The invasive red fire ant is one of the most harmful invasive species in the world, and this ferocious ant not only destroys ecosystems and agricultural production, but also threatens the personal safety of its inhabitants. In recent years, the spread of red fire ants in China has become more and more intense, and has now spread to 12 provinces and more than 300 districts and counties across the country.
Red fire ants
At present, the prevention and control methods of all countries in the world are mainly poisonous bait. On the basis of the implementation of chemical control, the addition of biological control factors can further optimize the control effect. This article introduces two promising biological control factors here, one is to use indigenous dominant ant species to fight red fire ants, and the other is to weaken the competitiveness of red fire ants with "red fire ant viruses" that specifically infect red fire ants.
<h1 class="pgc-h-decimal" data-index="01" > bilodal spiny ant, a native ant that is expected to be an ecological guardian against the invasion of red fire ants</h1>
Among the common native ants in China, there are not no ant species that can compete with red fire ants. In the past, scholars have pointed out that there are often two-toothed spiny ants in the red fire ant occurrence area, which have a strong sense of territory and have a tendency to attack red fire ant worker ants.
Two-toothed spiny ant
Double-toothed spiny ant, distributed in East and South China, in Japan, Southeast Asia and Australia are also distributed. Worker ants are black, have short golden hairs, and the body size differentiation is not obvious, most of them are about 6 mm, and only a few particularly large worker ants in the red fire ant can be about the same size as it, most of which are much smaller.
This ant likes to nest in trees and is not uncommon in grass, so it has a certain similarity in habitat selection to grassland-loving red fire ants. The total number of worker ants in China's double-toothed spiny ant colony is usually thousands to tens of thousands, and the malaysian double-toothed spiny ant colony has only 1,000 to 2,000 worker ants, but Okinawa, Japan, once found a large colony containing 104 ant nests, covering an area of more than 700 square meters, with a total of 876,069 worker ants.
In contrast, the mature community of red fire ants in China often exceeds 60,000 worker ants, 200,000 or 300,000 are not uncommon, and the especially large colony of worker ants can exceed one million.
<h1 class="pgc-h-decimal" data-index="02" > one-on-one head-to-head, two-toothed spiny ants like to take the initiative to attack, and have an advantage in casualty rates</h1>
Experts placed a spiny worker ant and a red fire ant worker ant in a Petri dish with a diameter of 5 cm and observed their interaction process and results. A total of 132 such experiments were conducted, of which 72 were double-toothed spiny ants against large worker ants of red fire ants (body length 3 to 5 mm) and 60 times were faced with small worker ants (body length 1.6 to 3 mm).
The results showed that the two-toothed multi-thorn ants always chose to attack more than to defend, while the red fire ants were mainly defensive. When fighting different sizes of red fire ants, the multi-spiny ant strategy is also different, such as more active attack when facing small worker ants of red fire ants, and when the opponent is replaced by a large worker ant, the multi-thorny ant will reduce the attack and increase the defense.
Both types of ants are both physical and chemical, and the physical attack method is the same, that is, the jaw is open for biting, while the chemical attack is different, the bi-toothed spiny ant is to spew acid from the end of the abdomen, and the killer of the red fire ant is to inject venom with a tail needle.
The casualty ratios of the two groups of confrontations varied widely. The bilobitten multi-spiny ant suffered few casualties in the face of small red fire ants, while the small red fire ants suffered heavy losses, with a total of 22 casualties, of which antennae and legs were the most commonly bitten off, and some were abdominal injuries, and these red fire ants with injuries to the abdomen tended to die within a few hours.
The red fire ant large worker ants are obviously not easy to provoke, they have few casualties, and most of them are minor injuries that have lost their tentacles or one leg, and the number of serious injuries or deaths is very small, and the total number of casualties is only about 5, which is lower than the number of casualties of double-toothed multi-thorn ants (7). That is to say, in a one-on-one head-to-head, large red fire ants have a slight advantage, while small red fire ants lose to double-toothed spiny ants.
