The culture and colonization of natural enemies are fundamental to biological control work. The three principal reasons for culturing parasitoids, predators, and pathogens are to provide field-release organisms for permanent establishment, periodic colonization, and inundative releases. Foods employed in rearing the hosts of entomophagous organisms are in decreasing order of difficulty of provision—living plants; harvested plant parts; tubers, fruit, and other produce; and prepared diets. The actual laboratory production of insects is dependent on the environmental conditions. Combinations of light, temperature, and humidity, as well as the sequences of these combinations, are particularly critical in managing the development of insects that undergo facultative or obligatory diapause. Obligatory diapauses, in particular, cause severe production problems, but both facultative and obligatory diapauses are useful for long-term insect storage. There are many and varied techniques for arthropod rearing. Stockpiling refrigerated hosts is very helpful and the determination of the effects of refrigerated host material on parasitoid and predator production must be on a case-by-case basis. Differential cold storage of the sexes is useful for synchronizing emergence, because males of most of the insects develop more rapidly than females and emerge first.

CHAPTER 7 – Culture and Colonization

Most Symphyta are phytophagous and lay their eggs in the host plant in contact with the plant tissue. We tested the hypothesis that Diprion pini L. egg hatching and larval survival vary between Scots pine clones with particular foliage characteristics. We also tested the influence of water limitation on hatching rates. Larval survival and hatching rate of D. pini eggs differed significantly among Pinus sylvestris L. genotypes and they were not correlated. We confirmed that the presence of taxifolin, a phenolic compound, and quantity of 3-carene were correlated with low larval survival. Foliage analysis showed an inverse relationship between hatching rate and dry matter content of foliage. The hatching rate on a tree varies, according to needle water content. This suggests that the success of egg development might be important for the population dynamics of D. pini.

Relationship of Scots Pine Clone Characteristics and Water Stress to Hatching and Larval Performance of the Sawfly Diprion pini (Hymenoptera: Diprionidae)

The sawfly, Diprion pini L., is a pest of Finns in Europe and is mainly found on P. sylvestris L. and P. nigra laricio Poiret. The relative importance of female oviposition capacity and behaviour, egg development, and larval survival on a new host plant was measured on 11 pine species. Five were natural host plants and six non-host plants, five of which are not indigenous to Europe. Oviposition choice tests showed that females discriminated between the pine species. Egg and larval development also differed between pine species. However, the female choice was not linked with hatching rate and larval development. Results of biological tests clearly indicated that there were different response patterns of D. pini life stages in relation to pine species, and these patterns were the same with insects of four different origins. We discuss the importance of each potential barrier to colonisation of a new host.

Preference and performance of the sawfly Diprion pini on host and non-host plants of the genus Pinus.

Summary

1 When laying eggs, adult female Diprion pini discriminated between clones of Scots pine, Pinus sylvestris.



2 Larval survival was affected by Scots pine clone but was not correlated with oviposition preference.



3 Diprion pini laid most eggs on tougher needles of Scots pine.



4 There was no evidence to suggest that D. pini is responding to the monoterpene composition of the foliage.

Oviposition preference and larval survival of Diprion pini on Scots pine clones in relation to foliage characteristics

Feeding bioassays were conducted on several Pinus sylvestris clones to establish if there were any differences in suitability for two pine defoliators: the sawfly Diprion pini L. (Hym., Diprionidae), which causes considerable damage in Europe, and the rare and protected moth Graellsia isabellae galliaegloria Oberthur (Lep., Attacidae). There were significant differences in survival, weight, sex-ratio and female fecundity of D. pini on Scots pine clones. However, sawfly survival appeared to be the most stable variable in time and three clone categories were revealed by conducting feeding bioassays on 16 clones. The survival of G. isabellae galliaegloria until the formation of the chrysalis was significantly different among clones. It varied from 35 to 75% but no clear clone category was distinguished. The two clone classifications according to insect survival showed differences. In particular, one unsuitable clone for D. pini development appeared to be favourable to moth development. The 3-carene richness of foliage was significantly linked with sawfly survival and the monoterpene composition of foliage was not linked with G. isabellae galliaegloria survival.

Variation in the suitability of Pinus sylvestris to feeding by two defoliators, Diprion pini (Hym., Diprionidae) and Graellsia isabellae galliaegloria (Lep., Attacidae)

Un elevage permanent de Diprion pini L. est obtenu en laboratoire a partir d'insectes provenant de Sologne et de la foret de Rambouillet au sud de Paris. Les insectes ont ete eleves depuis plus de 10 generations en ne reproduisant a chaque generation que des individus non diapausants et en maintenant les larves dans des conditions de photoperiode et de temperature propres a eviter la diapause

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C. Geri

Papers

Mise au point d'un élevage permanent de Diprion pini L. (Hym. diprionidae) en laboratoire