The ability of D. However, the fact is that the South American pest Diabrotica pose different problems to the North American species. Almost exactly the reverse of the oviposition preference. Corn rootworm rearing methodologies. Multivoltinism and lack of egg diapause was demonstrated for the three species, and field data suggest other South American species present the same traits.
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Coleoptera: Chrysomelidae: Galerucinae , and other Diabroticina are described. These Diabroticina are pests of several crops in South and Central America. The adult feeding hosts were compared, among species, and within species in different seasons. Laboratory oviposition and larval development tests on several hosts, provided the basis to construct a table of putative hosts, and general reproductive traits related to two species groups of Diabrotica virgifera and fucata.
Eggs of D. Multivoltinism and lack of egg diapause was demonstrated for the three species, and field data suggest other South American species present the same traits. Diabrotica speciosa fucata group larvae developed well on maize Zea mays L.
Merrill roots, and not so well on pumpkin Cucurbita maxima Duchesne and Cucurbita andreana Naudin , beans Phaseolus spp. Oviposition preferences roughly paralleled larval suitability, but there was a clear preference for cucurbits as adult food, when available; pigweed Amaranthus quitensis Kunth , sunflower Helianthus annuus L. Diabrotica viridula virgifera group , preferred maize as adult and larval food, and for oviposition. Acalymma spp. Other species showed varying degrees of preference for oviposition and feeding, but in general, cucurbits were the preferred adult feeding hosts, followed by several wild plants, and maize the preferred oviposition host.
Whereas cucurbits were consistently visited by the adults of every species, the virgifera group species oviposited and developed exclusively on Monocotyledonae. However, D. This new knowledge on South American Diabroticina is discussed in the context of the current knowledge on North American Diabroticina. Differences and similarities are discussed in connection with their pestiferous status, and their potential for adaptation to new hosts.
Of these, the genus Diabrotica Chevrolat includes the greatest number of pest species, including some of the most important row crop and vegetable pests of the Americas, be it the foliage, fruit- or flower-feeding adults, or the root-feeding larvae. In South America, the most common and problematic species is Di-abrotica speciosa Germar.
The adults cause important damage in maize Zea mays L. Merrill , and damage to the tender parts of almost every crop Christensen , Link and Costa They may also transmit bacterial wilt in cucurbits unpublished data.
Although the effect of the larvae on the crops they feed on has not been evaluated rigorously, there is sound evidence that they seriously damage maize, potatoes Solanum tuberosum L.
Sarasola et al. Diabrotica speciosa belongs to the fucata group of Diabrotica, to which the North American banded, spotted or southern corn rootworm , and western spotted cucumber beetles belong Diabrotica balteata LeConte, Diabrotica undecimpunctata howardi Barber, and Diabrotica u. Another group within the genus, the virgifera group, includes the northern Diabrotica barberi Smith and Lawrence , western Diabrotica virgifera virgifera LeConte , and Mexican Diabrotica v.
The sole South American species of this group considered a pest is Diabrotica viridula F. Species such as Acalymma albidovittata Baly , Acalymma bivittula Kirsch , and Acalymma bruchii Bowditch , often reach very high populations on cucurbit cultures, causing significant damage to flowers, foliage, and young fruit unpublished data. Reproductive traits, natural larval hosts, adult feeding and oviposition hosts, and overwintering mechanisms of the different species of Diabroticites, present certain generalizations that can be extracted from former studies: the virgifera species larvae studied up to now show a strict association to both cultivated and wild Monocotyledonae, and although generalist feed ers as adults, they are still more abundant on cereals than cucurbits, forbs, or vegetables Branson and Ortman , , However, at least one species in the group, D.
Species of the fucata group, however, are generally multivoltine, polyphagous, and are not known to have species with diapausing eggs, but rather overwintering adults Krysan and Smith They are more commonly associated with cucurbits, allegedly the ancestral host of the Diabroticina, and, at the same time, more generalists both during the adult and immature stages.
Another relatively unexplored area of the behavior of Diabroticites is the relationship between oviposition and feeding preferences. Although Diabroticites will oviposit on several moist substrates, such as sand, soil, cotton wool, and paper, the presence of fresh food, and especially the larval host, will greatly stimulate oviposition Branson et al.
Furthermore, the larvae seem to be unable to choose a suitable host other than by taste Branson and Krysan , Bernclau and Bjostad This unspecific behavior, would be compensated by the narrow oviposition host range observed so far in the species of the virgifera group Branson and Krysan , a trait of unquestionable adaptive utility in a natural environment, where adequate hosts may grow disseminated.
However, all these studies deal with North American Diabroticina, but their extension to South American species is yet to be confirmed. The host preferences and ecology of D.
Relevant related data on other Diabroticina collected in the field, and reared in the laboratory for natural enemies and biology studies, are also presented.
