Some factors relating to the larval growth of the Colorado potato beetle, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), on artificial diets

A brief account of the history of the development of artificial diets for phytophagous insects is given. Some conceptions with regard to terminology are discussed (chapter 3).

Artificial diets for the larvae of the Colorado potato beetle, Leptinotarsa decemlineata Say, were developed and in addition some factors determining the feeding and rate of growth of the larvae have been brought to light.

Larvae of the four consecutive instars reared on a diet were compared concerning their feeding and growth response (chapter 4). From the increased feeding activity of the larvae of the successive instars it appeared that an advance in tolerance towards the diet was observed as the larvae grew older. In addition it was noticed that as being in an advanced instar, the larvae were better able to accomplish their development on the diet.

Because of the above mentioned phenomenon diets for the third instar larvae were based on the results of tests on the effects of various substances on larval growth (chapter 5). The nature of the substances tested as well as the concentration ratios of the dietary constituents appeared to be the most critical factors. Macro-molecular substances had to be included in the diet in view of the physico-chemical requirements for feeding and growth.

First instar larvae reared on the best diets formulated so far for the third instar, could only attain the third instar.

Non-aseptic rearing of newly hatched larvae on an autoclaved diet revealed that although palatability remained unchanged, the nutritive value of the diet was increased remarkably by heat treatment (chapter 6, section 6.5). Further experiments, however, are required to determine the factors causing this positive effect of autoclaving.

In many cases during subsequent experiments 50 % or more of the individuals reared on an autoclaved diet from the time of hatching attained maturity. Addition of potato leaf powder appeared to promote feeding; however, it has no effect on growth. Inclusion of fresh potato leaves in the diet at a level of 10 % led to an increased feeding activity as well as an improved growth rate. However, growth ceased after two generations on diets with or without crude material from the host plant.

In the present study it has been shown that ascorbic acid is required for larval growth. Commercial β-sitosterol, stigmasterol, cholesterol and ergosterol proved to be equally effective as sterol sources.

An aseptic rearing technique for studies of the nutritional requirements was also developed, however, without satisfactory results.

The improved quality of the diet by means of autoclaving enabled a mass rearing of larvae under non-aseptic conditions.

In the general discussion (chapter 7) it was concluded that in principle the Colorado potato beetle could be reared on an artificial diet without addition of specific substances from the host plant. The results of the present study support the general opinion that the nutritional requirements for phytophagous insects are qualitatively more or less similar, but differ to a great extent quantitatively between species.