07/06/2013

After the rain the heat. It ‘s time to think about mosquitoes

Like every year, from March to November, municipalities and individuals are engaged in the mosquito treatments whether larvicide or adulticide.

The first one, eliminate the insects in the larval stage so as to limit the growth into the adult stage; the adulticide treatment, has the function of breaking down the existing population.

While the former is typically done with effervescent tablets to dissolve in areas where there are water stagnation – carrier element for mosquito breeding – the adulticide treatment can be performed through the spraying of a micro-emulsion distributed, preferably, with a mist-blower.

Mosquitos: only troubles?

Having said that, before moving on to the most practical treatment, it should be clarified that in any case, we are going to use products that may have harmful implications for humans, the environment and for what normally lives the environment.

Mosquitoes, Diptera culicidae whose  female have a biting sucking mouthparts, contrary to what is normally thought, have their own important role in the ecosystem.

Because of their diet based on plant nectar – only the fertilized female feeds on blood, allocating the protein of the latter to the maturation of the eggs before their deposition – they are an important vector of pollination for the plants. The grubs are a food source for fish, and when, before the emerging from the cocoon, they reach a more mature stage, they become appetizing to birds, bats, amphibians and various other insectivorous animals.

We are not suggesting a ‘peaceful coexistence’ with these pesky insects and in some cases dangerous to human health; the suggestion is to act wisely and consciousness, aware of the fact that we are going to use substances not without negative effects on the environment and human health.

Which are the mosquitoes in Italy?

Throughout the country there are about seventy different species of mosquitoes, each one with different characteristics habits. Trying to know the major species is not a mere entomological exercise , but an important and useful information to intervene with the utmost efficiency and the lowest environmental and economical  impact

In recent decades, to the common mosquito that makes its appearance at dusk – Culex pipiens – light brown in color, active at night and in the early morning, was added a few diurnal species – caspius Aedes albopictus – the latter known as tiger mosquito, black with white stripes, the more nasty and aggressive, introduced by the United States with loads of used tires. Of Asian origin, due to the ability of its eggs to overcome the severe winter temperatures, has rapidly spread throughout the country. Fortunately they  little flies and for that reason you can narrow down the infested area, by contrast, even small amounts of water, permit the reproduction.

it is up to the provinces and regions, finally, the containment of the mosquito of the paddy field – Ochlerotatus caspius – brown with light streaks, able to fly for several kilometers and active, especially at night when it moves in swarms.

A curiosity, the vibration of the wings is characteristic of virgin females and it is emitted from a stridulating organ located at the base of the wings. This hum is only felt by young males who are attracted for mating stimulated, then, by a pheromone aphrodisiac.

Larvicides Treatments

This type of intervention is characterized by a high degree of effectiveness: one get to hit even 85 percent of the population.

The mosquito as we used to know, before taking on the appearance of winged insect, passes through the stage of grub, with four molts, becomes pupa to accomplish finally, the metamorphosis that will transform it into an adult.

The grub feed with organic material present in the water, for this reason, ponding water, sheltered from the sun, with the presence of leaves, wood or other organic materials represent the ideal breeding habitat and should be avoided.

The process that, starting from oviposition leads to the adult stage, has a variable duration depending on the species the environmental temperature, whose  phase of maximum reproductivity is about 7-14 days.

Among the products you can use, we mention the growth regulators with larvicidal ovicidal action and  products whose biological active ingredient is protein-based. To mention a few, belong to the first type the Pyriproxifen Diflubenzuron – name of the active ingredients – that act on hormonal mechanism at the basis of the molt and have a persistence of about three weeks, but are not selective, that is they act indiscriminately hitting even other insects and crustaceans. It is of the second type the Bacillus thurigensis israeliensis variety characterized by a lower environmental impact compared to the first and of most common use. It is a bacterium that produces an endotoxin or a crystal that ingested by the grubs frees the real lethal toxin. Due to its biological nature it is rapidly degraded, so the treatment should be repeated every 7-10 days.

Adulticide treatments

These treatments have an immediate effect in the short term reducing the population present at the time of treatment and are usually implemented with Pyrethrum-based products. it is good, at this point, to emphasize the difference between Pyrethrins – natural compounds extracted from chrysanthemums with insecticidal properties used in household insecticides – Pyrethroids – synthetic insecticides much more toxic persistent in the environment that unlike Pyrethrins are not photolabile. The most common are permethrin, cypermethrin and deltamethrin; Pyrethrins Pyrethroids are one of the most widely used insecticides.

In order to make  the treatment effective it is good to identify the time slot in which carrying them out out also considering the specie of  mosquito to hit. If we’re going to act towards common mosquito – Culex – it will be good to intervene in the early hours of the evening or at dawn, in case the target was the tiger , the late afternoon is the best time.

The treatment, whose frequency will be quite close in most critical months – from April to October – can be done with different mechanical systems.

The advantage of a knapsack lies in its ability to distribute the product in a targeted and accurate way either  in areas  that are not so wide, in areas difficult to reach by the means carried and therefore less agile. The use of a  mist blower also has the advantage of exempt the operator from the drudgery of pumping, implicit in the use of knapsack manual even if it were gardens or small plots.

In addition, thanks to the micronization and the air that acts as a carrier for the chemical and creates movement in the vegetation, better results can be obtained.  This is even more true in the mosquito treatments that  during the hottest hours they find shelter in areas of dense vegetation.

The contact between the mosquito and the product used,  may take place both during the flight of the insect either when it is laying on the surface of the treated plant.

Of course, should be carefully observed the doses indicated on the product chosen to be distributed on vegetation, up to two meters of height along the perimeter sides avoiding the areas of sunny lawn where would have little or no use. Also in this case the device is valid for all pesticide treatments: the product will distributed in very windy days or in days or weeks in which rains are foreseen.

When it is appropriate  to effect the treatment?

From November to March, temperatures can only do their part; periods of a few days – 2 or 3 – below ten degrees Celsius, can indeed neutralize the tiger mosquito eggs; since March, when temperatures rise above 10 degrees, and the photoperiod lengthens, it is time to act the prevention practices such as mosquito magnets and larvicides but also being careful to eliminate standing water, covering the bins for the collection of rainwater, weekly emptying into the ground and not in the drains water from saucers, small troughs, watering cans or other containers and ensuring a periodic cut of the grass. In June, the heat and humidity cause a veritable explosion of these insects. At this point, if you have done a good treatment before, the situation will be livable, otherwise you will have to make  the practices of sanitation views on adults.

In late August, the peak of infestation reaches its maximum level but from here until the following year, the way will be down , with the end of summer and the onset of lower temperatures, in fact, the presence of these insects diminishes until they disappear.