Neodiprion abietis

Neodiprion abietis
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Suborder: Symphyta
Family: Diprionidae
Genus: Neodiprion
Species: N. abietis
Binomial name
Neodiprion abietis

Neodiprion abietis, a Diprinoid phytophagous specialist commonly known as the balsam fir sawfly is an insect found within Canada and throughout the United States.[1]

Evolutionary relationship

N. abietis is considered to arise from a monophyletic group.[2]

Internal anatomy

The larva of N. abietis have salivary glands with a lumen that is lined by microvilli and it also has a single layer of epithelial cells present. Moreover, they have fat body cells against the anterior duct of the lumen. Balsam fir sawfly have a pair of diverticular pouches which are used to store terpenoids which they regurgitate as a form of defense. These pouches are lined with a layer of an impermeable cuticle. The amount of liquid regurgitated is a reflection of the food that they ingest. The rectum of the Neodiprion abietis larva has a rectum similar to other Diprionidae. The rectum consists of a thin cuticle, a single layer of epithelial cells, and contains muscles.[3]

Physical characteristics

The heads of instars differ in color, newly hatched first instars have a light brown head and prior to molting into second instars, their heads change to a dark brown color. Their heads then turn black in color during the second to fifth instars. A range of 0.48 mm to 0.60 mm is seen with the size of head capsules. The stripes on their body also differ in larval instars. The first and second instar lack longitudinal stripes. The third, fourth, and fifth instar has three pairs of longitudinal dark stripes. The stripes on the third instar are considerably shorter than the fourth and fifth instar, while the stripes of the fourth and fifth instar are very similar causing difficulty for differentiating. The body color and length also varies between instars. Initially, a translucent body is seen, then becomes light green during the first instars. The body length rages anywhere from 2.43 mm to 3.15 mm. The antennas, more specifically their segments, differ between male and female. Male antennas consist of 21-23 segments while female antennas consist of 18-20 segments.[4]

Life cycle

Female sawflies in Newfoundland lay their eggs in late September or early October using their saw-like ovipositor into foliage of the current year or foliage of the previous year. Months later, around June or mid-July, the eggs hatch and the larvae feed immediately on needles of the balsam fir. Interestingly, the larvae do not eat balsam fir foliage of the current year. The development of male and female sawfly vary slightly. Females can have five or six instars whereas males only have five instars. Secondly, females take slightly longer than males to complete their development. A female's developmental period lasts 35 days whereas males complete their development within 30 days. Male and female sawflies spin a cocoon on the foliage during their last-instar larva, they pupate inside, and adults emerge from the cocoon within 2–3 weeks. Unlike many other cocoon-spinning insects, N. abietis spin their cocoon in the ground instead of on tree branches.[5]

Reproduction

Mated females can produce male and female offspring while unmated females can only produce male offspring, a form of parthenogenesis known as arrhenotoky.[3]

Feeding

The balsam fir sawfly feeds on Abies balsamea, a type of fir, Picea glauca, Picea mariana types of spruce, and Larix laricina, a larch.[6] The first instar feeds on the whole crown of one-year-old foliage following egg hatch and the larvae in a group feed together by moving from one shoot to another.[7] Females, however, have a greater sensitivity to foliage than males and it’s suspected that it is due to their longer developmental time. N. abietis larvae have optimal development when they are able to feed on different-aged foliage thus allowing for maximization of their resources.[8] Moreover, the balsam fir sawfly are considered to be wasteful feeders because only the outer portions of needles are consumed during the early-instar larvae. Late instars, however, consume more needle tissue type but it never consumes the needle in its entirety. The balsam fir sawfly larvae generally feed on foliage that are of current year or of past years.[9]

Ecological importance

The balsam fir sawfly is known as an insect pest with outbreaks lasting anywhere from 4 years to 5 years. The outbreaks of the balsam fir sawfly causes a reduction in tree growth which in turn can cause tree mortality. The balsam fir sawfly, more specifically third to fifth instar larvae are responsible for defoliation and foliage weight loss in trees. The balsam fir sawfly do not stimulate the release of buds or shoots while they feed which contributes to a slow recovery and severe impact on the balsam fir.[6]