Special emphasis was placed on the adult, larval, and oviposition host ranges, and egg and adult overwintering strategies. Materials and Methods Field Collections and Observations The beetles used for observations, and to establish laboratory colonies were collected with sweep nets, funnels, and aspirators on at least 20 cultivated and wild host plants: mainly cucurbits, maize with fresh pollen and immature ears, and sunflower.
Together with these methods, polyester cloths sprayed with root or berry extracts of the wild, perennial cucurbits, tayuya Cayaponia spp. Also, data on adult feeding hosts, and host range shifts related to the season, were gathered through direct observation in the field. The favorite adult hosts of D. The proportion of beetles of each species per host was calculated, and averaged for every site per season.
The average proportion of beetles collected on each host per season was taken as a measure of host preference. Laboratory Rearing and Handling Adults, both field and laboratory reared beetles, were kept in cages: up to beetles in 1.
Diabrotica speciosa, D. Young beetles were provided thin slices of raw squash as fresh food to increase survival. The other species collected were also offered a meridic diet, but they survived better on squash slices and seedlings unpublished data.
Water was provided from ml plastic cups with cotton wicks through the lids. Tests on oviposition preference were performed using these cups with maize, cucurbits butternut squash Cucurbita pepo L. Potato plants were tested in ml containers, to accommodate the germinated tubers. Maize was considered the control host for Diabrotica spp. Moist cloth squares alone were also offered, and considered second controls to compare with the rejected, or nonpreferred, putative hosts.
In preliminary multiple-choice experiments, where several putative hosts were offered simultaneously, oviposition was greatly reduced, and results were inconclusive unpublished data.
When possible i. Larval Host Range The larval host range was tested for D. The larvae were incubated on seedlings and sprouted tubers in the case of potatoes, C. Then 60 seeds, or one sprouted tuber, were buried in the container. Finally, — eggs, depending on the number of eggs available, were pipetted from a beaker, and spread on the culture. The container was covered with a plastic lid that had a 4-cm opening covered with a fine mesh.
The timing for sowing the eggs was dependent on the host plant. For corn, squash, and beans, eggs, and seeds were sown at the same time, because the root mat was adequately developed by the time the eggs hatched Cabrera Walsh For the other plants the eggs were not scattered until an important root mat had formed, which could be between 1 wk and 25 d, according to the species.
The number of adults emerged, the time lapse from egg to adult, and the emergence span average range in d from the first to the last adults emerged was considered to indicate the suitability of each host. A minimum of five replications were tried for each species on each putative host. Plants with zero larval survival were not tested again, the others had 10 more repetitions.
Neither all the plant species, nor all the beetle species could be tested at the same time for reasons of space, egg or host plant availability. However, every plant species was tested alongside with maize as a control host for Diabrotica spp. Wild and cultured cucurbits, grain crops, pasture crops, and wild species that are common hosts of adult Diabroticites, were sampled from the year to the year , to verify larval hosts in the wild.
The plants were pulled or dug up, and the roots, and the soil surrounding the roots were shaken onto a white canvas, and visually inspected. When any chrysomelid larvae were found, they were placed in a maize seedling culture, and transported to the laboratory for identification.
For this, five 1-d old cohorts of around 1, D. The production of diapausing eggs was also tested for D. Six colonies of D. Ten colonies of D. Five colonies of D. At least species in 24 families were examined in southern South America, and found to host feeding adult beetles at least once Table 1. The results in Table 2 , indicate the favorite hosts of D. However, because not all the hosts were present at each collection site, the average proportions do not necessarily sum 1.
The best collections of D. This pattern held during fall, although alfalfa and soybeans were regularly found to host a large proportion of beetles as well. In winter, however, a drastic shift was observed, being pigweed, maize silks, leaf vegetables, especially spinach SpinaciaoleraceaL.
Table 1. Table 2. Host preference of D. Table 3. Host preference of several common Diabroticites according to season a Measured as the avgerage of proportions of beetles collected on each host per hour, per person. Open in new tab The results in Table 3 show the favorite hosts of the other common Diabroticina, in terms of average proportion of beetles per host, in different seasons.
Again, however, not all the hosts were present at each collection site, so the average proportions do not necessarily sum one for all the hosts for each species. Diabrotica viridula, of tropical and subtropical distribution, was found more on maize mainly silks, but also tassels than cucurbits, as compared with D. In winter it was only found on maize silks.
The collection data of this species Table 3 , show a polyphagous species, but more closely associated to maize than D. All the species of Acalymma sampled were found exclusively on cucurbits. Diabrotica limitata, was consistently found on pumpkin and maize silks, and only maize silks in winter. Diabrotica emorsitans was consistently found on pumpkin and tayuya, and in D. Oviposition Host Range Clear preferences were observed in the number and regularity of eggs laid on the different hosts.
Because of the lack of sufficient field beetles, not every host chosen could be tested on all the species, only the ones reared at the laboratory. Diabrotica speciosa significantly preferred maize over C.
EPPO Global Database
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