Insect Diapause

Mass rearing for commercial production of high quality beneficial insects is considered as an important tool for biological control programmes worldwide, especially those based on augmentative releases. Low temperature storage is a valuable method for increasing the shelf life of entomophagous insects. Insect predators and parasitoids are used extensively in biological control programmes and, because of this, studies on cold storage started over 90 years ago. The ability to store reared biocontrol agents at low temperatures for certain duration provides an opportunity to accumulate or stockpile sufficient number of entomophagous insects for field release at proper weather conditions and make them available during high demand periods to the concerned farmers. Cold stored natural enemies can be synchronously released in the fields during critical stages of pest outbreaks. Cold storage also helps to keep viable stock of natural enemies when not needed and to minimize laboratory operations by prolonging their survival and delaying eclosion. Cold storage tolerance is highly plastic trait influenced by a range of biotic and abiotic factors experienced before, during and after cold exposure. These factors ultimately affect the development, longevity, fecundity, parasitization, sex-ratio and other fitness parameters along with morphology, behaviour and physiology of entomophagous insects. For the successful implementation of a cold storage project, knowledge of these diverse factors that cause storage and post-storage effects is essential. The potential of cold storage protocols in improving mass rearing and commercial production of bioagents is thus reviewed to access the strategies, innovations, techniques, devices and wisdom involved in the process of cold storage of entomophagous insects worldwide.

/pdf/retracted-article-impact-of-cold-storage-on-the-performance-4nejke10bw.pdf

RETRACTED ARTICLE: Impact of cold storage on the performance of entomophagous insects: an overview

Diapause control is one of the successful methods for long-term cold storage of biological control organisms without decreasing their fitness. Sufficient preparation before diapause is essential for successful diapause initiation and maintenance. Harmonia axyridis, an important biocontrol agent in its native place, can enter reproductive diapause for overwintering. However, the key preparatory events before diapause in H. axyridis, such as specific developmental trajectory, timing, and physiological changes, remain unclear. We compared differences in the development of internal reproductive organs, feeding amount and nutrient storage between pre-diapause and pre-reproductive adult H. axyridis which had been reared at 20 °C under a short-day (10L:14D) and long-day (14L:10D) condition, respectively. The results showed that there were obvious morphological differences in internal reproductive organs of diapause and reproductive H. axyridis. The development of internal reproductive organs was suppressed at early adult stage in pre-diapause beetles compared to pre-reproductive beetles. Feeding amount in both pre-diapause and pre-reproductive beetles increased for more than ten days after eclosion. The feeding amount of pre-diapause beetles sharply decreased from the 15th day after eclosion in females and the 14th day after eclosion in males, which implied the initiation of diapause. During the pre-diapause stage, carbohydrates and lipids were mainly accumulated by females, whereas males mainly accumulated carbohydrates. Our results not only provide basic information about the diapause process of pre-diapause stage, but also give tips to better utilization of diapause strategy during mass production and storage of H. axyridis.

https://www.mdpi.com/2075-4450/10/8/243/pdf

Differences in the Development of Internal Reproductive Organs, Feeding Amount and Nutrient Storage between Pre-Diapause and Pre-Reproductive Harmonia axyridis Adults.

The main function of small heat shock proteins (sHSPs) as molecular chaperones is to protect proteins from denaturation under adverse conditions. Molecular and physiological data were used to examine the sHSPs underlying cold-hardiness in H. axyridis. Complementary DNA sequences were obtained for six Harmonia axyridis sHSPs based on its transcriptome, and the expression of the genes coding for these sHSPs was evaluated by quantitative real-time PCR (qRT-PCR) in several developmental stages, under short-term cooling or heating conditions, and in black and yellow females of experimental and overwintering populations under low-temperature storage. In addition, we measured water content and the super cooling and freezing points (SCP and FP, respectively) of H. axyridis individuals from experimental and overwintering populations. The average water content was not significantly different between adults of both populations, but the SCP and FP of the overwintering population were significantly lower than that of the experimental population. Overall, the six sHSPs genes showed different expression patterns among developmental stages. In the short-term cooling treatment, Hsp16.25 and Hsp21.00 expressions first increased and then decreased, while Hsp10.87 and Hsp21.56 expressions increased during the entire process. Under short-term heating, the expressions of Hsp21.00, Hsp21.62, Hsp10.87, and Hsp16.25 showed an increasing trend, whereas Hsp36.77 first decreased and then increased. Under low-temperature storage conditions, the expression of Hsp36.77 decreased, while the expressions of Hsp21.00 and Hsp21.62 were higher than that of the control group in the experimental population. The expression of Hsp36.77 first increased and then decreased, whereas Hsp21.56 expression was always higher than that of the control group in the overwintering population. Thus, differences in sHSPs gene expression were correlated with the H. axyridis forms, suggesting that the mechanism of cold resistance might differ among them. Although Hsp36.77, Hsp16.25, Hsp21.00, and Hsp21.62 regulated cold- hardiness, the only significant differences between overwintering and experimental populations were found for Hsp16.25 and Hsp21.00.

