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Animal mitochondrial genomes usually exhibit conserved gene arrangement across major lineages, while those in the Hymenoptera are known to possess frequent rearrangements, as are those of several other orders of insects. Here, we sequenced two complete mitochondrial genomes of Trichogramma japonicum and Trichogramma ostriniae (Hymenoptera: Chalcidoidea: Trichogrammatidae). In total, 37 mitochondrial genes were identified in both species. The same gene arrangement pattern was found in the two species, with extensive gene rearrangement compared with the ancestral insect mitochondrial genome. Most tRNA genes and all protein-coding genes were encoded on the minority strand. In total, 15 tRNA genes and seven protein-coding genes were rearranged. The rearrangements of cox1 and nad2 as well as most tRNA genes were novel. Phylogenetic analysis based on nucleotide sequences of protein-coding genes and on gene arrangement patterns produced identical topologies that support the relationship of (Agaonidae + Pteromalidae) + Trichogrammatidae in Chalcidoidea. CREx analysis revealed eight rearrangement operations occurred from presumed ancestral gene order of Chalcidoidea to form the derived gene order of Trichogramma . Our study shows that gene rearrangement information in Chalcidoidea can potentially contribute to the phylogeny of Chalcidoidea when more mitochondrial genome sequences are available.

This study investigated the parasitic selection preferences of female Trichogramma ostriniae on egg cards of different colors, considering the effects of inoculation time, generations, and learning experiences on wasp parasitism. The preferences of female T . ostriniae for oviposition were assessed across egg cards of different colors. Subsequent experiments identified the egg card background color most preferred by T . ostriniae and examined the influence of inoculation time, generations, and learning experiences on parasitism rates. The findings revealed a significant preference for T . ostriniae for yellow egg cards compared to other colors, with the highest parasitism rate observed on yellow and the lowest on red. Inoculation time had a significant effect on the parasitism of T . ostriniae on yellow egg cards, with the highest parasitism observed at 16h post-inoculation and a noticeable negative linear correlation with increasing inoculation time up to 48h (F = 8.73, P<0.05). The number of generations did not significantly affect the parasitism rate of T . ostriniae on yellow egg cards, nor did the learning experiences show a significant difference in the relative parasitism of T . ostriniae on yellow egg cards among the learning experiences. However, T. ostriniae had a significantly higher parasitization rate on yellow egg cards compared to white egg cards, regardless of generation or learning experience. Those results showed that female T . ostriniae strongly prefers yellow. The highest parasitism of female T . ostriniae on yellow egg cards was observed at 16h post-inoculation.

The Asian corn borer (ACB), Ostrinia furnacalis , is a serious maize pest in Southeast Asia, responsible for substantial economic losses to the maize crop every year. To establish insect biocontrol programmes, it is crucial to determine the ideal numbers and developmental stage of natural enemies to release. The purpose of the present study was to assess the parasitism ability of Trichogramma dendrolimi and Trichogramma ostriniae, which are the most promising biocontrol agents of the ACB, under two different methods of inundative release in maize fields. A total of 10,000 wasps of both species were released using two different methods, i.e. wasps at the same developmental stage (SDS) and wasps at different developmental stages (DDS). The results showed that T. dendrolimi wasps exhibited significantly higher parasitism of ACB eggs when they were released with the DDS method than when they were released with the SDS method. In the SDS release method, T. dendrolimi parasitized ACB eggs for only 3 days after release, while in the DDS release method, parasitism of ACB eggs occurred for 6 days. However, the two release methods had no significant impact on the performance of T. ostriniae in maize fields. In both release methods, T. ostriniae parasitized a high percentage of ACB eggs. The results of the present study clearly indicate that the poor field performance of T. dendrolimi due to the host-age factor can be improved using the DDS release method.

