Crippled Trap, Toasted Flies, and Assassin Spods

We began with a short update on the tabanid trap and the spod trays deployed earlier in the week. The tabanid squad was able to set up 1 and ¾ of a trap at the equine center and the beef cattle feedlot in the morning. Unfortunately, both traps yielded nothing. The spod trays on the other hand appeared to have performed relatively well. Aside from the expected conspecific cannibalism, no other casualties were reported. The caterpillars looked vigor and content in their trays. Among the five trays, two parasitic wasps were found stuck to the tanglefoot, suggesting that this new method is effective. We placed the exposed caterpillars in the bug dorms temporarily. This is because of the housing shortage created by the rising demographic of mid to late instar caterpillars.

After the discussion, we quickly moved on to complete a number of tasks.

Spod Rehousing Project

With the growing risk of cannibalism among the smaller spods, we moved them into solitary confinement with their new diet. The larger caterpillars were sent off to feed the Tachinids (Fig. 1). Sick caterpillars infected with fungus were also exterminated due to public health concerns. However, these were not enough to alleviate the housing crisis. As such, we decided to evict some of the survivors of the spod pockets. We recorded the data and kept those that are still pupating. Louie suggested that it might be worthwhile to conduct the landing experiment with every flying thing we can get a hold of. Hence, some of the adults were also kept and later used in a pilot experiment. Though, due to the poor living conditions, many adult spods are weak, deformed, and malnourished. Most will die within a week.

Fig. 1. One of the Seven Offerings to the Tachinid Gods

Pilot Landing Experiments

We tested two new species of flying insects: the adult Spodoptera exigua we reared from the spod pockets and Drosophila melanogaster obtained from an insect physiology lab. For the adult moths, it was reported that they remain relatively still after they have landed. Thus, some suggested that perhaps first choice is the only meaningful behavioral parameter that we should measure. It is unclear whether the pilot was successful. More effort is needed in this inquiry.

For the fruit fly pilot, we quickly realized that the tupperware is too large for individual flies to reliably land on the ground. Therefore, we replaced the tupperware with normal sized and smaller sized petri dishes. We found that Drosophila need a long acclimation period (7 min) and are much more active under the sun. Anecdotally, it also appears that the effect of stripe is stronger under the sun. Although the flies may not necessarily land on the grey surface, they seemed to stay in the grey hemisphere longer (but confirmation bias is a thing, so who knows? The data we attempted to collect certainly does not support this suspicion). Within one or two minutes we noticed that the fruit flies started to show signs of overheating. They overwhelmingly preferred the side facing the nearest shade. They also became more erratic, which soon turned into a lost of motor coordination then death.

In light of this, we decided to put the Drosophila back in the classroom and use a camera to examine their behavior over a longer timescale. The camera is set up to take a photo every minute until the battery runs out (Fig. 2).

Fig. 2. A Lone D. melanogaster Under Constant Surveillance.

Another apparatus was used to test the behavior of the fruit flies (Fig. 3). After 20 minutes of light exposure, 10 overheated and died, 7 ended up in the right chamber (grey), and 8 in the left chamber (stripe). Interestingly, after 16 hours in dim indirect light, every single fly returned to the original container with the diet. This behavior lends itself to exploitation in future modifications of this experiment.

Fig. 3. Around Fifty D. melanogaster in the Fly Arena.  

We gathered at the end of the class and discussed. Several people suggested that the spod housing program is not a good investment of time. Some even questioned the usefulness of keeping spods around. We decided to hold off on ordering more eggs and try to be as lazy as possible when caring for spods. We also decided to put out painted caterpillars and smaller instars in the future.

Moreover, Annabelle proposed a novel way of testing our hypothesis. The idea is to put out clay models of caterpillars and cover the dorsal side with tanglefoot. Parasitoids attempting to parasitize the fake caterpillar will get stuck to it, allowing us to quantify the parasitism rate by counting the number of carrion (similar to Fig. 4). We will entertain this proposal next week.

Related image
Fig. 4. An Assassin Bug

For next Tuesday:

  1. Mold cats + tanglefoot
  2. Painting cats?
  3. Make stencil
  4. Check tabanid trap
  5. Report on current experiment

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