Bathyplectes anurus and B. curculionis

In the spring both B. curculionis and B. anurus adults emerge from overwintering cocoons. Their lifecycles are similar with a few key developmental differences. Bathyplectes anurus has a single yearly generation while B. curculionis has 1 complete and part of another generation each year. In the spring after B. anurus parasitizes an alfalfa weevil larva the new parasitoid larva emerges, spins a cocoon and diapauses over the summer. In fall, B. anurus larvae become active again, pupate and develop into adults. These adults remain within their cocoon and enter diapause to overwinter. In contrast, the first cocoons produced by B. curculionis in the growing season are often non-diapausing cocoons, which tend to be lighter in color than late season cocoons. Individuals in these cocoons develop and emerge as adults that parasitize alfalfa weevil still present. This second generation is generally composed of darker colored diapause cocoons. This generation of B. curculionis remains in the larval form to overwinter. Their lifecycle is completed the following spring. 

Bathyplectes anurus cocoons possess the unique ability to jump through larval movement within its cocoon. This ability is not shared by B. curculionis. It has been proposed that this jumping habit may contribute to survival in B. anurus by helping prevent predation and parasitism or by allowing it to avoid harmful environmental conditions.

Bathyplectes curculionis was first introduced to Utah in 1911 where it quickly became established. Subsequent introductions that led to successful establishment include California starting in 1933, the Northeastern US from the 1950s to 1960, and Ontario, CA in 1970. Releases of B. curculionis in Arizona in 1941 led to less success and low levels of establishment in the southwestern US. Bathyplectes curculionis has been extremely successful at establishment and can be found virtually everywhere alfalfa weevil is located in North America. It has been recorded in Canada from British Columbia to Quebec and across the United States.  

Bathyplectes anurus was not established in North America until much later than B. curculionis. The first introduction that led to establishment was in the Northeastern US in 1960. Although B.anurus establishment was successful it spread slowly so redistribution efforts and introductions to Ontario in 1970 helped grow its range across eastern North America. Bathyplectes anurus is documented as established in much of the United States including in the northeastern states, Florida, and California. It is not established in many states in the Western US and in Canada it is only found in Ontario. 

Although Bathyplectes curculionis is more widely distributed, B. anurus, where established, tends to control alfalfa weevil better and displace B. curculionis. This could be due to lifecycle and fitness differences, and varying defensive abilities. In the southern part of their range, B. anurus may be more compatible with alfalfa weevil due to their single generation lifecycle while the second, later season, generation of B. curculionis that emerges must locate a host when they are not abundant. Also, B. anurus preferentially parasitizes slightly older alfalfa weevil larvae which may increase the chance of completing their development. Other factors which have been documented and may contribute to the competitive abilities of B. anurus are higher fecundity, superior host searching and handling, and its ability to quickly eliminate conspecifics as a larva in its host. Finally, survival may be higher in B. anurus due to the jumping ability their cocoons have and their encapsulation differences. 

Encapsulation is the ability of alfalfa weevil larvae have to encapsulate certain parasitoid eggs allowing them to prevent parasitoid development. The Egyptian and eastern alfalfa weevil strains commonly encapsulate B. curculionis while the western strain does not often encapsulate B. curculionis. Bathyplectes anurus is not susceptible to encapsulation by any of the alfalfa weevil strains found in North America. This may potentially contribute to B. anurus ability to out compete B. curculionis outside of the western US.