The age of Trichogramma parasitoids could influence biological traits which are of great importance for effectiveness of mass rearing systems. Recent studies demonstrated that Trichogramma ostriniae (TO) could parasitize Antheraea pernyi eggs through multiparasitism along with other  Trichogramma species, although few adults could emerge successfully. It is important to characterize the factors modulating the performance of TO on A. pernyi eggs, notably in order to try enhancing its quantitative emergence through multiparasitism for further use in biological control. In this context, irrespective of host age, we tested different ages of TO females (from 0.5-day- to 6-day-old postemergence) in multiparasitism with Trichogramma chilonis (TC) on A. pernyi eggs. The results of the present study confirmed that TO parasitism on A. pernyi eggs was largely age dependent. Higher percentage of multiparasitism and higher number of emerged TO adults were recorded in the treatment where 3-day-old TO females were used for parasitization with TC on A. pernyi host. In addition, we also tested different female ratios of both Trichogramma  species to find out an optimal ratio for use in mass production. The highest percentage of multiparasitism, emergence and optimum emerged number of TO (per A. pernyi egg) was observed with the ratio 3:2 (TO:TC) per 1 host egg. This study demonstrated that the age of TO females can significantly affect their performance in multiparasitism of large A. pernyi eggs. These results prompt for more research in order to develop an effective multiparasitism-based production of TO at the industrial scale.

Trichogramma ostriniae is one of the most successfully used natural enemies in the integrated management of agroforestry pests. However, the extensive use of insecticides poses a significant threat to the survival and efficacy of T. ostriniae . To assess the compatibility of chemical pesticides with T. ostriniae , we investigated the acute toxicity, risk level, and sub-lethal effects of four insecticides (chlorfenapyr, emamectin benzoate, phoxim, and lambda-cyhalothrin) on reproduction, parasitism, detoxification enzymes, protective enzyme activities, and active substances under laboratory conditions. The results revealed that phoxim had the highest acute toxicity, with a median lethal concentration value of 2.8 × 10 −7 mg/mL, whereas chlorfenapyr had the lowest at 5.06 × 10 −3 mg/mL. Emamectin benzoate was classified as high risk, whereas the others were classified as extremely high risk. Insecticide exposure during the larval and pupal stages significantly reduced the emergence of T. ostriniae ( P < 0.05). Lambda-cyhalothrin, emamectin benzoate, and chlorfenapyr extended the time required for prey-handling and reduced parasitism efficiency by 0.70%, 2.45%, and 4.50%. In contrast, phoxim increased the time required for prey-handling and improved parasitism efficiency by 25.37%. All insecticides affected protective enzyme activities, induced detoxification enzyme activity, reactive oxygen species, malondialdehyde and mitochondrial respiratory chain complex I levels, and decreased the adenosine triphosphate level. These findings underscore the differential impacts of insecticides on T. ostriniae and emphasize the need for cautious pesticide selection to balance pest control and natural enemy conservation, providing essential scientific guidance for sustainable agroforestry pest management.

Trichogramma parasitoids are important biological control agents for insect pest management. However, efficient means for mass production of Trichogramma parasitoids are needed, particularly for T. ostriniae , which often fail to form emergence holes on host eggs of Chinese oak silkworm, Antheraea pernyi , because of the hard chorion. In the present study, we evaluated the possibilities to enhance adult emergence of T. ostriniae by utilizing emergence holes made by T. dendrolimi during multiparasitism on host eggs of A. pernyi and other biological parameters such as pre-emergence time, parasitism rate, and emergence rate of the two parasitoids, which were also evaluated between the two parasitism regimes of multi- and monoparasitism. Our data showed that multiparasitism on host eggs of A. pernyi significantly facilitated the emergence of adult T. ostriniae . Generally, both Trichogramma species favored parasitizing A. pernyi eggs, with multiple parasitoid adults emerged per host egg. The overall performance of T. dendrolimi was similar between the two parasitism regimes, although a significantly higher number of unemerged adults were found in the multiparasitized eggs than in the monoparasitized. For T. ostriniae , significantly more adults emerged, and a higher emergence rate was recorded on host eggs multiparasitized with T. dendrolimi than that on monoparasitized. Furthermore, significantly fewer unemerged adults were found in multi- than monoparasitized host eggs. The results of this study provided useful information on the feasibility of mass production of T. ostriniae via multiparasitism with T. dendrolimi on large eggs of A. pernyi .

