Decaying Wood Preference of Stag Beetles (Coleoptera: Lucanidae) in a Tropical Dry-Evergreen Forest

Larvae of many insect species, including stag beetles, have a limited mobility from their initial oviposition site. The fate of immature stages, therefore, depends on the maternal choice of oviposition site. Decaying wood preference by stag beetles was studied in a dry-evergreen forest in Chanthaburi province, Thailand. From a total of 270 examined logs, 52 contained stag beetles (255 total), which were identified to eight species from five genera. Aegus chelifer chelifer MacLeay, 1819 (Coleoptera: Lucanidae) was the dominant species both by occurrence and by number of individuals. The occurrence and numbers of stag beetle larvae found in logs was more frequent in those of a moderate decay class, which had moderate hardness and water content. Principal component analysis (PCA) revealed that logs with stag beetles had relatively high nitrogen content and fungal biomass. Thus, selection of oviposition sites by stag beetles was likely to depend on both the log decay stage (or hardness) to protect immature stages from natural enemies and its nutritional properties to enhance the larval performance.

Host plant, temperature, and photoperiod effects on ovipositional preference of Frankliniella occidentalis and Frankliniella fusca (Thysanoptera: Thripidae)

Host plant effects of tomato, Lycopersicon esculentum Mill., and chickweed, Stellaria media (L.) Vill., foliage infected and uninfected with Tomato spotted wilt virus (family Bunyaviridae, genus Tospovirus, TSWV) on the ovipositional preferences of western flower thrips, Frankliniella occidentalis (Pergande), and tobacco thrips, Frankliniella fusca (Hinds), were investigated for whole plants in the greenhouse. In addition, the preference for leaf disks from the same host plants was investigated under a range of temperatures, 15-30 degrees C at a photoperiod of 12:12 (L:D) h, and at three photoperiods, 6:18, 12:12, and 18:6, at 20 degrees C in no-choice and choice studies conducted in growth chambers. In a choice test, F. fusca oviposited significantly more eggs per whole plant foliage over a 7-d period than F. occidentalis by an average ratio of 3:1 over both tomato and chickweed. The optimum temperature for oviposition of F. occidentalis and F. fusca was 24.5 and 24.9 degrees C, respectively. Both species laid significantly more eggs under the longest daylight hours tested, 18:6, in the choice study. Temperature and photoperiod did not significantly interact in terms of thrips ovipositional preference. Ovipositional preference for chickweed or tomato foliage was different for each thrips species in the choice and no-choice tests. However, both thrips species laid significantly more eggs per square centimeter of leaf area in chickweed than in tomato in the whole plant choice test.

Kunitz-type trypsin inhibitor from durian (Durio zibethinus) employs a distinct loop for trypsin inhibition

Kunitz-type trypsin inhibitors are ubiquitous in plants. They have been proposed to be a part of a defense mechanism against herbivores. Trypsin inhibitors also have potential applications in the biotechnology industry, such as in mammalian cell culture. We discovered that durian (Durio zibethinus) seed contains Kunitz-type trypsin inhibitors as identified by N-terminal sequencing and mass spectrometry. Eleven new trypsin inhibitors were cloned. The D. zibethinus trypsin inhibitors (DzTIs) that are likely expressed in the seed were produced as recombinant proteins and tested for trypsin inhibitory activity. Their inhibitory activity and crystal structures are similar to the soybean trypsin inhibitor. Surprisingly, a crystal structure of the complex between DzTI-4, the DzTI with the lowest inhibitory constant, and bovine trypsin revealed that DzTI-4 utilized a novel tryptophan-containing β1-β2 loop to bind trypsin. Site-direct mutagenesis confirmed the inhibitory role of this loop. DzTI-4 was not toxic to the HEK293 cells and could be used in place of the soybean trypsin inhibitor for culturing the cells under serum-free conditions. DzTI-4 was not toxic to mealworms. However, a mixture of DzTIs extracted from durian seed prevented weight gain in mealworms, suggesting that multiple trypsin inhibitors are required to achieve the antinutritional effect. This study highlights the biochemical diversity of the inhibitory mechanism of Kunitz-type trypsin inhibitors and provides clues for further application of these inhibitors.

Larval performance and adult phenotypic variation of Acraea terpsicore (Lepidoptera: Nymphalidae) on congeneric Passiflora host plants

The introduction of exotic plants into different habitats can have varied consequences for local herbivorous insects, such as altered the nutrient profiles that induce the host plant shifting or reduced food availability by competition with native plants. Acraea terpsicore (Linnaeus, 1758), a common butterfly in Southeast Asia that uses Passiflora as a host plant, has been studied to compare larval performance and adult phenotypes on one local wild Passiflora plant, P. foetida and 3 exotic congeneric plants, P. edulis, a fruit crop plant, and P. x alata-caerulea and P. x coccinea-caerulea, both hybrid ornamental plants. Laboratory caterpillars that fed on P. edulis and P. x alata-caerulea died within 1-10 days, while caterpillars fed on P. foetida and P. x coccinea-caerulea completed their life cycle in 30.42 ± 0.25 days. Although the caterpillars differed in several food utilization indices, the relative growth rate and consumption index were not affected. Adult butterflies that hatched from caterpillars fed on these experimental plants had different phenotypes, especially wing colors. Therefore, although some congeneric exotic plants may have a negative impact on the butterfly population, some exotic plants can serve as alternative larval host plants and expand the ecological niche of butterflies. Difference in the composition and concentration of nutrients and defensive chemicals in each host plant may exert an impact on the phenotypic traits of butterflies, such as their body size, coloration, and wing shape. Whether butterflies may separate into different subpopulations in the future due to phenotypic variation should be further examined.

Dominant strain shift in the invasive fall armyworm (Lepidoptera: Noctuidae) populations in Thailand as inferred from mitochondrial COI and nuclear Tpi genes

The fall armyworm, Spodoptera frugiperda (J. E. Smith, 1797) (Lepidoptera: Noctuidae), is a significant global pest, that exhibits 2 discernible strains, corn strain (CS) and rice strain (RS). After initial detection in the eastern hemisphere in 2016, the dominant strain was identified as RS based only on cytochrome C oxidase subunit I (COI) mitochondrial gene from limited samples from various countries, including Thailand. This study aimed to assess strain and haplotype variation in the S. frugiperda populations in Thailand using both mitochondrial COI and nuclear triosephosphate isomerase (Tpi) genes. Analyses of COI sequences (n = 105) revealed 2 predominant haplotypes, COICSh4 (82.86%) and COIRSh1 (17.14%), and the analyses of Tpi sequences (n = 99) revealed 6 haplotypes, with TpiCa1a (53.53%) being the most prevalent. Of the 98 caterpillar samples, the majority exhibited true CS (83.67%) for both genes. Meanwhile, interstrain hybrids, indicated by gene discordance, accounted for the minority (16.33%). Interestingly, despite the initial dominance of RS during the 2018 outbreak, the current study identified CS as the prevalent strain across all localities in Thailand. These findings suggested a shift in S. frugiperda dynamics in Thailand that was possibly influenced by factors, such as competitive exclusion principle, pesticide usage in rice cultivation, and preferences for corn over rice. Our study suggests a need to reexamine the previous reports of rice-strain dominance in various countries in the eastern hemisphere after the initial invasion.