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Baby bugs team up for sex scam

Sept. 11, 2006
Special to World Science

The mo­ment they’re born, bee­tles of the spe­cies Meloe fran­cis­ca­nus team up for an un­u­su­al drill. Af­ter crawl­ing out of their eggs at the base of a plant, up to 2,000 of the lar­vae group to­geth­er and squirm up the plant, to the tip of a branch.

Blis­ter bee­tle lar­vae ag­gre­gate on a grass blade. (Cour­te­sy PNAS)

There, amid the des­ert sand dunes of the South­west­ern Unit­ed States, they form a tight lit­tle ball. They then waft out a scent that the lo­cal bees re­c­og­nize: a mat­ing che­m­i­cal re­leased by fe­ma­le bees of the so­l­i­tary spe­cies Ha­b­ro­proda pal­l­ida.

Next the bugs, com­mon­ly known as blis­ter bee­t­les, wait. With luck, a male bee will show up and try to have sex with the lit­tle bun­dle, com­posed of at least about 120 in­sects.

The oval or round ball doesn’t look much like a female bee to us. But it’s about the size and co­l­or of a ty­p­i­cal fe­male bee, and per­ch­es in the same type of place where she would be found. Often that is enough to do the trick. 

For the larvae, a male bee rep­re­sents de­liv­er­ance. If it nev­er shows up, they die wait­ing. 

If it does, they’re swept away—literally. The mo­ment he makes con­tact, they swarm all over it and hitch a ride. Be­fore long, they’re al­so clam­b­er­ing all over a real fe­male of the bee spe­cies; this hap­pens when their car­ri­er bee lat­er meets her for a mat­ing. 

Fi­nal­ly, with a lift from the fe­ma­le bee, the lar­vae reach their real des­ti­na­tion, her nest. There, they spend the rest of their youth grow­ing by eat­ing her sup­plies of nec­tar and pol­len, and her egg. Even­tu­al­ly they emerge, mate, and start the cy­cle again.

A ma­le bee cov­ered with par­a­sit­ic blis­ter bee­tle lar­vae. (Cour­te­sy PNAS)

This ac­count of the beetle’s life ap­pears in an anal­y­sis in this week’s ear­ly on­line edi­tion of the re­search jour­nal Pro­ceed­ings of the Na­tio­nal Aca­de­my of Sci­en­ces. 

The love de­cep­tion is “an ex­treme­ly ef­fi­cient so­lu­tion” to the prob­lem of find­ing re­sources in a harsh des­ert, wrote the au­thors, Les­lie S. Saul-Gershenz and Joc­e­lyn G. Mil­lar of the Cen­ter For Ec­o­sys­tem Sur­viv­al in San Fran­cis­co and the Uni­ver­si­ty of Cal­i­for­nia, Riv­er­side, re­spec­tive­ly.

For the lar­vae, food sources are “is­lands in a sea of sand,” they added.

The au­thors de­scribed the trick as an un­u­su­al form of phor­e­sy, a tac­tic in which one or­gan­ism hitches a ride on an­oth­er. Phor­e­sy is com­mon among arthro­pods, they added, the group of exoskeleton-bearing crea­tures to which in­sects be­long along with spi­ders and crus­taceans.

It’s “an ef­fec­tive means of dis­per­sal,” they wrote, “for or­gan­isms with lim­it­ed mo­bil­i­ty, par­tic­u­lar­ly in ex­treme en­vi­ron­ments.”

The find­ings also of­fer a new win­dow in­to in­sect co­op­er­a­tion, they added. Team­work is com­mon among so­cial bugs such as bees, wasps, ants, and ter­mites, they wrote, but has­n’t been re­ported in spe­cies that “use ag­gres­sive mim­ic­ry to ma­nip­u­late and ex­ploit prey or host­s.”

The moment they’re born, beetles of the species Meloe Franciscanus team up for an unusual drill. After crawling out of their eggs at the base of a plant, hundreds of the larvae group together, squirm up the plant and move to the tip of a branch. There, in the desert sand dunes of the Southwestern United States, they form a tight little ball and start wafting out a scent that the local bees recognize. It’s a mating chemical released by a female bee of the solitary species Habroproda Pallida. Then the bugs wait. With some luck, a male bee will show up and start trying to have sex with the little bundle, which contains about 120 to over 2,000 bugs. The oval or round ball is around the size and color of a typical female bee, and also perches in the same type of place where a female bee would be found. For the babies, a male bee represents deliverance. If it never shows up, they die waiting. If it does, the moment it makes contact, they swarm all over it and hitch a ride. Before long, they’re also swarming all over a real female Habroproda Pallida; this happens when their carrier bee later meets her for a mating. Finally, with a lift from the female bee, the larvae reach their real destination, her nest. There, spend the rest of their youth growing by eating her supplies of nectar, of pollen, and her egg. Eventually they emerge, mate, and start the cycle all over again. This account of the beetle’s life appears in a new analysis in this week’s early online edition of the research journal pnas. The love deception is “an extremely efficient solution” to the problem of finding resources in a harsh desert, wrote the authors, Leslie S. Saul-Gershenz and Jocelyn G. Millar of the Center For Ecosystem Survival in San Francisco and the University of California, Riverside, respectively. For the larvae, food appears in “islands in a sea of sand,” they added. The authors described their trick as an unusual form of phoresy, a tactic in which one organism hitches a ride aboard another one. Phoresy is common among arthropods, they added, the group of exoskeleton-bearing creatures to which insects belong along with spiders and crustaceans. It’s “an effective means of dispersal,” they wrote, “for organisms with limited mobility, particularly in extreme environments where harsh conditions and the scarcity and patchiness of critical resources present formidable obstacles to survival.” The findings offer a new window into insect cooperation, they added. Teamwork is common among social bugs such as bees, wasps, ants, and termites, they added, but hasn’t been reported in species that “use aggressive mimicry to manipulate and exploit prey or hosts.”