Questions and assignments to Lecture 6

1. Build a life table for an aphid population (aphids reproduce parthenogenetically). Estimate lx, dx, mx, Ro, T, and r. (See a picture of aphids!)

Age, days (x)Number of survivalsMean number of offsprings per parent

2. Partial life-table. The European pine sawfly, Neodiprion sertifer, cocoons were collected at the beginning of August and dissected. Results of dissection of new (current year) cocoons are the following:

Healthy sawfly eonymph144
Eaten by predators125
Exit hole of parasitoid Drino inconspicua 15
Exit hole of parasitoid Pleolophus basizonus78
Larvae of parasitoid Exenterus abruptorius210
Exit hole or larvae of gregarious parasitoid Dahlbominus fuscipennis 23
Fungus disease205

Life-cycle information:

Excellent images of parasitoids are available from the PHERODIP homepage.

  • Parasitoids D.inconspicua, P.basizonus and D.fuscipennis have several generations per year, whereas E.abruptorius has only 1 generation.
  • D.inconspicua (Tachinidae) is an endoparasite and attacks larvae (4-5 instar). It emerges from the host immediately after host cocooning. It develops very fast and wins the competition with any other parasitoids.
  • E.abruptorius is an ectoparasite, attacks host eonymphs a day prior to cocooning. Parasitoid larvae emerges inside the cocoon, eats the host and overwinters as larvae inside host cocoon. If the host was previously parasitized by D.inconspicua, then E.abruptorius dies.
  • P.basizonus and D.fuscipennis attack host cocoons. They are ectoparasites. If another parasite (E.abruptorius) is already present in the cocoon, it will be eaten first. D. fuscipennis wins the competition with P.basizonus.
Estimate mortality caused by each natural enemy, convert it into k-value. Check that the sum of all k-values is equal to the total k-value for sawfly cocoons. Write results in the table, putting mortality processes in the order of their operation.

Simple example:

Healthy eggs200
Desiccated eggs100
Parasitized eggs200

Mortality process Number of eggs in which this mortality process can be detected Number of killed eggsMortalitySurvival k-value
1. Desiccation 500 1000.20.8 0.223
2.Parasitism 400 (500-100) 2000.50.5 0.693
Total 500 3000.60.4 0.916

3. Estimate mortality in a predator-exclusion experiment. The fall webworm, Hyphantria cunea, larvae in colonies were counted at the beginning and at the end of experiment:
A. Control - without protection
B. Exclusion of large predators: prey were protected by a 1/2 inch cell hardware cloth
C. Exclusion of all predators: prey were protected by 1 mm cell mesh
Estimate: mortality caused by large and small predators, convert it to k-value.

Initial larvae in 10 coloniesLarvae alive at the end
Large predators excluded35002900
All predators excluded32003100

4. Estimate gypsy moth mortality due to virus (NPV).
Gypsy moth larvae were collected in the forest at 7-day intervals and placed individually in the cups with diet. Incubation period of viral infection (from infection till death) is 7 days. Estimate: total mortality caused by virus and the k-value.

Collected larvaeLarvae that died in 7 days since collection
1-st week20023
2-nd week2007
3-rd week2005
4-th week20030
5-th week20058
6-th week200115

5. Estimate the rate of simultaneous mortality processes
Gypsy moth (Lymantria dispar) pupae are destroyed by small mammals and by invertebrates. 300 laboratory-reared pupae were placed on tree boles. Three days later, 200 of them were damaged by small mammals and 50 were damaged by invertebrate predators (Calosoma sycophanta). Each pupa can be eaten just once. Estimate mortality caused by each predator guild if another predator guild was absent (note: use k-values!).

Alexei Sharov 1/11/96