Elachertus cacoeciae

(Howard, 1885)

Elachertus cacoeciae is a gregarious idiobiont ectoparasitoid in the Eulophidae that specializes in attacking larvae of the spruce budworm (Choristoneura fumiferana), a major forest pest in North American coniferous forests. The exhibits pronounced seasonal dimorphism: spring females produce with approximately 75% females and only 2% of offspring enter , while summer females produce broods with ~95% diapause rates, possibly adapted to alternate . Development from to takes approximately 20 days at 20.6°C, with a time of about 31 days for spring females.

Pronunciation

How to pronounce Elachertus cacoeciae: /ɛˈlækərtəs kæˈkoʊəʃiiː/

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Identification

Identification from similar Elachertus requires examination of morphological characters not detailed in available sources. As a eulophid , it is likely small-bodied (typical of the ), but specific diagnostic features for field identification are not documented in the provided literature.

Habitat

Associated with balsam fir (Abies balsamea) and spruce-fir forests where the Choristoneura fumiferana occurs. Field studies were conducted by implanting host larvae on current-year balsam fir shoots, simulating low- budworm .

Distribution

Canada: recorded from Alberta, British Columbia, Manitoba, and New Brunswick.

Seasonality

Spring females are active from the predicted peak of fourth-instar spruce budworm larvae through approximately 10–12 days after the predicted peak of the pupal stage. Summer females represent a distinct seasonal cohort with different strategies.

Diet

females feed on honey water in laboratory conditions; larvae are ectoparasitic, feeding externally on spruce budworm larvae. Spring females also engage in feeding without oviposition on additional hosts.

Host Associations

Choristoneura fumiferana - primary Attacks fourth-, fifth-, and sixth-instar larvae; fifth instar preferred for oviposition and yields fastest development

Life Cycle

-to- development approximately 20 days at 20.6°C. Egg-to-egg time approximately 31 days for spring females. Pre-oviposition period 11.5 days; oviposition period 76.3 days; post-oviposition period 18.5 days. Approximately 2% of spring female offspring enter as pupae, versus ~95% of summer female offspring.

Behavior

Gregarious : multiple offspring develop on a single . Idiobiont: host is permanently paralyzed and does not continue development. Females exhibit size-selective oviposition, preferring intermediate-sized (fifth-instar) hosts. Spring females host-feed without oviposition on additional hosts beyond those used for . Exhibits seasonal with distinct spring and summer female morphs differing in strategy.

Ecological Role

Ectoparasitoid contributing to top-down of spruce budworm during low- periods between . Competes with the koinobiont endoparasitoid Tranosema rostrale; the two show density-dependent negative correlation in frequency, suggesting adaptive temporal or -use partitioning to minimize direct competition.

Human Relevance

Potential agent for spruce budworm, a destructive forest pest. Has been studied for characteristics relevant to augmentative or in coniferous forest management.

Similar Taxa

Tranosema rostraleAlso a of spruce budworm larvae, but distinguished by being a koinobiont endoparasitoid (allows to continue development) versus the idiobiont ectoparasitoid strategy of E. cacoeciae. The two compete for hosts but exhibit temporal partitioning.
Other Elachertus speciesCongeneric may overlap in geographic range and general ; specific identification requires detailed morphological examination.

More Details

Sex allocation and host size

sex ratio (proportion of females) increases with instar, with more females produced on larger hosts. Female offspring size increases with host instar and with brood sex ratio, but male size is not related to brood sex ratio. Larger females have greater longevity and lifetime .

Competitive superiority

E. cacoeciae is described as 'competitively superior' to Tranosema rostrale in direct competition within a larva, likely due to its idiobiont ectoparasitoid strategy which kills the host immediately versus the koinobiont strategy of T. rostrale.

Summer female alternate host hypothesis

Laboratory results suggest summer females may be adapted to parasitize alternate (s) rather than spruce budworm, given their different strategy and timing.