Medfly eggs as food for mass production of the minute pirate bug Orius laevigatus

Introduction

Orius laevigatus is a generalist predator used successfully as a biological control agent against several crop pests worldwide. At BioBee Sde Eliyahu Ltd. we have developed a commercial highly efficient mass rearing system of this predator, which peaks at a capacity of 40 Million individuals per week. Traditionally, mass rearing of O. laevigatus at BioBee is based exclusively on eggs of the Mediterranean flour moth, Ephestia kuehniella as a food source for juveniles as well as adults.
BioFly, a subsidiary of BioBee, specializes in mass production of the Mediterranean fruit fly (Medfly) Ceratitis capitata for the use in SIT projects. BioFly has developed a unique, patented, process to turn harvested Medfly eggs into food of high nutritional value for predatory insects, with a long duration of storage capacity.
In the study reported herein the quality of processed Medfly eggs as an alternative food for Mass rearing of juveniles and adults O. laevigatus was examined in comparison with E. kuhniella eggs, at low and high feeding rates. Further, the effect of different storage duration was tested under different feeding regimes, and finally, we examined the possibility of different mixing rates between E. kuhniella eggs and medfly eggs.

Feeding experiments with Medfly eggs

All trials were conducted at Bio-Bee in O. laevigatus mass rearing facility on an industrial scale.

Experiment 1- Effect of diet source on juvenile’s development and adult’s survival: The effect of diet type (E. kuhniella eggs/ Medfly eggs) and the amount of food presented (high/low) on development and survival of O. laevigatus was tested. Each treatment was replicated 3 times. Ca. 35,000 newly hatched nymphs of O. laevigatus were fed with each of the above mentioned treatments in each experimental unit. By the end of nymphal development the bug’s yield was assessed.
To test the effect of juvenile diet on adults’ shelf life, 90,000 adults from each treatment were then stored for two weeks at 11oc, after which the percentages mortality was determined.

Experiment 2 – Effect of diet source on fecundity: to test the effect of diet source on the bug’s fecundity, nymphs were reared either on E.kuhniella eggs or Medfly eggs. Once reached adulthood, 20 couples of adults obtained from each diet type were used for assessing fecundity in individual arenas. In addition, industrial production units were established in which the adult bugs were fed with the same diet they had as juveniles and the total amount of offspring produced from each diet source was assessed.

Experiment 3- Effect of 8 month storage on Medfly egg’s quality: A similar experiment to experiment No.1 was conducted; however this time Medfly eggs were stored 8 months under deep-freeze conditions.

Experiment 4- Effect of Mixing Medfly eggs and E. kuhniella eggs: similar to experiment No.1 with additional two treatments of mixing between the two eggs sources. In one treatment, O. laevigatus were fed with a mixed diet in a ratio of 70% Medfly eggs and 30% E. kuhniella eggs, throughout the nymphal stage. In the second treatment the newly hatched O. laevigatus nymph were fed for the first few feedings with solely E. kuhniella eggs diet and then diet was switched to solely Medfly eggs, until reaching adulthood. In that way E. kuhniella comprised 30% and Medfly eggs comprised 70% of total feeding amount during the nymphal stage. Each treatment was replicated 5 times, with Ca. 38000 O. laevigatus nymphs in each experimental unit.

Results

Experiment 1:
Juvenile development: The yield of bugs on the different diets was significantly lower when fed a low amount of food; however, was it remained similar between different types of diet (fig. 1).
Storage: No effect of juvenile diet on adult’s storage was found; the rate of mortality was low in all the treatments and did not differ significantly (fig. 2).

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Experiment 2- Fecundity:
Individual arenas – No significant differences were found in the amount of eggs deposited by a single O. laevigatus female from the different treatments (fig. 3).
Industrial production – The offspring production of industrial units was similar between the different treatments regardless of the juvenile diet used (fig. 4).

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Experiment 3- Storage effect on Medfly egg’s quality
The number of bugs produced was significantly lower when fed a low amount of food, but was similar between different types of food (fig. 5). Mortality rates were negligible in all treatments.

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Experiment 4- Different mixing of Medfly eggs with E.kuhniella eggs
The two strategies of mixing Medfly eggs with E. kuhniella eggs yielded the same offspring numbers, which were also similar to the yields of each egg source individually.

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Conclusions

Medfly eggs proved to be an eligible alternative food source for mass rearing of the predatory bug O. laevigatus both as a standalone product as well as mixed with E.kuhniella eggs. Medfly eggs attain the advantage of preserving a high nutritious value after a storage period of at least 8 months, under standard deep freeze conditions.