Biology of two members of the Euwallacea fornicatus species complex (Coleoptera: Curculionidae: Scolytinae), recently invasive in the U.S.A., reared on an ambrosia beetle artificial diet

Abstract

Recent molecular studies have found that the ambrosia beetle Euwallacea fornicatus Eichhoff (Coleoptera: Curculionidae: Scolytinae) is a complex of cryptic species, each carrying a different species of symbiotic fungus, in the genus Fusarium, which they farm within galleries inside woody hosts. Several of these beetle species have become invasive pests around the world for attacking and infecting healthy trees with their phytopathogenic fungal symbionts. Diet and rearing protocols were developed for two members of the E. fornicatus species complex, polyphagous shot hole borer (PSHB) and tea shot hole borer (TSHB), using sawdust from host trees, allowing collection of data on beetle biology, phenology and sex ratios. Adults developed within 22 days at 24 °C. Single PSHB or TSHB foundresses averaged 32.4 and 24.7 adult female offspring, respectively, and up to 57 and 68 female adults within 6–7 weeks. A strong predictor of the number of offspring in a colony was the number of entry holes. Average sex ratios (% male) for PSHB and TSHB, respectively, were 7.4% and 7.2%. Being haplodiploid, virgin PSHB foundresses were able to produce and mate with male offspring, then subsequently produce female offspring, confirming that they have arrhenotokous reproduction. A cold tolerance study found significant mortality rates among PSHB colonies exposed to −5° or −1 °C but not colonies exposed to 0°, 1° or 5 °C. Given Hamilton's local mate competition (LMC) theory, a number of LMC predictions were violated. PSHB sex ratios were not affected by the number of foundresses; approximately 14% of broods did not contain males; males did not usually eclose before females but eclosed around the same time (22–23 days); and PSHB males were found walking outside of their natal galleries on the trunk of a heavily infested tree in the field. Alternatives to LMC are considered, such as early forms of sociality (maternal care, cooperative brood care), local resource enhancement and kin selection.

The Essential Role of Taxonomic Expertise in the Creation of DNA Databases for the Identification and Delimitation of Southeast Asian Ambrosia Beetle Species (Curculionidae: Scolytinae: Xyleborini)

“…The uncommon haplodiploid mating system of Xyleborini may provide the best explanation for the high intraspecific COI sequence differences. The diploid female/haploid male sex-ratio is skewed on average 13:1 and ranges from 2:1 to 83:1 (French and Roeper, 1975;Beaver and Browne, 1979;Kirkendall, 1993;Cooperband et al, 2016;Castro et al, 2019). A female has an apparent greater chance of reproducing compared to diploid-diploid species because if unmated she lays a haploid egg which produces a male.…”

“…Xyleborine ambrosia beetles (Curculionidae: Scolytinae) occur throughout the world's forests with most of the diversity in the moist tropics where they comprise the majority of the scolytine diversity (Browne, 1961;Wood and Bright, 1992;Hulcr et al, 2015). These beetles exhibit two conspicuous life history traits: they cultivate symbiotic fungi for food in tunnels that they bore into recently dead trees (and their parts), and they are haplodiploid and highly inbred with female-skewed sex ratios averaging 13:1 (Kirkendall, 1993;Cooperband et al, 2016;Castro et al, 2019). These traits have allowed these beetles to colonize the world and gave them their infamous reputation as potential invasive species (Jordal et al, 2001;Gohli et al, 2016;Brockerhoff and Liebhold, 2017).…”

Temperature can limit the invasion range of the ambrosia beetle Euwallacea nr. fornicatus

“…Both the immature and adult stages are reliant on the fungi for nutrition and do not actually feed on the wood of the host tree. All stages of development occur within the host tree and offspring may produce their own galleries within the same host upon reaching maturity (Cooperband et al ., ). The smaller, flightless males develop faster than their sisters to ensure that ready mates are available for maturing females and sibmating occurs inside the natal galleries prior to female dispersal.…”

Distribution, Pest Status and Fungal Associates of Euwallacea nr. fornicatus in Florida Avocado Groves

“…#2. In addition, Cooperband et al [9] observed that a single foundress produced her first adult female offspring within 22 days of gallery initiation at 24 °C, and averaged 24.7 adult female offspring within 6–7 weeks, and that the average sex ratio (% male) was 7.2%.…”