Management of Diaphania hyalinata caterpillars in Japanese pumpkin cultivation

In February 2014, the Embrapa Clima Temperado Entomology team was called to learn about an unusual occurrence in Capão Seco, Barra Falsa road, 3rd district of the municipality of Rio Grande, Rio Grande do Sul (31º51'09.01''S, 52º18'45'20''0), property of Jorgina Vaz Ávila: a large outbreak of caterpillars in a field of approximately one hectare of Japanese pumpkin. The farm was located in a region of flat land (4m above sea level), where the main agricultural activity is dairy farming and rice cultivation. Around the area there was a small forest, marshes and a hose for cattle, next to the owners' residence.

According to reports from the owners, the caterpillars would have come from the region where the wetlands are located. At first, the team, upon approaching the area in question, noticed that the general appearance was that someone had sprayed herbicide on the crop, as it had a yellowish-golden color, as if it had been burned. Practically the only plant parts that could be seen were the petioles of the vast majority of plants and some fruits. In a small area, some plants still had leaves that were being devoured by caterpillars. The owner reported that, initially, a dark spot on the crop could be seen from afar, appearing to be due to some disease.

When approaching the crop, the owner was able to see what was happening, that is, that it was not a disease but rather the presence of many caterpillars in the crop. She recommended that family members, who work on the property, immediately harvest the fruits, fearing a great loss, as wherever the caterpillars passed, they “devoured everything”. And she was not mistaken, as in around five days the crop was practically decimated by the caterpillars. The owner reported that the outbreak was happening in bands and the fruits, as they were being harvested, were left at one point in the field, waiting to be collected later, long enough to be completely infested with larvae, such was the infestation in the area. After learning about these facts, some larvae were examined more carefully, and it was suspected that they were caterpillars. Diaphania sp. When walking among the fallen plants, some adults were found on the plants, in small quantities, confirming that it was the species Diaphania hyalinata (L. 1758). This species is distributed from Canada to South America and is a key pest of cucurbits, being studied mainly in crops of economic interest such as melon and watermelon.

As they belong to the order of Lepidoptera (butterflies and moths), they go through the stages of egg, larva (or caterpillar), pupa (or chrysalis) and adult during their life cycle. The larvae stage is what causes damage, as they attack leaves, new shoots, branches, flowers and fruits not only of pumpkins, but also of melons, watermelons, cucumbers, loofahs and gherkins. The presence of this caterpillar can be seen in large quantities, mainly inside the stems, where they feed. Attacking the branches can induce drought in the aerial part of the plant, but in this case what was observed is that, due to the very large number of caterpillars, the first food consumed was the leaves and, later, the petioles. Then, it was time for the fruits. The attack occurred massively, with hundreds of caterpillars initially scraping the seed coat and then delving deeper into the plant's tissues until its complete destruction. The larvae go through five larval instars and, when they reach their maximum size, they reach around 20mm in length. They are light green in color with two white dorsal stripes. When they pupate, they look for decomposing organic material, where they weave a cocoon and transform into a pupa. In the vegetation surrounding the pumpkin crop, a large number of pupae were observed among the leaves of trees and bushes and also caterpillars looking for a place to pupate, joining two leaves or folding the edges of the same leaf, one over the other, to pupate between them. . Dozens of pupae were found D. hyalinata in sudan grass [Sudanese sorghum (Piper) Stapf.], Capsicum sp., wild smoke (Solanum mauritanum Scop.) and camboim (Eugenia crenata Vell) probably due to the fact that there is no longer any pupation site in the farming area, due to the destruction of pumpkin plants. In general, the larval stage lasts six to eight days. The adult of D. hyalinata It is a moth with white wings, with a straight dark brown stripe on the edges, except for those on the hind wings. On the last abdominal segment there is a tuft of dark bristles. They can reach a wingspan of 30mm. The duration of this phase varies from three to 16 days. They lay eggs singly or in small groups on leaves, flowers and fruits. The incubation period is four days at 25 ± 1ºC. The newly hatched larvae feed on leaves, stems, flowers and fruits. The life cycle lasts 27 to 34 days.

Cucurbits represent around 20% of vegetable production in the world and are a source of income for many farming families. D. hyalinata causes economic losses in cucurbit species in the various countries where its occurrence is reported. On the property in question, losses were in the order of 80% of production. On family production properties, generally no type of control is carried out. In commercial production, control is generally carried out over the larvae that feed on the leaves, with the application of insecticides, normally not recommended, given the reduced number of products recommended for the crop and the non-availability of these pesticides, often , in local commerce. This has favored outbreaks of other pests. There is a lack of knowledge about the factors determining the attack of this pest. In this sense, studies to understand the population dynamics of this species, which factors affect the intensity of attack on cucurbits and their relationship with the climate and natural enemies, are of utmost importance, as they will serve as a basis, together with other methods, for the integrated management of this insect. Furthermore, damage and control level studies are also very important, providing data for decision making.

Cucurbits, as they are important sources of food for several species of insects and dependent on pollinators, require studies of products with low environmental impact. Along these lines, the Bacillus thuringiensis has shown good results in controlling this insect. Various works in the line of resistance of cucurbit species, testing with products of plant origin, with low environmental impact, cultivation systems (rotation and staggering of sowing), use interspersed with trap plants and their effects on the incidence of pests and their bioregulators have been carried out. It is recommended to destroy the parts attacked by the pest as part of the insect management process. But the suggested methods will only be effective if the producer carries out periodic and systematic monitoring of the crop, as insects require continued attention, otherwise they will cause damage to production. Awareness about the events that occur in the field is a fundamentally important factor for the adoption of efficient control measures.

This article was published in issue 88 of Cultivar Hortaliças e Frutas magazine. Click here to read the edition.