The Common green lacewing (Chrysoperla carnea Stephens, 1836) is an insect belonging to the Chrysopidae family.
From the systematic point of view it belongs to the Eukaryota Domain, Animalia Kingdom, Subarign Eumetazoa, Phylum Arthropoda, Subphylum Tracheata, Superclasse Hexapoda, Insecta Class, Subclass Pterygota, Endopterygota Cohort, Superorder Oligoneoptera, Subphylum Tracheata, Superclasse Hexapoda, Insecta Class, Subclass Pterygota, Endopterygota Cohort, Superorder Oligoneoptera, Neuropopteroidea Section, Order Neuropidae to the genus Chrysoperla and to the C. carnea species.
Geographic Distribution and Habitat –
Chrysoperla carnea is an almost cosmopolitan species, also present in cold regions.
In Italy it is one of the most common Chrysopids and its most favorable natural is represented by the vegetation, spontaneous or not, infested by aphids, even if due to the polyphagous dietary regime, the chrysopus adapts easily also to the predation of other small phytophages, in particular other Rincoti and micro lepidoptera. In cultivation it adapts better to plantations that form a continuous vegetation along the row and tends to desert the species that have pubescent leaves and shoots.
Due to its characteristics as a predatory insect, it is also bred in various biofactories in America and Europe for use in biological control, mainly in protected crops, but it is also very common in nature in agroecosystems where there is no massive use of pesticides.
The adult of the Chrysoperla carnea is recognized by the body of medium size, slender and delicate, with an inconspicuous livery among the vegetation, also due to the presence of green-yellowish tones; the color is uniform light green, devoid of spots, with a dorsal yellow streak extending longitudinally over the whole thorax and abdomen. It has a hypognato head, with small, prominent, well-spaced and reddish-brown eyes; the antennae are filiform and elongating, about as long as the rest of the body; the mouthparts are chewing.
The thorax of this insect is slightly wider than the head and abdomen and has an elongated pronotum.
The legs are slender and the transparent and iridescent wings, richly branched; in rest they are folded over the abdomen. The wingspan is 2.5-3 cm.
The abdomen is cylindrical, clearly shorter than the wings.
The larva is campodeiform, elongated and fusiform, with gray-brown colors, provided with three slider legs. At the dorsal level it is crossed by a very thin brown streak and laterally by two series of tuberculous prominences, also brownish in color.
The larvae of the first age are just 1 mm long while those of the later ages are 7-8 mm to 10-15 mm long. The forceps, the pungent-sucking mouthparts are always evident.
The formation of pupae takes place inside a small white cocoon, built with the silk secreted by the Malpighian tubes of the larva. The pupae are mobile and have articulated jaws; at maturity these leave the cocoon and move to fix themselves on a support before flickering. The mobile pupa (farata phase) is in fact an intermediate form between the quiescent pupa and the adult insect; moreover, from the morphological point of view it is very similar to the adult, from which it differs for the absence of wings.
The egg is the typical one of Chrysopids, oblong in shape and supported by a thin peduncle. The eggs are laid isolated or in small groups of 2-3; these, initially, are greenish, but then turn to gray-brown. The biological function of the peduncle is to protect the egg from the action of natural antagonists, in particular ants.
Attitude and Life Cycle –
The biological cycle of Chrysoperla carnea is subject to climatic trends and latitude. In the warmer regions it carries out its cycle uninterrupted, while in the temperate regions it completes from 2 to 4 generations a year (2 in central and northern Europe, 3 in northern Italy, 4 in southern Italy and the islands).
The insect overwinters at the adult stage which enters diapause surviving for up to 9 months, but during the favorable season, a female has an average duration of two months.
In Italy, in open field conditions, the period of intense activity goes from the month of May to the month of September, while in the other months the predator’s activity is significantly reduced until it stops completely, even if the insect is present in the ‘environment.
It should be emphasized, however, that this insect also resists strong drops in temperature, close to zero, as long as they are limited to a few hours during the day, so it can also be used to combat Aphid infestations in spring, when the auxiliaries natural are not very active, and, in southern Italy, in a cold greenhouse during the winter.
In any case, predatory activity manifests its greatest intensity around 27 ° C.
Ecological Role –
The Common green lacewing is a predator at the larva stage and is one of the most interesting species in the biological control sector due to the remarkable activity of the larvae, especially in the fight against Aphids. In general it is an active predator of aphids, mites, lepidoptera, beetles, scale insects, on different crops (cotton, potato, vegetables, strawberry, olive, etc.).
The natural presence of Chrysoperla carnea in agroecosystems is a prerequisite for the adoption of the protective method both in biological and integrated pest management. Furthermore, the possibility of mass breeding this species makes it interesting especially for use with the flooding method.
However, it must be emphasized that the mortality of this insect is high in 1st age larvae, which represent the most vulnerable stage. Among the main natural antagonists of Chrysoperla carnea are the ants which, in their general defense action against aphids, are in fact active both in the destruction of the ovature and in the removal of the larvae from the aphid populations.
However, the major risk factor is the use of chemical phytosanitary treatments. The greatest sensitivity is shown towards insecticides and acaricides, while fungicide treatments are generally harmless, except for pyrazophos.
