Question 5

Alfalfa weevil larvae are insect pests that feed on alfalfa crops. They can be controlled by natural predators such as parasitic wasps and ladybird beetles.

Draw a food chain showing the relationship between alfalfa crops, alfalfa weevil larvae, and parasitic wasps.

A biologist wanted to compare the effectiveness of these two different predators to control the alfalfa weevil larvae. Parasitic wasps were released on day 0 into one alfalfa field (Field A), and ladybird beetles were released into a different alfalfa field (Field B).

The table below shows the results of this study:

Time\multicolumn2c∣Field A (Parasitic wasps)\multicolumn2cField B (Ladybird beetles)\cline2−5(days)Weevil larvae per m2Wasps per m2Weevil larvae per m2Ladybird beetles per m2060020610204580404208085509518015012490180151201615025082520024014002402354200\begin{array}{c|c|c|c|c} \hline \textbf{Time} & \multicolumn{2}{c|}{\textbf{Field A (Parasitic wasps)}} & \multicolumn{2}{c}{\textbf{Field B (Ladybird beetles)}} \\ \cline{2-5} \textbf{(days)} & \textbf{Weevil larvae per } \text{m}^2 & \textbf{Wasps per } \text{m}^2 & \textbf{Weevil larvae per } \text{m}^2 & \textbf{Ladybird beetles per } \text{m}^2 \\ \hline 0 & 600 & 20 & 610 & 20 \\ 4 & 580 & 40 & 420 & 80 \\ 8 & 550 & 95 & 180 & 150 \\ 12 & 490 & 180 & 15 & 120 \\ 16 & 150 & 250 & 8 & 25 \\ 20 & 0 & 240 & 140 & 0 \\ 24 & 0 & 235 & 420 & 0 \\ \hline \end{array}

Use the information in the table to answer the following questions:

Suggest two reasons why parasitic wasps might be a better biological control agent to use than ladybird beetles.

Suggest one reason why ladybird beetles might be a better biological control agent than parasitic wasps.

Other than predation, name two biotic (living) factors that may affect alfalfa weevil larvae numbers.

Name two abiotic (non-living) factors that may affect alfalfa weevil larvae numbers.