Comparison of the Parasitization of Chelonus inanitus L. (Hymenoptera: Braconidae) in Two Spodoptera Pests and Evaluation of the Procedure for Its Production

Chelonus inanitus (L.) is an egg-larval parasitoid of noctuids Spodoptera exigua (Hübner) and S. littoralis (Boisduval), whose mass rearing or real potential has not been targeted yet. To improve the rearing in the factitious host Ephestia kuehniella Zeller, we investigated the influence of host age and number of females parasitizing simultaneously on the overall rearing success, the influence of host age on the life cycle, and the influence of host species on the parasitoid body size. The proportion of emerging C. inanitus was higher from young host eggs, but more females emerged from mature eggs. Under high parasitoid competition, we observed a reduction in non-parasitized hosts without reducing parasitoid emergence. The parasitoid life cycle was longer in females, but the mismatch between sexes was smaller in mature eggs. The parasitoid size was smaller in the factitious host than in the natural hosts. Under semi-field conditions, we investigated the competition among parasitoid females on the overall parasitism success. The reproductive parasitism was more successful in S. exigua than in S. littoralis, and the maximum emergence was reached with three and four females, respectively. The control of S. littoralis may be attributed to the high developmental mortality, a non-reproductive parasitism that is often underestimated.

Root-Associated Entomopathogenic Fungi Modulate Their Host Plant’s Photosystem II Photochemistry and Response to Herbivorous Insects

The escalating food demand and loss to herbivores has led to increasing interest in using resistance-inducing microbes for pest control. Here, we evaluated whether root-inoculation with fungi that are otherwise known as entomopathogens improves tomato (Solanum lycopersicum) leaflets’ reaction to herbivory by Spodoptera exigua (beet armyworm) larvae using chlorophyll fluorescence imaging. Plants were inoculated with Metarhizium brunneum or Beauveria bassiana, and photosystem II reactions were evaluated before and after larval feeding. Before herbivory, the fraction of absorbed light energy used for photochemistry (ΦPSII) was lower in M. brunneum-inoculated than in control plants, but not in B. bassiana-inoculated plants. After herbivory, however, ΦPSII increased in the fungal-inoculated plants compared with that before herbivory, similar to the reaction of control plants. At the same time, the fraction of energy dissipated as heat (ΦNPQ) decreased in the inoculated plants, resulting in an increased fraction of nonregulated energy loss (ΦNO) in M. brunneum. This indicates an increased singlet oxygen (1O2) formation not detected in B. bassiana-inoculated plants, showing that the two entomopathogenic fungi differentially modulate the leaflets’ response to herbivory. Overall, our results show that M. brunneum inoculation had a negative effect on the photosynthetic efficiency before herbivory, while B. bassiana inoculation had no significant effect. However, S. exigua leaf biting activated the same compensatory PSII response mechanism in tomato plants of both fungal-inoculated treatments as in control plants.

CRISPR/Cas9 mutagenesis against sex pheromone biosynthesis leads to loss of female attractiveness in Spodoptera exigua, an insect pestt

Virgin female moths are known to release sex pheromones to attract conspecific males. Accurate sex pheromones are required for their chemical communication. Sex pheromones of Spodoptera exigua, a lepidopteran insect, contain unsaturated fatty acid derivatives having a double bond at the 12th carbon position. A desaturase of S. exigua (SexiDES5) was proposed to have dual functions by forming double bonds at the 11th and 12th carbons to synthesize Z9,E12-tetradecedienoic acid, which could be acetylated to be a main sex pheromone component Z9,E12-tetradecenoic acetate (Z9E12-14:Ac). A deletion of SexiDES5 using CRISPR/Cas9 was generated and inbred to obtain homozygotes. Mutant females could not produce Z9E12-14:Ac along with Z9-14:Ac and Z11-14:Ac. Subsequently, pheromone extract of mutant females did not induce a sensory signal in male antennae. They failed to induce male mating behavior including hair pencil erection and orientation. In the field, these mutant females did not attract any males while control females attracted males. These results indicate that SexiDES5 can catalyze the desaturation at the 11th and 12th positions to produce sex pheromone components in S. exigua. This study also suggests an application of the genome editing technology to insect pest control by generating non-attractive female moths.

The effect of application of control techniques to the population, damage intensity of onion caterpillar (Spodoptera exigua hubner) and yield of shallots

Shallot is an important cash crop in Indonesia. However, its productivity is relatively low, due to the attack of the onion caterpillar (Spodoptera exigua Hubner). This study aimed to identify the effect of the application of control techniques on the population, damage intensity, and shallots yield. This research was conducted by field experiment. Control treatment consisted of covering shallots by using gauze/net and insecticide treatment with active ingredients of profenofos, metomil, and carbosulfan. The research variables consisted of the population and the damage intensity of S. exigua, as well as the yield of shallots. The results showed that the caterpillars population of S. exigua was found at 16 DAP and increased up to before harvest at 44 DAP. Covering shallots with gauze effectively suppressed the population of S. exigua (0.0 per hills), followed by treatment with profenofos (0.14 per hills), carbosulfan (0.15 per hills), and methomyl 0.32 per hills). The damage intensity of S. exigua in the plot gauze covered was 0%, lower than 32%, 25%, 12%, 10%, respectively, in the control plot, treatment of metomil, carbosulfan, and profenofos. Covering shallots with gauze also increased the weight of wet-harvested tubers (50.83 g per hills).