Lntraspecific Variation in Bionomic Characters of the Mexican Bean Weevil, Zabrotes Subfasciatus

P. F. Credland & J. Dendy Department of Biology, Royal Holloway and Bedford New College, University of London, Egham Hill, Egham, Surrey TW20 OEX, U.K.

Accepted: May 1, 1992

Key words: Development, fecundity, geographical variation, Coleoptera, Bruchidae, ecology, Phaseolus

Abstract

Zabrotes subfasciatus (Boheman) (Coleoptera:Bruchidae) is native to parts of Central and South America but has now been spread to many others areas. It commonly infests the seeds of both Lima beans, Phaseolus lunatus, and common beans, Phaseolus vulgaris. Five geographic populations were found to differ in fecundity, patterns of egg distribution, times of development and adult sizes when they were kept under the same conditions. Each population also differed unpredictably from the others in its response to different cultivars of host seed. These differences have been shown to be of considerable importance in determining the potential pest status of the populations and should also promote caution in making predictions about the responses of different populations to new cultivars of bean for agricultural use.

Introduction immature development within the single bean which is therefore the sole source of nutrients. Zabrotes subfasciatus (Boheman), otherwise Around 5,500 years ago man began the collection, known as the Mexican bean weevil, originally cultivation and storage of the seeds of P. lunatus lived on the Lima bean, Phaseolus lunatus, and (Kaplan, 1965) and the beetle has now become a probably also the wild ancestors of its close rela major pest of the stored seeds of several species tive, the common bean, P. vulgaris, in Central oflegume including some which were initially out America and the northern parts of South Amer side its geographical range (Meik & Dobie, 1986). ica (Bonet et al., 1987; Pimbert & Jarry, 1988). Furthermore, Z. subfasciatus has itself spread, al The female oviposits on the naked seeds after pod most certainly through trade in bean seeds, to dehiscence or may attack seeds inside pods which many parts of the tropics and subtropical areas of have previously been holed by other phytopha the world, in many of which it has become per gous insects. Unlike those of many other manently established (Southgate, 1978). bruchids, females will not attach eggs to the pods It has previously been shown that many larvae themselves (Pimbert, 1985) and they need contact may complete their development in a single seed with seeds to stimulate ovarian production (Pim both in the field and in store. Individual Z. sub bert & Pierre, 1983). The larva bores into the seed fasciatus may actually limit their oviposition to to which the egg was glued and completes its only a few of the available host seeds, laying several eggs on each (Dendy & Credland, 1991). This Materials and methods aggregated distribution among seeds is in addi tion to the clumping of eggs on each seed, whereby Origin and maintenance of the insects many of the eggs on a single seed are laid in close proximity to each other, as first reported by Utida Samples of five different field populations ol ( 1967). Thus, competition within a single seed Zabrotes subfasciatus were collected at differen1 may be intense and have important consequences times and have since been cultured in various . for larval survival and/or the fitness of the emerg laboratories. Colombia I was otherwise known as ing.adult beetles. stock 100 in the laboratory of the Natural Re In other species of bruchid, notably Callo sources Institute (NRI). It was obtained in 1984 sobruchus maculatus and Callosobruchus chinensis, from the Centro Internacional de Agricultura there are some fundamental bionomic differences Tropical (CIAT) in Colombia and returned im between populations, which extend to their re mediately to Slough where the laboratory was sponses to resistant cultivars of individual host then based. It has since been cultured continu species (Dick & Credland, 1986; Credland, 1990). ously on commercial red kidney beans (RKB), To date, there have been no attempts to compare Phaseolus vulgaris, in a constant temperature and populations of Zabrotes subfasciatus under uni humidity (CTH) room at a temperature of form conditions and thereby determine whether 27 ± 1 °C and 70 ± 10% RH. The population was variation has arisen between the populations subcultured after each generation by transferring which now have a discontinuous distribution. 150 individuals to approximately 1000 ml of fresh Since efforts are cun-ently being made to breed seeds. This was the Colombian stock used by cultivars of Phaseolus vulgaris with bruchid, spe Meik & Dobie (1986). cifically Zabrotes, resistance (Cardona et al., Colombia II was known as stock 107 in the 1989; Dobie et al., 1990) it seems highly desirable laboratory of the NRI. The culture was started in to rectify this omission from our understanding of 1986 from a field collection made in Colombia their biology. To this end a number of basic pa and has since been maintained in the same way rameters have been selected and compared both as the previous stock. between cultures established from different pop The Uganda stock was collected in 1980 from ulations and also among representatives of the around Kampala, where it was found on cow same cultures reared in different, susceptible cul peas. The culture has been maintained on cow tivars of the same host species. peas in the laboratory since that time in the same The case of Zabrores subfasciatus may repre CTH as the other stocks. This was the cowpea sent a situation which is increasingly common as feeding stock used by Meik & Dobie (1986). commodities are transported around the world The Zimbabwe stock was a gift from Dr. D. more often and at greater speed than has been Giga who collected it from the Grain Marketing possible in the past. The brevity of the journey Board in Harare, Zimbabwe, in 1986 and main undoubtedly increases the chances of insects' sur tained it at the University of Zimbabwe until a vival. Thus, the kind of differences which have sample was dispatched to the U.K. on 'speckled arisen between populations of Z. subfasciatus beans', a local cultivar of P. vulgaris, in 1989. It could be typical of those to be found among other has been maintained continuously on RKB since species of (stored product pest) insect and there its arrival in the U .K. fore have wider relevance than is immediately The Mexico stock was collected from the obvious. Due to the relative simplicity of the en Cuernaraca/Morelos area of Mexico in 1988 and vironment, it is also possible to estimate the cultured locally until 1989 when a sample was importance of such differences in terms of provided to NRI. A subsample was transferred the population growth and their damage poten from there to our laboratory. It has been cultured tial. continuously on RKB. 41

