development under 5 photoperiods （i.e., 8L： 16D, 10L ： 14D, 12L ： 12D, 14L ： 10D and 16L ： 8D; light and dark hours per day） and its effect on body mass and reproductive attributes in 2 aphidophagous ladybirds, Menochilus sexmaculatus （Fabricius） and Propylea dissecta （Mulsant） was examined on Aphis craccivora Koch at 27 4- 1 ~C temperature. A clear bimodal （2 peaks, where the first peak represented the fast developing and the 2nd peak slow developing individuals） pattern of distribution at each photoperiod was found. The proportion of slow and fast developing individuals in a cohort differed with photoperiods. The slow developing individuals were more in numbers at 8L ： 16D, in equal numbers at 14L ： 10D and in less numbers at 16L： 8D, indicating that the variation in emergence was owing to exogenous cues influenced differential rates of mortality. Slow developing individuals had female biased sex ratio, higher longevity and lower body mass than fast developing individuals. Fast developing females laid higher numbers of eggs with higher egg viability than slow developing females. Study of such variations in development at different photoperiods is helpful to understand its role in the development of insects particularly ladybirds and permits the selection of fast developing bioagents for their use in biocontrol of pest species.