Emergence, male behavior, and mating in the alkali bee, Nomia melanderi cockerell (Hymenoptera: Halictidae)

The alkali bee, Nomia melanderi Cockerell, is solitary but nests in dense ag gregations which may cover many acres and contain millions of individuals. Adult emergence is protandrous with the first males preceding the first females by a day or two to a week or more. Males patrol the nesting site searching for newly emerged, receptive, virgin females. Aggressive interactions between males are rare. Only newly emerged females are receptive to mating. Receptive females are located by males using pheromonal cues. The probable source of the female sex pheromone is the abdomen. Mating takes place on the surface of the bee bed and generally lasts fewer than 30 seconds. Females appear to mate only once after which they become non-receptive. Non-receptive females remain attractive to males for less than a day during which they may be repeatedly pounced upon by a succession of males. By the time females have begun to nest their attractiveness has waned and they are not bothered by males. The value of the alkali bee, Nomia melanderi Cockerell, in the production of al falfa seed in the Pacific Northwest was recognized nearly 50 years ago. Consequently many aspects of its biology, nesting requirements, management for pollination, nat ural enemies, etc. have been studied over the years. One area that has received little attention, however, is male behavior and mating in this solitary, gregariously nest ing bee. Mating has been observed at the nesting site, or bee bed, where males pounce on emerging females (Johansen and Mayer, 1976). They provided no data but stated that copulation lasted about 15 seconds and that males may mate several times but believed females to mate only once. No information has been reported re garding mate location by males, precopulatory behavior of males, male courtship, competition among males for receptive females, or possible female sex pheromones. This paper reports the results of our studies on emergence, male behavior, and mat ing in N. melanderi between 1988 and 1996. Materials and Methods This study was conducted on commercially managed alkali bee nesting sites, "bee beds," in southeastern Washington near Touchet, Walla Walla County. Alkali bee emergence patterns were monitored during the 1988 and 1990 seasons using 3 mm mesh hardware cloth cone traps. Base diameter of a cone was 61 cm and height was 76 cm. The apex of a cone was open and a plastic bag was attached to it to capture emerging bees. Four traps were placed at a single bee bed prior to the start of bee emergence in 1988. They were located in areas where nesting had been good the previous year. Traps were monitored on 18 days from 24 May to 18 July. Three traps were placed on each of four bee beds in 1990 and visited eleven times from 31 May to 29 June. At each visit male and female alkali bees were counted and released. Accepted for publication 10 May 1998. This content downloaded from 157.55. 39.212 on Fri, 10 Jun 2016 06:09:39 UTC All use subject to http://about.jstor. org/terms 62 JOURNAL OF THE KANSAS ENTOMOLOGICAL SOCIETY Table 1. Numbers of male and female alkali bees found in emergence traps on each of 18 days dur ing 1988. Numbers are totals for four traps. Total bees = 181:167. Date 5/24 6/7 6/13 6/17 6/20 6/21 6/22 6/23 6/24 #M:#F 0:0 1:0 7:1 51:7 19:7 38:22 17:19 20:13 3:3 Date 6/27 6/28 6/30 7/1 7/7 7/12 7/13 7/18 7/21 #M:#F 12:30 1:8 0:7 0:4 0:7 0:9 0:8 0:7 0:2 Experiments were conducted on the response of male alkali bees to females or parts of females. Individual female bees were divided into three parts (head, thorax, and abdomen) with a clean razor blade. Legs and wings were removed from the tho rax. Each body part was pierced with an insect pin and affixed to the surface of the nesting site. Head, thorax, and abdomen were arranged in a line with the parts 42 cm apart. Male responses were recorded during a five minute observation period. Only actual contacts by a male bee with a female body part were counted. Length of contact ranged from less than a second to three or four seconds. Males frequently landed on the abdomen, rapidly crawled over it for several seconds, and often ap peared to try to mate with it. Females for use in the experiments were collected in a variety of ways. Virgin fe males were captured in simple cages made of aluminum window screen (35.6 cm x 35.6 cm x 5.1 cm). These were placed before emergence over areas of the nesting site where nesting had been dense the previous year. Bees emerging into the cages were captured and placed in plastic vials until used. These cages were also used to monitor bee emergence on 9 and 10 June 1995. Other methods of capture are de scribed under the results of individual experiments. Observations of bee activity were recorded with a portable cassette recorder and transcribed later in the laboratory.