A review was made on notorious insect pests and diseases of crops, resulting about 25-35% yield loss annually in Nepal. Among the insect pests; brown planthopper (Nilaparvata lugens) in rice, cotton bollworm (Helicoverpa armigera) in various crops, armyworm (Mythimna separate) in rice and maize, white stemborer (Xylotrechus quadripes) in coffee, Potato tuber moth (Phthorimaea operculella) and red ants (Dorylus orientalis) in potato are causing periodically havoc. Whiteflies, mealybugs and leaf miners are emerging as major pests. Recently introduced South American tomato leaf miner (Tuta absoluta) in tomato, officially identified in 2016 from Kathmandu valley is reported as possible dangerous pest. Similarly, blast (Magnaporthe grisea) and bacterial leaf blight of rice, late blight and bacterial wilt of tomato and potato, club root and black rot of crucifers, downy mildew and virus complex of cucumber, citrus greening (Liberobacter asiaticum), leaf and stripe rusts of wheat, northern leaf blight of maize, panama wilt of banana etc. are considered as major diseases of economic importance. Bacterial stem rot (Erwinia caratova) of tomato and gray leaf spot (Cercospora zea maydis) of maize are emerging for significant yield loss. The newly introduced coffee rust (Hemileia vastatrix) is now becoming serious threat to coffee plantation. Fall armyworm (Spodoptera frugiperda) and UG99 virulence race of Puccinia graminis need to prevent becoming dangerous from their entry. This review would be helpful to policy planning, future research and extension works.

The oral toxicities of symbiotic bacteria Photorhabdus temperata ssp temperata (Ptt), mutually associated with entomopathogenic nematode Heterorhabditis megidis, and P. luminescens ssp. laumondii (TT01) with H. bacteriophora, were demonstrated to adults of the sweetpotato whitefly Bemisia tabaci. Sucrose solution (25%) containing bacteria-free supernatant of culture media of symbiotic bacteria was ingested into adult whiteflies within the glass tube. Whitefly mortalities were shown similar patterns against two bacterial media. Mortalities were significantly increased to 60-64% at 36 hours and almost 100% at 60 hours after treatments. In addition, We demonstrated the effect of oral ingestion of symbiont culture media on the gene expression of B. tabaci. Several genes fluctuated those expression levels. Our results suggest that oral ingestion of symbiont culture media of entomopathogenic nematodes significantly changed metabolic rates and highly lethal to whiteflies. The use of symbiotic bacteria of entomopathogenic nematodes provides a great potential as an alternative genetic resource of Bacillus thuringiensis, a major resource of microbial insecticide.

Oral toxicities of 5 Photorhabdus temperata ssp. temperata (Ptt) strains collected in different regions of Korea were determined against the larvae of Plodia interpunctella, Galleria mellonella, Lucilia caesar, Culex pipiens pallens and Paratlanticus ussuriensis. When a diet or water containing culture media of 5 different Ptt strains were ingested to immature insects, mortalities of the first instar larvae of G. mellonella, L. caesar, P. ussuriensis and young nymphs of C. pipiens pallens were rapidly increased and 100% within 3-5 days after treatments. However, mortality of P. interpunctella neonate larvae was slightly slower and 94.4-100% within 7 days after treatments. As controls, a diet containing either water, the medium without culturing bacteria, or E. coli culture medium did not effective on their mortalities. As another control group, the culture medium of P. temperata ssp. laumondii (KACC) were variously effective to mortalities of 4 species, namely, 100, 45.3, 2.8 and 0% to Galleria, Lucilia, Plodia and Culex, respectively. Culture media of Ptt strains inhibited developmental late of late larvae of P. interpunctella. Our results suggest that the oral administration of the culture medium of Ptt symbiotic bacteria was highly effective to control various immature insects.