Smad on X is vital for larval-pupal transition in a herbivorous ladybird beetle.

Insect development is regulated by a combination of juvenile hormone (JH) and 20-hydroxyecdysone (20E). Production of both JH and 20E is regulated by transforming growth factor-ß (TGFß) signaling. TGFß can be classified into two branches, the Activin and Bone Morphogenetic Protein (BMP) pathways. In Drosophila melanogaster, BMP signaling is critical for JH synthesis, whereas Activin signal is required to generate the large pulse of 20E necessary for entering metamorphosis. However, to which extent the roles of these signals are conserved remains unknown. Here we studied the role of an Activin component Smad on X (Smox) in post-embryonic development in a defoliating ladybird Henosepilachna vigintioctopunctata. RNA interference (RNAi)-aided knockdown of Hvsmox inhibited larval growth, and impaired larval development. All Hvmyo RNAi larvae arrested at the fourth-instar larval stage. Moreover, knockdown of Hvsmox delayed gut and Malpighian tubules remodeling. Furthermore, the expression of a JH biosynthesis gene (Hvjhamt), a JH receptor gene HvMet and a JH response gene HvKr-h1 was greatly enhanced. Conversely, the expression levels of an ecdysteroidogenesis gene (Hvspo), a 20E receptor gene (HvEcR) and six 20E response genes (HvBrC, HvE74, HvE75, HvE93, HvHR3 and HvHR4) were significantly lowered. Knockdown of HvMet partially restored the negative phenotypes in the Hvsmox RNAi beetles. Our results suggest that Smox exerts regulative roles in JH production, ecdysteroidogenesis and organ remodeling, thus contributing to modulate the larva-pupa-adult transformation in H. vigintioctopunctata.

Importance of Taiman in Larval-Pupal Transition in Leptinotarsa decemlineata.

Insect Taiman (Tai) binds to methoprene-tolerant to form a heterodimeric complex, mediating juvenile hormone (JH) signaling to regulate larval development and to prevent premature metamorphosis. Tai also acts as a steroid receptor coactivator of 20-hydroxyecdysone (20E) receptor heterodimer, ecdysone receptor (EcR) and Ultraspiracle (USP), to control the differentiation of early germline cells and the migration of specific follicle cells and border cells in ovaries in several insect species. In holometabolous insects, however, whether Tai functions as the coactivator of EcR/USP to transduce 20E message during larval-pupal transition is unknown. In the present paper, we found that the LdTai mRNA levels were positively correlated with circulating JH and 20E titers in Leptinotarsa decemlineata; and ingestion of either JH or 20E stimulated the transcription of LdTai. Moreover, RNA interference (RNAi)-aided knockdown of LdTai at the fourth (final) instar stage repressed both JH and 20E signals, inhibited larval growth and shortened larval developing period. The knockdown caused 100% larval lethality due to failure of larval-pupal ecdysis. Under the apolysed larval cuticle, the LdTai RNAi prepupae possessed pupal thorax. In contrast, the process of tracheal ecdysis was uncompleted. Neither JH nor 20E rescued the aforementioned defectives in LdTai RNAi larvae. It appears that Tai mediates both JH and 20E signaling. Our results uncover a link between JH and 20E pathways during metamorphosis in L. decemlineata.

[Effects of temperature on population parameters of Therioaphis trifolii (Monell) (Homoptera: Aphididae)].

To investigate the effects of temperature on the population growth of Therioaphis trifolii (Monell) (Homoptera: Aphididae), a laboratory experiment was conducted to study the development, reproduction, and life table of the spotted alfalfa aphid at nine constant temperatures ranged from 15 to 35 degrees C. The aphid could not survive at 35 degrees C. The total nymphal period shortened significantly with increasing temperature. From birth to adult stage, it required 18.33 days at 15 degrees C, but only 4.02 days at 32 degrees C. The survivorship of the nymphs ranged from 40.0% (32 degrees C) to 83.6% (25 degrees C). The average longevity of the adults ranged from 10.64 days at 32 degrees C to 20.87 days at 23 degrees C. The reproductive peak was advanced with increasing temperature, and the reproduction duration at all test temperatures was 3-6 days except that at 15 degrees C (15 days). The average fecundity and the highest fecundity were the highest at 25 degrees C, being 82.0 and 149.0 offspring per female aphid, respectively. When the temperature increased, the mean generation time was gradually decreased from 31.17 days at 15 degrees C to 10.17 days at 32 degrees C. The net reproductive rate was the highest (68.62) at 25 degrees C and the lowest (13.96) at 32 degrees C. The intrinsic rate of increase was 0.10-0.30 per day, with the highest at 28 degrees C but the lowest at 15 degrees C. The developmental threshold temperature and thermal constant of the nymphs were 9.35 degrees C and 97.83 day-degrees, respectively. Unary quadratic equation could be used to describe the relationships of the fecundity, net reproductive rate, and intrinsic growth rate with the temperature.