National Geographic : 1970 Apr
100 large pea aphids or 300 smaller spotted alfalfa aphids to produce a cluster of eggs. One ambitious female in my laboratory laid 1,346 eggs over a 74-day period. During this time she ate 7,325 spotted alfalfa aphids. The average female lays about 400 eggs in her lifetime. Should all hatch, these larvae could destroy 140,000 spotted aphids before becoming pupae. Some alfalfa fields in the Central Valley have been known to harbor more than half a million hungry ladybug lar vae. Failing to find aphids, the larvae eat one another. After rodolia's success against the cottony cushion scale, California State entomologists collected ladybugs in the mountains and dis tributed them to valley farmers as an experi ment in aphid control. Five years of study revealed that about 90 percent of the beetles promptly flew away from the site of release. As a result, the state abandoned its program, but several prospectors gave up the search for gold and turned to "mining" the big ag gregation sites for ladybugs to be sold to agri cultural supply firms. In the High Sierra, some people still gather ladybugs for sale, 550 scooping them by hand into plastic mesh bags. Despite negative views of entomologists, mountain-collected ladybugs find a ready market at prices as high as $10 a gallon roughly 70,000 beetles. From cold storage many shipments go to nurserymen and ama teur gardeners who believe that enough bee tles remain where released to help control rose and other aphids.* Some dealers attrib ute a recent boom in ladybug sales to grow ing concern over the use of pesticides. How to Keep Them Down on the Farm? One of my first assignments at the Univer sity of California was to learn why ladybugs flew away from release points, and to prevent their departure if possible. That was 17 years ago, and we now know a lot more than we did then, though we still don't have all the answers. The convergents' "fly-first, eat-later" habit can be changed, I found, by caging mountain collected beetles that have wintered over in the heights and feeding them artificial diets *See "Rose Aphids: Cameras Probe the Bizarre World of a Garden Pest," by Treat Davidson, NATIONAL GEO GRAPHIC, June 1961.