These outbreaks are treated by a baculovirus known as nucelopolyhedrovirus (NeabNPV) which limits outbreak densities to last for 2 to 4 years instead. NeabNPV works by infecting the epithelial cells of the larvae midgut, this infection can be carried within the midgut through to adulthood.[10] When populations of the balsam fir sawfly remain high factors like immigration, female-biased sex ratios, and survival of old instar larvae cause the population to continually increase in density.[8]

Other than presenting the NeabNPV, N. abietis outbreaks can be treated by the thinning of forests which causes a reduction in foliage quantity and a limitation to the available preferred foliage.[11] Neemix, an insect growth regulator is also used to slow down larval and pupal development by decreasing pupal weight and the ability of the adults to emerge from their cocoon.[12]

References

  1. ↑ R.C. Johns, J. Fidgen, and D.P. Ostaff (2013). Host–tree oviposition preference of balsam fir sawfly, Neodiprion abietis (Hymenoptera: Diprionidae), in New Brunswick, Canada. Canadian Entomologist. 145(4): 430-434.
  2. ↑ C.R. Linnen and B.D. Farrell(2008). Phylogenetic Analysis of Nuclear and Mitochondrial Genes Reveals Evolutionary Relationships and Mitochondrial Introgression in the Sertifer Species Group of the Genus Neodiprion (Hymenoptera: Diprionidae) Molecular Phylogenetics and Evolution. 48(1): 240-257.
  3. 1 2 C.J. Lucarotti, H.W.W. Beatrixe, and D.B. Levin (2011). Histology of the Larval Neodiprion abietis (Hymenoptera: Diprionidae) Digestive Tract. Journal of Entomology. 2012: 1-10.
  4. ↑ S. Li (2003). Notes on larval instars and adult antennae of Neodiprion abietis (Hymenoptera : Diprionidae). Canadian Entomologist. 135(5): 745-748.
  5. ↑ D.R. Wallace and C.R. Sullivan (1973). Photoperiodism in the Early Balsam Strain of the Neodiprion abietis Complex (Hymenoptera: Diprionidae). Canadian Journal of Zoology. 52: 507-513.
  6. 1 2 P.D. Simon, M.Y Aaron, B. Morin, C.J. Lucarotti, B.F. Koop, and D.B. Levin (2006). Sequence Analysis and Organization of the Neodiprion abietis Nucleopolyphedrovirus Genome. Journal of Virology. 80(14): 6952-6960.
  7. ↑ L.J. Anstey, D.T. Quiring, D.P. Ostaff (2002). Seasonal Changes in Intra-tree Distribution of Immature Balsam Fir Sawfly (Hymenoptera: Diprionidae). Canadian Entomologist. 134: 529-538.
  8. 1 2 G. Rogers, D.T. Quiring, and C.J. Lucarotti (2012). Transmission of a Gammabaculovirus within Cohorts of Balsam Fir Sawfly (Neodiprion abietis) Larvae. Journal of Insects. 3(4): 989-1000.
  9. ↑ G. Moreau, D.T. Quiring, E.S. Eveleigh, E. Bauce (2003). Advantages of a Mixed Diet: Feeding on Several Foliar Age Classes Increases the Performance of a Specialist Insect Herbivore. Oecologia. 135: 391–399.
  10. ↑ C.J. Lucarotti, H.W.W Beatrixe, R. Lapointe, B. Morin, D.B. Levin (2012). Pathology of a Gammabaculovirus in Its Natural Balsam Fir Sawfly (Neodiprion abietis) Host. Journal of Entomology. 2012: 1-13.
  11. ↑ G. Moreau, E.S. Eveleigh, C.J. Lucarotti, and D.T. Quiring (2006). Ecosystem Alteration Modifies the Relative Strengths of Bottom-up and Top-down Forces in a Herbivore Population. Journal of Animal Ecology. 75: 853–861.
  12. ↑ S.Y. Li, A.C. Skinner, T. Rideout, M.D. Stone, H. Crummey, and G. Holloway (2003). Lethal and Sublethal Effects of a Neem-based Insecticide on Balsam Fir Sawfly (Hymenoptera: Diprionidae). Journal of Economic Entomology. 96(1): 35-42.
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