Allochronic isolation on a latitudinal gradient in the polyphagous moth Hyphantria cunea

Allochronic speciation, where reproductive isolation between populations of a species is facilitated by a difference in reproductive timing, depends on the existence of seasonality. Seasonality is strongly driven by latitude, so there may be a relationship between latitude and divergence among populations separated by life history timing. Here we explore the relationship between allochronic speciation and latitude using Hyphantria cunea (the fall webworm), a Lepidopteran defoliator with red and black colour morphs that may be undergoing an incipient allochronic speciation. We annotated >9000 community science observations of fall webworm to model colour morph phenology and differences in phenotype across North America. We also examined the physiology of two sympatric populations to determine differences in diapause intensity. We found the fall webworm is multivoltine with differing numbers of generations between colour morphs at lower latitudes, and univoltine at latitudes higher than 41°. This shift to univoltism correlated with a decline in morphological differentiation. This shows that conditions at lower latitudes facilitate greater divergence in an incipient allochronic speciation potentially due to longer reproductive seasons allowing for greater mismatches in generations. Our results demonstrate how latitude affects allochronic speciation, and how sympatric speciation along latitudinal gradients contributes to trends in global biodiversity.

Functional Identification and Characterization of Leucokinin and Its Receptor in the Fall Webworm, Hyphantria cunea

Neuropeptides function as central neuromodulators and circulating hormones that modulate insect behavior and physiology. Leucokinin (LK) is an intercellular signaling molecule that mediates many physiological and behavioral processes. However, the functions of LK associated with environmental stress and feeding behavior in the fall webworm, Hyphantria cunea, is little known. Our primary objective is to understand the function of LK and LK receptor (LKR) neuroendocrine system in H. cunea. In the present study, the results showed that LK/LKR are expressed at different developmental stages and in various tissues of H. cunea. A candidate receptor–ligand pairing for LK was identified in the larval transcriptome of H. cunea. In a heterologous expression system, the calcium assay was used to demonstrate that LKR is activated by HcLKs in a dose-dependent manner, with 50% effective concentration (EC50) values of 8.44–90.44nM. Knockdown of HcLK and HcLKR by microinjecting target-specific dsRNA leads to several effects in H. cunea, including feeding promotion, increase in resistance to desiccation and starvation stress, and regulation of water homeostasis. The transcript levels of HILP2 (except in the LK knockdown group), HILP5, and HILP8 increased, whereas those of HILP3, HILP4, and HILP6 decreased; HILP1, HILP2 (in the LK knockdown group), and HILP7 gene expression was not influenced after LK and LKR knockdown. Variations in mRNA expression levels in insulin-like peptide genes in the knockdown larvae suggest an essential role of these genes in survival in H. cunea. To our knowledge, the present study is the first comprehensive study of LK and LKR – from gene to behavior – in H. cunea.

On the virulence of two Beauveria bassiana strains against the fall webworm, Hyphantria cunea (Durry) (Lepidoptera: Erebidae), larvae and their biological properties in relation to different abiotic factors

Background The genus Beauveria is frequently used as a mycoinsecticides in many countries to control insect pests in agriculture, it is being very effective against the fall webworm, Hyphantria cunea (Durry) (Lepidoptera: Erebidae), which is a pest of trees in forests and orchards. Multiple abiotic factors during fungal growth are well known to influence mycelial growth and several physiological adaptations in the conidia produced. Results In this study, the pathogenicity of the Beauveria bassiana strains Bb10331 and Bb7725 against H. cunea was evaluated. Peptone potato dextrose agar (PPDA) was used as the medium and colony diameter, conidiation capacity, conidial germination rate were directly affected by relative humidity (RH), illumination, and the ambient pH. The LC50 values of Bb10331 and Bb7725 to H. cunea were 4.72 × 106 and 3.28 × 106 conidia·ml−1, respectively, after 120 h post treatments, while their corresponding LT50 values were 71.13 and 74.54 h at the concentration of 1 × 108 conidia/ml. The Bb7725 had a conidial germination rate than did Bb10331 at the same RH. The two strains grew faster under a dark:light (D:L) photoperiod of 12:12 h, and this particular light condition was also most suitable for their conidia production. The optimum pH for the growth and conidiation of the two strains was approximately 7.0. Conclusions Both strains are promising for pest control, possessing effective virulence against H. cunea, but this is slightly stronger in Bb7725 than Bb10331. The values of abiotic factors apt to promote the biological properties of each B. bassiana were different.

Plasticity of nutrient accumulation patterns in diapausing fall webworm pupae

The accumulation of nutrients during diapause preparation is crucial because any lack of nutrition will reduce the likelihood of insects completing diapause, thereby decreasing their chances of survival and reproduction. The fall webworm, Hyphantria cunea, diapause as overwintering pupae and their diapause incidence and diapause intensity are regulated by the photoperiod. In this study, we test the hypothesis that photoperiod influences energy reserve accumulation during diapause preparation in fall webworm. We found that the body size and mass, lipid and carbohydrate content of pupae with a short photoperiod during the diapause induction phase were significantly greater than those of pupae with a relatively short photoperiod, and the efficiency of converting digested food and ingested food into body matter was greater in the short-photoperiod diapause-destined larvae than the relatively short-photoperiod diapause-destined larvae. We also observed higher lipase and amylase activities in short-photoperiod diapause-destined larvae relative to the counterparts. However, no obvious difference was found in protein and protease in the pupae with a short photoperiod during the diapause induction phase and short-photoperiod diapause-destined larvae compared with the counterparts. Therefore, we conclude that the energy reserve patterns of diapausing fall webworm pupae are plastic and that short-photoperiod diapause-destined larvae increase their energy reserves by improving their feeding efficiency and increase their lipid and carbohydrate stores by increasing the lipase and amylase activities in the midgut.

Effects of Autumn Warming on Energy Consumption of Diapausing Fall Webworm (Lepidoptera: Arctiidae) Pupae

Since its invasion into China in 1979, the fall webworm, Hyphantria cunea Drury, has spread from Dandong city (about 40°N) in Liaoning Province to Nanjing city (about 32°N) in Jiangsu Province, and to other areas. Owing to geographic and latitudinal gradients in temperature, H. cunea will encounter temperature changes during the spreading process. In this study, we verified the hypothesis that autumn warming accelerates the energy consumption of H. cunea diapause pupae. We found that, after autumn warming, the body size and mass of diapause pupae decreased significantly and raised constant temperature accelerated carbohydrate and protein consumption in female pupae, while fluctuating temperature changes had a more pronounced effect on carbohydrate and protein consumption in male pupae. Contrary to expectations, the lipid content of diapause pupae did not decrease after autumn warming, and even increased significantly. We conclude that warming in autumn accelerates energy consumption by diapause pupae, and the autumn energy consumption of diapause pupae is dominated by carbohydrates, supplemented by protein when carbohydrates are overconsumed, while lipid use is dominated by anabolic metabolism during autumn.