Questions and assignments to Lecture 6-13

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.

Age, days (x) Number of survivals Mean number of offsprings per parent
0 1000 0
1 900 0
2 820 0
3 750 0
4 680 0
5 620 0
6 550 1
7 500 2
8 450 5
9 400 10
10 350 12
11 300 10
12 250 8
13 200 6
14 100 3
15 50 1
16 0 0


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 eonymph 144
Eaten by predators 125
Exit hole of parasitoid Drino inconspicua 15
Exit hole of parasitoid Pleolophus basizonus 78
Larvae of parasitoid Exenterus abruptorius 210
Exit hole or larvae of gregarious parasitoid Dahlbominus fuscipennis 23
Fungus disease 205
Total 800


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 eggs 200
Desiccated eggs 100
Parasitized eggs 200
Total 500


Mortality process Number of eggs in which this mortality process can be detected Number of killed eggs Mortality Survival k-value
1. Desiccation 500 100 0.2 0.8 0.223
2.Parasitism 400 (500-100) 200 0.5 0.5 0.693
Total 500 300 0.6 0.4 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 colonies Larvae alive at the end
Control 3000 1400
Large predators excluded 3500 2900
All predators excluded 3200 3100


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 larvae Larvae that died in 7 days since collection
1-st week 200 23
2-nd week 200 7
3-rd week 200 5
4-th week 200 30
5-th week 200 58
6-th week 200 115


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!).

.8. Questions and Assignments to Lecture 8.
8.1 Insect development rate. Development of pea weevil (Bruchus pisorum) eggs was studied in the laboratory at constant temperatures (Smith, A.M. 1992. Environ. Entomol. 21:314-321):
Temperature, C Egg development time, days
10.7 38.0
14.4 19.5
16.2 15.6
18.1 9.6
21.4 9.5
23.7 7.3
24.7 4.5
26.9 4.5
28.6 7.1



Plot development rate vs. temperature (use Excel)
Use linear regression to estimate lower temperature threshold and degree days required for egg development.
Average temperature in a sequence of days was: 15 20 25 20 15 10 15 10 15 20 15 20 15 10 15 20 25 20 15 20
When do you expect eggs to hatch if they were laid on the first day? (Note: ignore diurnal temperature change).