<h1 class="pgc-h-decimal" data-index="03" > community warfare, the exchange ratio of bidonted spiny ants is significantly better than that of red fire ants</h1>
Whether the two-toothed spiny ant can play a biological role in controlling red fire ants in the wild mainly depends on whether the spiny ants can attack and replace the red fire ants in the early colonization stage, in order to confirm this, experts have done small community confrontation experiments between the two ants.
The red fire ant queen has only a few worker ants, usually 10 to 20, so the new colony simulated by experts in the experiment consists of 1 queen, 10 egg larvae, and 20 worker ants. The two-toothed spiny ants are divided into three communities of different sizes, although the number of queens is 1, but the number of worker ants is 20, 40 and 80, and the number of eggs is 10, 20 and 40. In the experiment, a red fire ant colony with 20 worker ants will fight against three two-toothed spiny ant colonies of different sizes.
Schematic diagram of the test environment
The specific test environment is shown in the figure, flanked by two artificial ant nests, two nests and the middle foraging area (crickets and honeydew are placed in the test) connected by a catheter, equipped with a valve control switch, open the valve ant can enter the central foraging area.
The researchers divided the community confrontation experiment into three groups: group R, first open the channel on the side of the red fire ant, let the red fire ant occupy the food in the foraging area first, and then open the switch on the side of the double-toothed spiny ant; group G, first let the double-toothed spiny ant occupy the foraging area, and then let the red fire ant enter; group S, the channel switch on both sides opened at the same time. These trials were repeated three times, and each time the number of worker ants died and where they died.
The test results are shown in the table, and we can see that even at the same number, the loss of red fire ants is more than that of bilodal spiny ants. Regardless of who enters the foraging area first, the two-toothed spiny ant can achieve a one-for-three exchange ratio; when both parties enter the foraging area at the same time, the loss of the two is the closest, and the red fire ant can almost trade with the double-toothed multi-thorn ant.
When the colony of bidonted spiny ants increased to 40, an interesting phenomenon occurred, in three sets of experiments, the bilobited spiny ants could only do one for two, and the red fire ants in the inferior number actually pulled the exchange ratio closer. In the face of up to 80 worker ant multi-thorn ant colony, the red fire ant colony killed as many as 15 worker ants, almost losing 75% of the worker ants, but at the same time they also made the opponent pay a heavy price, the double-toothed multi-thorn ants lost more than 9 worker ants in both the R group and the S group, and the average number of thorny ants could only be replaced by 1.6 red fire ants.
Why is it that after the community size of the two-toothed spiny ant increases, its exchange ratio with the red fire ant is gradually closer? This result may seem irrational at first glance, and is actually related to the habits of ants and changes in the nature of warfare.
In the past, some scholars have pointed out that in the early colonization of red fire ant colonies, worker ants tend to stay in the nest while reducing the frequency of going out to forage, and the small community of red fire ants in this experiment also showed a similar tendency, and there were fewer worker ants who went out to search for food. This low-key posture is very different from the hegemony of the community after maturity, and it can be said that they know the truth that they must be cautious in the early stage of entrepreneurship.
The opposite double-toothed spiny ant is different in habits, even the small colony of spiny ants also show a high degree of territoriality and active out of the nest patrol characteristics, when they find the nest of the red fire ant, a large number of worker ants immediately rushed into the red fire ant nest to attack, the greater the number of thorny ant colonies, the stronger the willingness to invade the nest to eliminate the opponent.
If the nature of the community conflict at the beginning is a battle for food resources, then from the moment the double-toothed spiny ant invades the nest of the red fire ant, the nature of the war has undergone a fundamental change, from a low-intensity food scramble to a fierce "war of annihilation", which is the life-and-death battle of the red fire ant colony, even if it is the red fire ant worker ant in the scramble conflict, it will inevitably erupt into a strong will to fight in this patriotic war.
When the red fire ants retreating into the nest show fierce confrontation, although the two-toothed spiny ants can kill most of their opponents with more numbers, they also need to pay a high price. Moreover, although the spiny ants have a 2-4 times the numerical advantage, they are unlikely to send all the worker ants at once. Zoology suspects that the spiny ant may have used the oil-adding tactic in battle, that is, to throw troops into the opposing nest one by one, so that the strength of the main battlefield may not be as large as one-to-two or one-to-four.
