A midgut-specific lytic polysaccharide monooxygenase of Locusta migratoria is indispensable for the deconstruction of the peritrophic matrix.

Lytic polysaccharide monooxygenases (LPMOs) are important enzymes that boost the hydrolysis of recalcitrant polysaccharides, such as chitin. They are found extensively in different insect species and are classified as auxiliary activities family 15 (AA15) LPMOs (LPMO15). Some of them were identified from the insect midgut and proven to act on chitin. However, knowledge about their physiological roles during insect growth and development remains limited. Here, we found that midgut-specific LPMO15s are widely distributed in different insect orders, such as the orthopteran Locusta migratoria and the lepidopteran Bombyx mori. Using L. migratoria as a model insect, the function of midgut-specific LmLPMO15-3 during development was investigated. Double-stranded RNA-mediated downregulation of LmLPMO15-3 expression at the 4th or 5th instar nymph stage severely decreased the survival rate and resulted in lethal phenotypes. Hematoxylin and eosin staining results indicated that the deficient individuals exhibited incompletely digested peritrophic matrix (PM), which suggested that LmLPMO15-3 is essential for the deconstruction of the PM during molting. This study provides direct evidence of the physiological importance of a midgut-specific LPMO15 during insect development. As L. migratoria is one of the most destructive agricultural pests, LmLPMO15-3 is a potential target for pest management.

Insect group II chitinase OfChtII promotes chitin degradation during larva-pupa molting.

The insect group II chitinase (ChtII, also known as Cht10) is a unique chitinase with multiple catalytic and chitin-binding domains. It has been proven genetically to be an essential chitinase for molting. However, ChtII's role in chitin degradation during insect development remains poorly understood. Obtaining this knowledge is the key to fully understanding the chitin degradation system in insects. Here, we investigated the role of OfChtII during the molting of Ostrinia furnacalis, a model lepidopteran pest insect. OfChtII was expressed earlier than OfChtI (OfCht5) and OfChi-h, at both the gene and protein levels during larva-pupa molting as evidenced by quantitative polymerase chain reaction and western blot analyses. A truncated OfChtII, OfChtII-B4C1, was recombinantly expressed in Pichia pastoris cells and purified to homogeneity. The recombinant OfChtII-B4C1 loosened compacted chitin particles and produced holes in the cuticle surface as evidenced by scanning electron microscopy. It synergized with OfChtI and OfChi-h when hydrolyzing insoluble α-chitin. These findings suggested an important role for ChtII during insect molting and also provided a strategy for the coordinated degradation of cuticular chitin during insect molting by ChtII, ChtI and Chi-h.

Phylogenetic relationships and biological features reveal that male Ostrinia furnacalis (Lepidoptera: Crambidae) in Northeast China can be categorized into postmedial line-based clades.

Ostrinia furnacalis (Guenée) (Lepidoptera: Crambidae), often called the Asian corn borer, is a complicated pest because of its complex biological features, such as its adult dynamics, host choice, and life span. This complexity has been causing difficulties in both pest forecasting and control for more than 60 years. One likely explanation for this complexity is that O. furnacalis has several varieties that vary based on some specific features. During 2015-2017, postmedial line-based varieties of male O. furnacalis were identified as distinct clades (I, II, and III), which were then compared based on COI gene sequences, male sacculus construction, life span, male dynamics, and host preference. The results showed that: (1) clades II and III were more closely related to each other than Clade I, because they both completed two generations per year, more were captured in 2016 or fewer were captured in 2015, and they were more closely related according to phylogenetic inference; (2) all three clades shared some features, such as life spans under various rearing conditions, similar dynamic trends, and three teeth on the male sacculus; and (3) all three clades were significantly different from O. nubilalis based on genetic sequences, postmedial line pattern of the forewing, and sacculus construction. Overall, if O. furnacalis is categorized into clades, the species' features are likely to be a combination or mixture of the features of each individual clade. Our findings help explain the biological complexity of O. furnacalis. Future investigations on each individual clade are essential for improving forecasting and control of this pest.