/pdf/molecular-cloning-and-induced-expression-of-six-small-heat-22raiqfnhh.pdf

Molecular Cloning and Induced Expression of Six Small Heat Shock Proteins Mediating Cold-Hardiness in Harmonia axyridis (Coleoptera: Coccinellidae)

Improved knowledge on the regulation of reproductive diapause in Coccinella septempunctata, an important predator of aphids, is crucial for improving shelf-life and mass production of the ladybeetles. In many insects, the absence of juvenile hormone (JH) is a central regulator of reproductive diapause. JH is principally degraded by JH esterase (JHE) and JH epoxide hydrolase (JHEH). Previous studies have shown that genes encoding these enzymes were upregulated in early diapause of C. septempunctata, but whether increased JH degradation contributes to the reduction of JH levels and facilitates reproductive diapause remains unknown. Here, we investigate the role of JH and JH degradation genes during reproductive diapause in C. septempunctata females. Applying methoprene, a JH analogue, to the diapause preparation females clearly elevated JH signaling and reversed diapause program, suggesting that a lower level of JH is critical for the induction of reproductive diapause in the ladybeetle. Full-length cDNA sequences of JHE and JHEH were cloned and characterized, and their deduced proteins contain all the conserved active domains and typical motifs as identified in other insects. The expressions of JHE and JHEH were both significantly increased in diapause preparation and remained at a high level for a period throughout diapause, and then decreased after the termination of diapause. Knocking down these JH degradation genes clearly increased the expression levels of JH-inducible genes Krüppel-homolog 1 (Kr-h1) and vitellogenin (Vg), indicating an elevated JH level. Simultaneously, silencing JH degradation genes distinctly reduced diapause-related features and promotes reproduction, indicated by accelerated ovary growth, yolk deposition, and suppressed lipid accumulation. These results indicate that the enhanced JH degradation plays a critical role in regulating reproductive diapause of C. septempunctata.

Enhanced Degradation of Juvenile Hormone Promotes Reproductive Diapause in the Predatory Ladybeetle Coccinella Septempunctata

The multicolored Asian ladybird beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), is considered an important generalist predator that can be used as a biological control agent against Hemiptera Sternorrhyncha, Thysanoptera, and the eggs and larvae of Lepidoptera, Coleoptera and Diptera. There are currently abundant natural resources of overwintering H. axyridis in Asia and North America. Given its potential as a biological control agent, methods can be developed to increase its effectiveness for pest control. The availability of an adequate cold storage method would enable the use of field-collected pre-wintering ladybirds for pest suppression in the following season. We studied the effect of cold storage (30, 60, 90, 120 and 150 days stored at −3, 0, 3 and 6°C) on survival, fecundity and predation in field-collected populations. The survival of both female and male ladybirds decreased significantly as storage duration increased at −3°C and 0°C. The ladybirds showed more than 80% survival when they were stored for 150 days at 3°C and 6°C. Long-term cold storage had different effects on the fecundity of H. axyridis at different temperatures. Prolonged cold storage at both 3°C and 6°C shortened pre-oviposition duration and had no adverse effect on reproductive capacity as compared to that of unstored individuals. The adults that experienced 90-day storage at 0°C had the shortest pre-oviposition duration and the largest reproductive capacity. The individuals that were stored for 150 days at 3°C consumed significantly more aphids than the unstored ones. Generally, 3–6°C is a suitable temperature for cold storage of the ladybird without any reduction in fitness. This study will help the exploitation and application of pre-wintering H. axyridis for the biological control of insect pests.