At the outset of the experiments there was no were counted and any which had failed to hatch evidence to indicate differences between the 5 were noted. The progeny were collected from each populations, stocks or cultures. Accordingly, they tube as they emerged. are described below simply as strains, since this Development periods were measured from the term does not carry the implication of others such time that the newly emerged adults were put onto as 'biotype' (Diehl & Bush, 1984). fresh seeds in their tube until the time of emer gence of each of their adult progeny. The mean period for the emergence of all the prog~ny of Experimental protocols each female was then calculated. It should be noted that the developmental periods cited below From each strain, newly emerged virgin females are not therefore the periods from oviposition to and males were collected and a pair, one female adult eclosion. Individual females and males from plus one male, was placed in a glass tube 5 cm in the tubes were weighed within 2 h of emergence. height and 2.5 cm in diameter with either 10 RKB, 10 seeds of the Calimacultivar of P. vulgariswhich were supplied by Dr. C. Cardona of CIA T, or Results either 10 or 30 seeds of a commercial variety of haricot, a small, white or cream coloured, ovoid Mean fecundity of females varied from 36.11 eggs cultivar of P. vulgaris. All the seeds were individ laid by the Uganda strain on 30 haricot seeds to ually inspected before use, and any with an im a maximum of 57. 78 laid by Colombia II on perfect testa were discarded. The tubes were Calima. There were significant differences in stoppered with porous foam bungs and then both the responses of the strains to each host housed in the CTR room. Between 10 and 20 (F(4 ,22 o) = 5.63***) and in the responses of each replicates were set up for each combination of strain to different hosts (F(3.:2:2o)= 5.43***). There host and insect strain. was a significant interaction between strain and

The distribution of eggs among the available host (F c12 ,220 > = 1.93*), indicating that the effects seeds was described by the 'index of uniformity' of different hosts on fecundity vary among the (U-statistic) of Messina & Mitchell (1989). This strains (Fig. la). essentially depends on calculating the number of In every combination of strain and host, be eggs which must be relocated from one seed to tween 89.7 and 99.6 % of all the eggs that were another to produce a uniform distribution of the laid hatched to produce viable larvae which pen total number of eggs laid on the seeds available. etrated the seeds to which the eggs were attached. A value of 1 would indicate perfect uniformity of An analysis of variance on transformed data egg distribution, 0 indicates a Poisson distribu (square root, arcsine) indicated that there were tion, and negative values indicate aggregation or statistically significant differences among the hyperdispersion. To compare egg dispersion strains (Fc4 , 182 ) = 7.19***) and the hosts (F(2,is2 > under different conditions, values of U had to be = 7.57*). Multiple comparison tests showed that transformed since many were negative and pos these were due to the Ugandan strain exhibiting itive values cannot exceed 1. To permit the use of reduced hatching in comparison with other strains an analysis of variance, 2 was added to each cal on RKB and haricot, and the Colombia I and culated value of U, the sum divided by 3, and the Mexican strains exhibiting depressed hatching on product subjected to the usual square root arcsine haricot as compared with the Calima cultivar. transformation. Multiple comparisons were un Any consequences of differential hatching are in dertaken using Student-Newman-Keuls tests and cluded in the subsequent data where adult emer reported differences were significant at the 5 % gence from seeds is recorded. level or less. The distribution of eggs among the available After 18 days all the eggs laid by each female seeds was aggregated or random (Table 1). A (a) (b)

