LIFE SCIENCE

Blocking the doorway to meet the enemy, why this swarm of Western bees “completely destroyed”


Over the course of biological evolution, bees have evolved a variety of strategies to defend against predators. These strategies tend to be more effective when both live in the same area for a long time; But when predators enter a new area as an “invasive species”, the original defense strategy of “indigenous” bees is likely to fail.

The team of Tan Ken, a researcher at Xishuangbanna Tropical Botanical Garden of the Chinese Academy of Sciences (hereinafter referred to as Banna Botanical Garden), collaborated with James Nieh, a professor at the University of California, San Diego, to study the relationship between predators and predators in the same and different domains, and the relevant results were recently published in the international authoritative journal “General Entomology” in the field of entomology.

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A. A small number of eastern honey bees use the ISY signal to expel the concave wasps away; B. A large number of western honey bees gather at the nest door to form a “bee blanket” to ward off the concave wasps. Photo courtesy of Banna Botanical Garden

Western bees lack co-evolution with “new enemies”

The Eastern bee is a native Asian bee, and the Western bee is native to Europe and Africa, which began to be introduced to China in the early 20th century due to their excellent production performance. The Grooved wasp is the most common predator of bees, originally distributed only in Asia, in the same domain as the Eastern honey bee, but began to invade Europe in the early 21st century and spread rapidly, and has become a major pest threatening bees worldwide.

With a height of one foot and a height of the road, the oriental bee has evolved many effective strategies to defend against the predation of the concave wasp.

Dong Shihao, an associate researcher at the Banna Botanical Garden, gave an example that when the concave wasp appears near the nest mouth of the eastern bee, the guard bee of the eastern bee will regularly shake its abdomen from side to side, which is a “I see you” (ISY) chase deterrent signal.

“The guard bee uses the ISY signal to warn the Grooves that they are ready for defense, warning the Veares that it is futile or dangerous to get closer and drive the Veares away. And if the vespa continues to approach, the guard bee will kill the vespa by clumping and producing heat. ”

In addition, some oriental bees will climb into the nest, and by issuing a voice alarm signal, tell their companions that there is a wasp predator at the door of the nest, and the companions will reduce the nest or increase their vigilance when leaving the nest.

Dong Shihao explained that it is precisely because of ISY, clumping heat production and other strategies that the concave wasp will not cause great harm to the eastern honey bee colony. Conversely, due to the lack of co-evolution, Western honey bees do not use ISY signals to drive back concave wasps, and the ability to defend against concave wasps through agglomerate heat production is also weak, and Western honey bee colonies tend to collapse quickly if left to prey.

“In fact, the number of Western honey bees caught by the nest gate is about 100 per day, which is far less than the daily egg production of the Western Honey Bee Queen, and the reasons for the rapid decline of the Western honey bee colony caused by the Grooved Wasp attack remains to be elucidated.” Dong Shihao believes that this is of great significance for understanding the harm of the spread of concave wasps to bees worldwide.

Ineffective defenses lead to social collapse

In order to explore the relationship between predators and predators in the same and different domains, researchers from the Chemical Ecology Research Group of Banna Botanical Garden studied the eastern honey bee and western honey bee colonies in the three bee farms of Kunming, Wuding and Malone for three consecutive wasp seasons (July to October every year). Among them, the bee farms in Kunming and Wuding suffer from the predation of concave wasps, and the Malone bee farms do not have the predation pressure of concave wasps.

The results show that in the apiary without wasp predation, the eastern and western bee colonies are normal, while in the bee farms with wasp predation pressure, the eastern bees are basically stable due to their effective defense, but the collection intensity is slightly weakened, and the number of guard bees increases to a certain extent.

However, under the predatory pressure of the grooved wasp, the collection activities of Western honey bees almost completely stopped, and a large number of gathering bees transformed into guard bees, gathering at the door of the nest to form a “bee blanket”, but this defensive behavior could not effectively stop the predation of the concave wasps.

“Because an increase in the number of bees involved in defense means a decrease in the number of bees to gather, resulting in insufficient food inflow, which in turn leads to problems such as reduced egg production by queens and insufficient replenishment of new bees.” Dong Shihao explained that ineffective defense will cause heavy damage to the production and reproduction of Western bees, and the direct loss of Western bee numbers cannot be compensated by queen spawning and new bee feathering, eventually causing all Western bee colonies to die after consuming stored food within 4-6 weeks.

In addition, the research team also monitored the voice alarm signal at the entrance of the concave wasp preying pressure bee colony, and found that the alarm signal produced by Western bees was dozens of times that of Eastern bees. Dong Shihao said that this shows that the attack of the concave wasp has caused a very large fear response in Western honey bees, which may also be one of the main reasons for the decline in the number of collecting bees.

A previous study by the research team showed that in the face of the predatory pressure of wasps, the alarm signal will cause the content of dopamine, the “pleasure factor” in the bee’s brain, to drop sharply, resulting in a weakening of the bee’s desire to collect. This also proves that predator wasps cause a chain of fear reactions from predator bees, which eventually lead to the collapse of the colony. (Source: Hu Minqi, China Science News)

Related paper information:https://doi.org/10.1127/entomologia/2023/1825



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