Humans using sugary poisons to kill cockroaches have inadvertently affected the bugs’ ability to mate, leading to a decrease in their sexual activity.
However, it seems that some cockroaches have modified the formula for the sugary substance that male roaches use to attract females. This modification has enabled the insects to resume their mating habits and reproduce once again.
The recent finding, which has been published in the scientific journal Proceedings of the Royal Society B, sheds light on a remarkable adaptation by one of the most resilient enemies of humanity.
According to Jessica Ware, an entomologist at the American Museum of Natural History who was not part of the study, cockroaches are not just nuisance pests. She believes that the recent discovery is a remarkable example of evolutionary ecology.
The German cockroach, scientifically known as Blattella germanica, has evolved to thrive exclusively in human-inhabited environments. This species is the most common indoor pest, and despite our repeated efforts to exterminate them, they have managed to adapt and survive.
Coby Schal, an entomologist from North Carolina State University, is well-acquainted with these insects and their mating behaviors.
Coby Schal places a female German cockroach in a container or dish in his laboratory. He waits a few minutes before introducing another roach into the same container.
Schal says, “Now, I have just added a male,” as he introduces an insect into the container. The male and female cockroaches are about the size of a lima bean.
A female roach, like the one in the container, emits a pheromone that acts as an alluring scent to attract males. The pheromone seems to be effective as the male in the container is now following the female. Schal points this out: “Look, he’s starting to follow the female.”
When the male and female cockroaches make physical contact, the male raises his wings to expose a gland on his back. This gland secretes a sweet chemical mixture that is considered a “nuptial gift,” and the female consumes it. However, in order to consume the gift, the female must mount the male.
Schal explains that the position the female takes while consuming the nuptial gift is ideal for the male to mate with her. The male has a telescoping penis that he extends to the female’s end while she feeds. He inserts the penis to mate with the female.
The male’s penis has a hook on it, which he uses to secure onto the female’s genitalia for a duration of about 90 minutes. During this time, the male produces a package of sperm which he transfers to the female for fertilization.
When it comes to reproducing and having baby cockroaches, having a palatable nuptial gift is essential. This is why these gifts usually contain glucose, a basic form of sugar that serves as a fundamental source of energy for many organisms.
The female cockroach receives the nuptial gift
It was the German cockroach’s affinity for glucose that pest control experts began taking advantage of in the mid-1980s. They developed baits containing insecticides that were infused with glucose or other sugars that can break down into glucose rapidly. The outcome was evident right away, with numerous German cockroaches dying due to the bait.
However, a few years later, a pest control company observed a concerning trend. “There was a colony of cockroaches residing in a Florida apartment that simply could not be eradicated,” says Schal.
Upon further investigation, it was discovered that some of the cockroaches had undergone an evolutionary adaptation and developed a glucose aversion. Glucose no longer tasted sweet to them but rather had a bitter taste. Consequently, the cockroaches refused to consume the bait.
Schal says, “Over the past decade, there has been a significant rise in the usage of baits, and I believe this has resulted in a substantial increase in glucose-averse cockroach populations.”
The evolution of glucose aversion gave the German cockroach a significant advantage in its battle against humans. However, this adaptation also posed a problem for the cockroaches themselves. Any glucose present in the male’s nuptial gift becomes repellent to these glucose-averse females.
Schal explains, “As soon as the female detects any glucose in the nuptial gift, she stops feeding and dismounts the male, walking away. The male loses the chance to mate with the female, and this adaptive trait becomes maladaptive in the context of sexual interactions.”
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The female cockroach refuses the nuptial gift
Despite the challenges, cockroaches are known for their ability to reproduce rapidly. When confronted with a problem such as an inability to attract a mate, they always seem to find a solution. In this particular case, their solution involved two genetic modifications.
Schal demonstrates, “The first genetic change is that the male cockroach altered the chemical composition of the nuptial gift he presents to the female.”
The male cockroach has modified the recipe for the nuptial gift by reducing the levels of glucose and another simple sugar and increasing the quantity of a sugar known as maltotriose. Females are fond of maltotriose, and it does not break down into glucose as quickly as other sugars, which allows the gift to retain its sweetness.
The second genetic modification pertains to the duration of time that the male locks onto the female’s genitalia, which typically lasts three to four seconds. However, males have adapted and can now complete the process in less than three seconds “before the female can detect any glucose in her mouth,” according to Schal.
Schal summarizes the male cockroach’s strategy as follows: “In essence, the male’s solution is to gain more time but hasten his mating attempt.”
Jessica Ware, the entomologist who was not part of the study, commends the recent research.
Ware comments, “The research demonstrates how the complex behavior of the nuptial gift, which likely evolved over millions of years, has been significantly altered by humans in a short span of time.”
Schal suggests that it may be wise to change the bait formulation, perhaps by adding some type of fat. However, even if we manage to deceive the cockroaches once again, it’s likely that their population will eventually rebound.