Food quality effects on instar-specific life histories of a holometabolous insect
Cite this dataset
Holmes, Leslie; Nelson, William; Lougheed, Stephen (2020). Food quality effects on instar-specific life histories of a holometabolous insect [Dataset]. Dryad. https://doi.org/10.5061/dryad.d7wm37px7
- It is a long-standing challenge to understand how changes in food resources impact consumer life history traits and, in turn, impact how organisms interact with their environment. To characterize food quality effects on life history, most studies follow organisms throughout their life cycle and quantify major life events, such as age at maturity or fecundity. From these studies, we know that food quality generally impacts body size, juvenile development, and life span. Importantly, throughout juvenile development, many organisms develop through several stages of growth that can have different interactions with their environment. For example, parasitoids typically attack larger instars, whereas larval insect predators typically attack smaller instars. Interestingly, most studies lump all juvenile stages together, which ignores these ecological changes over juvenile development.
- We combine a cross-sectional experimental approach with a stage-structured population model to estimate instar-specific vital rates in the bean weevil, Callosobruchus maculatus across a food quality gradient. We characterize food quality effects on the bean weevil’s life history traits throughout its juvenile ontogeny to test how food quality impacts instar-specific vital rates.
- Vital rates differed across food quality treatments within each instar; however, their effect differed with instar. Weevils consuming low quality food spent 38%, 37% and 18% more time, and were 1%, 8% and 60% smaller than weevils consuming high quality food in the second, third and fourth instars, respectively. Overall, our results show that consuming poor food quality means slower growth, but that food quality effects on vital rates, growth and development are not equal across instars. Differences in life history traits over juvenile ontogeny in response to food quality may impact how organisms interact with their environment, including how susceptible they are to predation, parasitism, and their competitive ability.
Four-day old eggs collected from stock Callosobruchus maculatus females were transferred to artificial seed pulses (pellets) for the three pellet quality treatments (100%, 95%, and 90% black-eye pea flour). Beginning on day 5 of the experiment, (i.e. 5-day old weevils), a single pellet was removed from the environmental growth chamber each day for 45 days (i.e. 50 days of weevil development from hatching) from each treatment in each replicate. Sampled pellets were placed in a -10°C freezer to stop growth and development of the larva, giving us cross-sectional data on development and survival every 24 h. We retrieved the larvae from each frozen pellet using a scalpel under a dissecting microscope. The experiment was replicated 40 times, such that the total number of sampled larvae (40 replicates X 46 days X 3 treatments) was: 5,520.
For each dissected pellet, we noted survivorship (i.e. whether an individual survived until its freeze date), identified larval instar (L1, L2, L3 and L4) by counting the number of head capsule molts recovered during dissection, measured larval head capsule width at its largest width, and quantified larval dry mass. Samples were dried in a drying oven at 76°C for 72 hours. Dry mass was measured three times and the average of these three measurements was used for all analysis.
Index of variables
Column 1: age - the age of the individual in days
Column 2: trt - the pellet quality treatment, 90 = 90% blackeye pea flour:10% filler, 95 = 95% blackeye pea flour:5% filler, and 100 = 100% blackeye pea flour
Column 3: stage - the stage of growth of each individual, L1 = 1st instar, L2 = 2nd instar, L3 = 3rd instar, L4 = 4th instar, L5 = pupa, L6 = adult
Column 4: counts - the number of individuals alive in each stage of development on each day of development summed across all 40 replicates.
Column 1: trt - the pellet quality treatment, 90 = 90% blackeye pea flour:10% filler, 95 = 95% blackeye pea flour:5% filler, and 100 = 100% blackeye pea flour
Column 2: age - the age of the individual in days
Column 3: hcw6X - the head capsule width, measured in micrometer ruler units at 6X the magnification, where each ruler unit at 1X the magnification equals 0.001mm.
Column 4: dead - identified which individuals were declared dead upon sampling, where 0 = alive, and 1 = dead
Column 5: stage - the stage of growth of each individual, L1 = 1st instar, L2 = 2nd instar, L3 = 3rd instar, L4 = 4th instar, L5 = pupa, L6 = adult
Column 6: mass - the average drymass of each individual measured in miligrams
Column 7: sex - indication of male or female for individuals that reached the adult stage. Note: sex could be determined for some individuals in the pupal stage.
Column 8: burrowed - indication of whether an individual successfully burrowed into the pellet from the egg on the surface of the pellet, where 0 = did not burrow, 1 = burrowed. Note: individuals that did not burrow were removed from our analyses on head capsule width and dry biomass.
Natural Sciences and Engineering Research Council of Canada
Canada Foundation for Innovation