Biological and population traits of parasitoids depend on several factors such as, the host plant, host species and, it’s physiological condition7,11, 18–20. The type of host plants involved in the developmental time period of parasitoids by shortening their preadults duration, increasing survival rate, adult body size, adult longevity, reproduction days and, fecundity21 as well as increasing the population growth parameters4. This research was studied owing to the importance of host plant type on the foraging behavior, physiological and population dynamics of parasitoids6, 22, 23, and consequently to have successful production of biocontrol agents. Alongside of our previous study16, the current research was reported the third-trophic level effects of the cereal flour on the biological, life table traits, and population projection of H. hebetor.
Our results demonstrated that usage of corn and barley cereal flour, accelerated the immature developmental time of H. hebetor, and increased the survival rate, adult longevity as well as reproduction days. Amir-Maafi & Chi4 reported a developmental time of 10.83 d for H. hebetor on the fifth instar larvae of E. kuehniella fed on wheat. The preadult periods of the parasitoid in our study are within the same range as this report. However,7 obtained a developmental time of 17.05 d of H. hebetor on the cotton bollworm, H. armigera, which fed on the leaf and fruit of tomato, it wasmore than in our study. Saadat et al. 6 concluded that host plants are rich in sugar and glycogen and provide more suitable physiological conditions than host species that contain terpenes and tannins for H. hebetor. Our results showed that the total number of eggs/female during the lifetime of H. hebetor varied from 70.87 to 91.20 eggs/female on E. kuehniella, which values are much higher than the 66.30 eggs/female on E.kuehniella 4 and 61.62 eggs/female on H. armigera 7. Variation in preadult developmental time and fecundity rates among these studies could be because of different host species, quality of host type, rearing conditions, and physiological condition of host species4,6,14. Seyedi et al. 14 stated that the highest protein content of corn (var. 704) resulted in the highest protein content and proteolytic activity of E. kuehniella. Similarly, Saadat et al. 6 stated that the quality and quantity of protease and amylase activity of H. hebector guts was greatest when reared on E. kuehniella. This fact implies the importance of the quality and quantity of host type on the physiological condition at the tritrophic level among host plants, phytophagous pests, and their natural enemies11,12.
Construction and analyzing the life table data based on the age-stage, two-sex life table24,25, not only consider the importance of each stages on the population dynamics,, but also it did not ignore the male population17,26. Our results demonstrated that the corn variety used in this research, was found to be more effective on H. hebetor population growth rate of offspring by increasing the net reproductive rate (R0), the intrinsic rate of increase (r), the finite rate of increase (λ), and shortening the mean generation time (T). The highest rate of intrinsic rates of increase on corn reflected the combined effects of age-specific fecundity (mx) and age-specific survival rate (lx)27. The population growth parameters of the parasitoid in our study are more than those of Amir-Maafi & Chi 4 study. These variations might be due to the variety of host types.
The uncertainty based on the 2.5th and 97.5th percentiles of the net reproductive rate (R0) is another advantage of the age-stage, two-sex life table theory. Our results showed the same trends of population projection with population parameters. The predicted population of H. hebetor was the fastest and highest on corn, followed by wheat, and barley, which was reported for the first time in this study.
In conclusion, corn is a more suitable host than wheat and barley for the parasitoid, which is reared on E. kuehniella. It is concluded that corn type, by providing more suitable nutrition, resulted in a shortening the developmental time, increasing the fecundity and survival rate. Interestingly, the suitability of the corn variety in this study, was confirmed once more by the estimation of population projection.