In China, the Asian corn borer (ACB), Ostrinia furnacalis (Guenee) (Lepidoptera: Pyralidae), is the most significant economic insect pest of corn, causing losses ranging from six to nine million tons annually by feeding on all parts of maize, including damaging ears and leaves and making tunnels in stems. In China, since the 1970s, the Trichogramma species have extensively mass-reared from factitious hosts to control ACB and support integrated pest management programs. The Trichogramma dendrolimi Matsumura and T. ostriniae Pang and Chen are the most efficient biocontrol agents for controlling ACB among the available Trichogramma species. To evaluate the reproductive success of Trichogramma dendrolimi and T. ostriniae, we assessed the impact of varying parasitoid ratios (5:1, 3:1, 1:1, 1:3, and 1:5 representing T. dendrolimi and T. ostriniae, respectively) on adult offspring emergence and mortality from ACB eggs over multiple generations (from first (F1) to third (F3) generations). We discovered that both Trichogramma species’ offspring emergence was significantly influenced by the parasitoid generations, parasitoid ratios, and their interactions. The offspring mortality in both Trichogramma species was significantly affected by parasitoid generations but was not significantly influenced by parasitoid ratios or interaction between parasitoid generations and parasitoid ratios. Furthermore, at parasitoid ratios of 5:1, 3:1, and 1:1, the emergence rate of the F1 generation of T. dendrolimi was significantly higher compared to the ratios of 1:3 and 1:5. However, in the F2 generation, the emergence of T. dendrolimi decreased considerably, and no emergence was observed in the F3 generation. A contrasting trend was observed in the emergence of T. ostriniae offspring. Overall, regardless of the parasitoid ratios, the offspring emergence of T. ostriniae in all three generations was significantly higher than that of T. dendrolimi. After assessing the offspring mortality in our research by dissecting the unhatched eggs, we found an inverse relationship between the T. dendrolimi generations and their mortality across different parasitoid ratios. Notably, mortality exhibited a significant decline with an increasing number of generations. A positive correlation was observed between the number of T. ostriniae generations and their mortality across different parasitoid ratios, indicating that mortality increased with successive generations. Overall, across all parasitoid ratios and generations, the offspring mortality of T. ostriniae was considerably greater than that of T. dendrolimi. These results suggest that mortality is a crucial empirical measure that validates T. ostriniae’s superiority over T. dendrolimi. These findings highlight the importance of selecting suitable parasitoid species when implementing Trichogramma for pest management.

The Asian corn borer (ACB), Ostrinia furnicalis, is a serious corn pest in south-east Asia, causing huge economic losses every year. Trichogramma dendrolimi and Trichogramma ostriniae, two egg parasitoids, have previously been identified as key biological control agents. To determine the age impact of ACB eggs on their effective biocontrol potential, herein we compared the biological parameters (i.e., number of parasitized eggs, emergence, developmental time, and sex ratio) of both parasitoids on ACB eggs of various ages (i.e., 0–4, 4–8, 8–12, 12–16, 16–24, 24–36, and 36–48 h old), respectively. Our results showed that the age of ACB eggs had a significant impact on the parasitization activity of T. dendrolimi in both choice and no-choice conditions. Trichogramma dendrolimi preferred to parasitize 0–8-h-old ACB eggs, and its parasitization dramatically declined on ACB eggs older than 8 h under choice and no-choice conditions. On the other hand, T. ostriniae showed high preference to parasitize all tested ACB egg ages. The age of ACB eggs had no significant impact on the parasitization of T. ostriniae under choice and no-choice conditions. Furthermore, the female progeny of T. dendrolimi decreased as the age of ACB increased, while no differences were found in female progeny of T. ostriniae. Trichogramma ostriniae also developed faster on each ACB egg age group in comparison with T. dendrolimi. Overall, the age of ACB eggs had a significant impact on T. dendrolimi performance, leading us to conclude that T. ostriniae is more effective than T. dendrolimi as a biocontrol agent of the ACB.

