Habrobracon hebetor
Habrobracon hebetor (Say) is a hymenopteran insect of the family Braconidae. Entomophage is considered cosmopolitan due to its wide distribution. It is an ectoparasitoid of a wide range of lepidoptera species. This list includes various types of owlet moths, pyralid moths, codling moths and other moths. It plays an important role in the fight against post-harvest pests. It is used everywhere in greenhouses and open ground, as well as in granaries.
Appearance
Habrobracon hebetor is a small parasitic wasp, whose length is only 2-3 mm, weight less than 1 mg. Outwardly resemble a small fly, the colour is a combination of 3 colours — yellow, brown and black. There are long antennae on the head. Sexual dimorphism consists in the presence of a small ovipositor and shorter antennae in the female.
Life cycle
The life cycle of Habrobracon hebetor has 4 main stages: egg, larva, pupa, imago.
The egg (0.52 mm long and 0.12 mm wide) is usually attached to the paralysed larvae of the host or laid nearby. At an optimal temperature, the egg develops for about 12 hours, after which entomophage larvae are born.
The larvae feed on the paralysed victim, due to which they continue their development. Within 3-5 days, the larva goes through the moulting stages 4 times. The last age stage (length 2.64 mm, head capsule 0.29 mm and width 0.95 mm) is ready for unwinding of small white cocoons for pupation.
The pupa represents an entomophage in a state of metamorphosis, hidden in a white cocoon and lasts for 3-5 days, followed by the adult stage.
Entomophage imagos begin to search for host larvae for parasitizing and lay eggs immediately after pupation. Females inject the toxin into the victim, causing paralysis, after which they lay eggs on or near the pest for the availability of the food base of the offspring.
The duration of development from egg to adult is extremely short and lasts about 12 days. The average number of adult offspring per female is 173.7 in 22 days, with a sex ratio of 1:1 in the offspring.
Female wasps prefer to parasitize the fourth or fifth age of lepidoptera hosts for egg laying. At 28 °C, the female Habrobracon hebetor lays 17-18 eggs per day on diapausing larvae and 9-10 eggs per day on non-diapausing larvae of barn firefly.
Imago females feed on the hemolymph of the pest in the process of piercing the victim and laying eggs. The larvae also feed on hemolymph and tissues. Males are capable of feeding on nectar.
They overwinter in a state of diapause in the recesses of the bark, on rolled leaves, in hollows and plant residues. Adult wasps, especially diapausing wasps, are less susceptible to low temperatures and can survive at -5 °C for up to seven days. The egg and pupal stages of Habrobracon hebetor had hypothermia points below -25 °C, but no pupa survived more than 12 days at -5 °C.
At 16-18 °C, the entomophage comes out of diapause and proceeds to continue rooting the population.
Application
Lepidopteran insects have a huge number of pests, such as owlet moths, pyralid moths, and other moths, which pose a danger to crops in closed and open ground, as well as to stored products. They also lead to serious economic losses due to contamination of goods in the ecosystems of stored grain. Granaries managers rely heavily on strategies involving the use of synthetic insecticides to control pests. Although insecticides can be effective, their repeated and indiscriminate use causes insecticide resistance and harmful non-targeted effects, potentially leading to loss of biodiversity. Models of the use of insecticides in integrated pest management (IPM) after harvest may expose farmers and warehouse workers to acute or chronic exposure to volatile fumigants. At the same time, consumers may potentially be exposed to pesticide residues in food. In addition, restrictions on the use of insecticides and the growing consumer demand for food products that do not contain pesticides stimulate the search for safe, non-toxic and sustainable pest control strategies in post-harvest systems. Biologists have proved in practice that in order to effectively combat many types of harmful insects of the Lepidopteran order, it is enough to release from 1000 to 3000 adult individuals of the Habrobracon hebetor per 1 hectare of crops in order to completely eliminate crop losses.
Conclusion
Parasitic wasps represent an alternative and environmentally compatible approach to solving the problems associated with the use of synthetic insecticides. Parasitoids do not have a negative impact on the environment, people or beneficial organisms. These natural enemies can reproduce continuously as long as hosts or alternative hosts are available, which ensures the sustainability of their populations for the long-term regulation of pest populations. Moreover, the released parasitoid wasps have the ability to disperse very quickly and find hosts by chemotaxis at any point of the location, be it a greenhouse plant or a granary. In addition, the number of potential allergens, including exuviums and insect fragments, is significantly reduced when using parasitoids compared to other IPM strategies. The parasitoids Habrobracon hebetor belong to the important ectoparasitoids of the order Lepidopteran.