Mattheau Comerford/Rice University
While still larvae, certain species of parasitic wasps secrete growth hormones that trick trees into growing tumorlike structures that shelter the young wasps as they grow. These small spherical growths, known as “galls,” also provide them with a steady supply of nutrients—great for the wasps, but bad for the trees.
But a new study suggests the nutrient-rich galls are themselves a target—for a creeping plant known as the parasitic love vine (Cassytha filiformis). In a recent survey of Belonocnema treatae wasps in southern Florida, scientists noticed the vine kept turning up in samples of the galls. On closer inspection, they discovered the vine was actually penetrating into the wall of the wasp’s growing chamber (above), sucking out nutrients and leaving behind a mummified corpse—great for the vine, but bad for the wasps.
After the discovery, the scientists looked for more instances of this new parasite-on-parasite interaction. They found that in 51 cases in which the love vine attached itself to the B. treatae gall, more than half contained a dead wasp, they report this week in Current Biology. In the absence of the vine, only two out of 101 galls contained a dead wasp. No word yet on exactly what this means for the trees.