Asian corn borer (ACB), Ostrinia furnacalis Guenee (Lepidoptera: Crambidae) and the rice moth (RM), Corycyra cephalonica Stainton (Lepidoptera: Pyralidae) are economically significant insect pests that threaten the agricultural products worldwide. Trichogramma parasitoids are successfully mass-reared using artificial host eggs, RM, and are often managed by economically important lepidopterous pests, such as ACB in China. Trichogramma ostriniae Pang and Chen (To) and T. dendrolimi Matsumura (Td) (Hymenoptera: Trichogrammatidae) are two important parasitoids of ACB. To determine the influence of interspecific competition between To and Td on their offspring’s emergence. We determine the emergence of wasp progeny from two distinct hosts (ACB and RM eggs) of varying densities (10, 20, 30, and 100) by examining the effect of three distinct oviposition sequences (To-Td, Td-To, and To+Td) by two Trichogramma species. We discovered that the progeny emergence rate of To and Td from the host was substantially influenced by the parasitoid types, host types, oviposition sequences, and host densities, and their two-, three-, and four-factor interactions while investigating the ACB and RM eggs after oviposition. Additionally, the progeny of Td emerged from 10, 20, and 30 ACB host eggs under three oviposition sequences, which was significantly higher than that of ACB eggs of 100 densities. Nevertheless, the optimum emergence rate of Td progeny was also observed in ACB eggs with a density of 100 under all oviposition sequences. The most suitable oviposition sequences for both wasp species are To-Td and Td-To, as they have the highest rate of progeny emergence. The progeny emergence of both Trichogramma species from RM eggs of varying densities was observed to be significantly different. Nevertheless, the most influential density is 100 RM eggs, as a result of the maximal emergence rate of To and Td. Overall, it is concluded that host eggs with a density of 100 are adequate to meet the oviposition requirements of both wasps in all oviposition orders, thereby limiting their interspecific competition. These findings provide insights into optimizing host density and oviposition strategies for mass-rearing Trichogramma species, which can enhance their efficacy in biological control programs. Future research should explore field-level applications to validate these laboratory findings under natural conditions.

In laboratories, the parasitism rate of Ostrinia furnacalis (Güenée) (Lepidoptera: Crambidae) eggs by Trichogramma dendrolimi Matsumura (Hymenoptera: Trichogrammatidae) is low; however, efforts to control O. furnacalis with T. dendrolimi in the field have been successful. In this study, the effects of the number of attacks by T. dendrolimi against O. furnacalis eggs and diet of O. furnacalis larva on wasp development were investigated. The results indicated that more attacks increased significantly not only the successful parasitism rate of O. furnacalis eggs by T. dendrolimi, but also the percentage of host eggs that failed to develop into either O. furnacalis larvae or T. dendrolimi. Both the size and female proportion of T. dendrolimi offspring decreased as the number of attacks increased. The number of T. dendrolimi eggs laid in per host egg increased significantly as the ratio of wasps to host eggs increased from 1:5 to 3:5. Host diet also significantly affected the developmental time of immaturity and the emergence rate of adults of T. dendrolimi. These results illustrate how inundative releases of T. dendrolimi can successfully control O. furnacalis despite the fact that pest parasitism by the subsequent wasp generation decreases sharply in the field. The suitability of O. furnacalis eggs to T. dendrolimi and the superparasitism effects on offspring of T. dendrolimi are discussed.