Colombia 1 Colombia 2 Uganda Mexico Zimbabwe Colombia 1 Colombia 2 Uganda Mexico Zimbabwe

- Haricot (10) EZ2JHaricot (30) EHERKB &'S3Calima - Haricot (10) EZ2JHaricot (30) EHERKB E:;s:'3Calima (c) (d)

· Development period (days) Mole weight (mg)

38 2.5

2 36 1.5 34

32 0.5

Colombia 1 Colombia 2 Uganda Mexico Zimbabwe Colombia 1 Colombia 2 Uganda Mexico Zimbobwe

- Haricot (10) EZaHaricol (30) EHERKB &'S3Calima - Horicol EEH3RKB &'S3Colima (e)

fem ale weight (mg)

4 Fig. 1. Bionomic parameters of 5 different strains of Zabrote: subfasciatus on red kidney beans, the Calima cultivar and whiti 3 haricot beans, all varieties of Phaseolus vulgaris. (a) The mear numbers of eggs laid by individual females; (b) The mear percentage of the eggs initially laid on different batches of hos seeds which produced adults; (c) The mean development pe Colombia 1 Colombia 2 Uganda Mexico Zimbabwe riods (see text for precise definition) of individual insects; (d The mean wet weight at emergence of males; ( e) The mean we - Haricot EHERKB f;S3 Calima weight at emergence of females. two-way analysis of variance revealed a signifi on 10 'haricot seeds than on the other hosts or cant difference among the strains (F(4 ,223 ) = which were aggregated. If the relative sizes anc 6.55***) and the hosts (F(3,223 ) = 8.21 ***) but a therefore surface areas of the seeds are consid· statistically insignificant interaction between the ered, it was to be expected that when all the seedi variables. Eggs were more randomly distributed were laid on the small surface of only 10 haricO' 43

Table 1. Mean values of 'U' for individual females of each strain offered different hosts for oviposition. There are significant dif ferences among the strains in response to the various hosts; the same superscripts indicate no difference at the 5 % level. There are also differences in egg distribution on the hosts; those hosts with the same superscript do not differ

Host (No.) Strain of Zabrotes subfasciatus

Colombia I" Colombia IP Ugandax MexicoY ZimbabweY

RKB(IOt 0.54 0.14 - 0.81 0.28 -0.43 Calima (IOt -0.69 -0.48 0.62 -0.50 0.23 Haricot (IO)h -0.44 0.32 0.41 0.05 - 0.10 Haricot (30t 0.65 -0.25 -0.77 0.59 -· 0.67 beans, then a random distribution was likely to As a percentage of the eggs laid, there was far result since the choice of oviposition sites was less variability in adult emergence among the severely limited. Eggs laid by the Colombia I and strains and hosts which were tested (Fig. 1b ). Ugandan strains were significantly more aggre Nevertheless there were significant differences gated than those laid by the other three strains. between the strains (f (4•228 ) = 10.49***) and

The mean number of seeds among those avail between the hosts (F<3 ,228 ) = 8.44***) but no sig able which bore eggs was obviously related to the nificance in the interaction between them aggregation of eggs onto some seeds at the ex (F(l 2 ,228 ) 1.68, N.S.) as determined by two-way pense of others (Table 2). However, aggregation analysis of variance on square root, arcsine trans does not imply that no eggs were laid on some formed data. seeds, merely that the majority were laid on a few Development periods ( as measured in the man of those available. Nevertheless, it is clear that in ner described previously) varied from a minimum many cases females concentrated their eggs onto of33.4toamaximumof37.6days(Fig. le). There only a few of the seeds available to them and laid were significant differences in the development no eggs on the remainder. periods (f <4 ,228 ) = 79.03***) of the strains on The smallest mean number (29.2) of adult each host, of each strain on different hosts progeny was produced by individual fem ales of (F(3,zzs)= 14.86***), and a small but significant the Uganda strain on Calima, and the largest interaction between them (F c12 ,228 ) = 2.10*). number was 52.3 produced by Colombia I on The mean live weights of individual males re RKB. It should, however, be noted that the vari corded at emergence varied from 1.83 to 2.36 mg ation recorded in these numbers is attributable (Fig. Id) but the lightest individual actually both to the number of eggs laid initially, the num weighed only 1.23 mg and the heaviest 2.84 mg. ber hatching, and survival of the immature stages There were significant differences between the in the seeds. weights of the strains (Fc4 •285 ) = 41.21 ***) and in

