Differential induction of NF-κB pathways by non-pathogenic and pathogenic bacteria in Helicoverpa armigera is critical for an efficient immune response and survival.

Following pathogen infection in a host, extensive changes occur in the host's gene expression pattern to suppress infection and increase the chance of host survival. Likewise, many pathogens have evolved to evade/suppress host immunity and increase their survival within the host. In this study, we assessed the NF-κB (Imd and Toll) essential gene expression response of Helicoverpa armigera to an entomopathogenic Serratia marcescens and non-pathogenic Escherichia coli. Bacterial cells of S. marcescens or E. coli were injected into the haemocoel of fifth-instar larvae of H. armigera, whereas distilled water was injected into control insects. Our results showed that the expression levels of the Imd and Toll pathway genes (i.e., Relish, imd, spätzle and dif) and the antimicrobial peptides (i.e., gloverin, transferin, gallerimycin, and galiomicin) were differentially expressed following the bacterial injections while control larvae showed no differences. The E. coli injection induced higher and longer-lasted gene expression than the S. marcescens injected larvae, in which the gene expressions were diminished from 24 h post injection. Transcript Knockdown of Relish increased the replication rates of S. marcescens and E. coli, and lowered the infected larvae survival rates. These results showed that H. armigera NF-κB immunity pathways (particularly Imd pathway) play a vital role in immunity against bacterial infections, and S. marcescens might modulate these pathways to survive and replicate in the host.

Pathogenicity of the entomopathogenic fungus Metarhizium anisopliae var. major on different stages of the sunn pest Eurygaster integriceps.

The sunn pest, Eurygaster integriceps Puton (Hemiptera: Scutelleridae), is the most important insect pest of wheat and barley. The population management of this pest is of major concern to wheat producers. One of the potential control strategies is to use entomopathogenic fungi. This study evaluates the pathogenicity of the fungus Metarhizium anisopliae var. major (Metchnikoff) Sorokin (Hypocreales: Clavicipitaceae) on the sunn pest, E. integriceps. Five concentrations of the fungus were utilized, ranging from 1×10(4) to 1×10(8) conidia/mL, accompanied by controls. Fifth instar nymphs and adults (a migratory summer population and a diapausing population) previously exposed to fungi were sown to isolate the fungi, and the growth parameters were analyzed. A direct spray technique was used to expose the isolates to the E. integriceps. The experiment was repeated four times, and mortalities of the insects for all treatments were recorded daily. The results showed that the mortality of infected nymphs was significantly higher than the mortality of control nymphs. Also, the longevity of infected adults was lower than the controls. The results also showed that diapausing adults of the sunn pest were much more susceptible to infection than the summer adults. Estimated LC50 values for the M14 isolate were 1.4 × 10(6), 1.4 ×10 (5) , and 2.3 × 10(3) spores/mL against the aestivation population, the diapausing population, and 5(th) instar nymphs, respectively. Estimated LT50 values using 10(8) spores/mL of the Mm isolate on the aestivation and diapausing populations were 11.9 and 5.11 days, respectively. The results demonstrated that M. anisoplaie was effective on all of stages of E. integriceps. In addition, the nymphal stage was more susceptible than the adults.