Initial detections and spread of invasive Spodoptera frugiperda in China and comparisons with other noctuid larvae in cornfields using molecular techniques

The fall armyworm,Spodoptera frugiperda,is a species native to the Americas and has spread to many countries in Africa and Asia in recent years.Proactive actions for potential invasion of S.frugiperda to China coordinated by government agencies and agricultural extension systems resulted in timely detection in January 2019 in Yunnan province neighboring onto Myanmar.The extensive monitoring in southern provinces of China since February 2019 resulted in dynamic tracking of S.frugiperda spreading to 13 provincial regions in China within 4 months by May 10,2019,which is crucial for timely management actions in the fields.The first detections of S.frugiperda(corn strain)in China were confirmed using cytochrome oxidase subunit 1(COl)and triosephosphate isomerase(Tpi)genes molecular marker method.In addition to S.frugiperda,larvae of three other noctuid species with similar morphological appearance(S.litura,S.exigna and Mythimna separata)can occur simultaneously and cause similar damage in cornfields in southern China.Thus,we can use both morphological and molecular marker methods to compare larval stages of four noctuid species.Further,we discuss the risk of potential spread of invasive S.frugiperda to other regions and impact on corn production in China.

Does Bt maize expressing CrylAc protein have adverse effects on the parasitoid Macrocentrus cingulum （Hymenoptera： Braconidae）？

The potential effects of insect-resistant, genetically engineered （GE） crops on non-target organisms, especially on predators and parasitoids, must be evaluated before their commercial cultivation. The effects of GE maize that produces CrylAc toxin on the parasitoid Macrocentrus cingulum were assessed by direct bioassay and indirect bioassay. In the indirect bioassay, parasitism rate, cocoon weight and the number of M. cingu- lure progeny produced per host were significantly reduced when M. cingulum-parasitized CrylAc-susceptible Ostriniafurnacalis were fed a diet containing purified CrylAc; how- ever, life-table parameters of M. cingulum were not adversely affected when the same assay was performed with Cry 1Ac-resistant （9. furnacalis. These results indicated that the detrimental effects detected with a CrylAc-susceptible host were mediated by poor host quality. In a direct bioassay, no difference in life-table parameters were detected when M. cingulum adults were directly fed a 20% honey solution with or without CrylAc; however, survival and longevity were significantly reduced when M. cingulum adults were fed a honey solution containing potassium arsenate, which was used as a positive control. The stability and bioactivity of CrylAc toxin in the food sources and CrylAc toxin uptake by the host insect and parasitoid were confirmed by enzyme-linked immunosorbent assay and sensitive-insect bioassays. Our results demonstrate that M. cingulum is not sensitive to CrylAc toxin at concentrations exceeding those encountered in Bacillus thuringiensis maize fields. This study also demonstrates the power of using resistant hosts when assess- ing the risk of genetically modified plants on non-target organisms and will be useful for assessing other non-target impacts.

Effects of photoperiod and temperature on diapause induction in Conogethes punctiferalis （Lepidoptera： Pyralidae）

The yellow peach moth, Conogethes punctiferalis （Guenee）, a multivoltine species that overwinters as diapausing larvae, is one of the most serious insect pests on maize in China. Effect of photoperiod and temperature on larval diapause was examined under empirical laboratory conditions. Short-day treatments caused larval diapause at 25℃, and the critical photoperiod was between 12 and 13 h （or 12 h 51 min） light per day. No sensitive instar was identified for diapause induction under alternated short- （L ： D 11 ： 13 h） and long-day （L ： D 14 ： 10 h） treatments at different larval stages. However, accumulative treatment of three instars and 10 d under short-day treatment was required for the induction of 50% larval diapause. All larvae entered diapause at 20℃, whereas less than 3% did so at 30℃, irrespective of the long- or short-day treatment. Furthermore, under the short-day treatment, more than 90% of larvae went into diapause with temperatures ≤ 25℃, but less than 17% did so at 28℃. In contrast, under the long-day treatment, less than 19% of larvae went into diapause with temperatures ≥23 ℃. The forward shift （5℃） of critical temperature under the long-day regime demonstrated the compensatory effect of temperature and photoperiod on diapause induction. In conclusion, C. punctiferalis had a temperature-dependent type Ⅰ photoperiodic diapause response; there was no sensitive instar for diapause determination, but the photoperiodic accumulation time countermeasures both of the short-day cycles and the number ofinstars exposed, and the photoperiodic diapause response, was a temperature-compensated phenomenon.

Seasonal and geographical variation in diapause and cold hardiness of the Asian corn borer, Ostrinia furnacalis

Asian corn borer, Ostrinia furnacalis （Guenee）, is a key corn pest in the Asian-Western Pacific countries. It overwinters as flail-grown larvae in plant stalks or in a spun-silk covering located in the plant debris in the temperate regions of China. Supercooling point （SCP） and survival rate after low sub-zero temperature treatment were assessed for field-collected populations in the laboratory using a cool bath with a 1 ℃/min cooling rate until -40℃. Mean SCPs were varied among geographical populations, with a significant decline from -22.7℃ of Haikou, the multivoltine tropical population in the south, to -28.5℃ of Gongzhuling, the univoltine temperate population in the northeast of China. In addition, there was more than 1℃ difference in SCP between Gongzhuling univoltine and bivoltine populations that were from the same geographic origin. Mean SCPs of the Guangzhou population fluctuated over the year, with significantly lower SCPs in winter than in other seasons, which correlated with a significantly higher proportion of diapausing larvae in winter than in other seasons. Over 41% of overwintering larvae from the northeast population could withstand to be supercooled for a few minutes to the low sub-zero temperature of-40℃, but only 6.7% of their southern counterparts did so. The findings from this study suggest that O. furnacalis mostly takes advantage of freeze avoidance as diapausing larvae for overwintering in the southern region, whereas it exhibits freeze tolerance in diapause in the northeastern region.

Comparison of larval performance and oviposition preference of Spodoptera frugiperda among three host plants:Potential risks to potato and tobacco crops

Fall armyworm(FAW),Spodoptera frugiperda(J.E.Smith),is a majorpolyphagous pest with the potential to seriously damage various crops.A better under-standing of FAW's performance on different hosts may help to predict which plants willbe attacked when the preferred host is absent,and facilitate the development of effectivepest management practices.We compared the larval performance of FAW fed on maizewith that of FAW fed on potato and tobacco,which are important crops in China,usingan age-stage two-sex life table and adult female oviposition preference experiments.Incage experiments with potato,tobacco,or maize as the host,FAW reared on maize exhib-ited the strongest performance with shorter developmental time in thc larval stage,longerlongevity,and a higher reproductive rate in adults.Females oviposited on maize in pref-erence to potato or tobacco.Compared with larvae fed on maize,those fed on potato andtobacco exhibited significantly lower survival,with only 31.61%and 8.13%developing tothe adult stage,respectively.Several life table parameters,including the mean generationtime(T),net reproductive rate(R^(0)),finite rate of increase(λ),and intrinsic rate of nat-ural increase(r)were negatively affected in FAW fed on potato and tobacco.Our resultssupport the preference-performance hypothesis,that is,that herbivore females maximizefitness by choosing host plants associated with strong larval performance.Although lar-vae and adults performed poorly on potato and tobacco,their offspring will be capable ofcstablishing populations on them,posing a potential threat to these crops in China.