Bessa harveyi

(Townsend, 1892)

Bessa harveyi is a tachinid fly that attacks the larch sawfly, Pristiphora erichsonii, in North American larch forests. The exhibits bivoltinism, with a partial second emerging in fall after larvae have completed feeding; these fall-emerging rarely reproduce successfully due to scarcity of alternate hosts. Despite being a common , it is ineffective at preventing or terminating of its host. are strongly influenced by and temperature, with warm, prolonged summers under long-day conditions increasing bivoltinism-related mortality.

Pronunciation

How to pronounce Bessa harveyi: /ˈbɛsə ˈhɑːrvi.aɪ/

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Habitat

Associated with larch stands (Larix spp.) where the larch sawfly, Pristiphora erichsonii, occurs; specifically in soil where cocoons are formed. In southeastern Manitoba, are tied to larch sawfly areas.

Distribution

United States and Canada; specifically recorded from southeastern Manitoba with North American distribution centered on larch forest regions.

Seasonality

synchronized with availability of larch sawfly larvae; individuals emerge in fall (September-October) after larvae have completed feeding and formed cocoons.

Host Associations

Life Cycle

with partial bivoltinism: main emerges in summer synchronized with larval availability; partial second generation emerges in fall after host larvae have completed feeding. do not contribute progeny to the next generation due to lack of suitable hosts, acting as a mortality factor. Females begin -laying 1–2 days after mating (which occurs within 3 days of ); mean female longevity approximately 12 days, male longevity approximately 7 days. Mean egg production 30–40 eggs per female, positively correlated with temperature, with maximum recorded at 169 eggs.

Behavior

Mating occurs within 3 days of . Oviposition targets larch sawfly larvae. Fall-emerging adults from the partial second have limited reproductive success due to unavailability.

Ecological Role

of larch sawfly; contributes to natural of this forest pest but is ineffective at preventing or terminating . Bivoltinism acts as a mortality factor, with weather variability and development timing influencing parasitoid population persistence.

Human Relevance

Studied as a potential agent for larch sawfly; survey methods for estimating rates have been developed for forest pest management.

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