Monophagous Insect Research Articles

New Host Plant Record for Toxotrypana curvicauda (Diptera: Tephritidae)

The papaya fruit fly, Toxotrypana curvicauda, has been considered to date a strictly monophagous species infesting wild and cultivated papaya (Carica papaya L.). Castrejon-Ayala (1987) reported infestations in another Caricaceae, Jacaratia mexicana A.D.C. (=Pileus mexicana) in the State of Morelos, Mexico. Baker et al. (1944) reported that T. curvicauda also infested a plant locally known as talayote or talayotillo but never provided any precise botanical identification. Here we report T. curvicauda infestations on Gonolobus sorodius A. Gray (Asclepiadaceae), locally known as pancolote. We collected 32 larvae of T. curvicauda infesting 6 fruit of G. sorodius during October, 1990 in Yautepec (Barranca Honda, San Isidro), Morelos, Mexico. Larvae, pupae and adults emerging from the larvae were sent to Vicente Hernandez (Instituto de Ecologia, A.C., Xalapa, Veracruz, Mexico) for taxonomic identification. Voucher specimens have been placed in the permanent insect collections of the Instituto de Ecologia, A. C. and the Centro de Desarrollo de Productos Bioticos del Instituto Politecnico Nacional. Taxonomic identification of G. sorodius was carried out by the Dept. of Botany at the Universidad de Morelos in Cuernavaca, Mexico. Our findings reported here confirm the report by Castrejon (1987), who also recovered T. curvicauda (not confirmed at the time) from G. sorodius fruit. Based on our findings, T. curvicauda should not be considered henceforth a monophagous insect. We thank Martin Aluja for reviewing and translating this note and Vicente Hernandez-Ortiz for identifying the T. curvicauda specimens reported here.

Jack of one trade, master of none: host choice by Drosophila magnaquinaria

Host selection by phytophagous insects is generally thought to be based on chemical or nutritional characteristics of the host. This is especially true for monophagous insects. However, many other factors may influence host choice. The present study examines host selection by Drosophila magnaquinaria, whose sole host is the yellow skunk cabbage, Lysichitum americanum. Utilization of skunk cabbage was tested relative to a set of alternative hosts. In the pre-alighting stage of host selection, skunk cabbage was found to be less attractive than tomato, cucumber, and commercial mushrooms. In pairwise oviposition tests, there were no differences among hosts. There were no differences in larval survivorship among skunk cabbage, tomato, cucumber, or Ramaria, and larvae developed into pupae earlier on tomato than on skunk cabbage. These results indicate that this monophagy is not based on characteristics of the host. We suggest that habitat selection is the more important factor in determining the association between D. magnaquinaria and skunk cabbage.

Leaf shape and the host‐finding behaviour of two ovipositing monophagous butterfly species

Abstract. 1. Ovipositing Eurema brigitta (Wallace) and Eurema herla (W. S. Macleay) butterflies were followed in the field to determine the nature and extent of the pre‐alighting discrimination shown by these insects towards their only host plant, Cassia mimosoides (L).2. Both species tended to search in areas where plants with long, thin leaves (primarily grasses) were less common, on average, than in randomly placed quadrats. Both species were also more likely to alight on non‐host plants with leaves of a similar size and shape to those of the host plant than on non‐hosts with leaf shapes dissimilar to that of the host.3. The search behaviour of these monophagous insects was not so specialized that the butterflies never alighted on non‐hosts; in fact the majority of alightings were on non‐host plants and the pre‐alighting discrimination shown by these insects is clearly not the prime behavioural determinant of their monophagy.

Geographic patterns in the flight ability of a monophagous beetle.

The migratory ability of a monophagous insect, Tetraopes tetraophthalmus (Coleoptera: Cerambycidae), was measured in ten populations in each of two regional types. In the first region, a river valley, populations were abundant and close together; in the second regional type, mountainous and peripheral areas, populations were uncommon and far apart. The data revealed that regional variation in migratory behavior occurred along two dimensions. Regions differed not only in the mean migratory ability of individuals (1st dimension) but in the amount of variation between populations (2nd dimension). Whereas river valley populations were found to be uniformly sedentary, mountainous and peripheral populations were found to be heterogeneous, some being very vagile, others being very sedentary. In the mountainous and peripheral areas, small and sparse populations were more vagile than large dense populations. The site to site variation in the mountainous and peripheral areas was due exclusively to females. In these areas, the mean migratory ability of females in a population was positively correlated with mean body size of the females, and inversely correlated with populations density. The data are consistent with the FLY hypothesis for this species (long distance migraters=Females, Large, and Young). Taken together, the geographical patterns support the "founding hypothesis" of migration. According to this theory, the inevitable selection against migration within populations is balanced by periodic extinctions of the populations and the founding of new populations by migrating individuals.