In general, the larger the spiny ant colony, the more it wants to invade and eliminate the red fire ant, and it will inevitably lead to more fierce resistance from the red fire ant. Under the oil-adding tactics, they did not concentrate all their forces to besiege the Red Fire Ant, so they could no longer play such an excellent exchange ratio in low-intensity conflicts.
<h1 class="pgc-h-decimal" data-index="04" > two-pronged approach, the use of the red fire ant virus has added wings to the double-toothed spiny ant</h1>
As we can see above, the double-toothed spiny ant can play a biological control role in the early colonization of the red fire ant, but when the red fire ant colony matures, because the red fire ant colony is too large, even the double-toothed spiny ant is powerless. For example, in Taiwan, China, the red fire ant has shown extremely strong adaptability and competitiveness since its invasion in 2003, and the local two-toothed spiny ant is simply powerless to stop it.
In recent years, control experts in Taiwan are trying to use a new biological control factor, that is, the red fire ant virus specifically for red fire ants, experts first let the double-toothed spiny ants drink the sugar water with the red fire ant virus, and then put these spiny ants carrying the virus into the area where the red fire ants are flooded. Ferocious and aggressive spiny ants will pass the virus to red fire ants when they clash with red fire ants, and the colony of red fire ants infected with the virus will weaken and become less competitive, giving the two-toothed spiny ants the opportunity to replace these sick red fire ants in large numbers.
Last year, it was reported that this control strategy has helped the two-toothed spiny ant replace 80% of the red fire ant colonies in the field in the trial, but the size of these colonies is still unclear, and whether it is so effective depends on the official research report.
So what is the so-called red fire ant virus? In 2004, scientists discovered the first RNA virus sinv-1 that can infect red fire ants, and in the following decades, researchers have discovered four more RNA viruses (SINV-2~5) in red fire ants, in addition to the only DNA virus SiDNV. The survey showed that sinv-1-4 viruses were detected in red fire ants of Florida and Argentina, while SINV-5 and SiDNV were only present in argentine populations, indicating that the source of red fire ant viruses is the origin. It is precisely because of the restrictions of various pathogens, natural enemies and competitors in the place of origin that the red fire ant is not in abundance in the local area.
The negative impact of red fire ant virus on red fire ants is significant. Queens infected with SINV-1 tend to be of smaller weight, which reduces the likelihood of a successful colony of queens, and colonies of red fire ants infected with the virus under laboratory conditions often lose large amounts of eggs and larvae.
SINV-2 significantly reduces the queen's ability to lay eggs and slows down the growth rate of the newborn community. SINV-3 also affects the reproductive ability of the queen, while also reducing the foraging efficiency of the worker ants, causing the entire colony to starve. These viruses are highly host-specific and tend to infect only a few of the fire ant species, and not other arthropods. Academics have tested 1989 species of arthropods in Florida, of which only red fire ants are infected with the virus SINV-1.
<h1 class="pgc-h-decimal" data-index="05" > conclusion</h1>
From the foregoing, we can know that the double-toothed spiny ant is a more aggressive native ant species, at the individual level it dares to take the initiative to attack when facing the red fire ant, and the two-toothed multi-thorn ant colony has a strong territoriality, likes to actively patrol the surrounding territory, once found just married red fire ant ant, can play a role in removal.
If the two-toothed spiny ant searches for a newborn red fire ant colony, the ant will actively attack, possibly eliminating the opponent before the red fire ant colony matures. Moreover, the habitats of the two species of ants overlap to a certain extent, and may compete for food resources. Therefore, it is appropriate to consider raising such ants in the wild, which may be a good helper for the prevention and control of red fire ants.
In addition, red fire ant virus is also a potential biological control factor, it has a strong host specificity, transmissibility and pathogenicity is also considerable. However, safety testing against viruses is necessary and can only be considered for use if it proves safe for other species.