For the survival of this predator, and therefore for its action of containment of insects potentially harmful to some agricultural crops, insecticides are the chemicals with the greatest impact; in fact this predator is particularly sensitive to a wide range of active ingredients, at the stage of larva or adult or both, including, in this range, both those with a broad spectrum of action and various substances with selective action and, therefore, theoretically compatible with the principles of integrated pest management.
In particular, broad spectrum insecticides, including almost all phosphoric esters and pyrethroids, are active both on larvae and on adults. For this reason, the use of these biocides should be avoided regardless as they are generally incompatible with integrated pest management. Only very few phosphorganics are exceptions (eg vamidothion), showing a weak or moderate toxicity towards adults.
Furthermore, the new generation insecticides, which due to their selective mechanism of action are low-impact principles, can represent a serious risk factor because many of them are active against the larvae. This problem is particularly noticeable for organic nitrogen chitin inhibitors, generally used in the integrated control against Lepidoptera and Coleoptera larvae. These active principles act by inhibiting the biosynthesis of chitin and therefore prevent the moult and the completion of the post-embryonic development of the phytophages. Highly toxic have proved to be, for example diflubenzuron, lufenuron, teflubenzuron, while moderately toxic is for example buprofezin.
As for white oils, on the other hand, they show low toxicity, even if they are active in particular on eggs. In any case, those activated with phosphorganics should be excluded, given the general toxicity of the latter.
It is then underlined that the use of aficides or, more generally of systemic insecticides, is the most important aspect, given the close association between this predator and aphids. For these insecticides two types of problems must be taken into consideration: on the one hand there is the problem of the exclusion, a priori, of non-selective active ingredients (e.g. imidacloprid, acephate, endosulfan, etc.) on the other there is that of frequent induction of resistance in aphid populations. In general, therefore, the field of use of the aficides is considerably reduced as the few compatible active ingredients must be discarded, due to the ongoing existence of resistance phenomena, or limited to one treatment per year, to limit the risk. to generate resistance phenomena. This problem occurs in particular in case of heavy infestations and insufficient activity of the auxiliaries.
Among the biotechnological insecticides, rotenone and abamectin, active in particular on adults, are cited as toxic. Bacillus thuringiensis deserves a special mention. The literature cites this biological insecticide as compatible with biological and integrated control and its specificity of action in general makes it harmless towards auxiliaries. However, a mortality rate of 66% was found in chrysopa larvae fed with surviving Ostrinia nubilalis larvae raised on BT transgenic maize. This toxic action of the BT corn has been confirmed by some researchers and could represent a serious limit to the use of Bacillus thuringiensis in a context of compatibility in the biological control conducted with the use of chrysopes in general. However, it should be noted that the communications relating to the role of the Bacillus thuringiensis toxin draw conflicting and not fully shared results.
Finally, it is emphasized how the impoverishment of environmental biodiversity, linked to intensive farming techniques and the continuous elimination of spontaneous species and ecosystems, is to the detriment of this predator as all the chrysopes, as polyphagous predators, benefit greatly from presence of spontaneous vegetation in agroecosystems, on which to complete their cycle at certain times of the year. The strong crop specialization, the elimination of the hedges, the weeding, are in general elements that hinder the spread of the chrysopes. However, this is a general concept that falls within the general guidelines relating to integrated production and, above all, in the future application of agroecology.
For the diffusion of Chrysoperla carnea in the needle ecosystems, two methods can be followed, namely that of flood launches and that of inoculation launches.
– for the use of Chrysoperla carnea in flood launches, the effectiveness varies according to different conditions, such as the type of crop, the incidence of mortality factors, the intensity of infestations, etc. The best results are obtained by using 2nd age larvae in place of eggs, intervening on infestations of minor aphids, operating in greenhouses or tunnels. In this case, the launch of the predator at the egg stage is uncertain as the eggs are easily subject to predation by the ants and the 1st age larvae are subject to a high mortality from various causes. The tests carried out identify as the operational context an intensity of 80 eggs per square meter with a quantitative ratio of 1 chrysopa egg every 1-4 aphids. The launch of the predator, on the other hand, at the 2nd age larva stage offers better results as the larvae are more active and better overcome adverse conditions. In this case, the reduction of the randomness also allows casts with lower percentages.
– the inoculation method is useful for introducing this predator in environments from which it has disappeared, for various causes, or simply to increase the population by integrating the natural one. This method can prove useful to fight some phytophages of orchards and olive groves, against mites, aphids and scale insects, or against some Lepidoptera at the egg stage. The inoculation launches require lower densities than the flooding ones because it is assumed that the adults, once released by the artificially introduced larvae, reproduce, increasing the population. The condition, however, that the inoculation launches can be effective is that the guidelines that define the protective method as a whole are adopted and that, above all, the causes that have led to a decrease in the natural population or its disappearance have ceased.
Finally some hints on the mass farming method. In general, the mass breeding of Chrysoperla carnea includes three distinct lines:
1. Breeding the replacement prey.
2. Breeding of the larvae.
3. Breeding of adults.
Insects are marketed in the form of eggs or 2nd age larvae. In the second case, the price is higher, due to the higher production costs, but the overall cost of a launch remains substantially unchanged as the density, expressed as the number of individuals per unit of surface area, is reduced by an average of 75%. .
– Wikipedia, the free encyclopedia.
– Russo G., 1976. Agricultural Entomology. Special Part. Liguori Editore, Naples.
– Tremblay E., 1997. Applied entomology. Liguori Editore, Naples.