Sexual dimorphism in between and within patch movements of a monophagous insect: Tetraopes (Coleoptera: Cerambycidae).

Movements of milkweed beetles (Tetraopes tetraophthalmus and Tetraopes femoratus) were monitored using mark-release-recapture techniques to compare the within- and between-patch movement patterns of individuals in a naturally occurring population. Within-patch and between-patch movement patterns differ in both frequency and distance traveled for males and females of both study species. Males move farther than females and are more likely to move between patches. Individuals recognize and alter movement upon encountering patch edges. Results suggest that laboratory estimates of Tetraopes vagility give a misleading indication of actual dispersal.

THE RICE BROWN PLANTHOPPER: Feeding Physiology and Host Plant Interactions

Rice, Oryza sativa L., is an ancient cereal crop domesticated about 10,000 years ago along the hilly tracts south of the Himalayas (8). Because of the long history of its cultivation and its widespread dispersal, rice is probably the most genetically diversified among the world's cereal crops. In all Asian countries, rice is by far the most important staple food crop, and approxi­ mately half of the people on earth obtain the majority of their caloric intake from rice. Among the rice herbivorous insects, the brown planthopper, Nilaparvata lugens (Stal) (hereafter BPH), is one of the most notorious pests. It causes economic damage to the rice crop directly by feeding ( 116) and also indi­ rectly by transmitting grassy stunt (8 1) and ragged stunt virus diseases (54). The BPH is a small (2-3.5 mm in body length), brownish, sucking insect, belonging to the suborder Homoptera, series Auchenorrhyncha, super­ family Fulgoridae, and family Delphacidae. Members of the genus Nilapar­ vata are characterized by several lateral spines on the hind basi-tarsus (69). The adult shows density-dependent wing dimorphism with macropterous and brachypterous forms (20). Macropterous adults have the ability to migrate over long distances. The BPH is endemic to the tropical oriental region, but its habitat can temporarily expand as far north as Japan and Korea every summer through long-distance massive migrations from the tropics (46). The BPH is a monophagous insect restricted to cultivated rice and its allied wild forms such as Oryza perennis and O. spontanea (45). Thus, the seasonal occurrence and relative abundance of the BPH depend largely upon cropping patterns and intensification of rice cultivation.

Different effects of variation in Xanthium strumarium L. (Compositae) on two insect seed predators

To determine the relative importance of variation in several plant characters on susceptibility to herbivores, we examined patterns of seed predation by two monophagous insect species and patterns of variation in ten populations of the cocklebur, Xanthium strumarium. Multiple regression analysis disclosed that one seed predator was most influenced by plant chemical variation, the other was significantly influenced by both chemical and morphological variation, but variation in yet another character, general burr size, was most important in conferring resistance to both insects simultaneously. The plant populations differed most in this character. Although many of the plant characters were correlated with each other, those important in determining susceptibility to each insect species were uncorrelated and independent of those conferring resistance to both insects simultaneously.These results imply that ecological similar herbivores may be influenced by different aspects of plant variation, and that predictions of evolutionary responses of local plant populations to herbivory may require knowledge of the structure of local herbivore communities and the dynamics of their establishment.

Choice of Food and Numerical Abundance Among Insects

Insects are not alone in almost unlimited capabilities for rapid multiplication, the limiting causes being prevalence of disease, parasites and available food supply. The remarkable instincts associated with the choice of food plants have been largely neglected by investigators. Certain insects like the migratory locusts are highly polyphagous, while others are limited to a single food plant, probably through a long evolutionary process. Agricultural pests may be either polyphagous, oligophagous or monophagous and under primitive conditions the former were represented by larger populations than those with more restricted diets. Only very exceptionally do natural associations of plants offer ideal conditions for monophagous insects, as in western coniferous forests and certain types of grasslands some oligophagous species are apparently composed of several phytophagic races propagating more or less independently. Species exhibiting remarkable capacity for shifting from one food plant to another, such as the cotton boll worm may become extremely abundant where its food plants are associated, though natural checks soon establish an approximate balance as a rule. Trees and plants with a long life cycle occupy a relatively insecure position with regard to insect damage.