Exploring Life History Choices: Using Temperature and Substrate Type as Interacting Factors for Blowfly Larval and Female Preferences

Summary

Herein, two protocols for assessing food source and oviposition preferences in larvae and females of blowflies are detailed. These comprise four choices with two interacting factors: substrate type and temperature. The assays enable the determination of the food source preference of the larvae and the oviposition site preference for the females.

Abstract

Blowflies (Diptera: Calliphoridae) present a wide range of larval lifestyles, typically classified as obligate parasitism, facultative parasitism, and complete sapro-necrophagy. Several parasitic species, both obligate and facultative, are considered to be of sanitary and economic importance, as their larvae can cause myiasis (maggot infestation in live tissue). However, it is noteworthy that the adult female plays a decisive role as she chooses the oviposition site, and, therefore, largely determines the feeding habit and developmental conditions of the larvae. In this study, two protocols are proposed to test larval feeding preference and female oviposition site preference considering two interacting factors: meat substrate type and temperature. The setups presented here allowed to test Lucilia cuprina larvae and gravid females in a four-choice assay with two temperatures (33 ± 2 °C and 25 ± 2 °C) and two types of meat substrates (fresh meat supplemented with blood and 5-day-old rotten meat). Larvae or gravid females can choose to burrow or lay their eggs, respectively, in either of the following: rotten meat at 25 °C (simulating a necrophagous species condition), fresh meat supplemented with blood at 33 °C (simulating a parasitic species condition), and two controls, rotten meat at 33 °C, or fresh meat supplemented with blood at 25 °C. The preference is assessed by counting the number of larvae or eggs laid in each option for each replicate. Comparing the observed results to a random distribution allowed for the estimation of the statistical significance of the preference. The results indicated that L. cuprina larvae have a strong preference for the rotten substrate at 25 °C. Conversely, oviposition-site preference by females was more varied for the meat type. This methodology can be adapted to test the preference of other insect species of similar size. Other questions can also be explored by using alternative conditions.

Introduction

Flies, particularly calyptrate muscoids (including blowflies, house flies, bot flies and flesh flies among others), exhibit a wide range of lifestyles, encompassing parasitic and necro-saprophagous behaviors¹. Parasitic species typically cause myiasis, an infestation of live tissues by maggots (larvae)². In the Calliphoridae family, both obligate and facultative parasitic species are major livestock pests responsible for economic losses and poor animal welfare due to maggot infestations^2,3,4,5<....

Protocol

Fly samples were obtained using traps and not on infested animals. A SISBIO license (67867-1) was issued to collect and keep flies of the Calliphoridae family in captivity in laboratory conditions. Insect samples are exempt from ethical evaluation in research in Brazil. Bovine meat and blood were obtained commercially, and no ethical clearance was required.

1. Larval feeding preference

1. Preparation of the Petri dishes containing 2% agar
   1. Prepare four Petri dishes with 2% agar. To do so, add 6 g of bacteriological agar to 300 mL of water and melt this mix in a microwave. Then, divide the volume evenly i....

Results

To demonstrate the effectiveness of the presented methods, the experiments were conducted using a laboratory population of Lucilia cuprina (family: Calliphoridae), a facultative parasitic blowfly². The entire raw dataset obtained for this species can be found in Supplementary File S3 with the results for the larval and female substrate preference tests. To assess if the larvae and females display a preference for any substrate, the observed data were compared to 1000 simu.......

Discussion

Understanding the evolution of feeding habits, particularly in the context of parasitism in blowflies, requires the examination of substrate preferences throughout different life stages for feeding or oviposition. Therefore, in this study, robust and straightforward methods were proposed for investigating substrate preferences in larvae and females of blowflies. These methods were tested in Lucilia cuprina, a facultative parasitic blowfly². Interestingly, the experiments unveiled a distin.......

Materials

Name	Company	Catalog Number	Comments
Agar	Sigma-Aldrich	05038-500G	For microbiology
Black cardboards	-	-	70x50 cm
Bovine blood with anticoagulat	-	-	50% pure bovine blood with anticoagulant (3.8% sodium citrate) + 50% of filtered water
Bovine ground Meat	-	-	Around 7-8% of fat
Brush	-	-	Made with plastic
Conical tube	Falcon or Generic	-	50 mL
Cross-shaped glass containers	Handmade	NA	48x48 cm, 8 cm of height and 8 cm of width
Erlenmeyer	Vidrolabor	NA	500 mL
70% Ethanol	Synth	A1084.01.BL	70% ethyl ethanol absolute + 30% filtered water
Graduated cylinder	Nalgon or Generic	-	500 mL and 50 mL
Heating pad	Thermolux	-	30x40 cm dimensions, 40 W, 127 V
Infrared thermometer	HeTaiDa	HTD8808	Non-contact body thermometer (Sample Rate: 0.5 S, Accuracy: ±0.2 °C, Measuring: 5-15 cm)
Petri dish (Glass)	Precision	NA	150x20 mm dimensions
			(Note: the petri dishes can be plastic if used only once)
Petri dish PS	Cralplast	18130	60x15 mm dimensions
Plastic Pasteur pipette	-	-	3 mL (total volume)
Sodium citrate	Synth	C11033.01.AG	3.8% Sodium citrate (38 g diluted in 1L of filtered water)
Spoons	-	-	More than one spoon is necessary. Use one for each type of meat substrate. Preferably stainless steel.
Stainless steel spatula	Generic	-	Flat end and spoon end
Stereomicroscope	Bioptika	-	WF10X/22 lenses
Tweezer	-	-	Metal made and fine point
White led light strips	NA	NA	4.8 W, 2x0.05 mm², 320 lumens, Color temperature:6500 K (white)