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Simple Summary: The beet webworm Loxostege sticticalis L. (Lepidoptera: Pyralidae) is one of the most disastrous pest insects that outbreak periodically in northern China. Developing a definite indicator depending on defining the ending and beginning of the occurrence period cycle is urgent for the population forecast and theoretical study of the beet webworm. Looking through the 38-year historical population survey data, we found a close connection between the sex ratio and the population occurrence cycle. To clarify how the sex ratio connects with the population occurrence cycle, we measured the maximum mating potential of both females and males and the population's net reproductive rate under different sex ratios. Our results showed that the population net reproductive rate fits a parabolic curve analysis according to the variation of sex ratio and topped at 1.82, which indicates that the population may begin a new period of the cycle when the sex ratio achieves 1.82. In contrast, collapse may happen when the sex ratio is less than one. Our findings accurately forecast long-term dimension population occurrence dynamics in the beet webworm. Beet webworms, Loxostege sticticalis L. (Lepidoptera: Pyralidae), are one of the most destructive pest insects in northern China, and their populations outbreak periodically. Developing an indicator that defines the ending and beginning of the occurrence period cycle is urgent for the population forecast and theoretical study. The sex ratio can be a primary pathway through which species regulate population size. We measured the maximum mating potential of both females and males and the population net reproductive rate under different sex ratios (e.g., 3:1, 2:1, 1:1, 1:2, 1:3). The maximum mating frequency of males was 2.91 times that of females. The progeny contribution per mating decreased with increased mating times in males. The variation in population net reproductive rate affected by the sex ratio fits the parabolic curve analysis and peaked at 1.82 for females vs. males. Our results illustrate the quantitative connection phenomenon shown by the historical data: population outbreaks occur at a sex ratio of two or more and collapse at a sex rate lower than one. Simultaneously, the sex ratio may be utilized as a definite indicator for the beginning and end of the future occurrence cycle in the beet webworm. [ABSTRACT FROM AUTHOR]

Simple Summary: Green manure application is an effective management practice for enhancing soil nutrient levels and organic matter, but pest management in green manure fields has traditionally been ignored. The beet webworm, a polyphagous insect, is currently experiencing an outbreak in northern China, and represents a significant migratory pest. We conducted a comprehensive evaluation of the effects of green manure crops on beet webworm by measuring its growth, development, fecundity, and flight ability on Chenopodium album (a suitable host), as well as three major legume green manure crops in China: Pisum sativam, Vicia sativa, and Vicia villosa. Our findings indicate that V. villosa does not serve as a host plant for the beet webworm, which experiences 100% mortality during its larval stage. This indicates that the large-scale cultivation of V. villosa as a green manure crop in northern China will not increase the risk of the beet webworm outbreaks. Although the beet webworm has a significantly lower host adaptability to P. sativam and V. sativa compared to C. album, it is still well adapted to these two green manure crops. Our research provides a foundation for selecting appropriate green manure varieties and implementing effective pest control measures during their cultivation. The application of green manure is crucial for achieving sustainable agriculture and animal husbandry, but pest management is often overlooked. Conducting a risk assessment for insect pests in green manure is essential. The beet webworm, Loxostege sticticalis, a polyphagous insect, is currently experiencing an outbreak in northern China, and represents a significant migratory pest. A two-sex life table and flight mill test approach was used to comprehensively evaluate the effects of three major legume green manure crops (Pisum sativam, Vicia sativa, and Vicia villosa) on the growth, development, fecundity, and flight ability of L. sticticalis in China. Our findings indicate that L. sticticalis cannot utilize V. villosa for generational development. L. sticticalis shows reduced performance on P. sativam and V. sativa compared to its suitable host Chenopodium album. However, both the population parameters (R0, r, λ, and T) and the population prediction results suggest that L. sticticalis can adapt to P. sativam and V. sativa. In the process of promoting green manure, careful consideration should be given to the selection of appropriate green manure varieties and the implementation of effective pest control measures during their planting. Our findings lay the groundwork for the promotion of green manure and implementation of an ecological management plan for L. sticticalis. [ABSTRACT FROM AUTHOR]

A facultative commitment to adult migration in the larval stage can be modified again after adult emergence in some Lepidoptera when influenced by an appropriate environmental cue during a sensitive stage. This phenomenon is termed secondary regulation of migration. The sensitive stage in adult beet webworm, Loxostege sticticalis L. (Lepidoptera: Pyralidae), was determined experimentally by starvation of presumed migrant females reared from gregarious-phase larvae (induced by crowding at 10 larvae per 650-ml jar). When presumed migrant adults were starved for 24 h on either of the first 2 d after emergence, the preoviposition period was shortened. In contrast, preoviposition periods were not significantly shortened for migrants starved on day 3 or when starvation lasted for more than 1 d after emergence. Because the preoviposition period corresponds to the migratory period in beet webworm, the results suggest that the first 2 d of adult life in the beet webworm is the sensitive stage during which presumed migrants can be switched to residents by an appropriate environmental cue. During the sensitive stage or not, starvation did not influence lifetime fecundity, oviposition period, longevity, or hatching rate of eggs laid by the starvation-stressed moths. Starvation on the first day also increased tethered flight performance and accelerated both flight muscle and ovarian development. The results suggest that a pulse of starvation in the sensitive period may inhibit the expected migration by accelerating and compressing the cycle of migratory flight muscle development and degeneration, while accelerating ovarian development, which is normally suppressed until after migration. [ABSTRACT FROM AUTHOR]

Transmission of parasites and pathogens is generally positively density-dependent: as an insect population's density increases, the risk of an individual becoming attacked or infected also increases. In some insect species, individuals experiencing crowded conditions are more resistant to natural enemies than those experiencing low density conditions, and they are predicted to divert resources to increase resistance. This phenomenon is called density-dependent prophylaxis. Here, possible expression of prophylaxis in fifth-instar larvae of Beet Webworm, Loxostege sticticalis, to biocontrol agents was investigated under rearing densities of 1, 10, and 30 larvae per jar (650 mL). Larvae reared at the moderate density and those reared in isolation displayed the greatest and lowest resistance, respectively, to an entomopathogenic fungus and a parasitoid. Moreover, larvae from the moderate density treatment exhibited elevated phenoloxidase, total haemocyte count and antibacterial activity in the haemolymph, whereas phenoloxidase levels in the midgut were not affected. The results suggest that larval rearing density significantly affects the immune system, and they provide evidence for density-dependent prophylaxis of larval L. sticticalis against its biocontrol agents. These results have implications for understanding the population dynamics and biocontrol of beet webworm. [ABSTRACT FROM AUTHOR]