Biology of Microlarinus lypriformis (Col.: Curculionidae) on Puncturevine in Southern California

Abstract

Eggs of Microlarinus lareynii (Jacquilin du Val) hatched 2–3 days after their deposition in pits chewed in the tender pericarps of immature fruit and, occasionally, in floral buds and flowers. Of 50 egg niches examined, 60% penetrated a seed chamber. Thus, most larvae immediately contacted a seed upon hatching, while some fed on the pericarp and interlocular tissues, sometimes quite extensively, before attacking a seed. All seeds were destroyed in 11, 35, and 20 of 100 infested, mature fruit sampled from low desert, inland valley, and coastal locations, respectively. The incidence of aborted carpels (those lacking seed) in those fruit in which all seed were destroyed was considerably higher (85%, 1.7/fruit) than in the remaining fruit in these samples (48%, 0.5/fruit) in which seed destruction averaged 68, 73, and 64%, respectively. External scarification of young fruit and other plant parts by ovipositing adults, as well as stem weevil ( M. lypriformis (Wollaston)) attack, apparently caused carpel abortion, and thus additional, indirect, reduced seed production, estimated at 24% of seed/fruit at one location. Larval development lasted 13–16 days. Pupation occurred in an open cell in an excavated fruit. The prepupal period lasted 1 day; the pupal stadium, 4–5 days. Egg-to-egg development for 20 individuals averaged 29 (range: 24–34) days. One, or sometimes 2 weevils emerged from a single fruit. Males and females mated repeatedly, and the latter lived an avg of 96±11 (SE) days. Mating was preceded by a brief series of antennal contacts. Oviposition began 4-9 days after pupal ecdysis. The oviposition periods averaged 78±7 days, during which 193±24 (max: 324) eggs were laid at a rate of 2.6±0.5 (max: 11) per day. Females favored the carpel junctures just below a lateral spine as ovipositional sites. Eggs in niches were capped with a dried, whitish, anal secretion often stained dark with feces.