Reaching the Seeds: Soapberry Bugs in the Courtyard Garden

Bugs on the Balloon Vine

1The courtyard garden at Las Palmas Middle School has a balloon vine climbing its fence. Its seed pods are puffy, papery balls, and the black seeds sit inside, near the center. In late summer the vine is covered with small red-and-black soapberry bugs. Garden club member Benedict Oyelaran learned that these insects feed by pushing a long, thin beak through the pod wall into a seed and sucking out the inside. Early in the year, the bugs also feed on old seeds lying on the ground, but by late summer most of those have been eaten.

2Benedict and his teacher, Ms. Greta Villanueva, measured the pods and found that the seeds sat about 6 to 10 mm below the outer wall, about 8 mm on average. Under a microscope with a tiny ruler, they also measured the beaks of 120 female bugs. The beaks ranged from 6.0 mm to 9.9 mm. They sorted the females into three groups and painted a small dot on each one's back to keep track of it.

3In Test 1, the club put 20 females from each group into mesh sleeves on the vine. Each sleeve held one bug and three pods, and there were no loose seeds inside. After 10 days, the students counted how many bugs had fed on a seed, how many were still alive and how many eggs each living female had laid. In Test 2, they kept the other 60 females in containers with plenty of loose seeds and the same water and temperature, and counted the same things. Afterward, all the bugs were released on the vine where they were caught.

4Last, the club tested whether beak length is passed on. They paired long-beaked females with long-beaked males and short-beaked females with short-beaked males. Both groups of young were raised in identical containers on loose seeds, so none of them had to reach into a pod. When the daughters grew up, their beaks averaged 9.0 mm in the long-beaked families and 7.1 mm in the short-beaked families.

5A soapberry bug lives only a few months as an adult, and several generations can hatch in one warm year, so Ms. Villanueva plans to measure the vine's bugs again next summer.