By Chris Patrick
Imagine combating stink bugs with … stink bugs.
Halyomorpha halys, the brown marmorated stink bug (BMSB), is a notorious, non-native agricultural pest — an indiscriminate destroyer of fruits, vegetables, and other farm crops. Managing this pest with a biological control agent (a living organism) is especially important for organic farmers whose regulations limit their use of pesticides.
Enter Podisus maculiventris, the spined soldier bug. A stink bug in the same insect family as the BMSB, the spined soldier bug is native to North America and is a predator of more than 70 insect species, including the BMSB. Researchers from West Virginia University are exploring the potential of exploiting this predator-prey relationship to control BMSB populations.
Spined soldier bugs and BMSBs coexist in time and space. They overwinter and emerge in the spring at about the same time. They lay a similar number of eggs and molt through five instars, or developmental stages, into adults at about the same rate.
“A reason this may be an effective tool is that they have a synchronous life cycle,” said John Moredock, a graduate student at West Virginia University who collaborated on research investigating which stages of spined soldier bug most successfully kill certain stages of BMSB. He presented a poster on the results at the Eastern Branch meeting of the Entomological Society of America in March 2015.
In the lab, Moredock and others pitted spined soldier bugs of different ages (third instar, fifth instar, and adult) against BMSBs of different stages (egg through adult). They found that spined soldier bugs are pretty good at killing BMSBs younger than the fourth instar, especially BMSB eggs and first instars.
BMSBs in their first instar remain clustered together on the eggs from which they hatched.
“If a spined soldier bug is able to locate a patch of eggs or aggregated first instars, they are able to feed on multiple BMSBs, which is good,” Moredock said.
But spined soldier bugs rarely kill BMSBs in their fourth instar or older, which limits their ability to control adult BMSBs emerging in the spring.
This is probably due to the spined soldier bug’s quirky eating style. To feed, the spined soldier bug attacks from the side, stabbing and sucking, reducing its prey into a shriveled corpse with its long proboscis. But it likes to lift its proboscis-pierced prey off the ground while it eats. So when a BMSB is larger than a spined solider bug — as they are in the fourth and fifth instars, and as adults — this lifting becomes a difficult task.
Spined soldier bugs still try to kill older, larger BMSBs — they’re just not successful, usually. The bigger BMSB either evades the spined soldier bug by flying away, or the spined soldier bug can’t pick up the larger insect.
The researchers also found that the older a spined soldier bug is, the more BMSBs it eats. Adult spined soldier bugs ate the most BMSBs. The fifth instars ate the second most, and the third instars the least.
The researchers observed this predator-prey relationship mostly in the lab, but findings thus far suggest that it’s time to take their studies to the field.
“Since [the spined soldier bug] is a generalist predator, we don’t know exactly what it will choose,” said Moredock. “It may feed on BMSB eggs, or it may go find a caterpillar.”
That’s not exactly the specificity they’re looking for to control the BMSB, but future research may reveal what the spined soldier bug prefers to snack on in a realistic setting.
How does Moredock envision farmers using this biological control?
“It wouldn’t be that you can just buy spined soldier bugs and they’ll control the BMSBs for you,” he said. “More than likely, they’ll have to use pesticides to get BMSBs down to a low level and then release spined soldier bugs.”
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Chris Patrick is a graduate student in the science writing program at Johns Hopkins University. Click here to read her blog.