Lacewing (Chrysopidae) Nutritional Requirements and Diets

Lacewings are generalist predators, and tend to have varied diets.  Additionally, different life stages have different nutritional requirements.  This post will cover:

• Natural Diets of Lacewings
• Nutrient Requirements
• Artificial Diets used in rearing

Natural Diets of Lacewings

Adults mostly subsist on sugar and pollen, although some species are omnivorous.  Larval prey includes:

• mites (Tetranychidae and Eriophyidae)
•  Hemipterans (from the suborder Sternorrhyncha, aphids of virtually all families, whiteflies, and psyllids),
• Auichenorrhyncha (families Cercopidae, Cicadellidae, Membracidae, and Fulgoridae),
• Lepidopteran eggs and larvae (families Noctuidae, Pieridae, Plutellidae, Pyralidae, Tortricidae, and Yponomeutidae)
• Psocids (Psocidae)
• Thysanopterans (thrips).

and less commonly:

• Beetle (Coleoptera) eggs and small larvae
• Dipterans
• Hymenopterans
• other Neutopterans

The numerous types of prey make up a diet that is nutritionally sufficient.  Some factors can lower prey value, such as the presences of absorbed allelochemicals.  Additionally, lacewings have a more difficult time consuming prey on plants with defenses, such as trichomes or waxy leaves, as they allow for less mobility and efficiency in prey location.

Nonpredaceous Adults 

Most adult lacewings don’t consume prey, and subsist off of metabolites from pollen, nectar, and honeydew (excreted by aphids).

Floral and extrafloral nectar serves as a source of sucrose, glucose, and fructose.  To a lesser extent, it is a source of protein, amino acids, lipids, antioxidants, alkaloids, phenolics, vitamins, saponins, dextrins, and inorganic substances (not all of these will necessarily be beneficial, however they all may be present).  Sugars make up between 15% to 75% of nectar weight. Amino acid concentrations range from 0.2 to 0.7 μmol/ml in nectar from trees and shrubs, and 0.4 to 4.7 μmol from herbaceous plants.  Nectar rarely contains the ten essential amino acids, but it is an excellent sugar source.

Pollen can contain 14 different carbohydrates (including common sugars), as well as a variety of other nutrients.  This is the main source for essential nutrients for reproduction, although it is supplemented by honeydew and nectar.  It can contain fatty acids and essential sterols, and proteins constitute 6-35% of pollen weight.  There are high concentrations of most of the necessary amino acids, except typtophan and phenylalanine.  Vitamins A, C, E, and many B complex may be present.

Honeydew contains sugars, some vitamin C, and B complex vitamins.  Amino acids may be present, however the concentrations will vary based on Hemipteran populations.  This is also a good strategy as it positions adults near a viable prey source for their newly hatched larvae.

Omnivory

Neonate larvae will also feed on nectar in pollen.  The reasons for this are not completely understood, however it could be due to a decrease in prey availability, or to supplement their intake of nitrogen and carbon.

Cannibalism

Larval and adult crysopids will engage in intraspecific (within the species) predation in the laboratory, usually only because food is scarce or unsuitable.  The most prevalent form of cannibalism is freshly hatched larvae climbing the egg stalks and then consuming them.  Additionally, females will sometimes eat their freshly laid eggs.  Larvae typically don’t try and eat eachother, possibly because the risk is likely to outweigh the reward.

Larval Consumption of Prey and Efficiency of Food Conversion

The third and final larval instar is when 75% of total food is consumed, and also represents most of the weight increase in the larval stages.  Lacewings convert their food relatively efficiently, however further research is needed to nail down a definitive conversion rate.  An estimate is about 40% to 60% gross conversion efficiency.

Nutritional Requirements

Chrysopidae have similar requirements to other predators, parasitoids, and some phytophagous insects.  They need about 30 chemical compounds, including:

• Protein
• Ten essential amino acids (arginine, phenylalanine, histidine, isoleucine, leucine, lysine, methionine, threonine, tryptophan, and valine)
• B complex vitamins (folic acid, nicotinic acid, pantothenic acid, biotin, pyridoxine, riboflavine, and thiamine)
• Water soluble growth factors (choline, inositol, and others)
• Fat soluble vitamins
• Cholesterol or phytosterol
• Polyunsaturated fatty acid
• Minerals
• Energy source (complex carbohydrates or lipids)

Larval Nutritional Requirements

*These studies all have a bias in that they are conducted in labs, on artificial diets.

Ten amino acids are required for molting, but many others could be removed without immediate adverse effects (at least for one generation).  This was discovered by Niijima (1989, 1993a,b) by starting with a diet of 23 amino acids, 17 vitamins, 11 minerals, 5 organic acids, 6 fatty acids, 2 sugars, a cholesterol, then removing amino acids and vitamins and observing the results. A 40% reduction in amino acids led to a much longer development time, and choline, absorbic acid, and some B vitamins proved essential for development.

Most artificial larval diets have failed in mass rearing systems, although Cohen and Smith (1998) developed a diet similar in composition and texture to prey, composed of beef, chicken eggs, sugar, honey, and yeast.  C. rufilabris larvae developed on this diet as well or better than natural diets, for 15 generations.  While this is more promising than other artificial diets, I would have to research it more before using it.  To me, it seems odd to base a diet on beef, considering insects generally have a superior conversion rate, however I’m not sure of the ratios or concentrations, and how sustainable it actually is.

Adult Nutritional Requirements

Females of all species require a protein source, or oviposition is not possible.  Other than that, much is still unknown, and this may be an avenue for my own research in the future.  Reproductive potential is often much more weighted on the larvae’s diet, and can also be dependent on dietary timing (whether it had a carb or sugar rich diet pre-diapause)

Additionally, the gut contains yeast symbionts that may synthesize amino acids, so nutritional requirements can vary by locality and over time.

Adult lacewings are generally fed artificial diets in rearing settings, and are generally low cost, efficient, and effective.  In some species, they do lower reproductive capacity, however this is likely to vary.

 

Conclusions

Lacewings natural diets can be quite varied, feeding on many different types of prey to meet all of their nutrient requirements.  In my own rearing setting, I was planning on using one species to feed them, and this may create less effective adults, so I’m thinking about how I can vary and supplement this, and possibly about nutrient trials, where I would monitor development and reproductive success based on which prey was presented.