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rom egg to adult: What does the surprising life cycle of the Carambola fruit fly reveal
Bactrocera carambolae, also known as the Carambola fruit fly, is a species of insect belonging to the family Drosophilidae, and it originates from Asia. This species was first described by Drew and Hancock in 1994 and is native to Malaysia, southern Thailand and western Indonesia. As the Indonesian fruit trade expanded, the species invaded South America in recent years and became a major exotic pest, marked as a high priority pest in the tropical fruit industry biosecurity program and a quarantine pest in Brazil. .
Identification
Phylogeny
Bactrocera carambolae belongs to the oriental fruit fly Bactrocera dorsalis species complex, which are genetically similar to each other, differing only in nuclear and mitochondrial DNA. Through DNA analysis, the study showed that B. carambolae forms a mutually monophyletic sister group, in contrast to the larger group containing the B. dorsalis species complex.
Morphological characteristics
Bactrocera carambolae is often difficult to distinguish from other species of the B. dorsalis complex. This species is characterized by a predominantly black chest and legs with brown lateral markings on the belly. It has a long central black band on its back and a pair of yellow elytra. In addition, it has a pair of membranous wings, and the hind wings have degenerated into a spherical structure. Adults can reach 6 to 8 mm in length, with the abdomen of females being relatively long, while that of males is relatively short and blunt-ended.
Life Cycle
Bactrocera carambolae is a polyphagous species that can infect more than 100 different host plant species, including squama, guava, mango, papaya and orange. The female B. carambolae lays her eggs under the skin of the host fruit. The eggs hatch in up to two days, and the larvae then enter the feeding stage. Over the next seven to ten days, the fruit ripens and falls to the ground, where the larvae burrow into the soil to pupate, hatching into pupae a week later. It takes about three weeks for the adult worm to reach full maturity, and the complete life cycle is about 35 days. The rate of development of the immature stages of B. carambolae increased with increasing temperature.
Symbiotic relationshipDifferent bacterial communities were associated with each other at different development stages of B. carambolae, including four major phyla; Actinobacteria, Bacteroidetes, Bacillus, and Pseudomonas. Proteobacteria dominated in each life stage, while Bacteroidetes were most abundant in the larval and pupal stages. These microbes are essential for courtship and reproduction in B. carambolae and other fruit flies.
Behavior
Foraging habits
Bactrocera carambolae usually feeds before laying eggs, so black spots or blemishes on the surface of the fruit can be used to indicate that it has been eaten. While there are no obvious signs of infestation on the fruit, black spots are particularly noticeable on fruits such as carambola, cherry and guava. These flies have a particular preference for tropical fruits, using their mouthparts to pierce the skin and suck the juice out of the flesh.
Mating and Pheromones
Only adult B. carambolae are capable of sexual reproduction, while larvae are able to produce pheromones to some extent. Male B. carambolae are strongly attracted to the globally present dimethylcoumarin (ME). When ingested, this compound is converted into a phenolic propylene compound called (E)-coniferyl alcohol. This compound is stored in the rectal glands of male fruit flies, ready to release the pheromone during courtship. As they age, production of these compounds increases and mating occurs during twilight hours.
Natural Enemies
The volatile substance 6-oxo-1-nonanol produced by male B. carambolae can be used as a repellent to natural enemies, such as some chameleons. This production varies with age and is a strong deterrent to feeding in larvae, but less so in male flies.
ImpactBactrocera carambolae poses a threat to the economy, biodiversity, food security and human health. Total crop failure often occurs in severely infested areas, causing significant economic losses to farmers and government agencies. Cash crops such as papaya and mango have been affected, leading to an increase in the use of pesticides, and the resulting environmental threats cannot be ignored. In Brazil, B. carambolae has been found in 21 host fruit species and the risk of spread is high due to high temperatures and the development of fruit agriculture.
Prevention and Control
The Amazonian Metarhizium fungus is an effective control of B. carambolae. Under the treated conditions, larvae and pupae of B. carambolae died, and those that survived and became adults died within five days of emerging from the soil. Due to the high reproductive capacity and long lifespan of this fruit fly, careful consideration must be given to prevention and control strategies. Wrapping fruit in newspaper or brown paper bags is one of the most effective control methods. This will prevent the deposition of eggs, especially if this measure is done before the fruit matures. In addition, bait spray is a more environmentally friendly agent than full spray, and it only needs to be applied to a few places to be effective for a long time.
The life cycle and behavioral patterns of Carambola fruit flies reflect the complexity and delicate balance of the ecosystem. In this real cycle of life, how many unknown influences are waiting for us to explore and think about?