Effect of long-term cold storage on the fitness of pre-wintering Harmonia axyridis (Pallas)

The invention provides a method for blended breeding of trichogramma dendrolimi and trichogramma ostriniae with oak silkworm eggs as hosts.In the process of using oak silkworm eggs for breeding a large amount of trichogramma dendrolimi and trichogramma ostriniae, trichogramma ostriniae and trichogramma dendrolimi bred with small eggs are mixed and connected into oak silkworm eggs at the proportion not lower than 4:1 and with the proportion of trichogramma to eggs not lower than 5:1, and the purpose of simultaneously and successfully breeding a large amount of trichogramma dendrolimi and trichogramma ostriniae with oak silkworm eggs can be achieved.By means of the method, a new concept of trying to developing one-egg-multiple-trichogramma series products based on oak silkworm eggs is provided, a trichogramma breeding and utilizing new mode based on oak silkworm eggs as intermediate hosts can be promoted, and large-area application and popularization of advantageous trichogramma except trichogramma dendrolimi and trichogramma ostriniae on agricultural production are greatly promoted.

Method for blended breeding of trichogramma dendrolimi and trichogramma ostriniae with oak silkworm eggs as hosts

The invention discloses a method for continuously releasing parasitic natural enemy insects, which includes distributing a plurality of release points in an area requiring control according to insect population density and control requirements, and installing a release apparatus at each point. A release cylinder of each release apparatus is in a tubular structure. A removable solid cover and a removable net cover are disposed at two ends of each release cylinder respectively. A partition net is disposed in the middle of each release cylinder. The release apparatuses for parasitic natural enemy insects are distributed in the control area, so that the natural enemy insects can be released continuously, and control time prolongation and control effect enhancement can be achieved for complex conditions of control objects, such as generation alternation, instar mixing and the like. Maintenance of populations of natural enemies is shifted to a user terminal, and easily obtained replacement hosts are used for maintenance of the populations of natural enemies, so that the intermediate procedures of control implementation are reduced, and bio-control cost is reduced. Especially, the natural enemies can be transferred to an application area in case of chemical control, so that both bio-control and chemical control can be implemented.

Method for continuously releasing parasitic natural enemy insects

The invention discloses a light environment control method for breeding trichogramma dendrolimi with oak silkworm eggs; the oak silkworm eggs on which the trichogramma dendrolimi are parasitical are adopted as parental eggs, and the fresh oak silkworm eggs on which nothing is parasitical are adopted as progeny eggs; the oak silkworm eggs are controlled to be under a purple light illumination condition; after a parasitic link is over, the parental eggs and the trichogramma dendrolimi are removed; the progeny eggs are placed under a red light illumination condition; after the growth and the eclosion of the trichogramma dendrolimi in the progeny eggs, the trichogramma dendrolimi can continue to serve as bees to repeat the process, so that the population is reproduced generation by generation, and finally a required number of trichogramma groups are finally obtained; and a biological-control finished product is processed. Due to the adoption of the light environment control method for breeding trichogramma dendrolimi with oak silkworm eggs, the parasitic rate of the trichogramma dendrolimi can be improved by 2.25 percent to 11.25 percent, the eclosion rate can be improved by 2.99 percent to 11.04 percent, and the number of identical bees and the legacy bee rate have no significant difference. In multi-generation breeding, the number values are further increased because the population is reproduced generation by generation.

Light environment control method for breeding trichogramma dendrolimi with oak silkworm eggs

The invention discloses a method for releasing trichogrammas bred in big and small eggs in a hybrid manner to prevent and control insect pests; according to the different varieties of insect pests, at the egg laying initial stage of the insect pests, the trichogrammas bred in big eggs and the trichogrammas bred in small eggs are released in the hybrid manner according to the ratio of (3-5):1, the trichogrammas are released for one time at each 5-7 days and are released for 3-4 times continuously; the trichogrammas bred in big eggs are trichogramma dendrolimi or trichogramma chilonis bred in eggs of oak silkworm; the trichogrammas bred in small eggs are trichogramma japonicum, trichogramma ostriniae and armyworm trichogrammas bred in rice moth eggs or sitotroga cerealella olivier eggs. Through releasing trichogrammas bred in big and small eggs in the hybrid manner, the prevention and control costs are reduced greatly under the precondition that the prevention and control effects are guaranteed; the mass development and application of trichogrammas on prevention and control of the agriculture and forestry insect pests are benefited, the usage of chemical pesticide can be reduced greatly, so the method is very important for human health and preservation of the ecological environment.

Method for releasing trichogrammas bred in big and small eggs in hybrid manner to prevent and control insect pests

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