Dechorionation and Permeabilization of Podisus nigrispinus (Heteroptera: Pentatomidae) Eggs: Limiting Factors for Cryopreservation

Effect of chemical dechorionation on silkworm embryo viability

The chorion covering/protecting insect egg, which has some effective functions such as providing mechanical strength, protecting eggs from external environments, and keeping moisture adjustment, is one of the principal barriers to manipulation, cryopreservation, and study of insect embryos. Here we evaluated the silkworm embryo viability after dechorionation using chemical reagents. We have developed an easy and effective method for chemical dechorionation that enables embryos to develop in culture, so that the larvae could normally grow. Eggs attached to a nylon net were treated with potassium hydroxide (KOH) and sodium hypochlorite (NaClO) to remove the chorion, washed with the Grace's insect medium, and then cultured using a dry-moist method which we created. The most effective treatment with regard to embryonic development, hatching, and production of second instar larvae was 30% KOH for 7 min and 2% NaClO for 5 min at 27 °C. Embryos at later embryonic stages were more tolerant to chemical dechorionation and over 75% of embryos treated at 168 h-old (Stage 25, appearance of taenidium) survived to the second larval instar, moreover, the larvae derived from the dechorionated embryos have developed into the moths which can lay the fertilized eggs. Our method would contribute to the establishment of cryopreservation using embryos and analysis of silkworm embryogenesis and might also be applicable to other insect species.

Towards a method for cryopreservation of mosquito vectors of human pathogens

Mosquito-borne diseases are responsible for millions of human deaths every year, posing a massive burden on global public health. Mosquitoes transmit a variety of bacteria, parasites and viruses. Mosquito control efforts such as insecticide spraying can reduce mosquito populations, but they must be sustained in order to have long term impacts, can result in the evolution of insecticide resistance, are costly, and can have adverse human and environmental effects. Technological advances have allowed genetic manipulation of mosquitoes, including generation of those that are still susceptible to insecticides, which has greatly increased the number of mosquito strains and lines available to the scientific research community. This generates an associated challenge, because rearing and maintaining unique mosquito lines requires time, money and facilities, and long-term maintenance can lead to adaptation to specific laboratory conditions, resulting in mosquito lines that are distinct from their wild-type counterparts. Additionally, continuous rearing of transgenic lines can lead to loss of genetic markers, genes and/or phenotypes. Cryopreservation of valuable mosquito lines could help circumvent these limitations and allow researchers to reduce the cost of rearing multiple lines simultaneously, maintain low passage number transgenic mosquitoes, and bank lines not currently being used. Additionally, mosquito cryopreservation could allow researchers to access the same mosquito lines, limiting the impact of unique laboratory or field conditions. Successful cryopreservation of mosquitoes would expand the field of mosquito research and could ultimately lead to advances that would reduce the burden of mosquito-borne diseases, possibly through rear-and-release strategies to overcome mosquito insecticide resistance. Cryopreservation techniques have been developed for some insect groups, including but not limited to fruit flies, silkworms and other moth species, and honeybees. Recent advances within the cryopreservation field, along with success with other insects suggest that cryopreservation of mosquitoes may be a feasible method for preserving valuable scientific and public health resources. In this review, we will provide an overview of basic mosquito biology, the current state of and advances within insect cryopreservation, and a proposed approach toward cryopreservation of Anopheles stephensi mosquitoes.