Table 2. The mean number of seeds bearing any eggs when females of different populations were each offered different kinds and numbers of host seeds

Host (No.) Strain of Zabrotes subfasciatus

Colombia I Colombia II Uganda Mexico Zimbabwe

RKB (10) 9.4 9.7 7.7 9.3 9.2 Calima (10) 9.2 9.9 6.9 8.8 9.6 Haricot (10) 8.8 9.7 8.7 9.7 9.5 Haricot (30) 20.2 22.3 17.1 18.0 19.0 beetles from different hosts (F<2,285 ) = 17.78***). during host changes (Taper, 1990). The difference Once again, there was a significant interaction in the development history of the Uganda insects between the factors under consideration should be noted throughout as a possible source (F(S,285) . 2.14*). of variation, but it does reflect a realistic variation Female weights varied in much the same way among longstanding populations which needs ta as those of the males (Fig. 1e) but were almost be considered. Egg hatching was high in every twice as great with a grand mean in excess of case and is unlikely to contribute significantly to 4 m_g.There were significant differences between differences in the number of adult progeny pro the strains on the same host (F(4 ,285 ) = 38.74***) duced by any female. and in the weights of each strain on different hosts It has previously been shown (Dendy & Cred

(F(2,285 ) 21.57***). The interaction between land, 1991) that a Colombian strain, aggregated hosts and strains was also significant (F(8,285 ) = its eggs onto a small number of the RKB or har 2.14*). icot host seeds available. Among the differen1 strains used in the experiments reported above. eggs were aggregated in almost every situation Discussion (Table 1), although the extent of the aggregatior. was variable. Generally, Colombia I and th<: It will be immediately obvious that in every re Ugandan strain aggregated their eggs more spect considered, there were statistically signifi strongly than the others. Eggs were laid morE cant differences between the populations of randomly on 10 haricot seeds than in the othe1 Zabrotes subfasciatus examined. Furthermore, it situations, presumably because the surface are.: is probable that in the small sample of popula available for oviposition is much smaller anc tions which were tested, the extremes of variation therefore the eggs were more likely to be laid or were not represented. Conversely, not every pop every available surface, leading to a more uniforrr ulation differed from every other in a consistent overall distribution. There is a clear associatior way. between the aggregation of eggs (Table 1) and tht Total fecundity for a female varied from a mean mean number of seeds bearing eggs (Table 2 of 36 to 58 (Fig. la) which compares very satis which is not overtly surprising, but is not an in factorily with the maxima recorded by Howe & evitable correlate since aggregation does not de· Currie (1964), Umeya (1966) and Meik & Dobie pend on some seeds bearing no eggs. It is simpl) ( 1986), all in the high 30's, and the highest value a measure of the distribution of eggs among th< previously recorded, 57, by Cardona et al. (1989). available seeds. At least some of this reported variation may now The number of adult progeny produced by , be attributed to differences among the insects em single female is a consequence of differences ir ployed. It may not simply be a consequence of the oviposition, hatching, and levels of mortalit; methods used in collecting the data but may re among immature insects. Since there were mino sult from genuine intraspecific variation. The fact differences in hatching, the best parameter fo that the insects from Uganda were reared in the determining differences in immature viability i: parental generation on cowpea rather than RKB the percentage of eggs laid which produced adults could have affected their fecundity, since different This figure excludes the differences in fecundit: hosts do have an effect on development. Never yet provides a simple and readily measurable pa theless to have switched them to a different host rameter. Although not widely different (Fig. lb) for the purpose of the experiments could also the variation is statistically significant, implyin: have produced unpredictable variation, since that there are important differences in larval phys there is evidence that in other bruchids such as iology which may have even greater significanc, Callosobruchus chinensis displacement of charac when reactions of strains to different hosts con ters such as development times and size can occur taining a wider diversity of allelochemicals ar 45 considered. Much the same deduction can be tions responded to 3 nominally acceptable and made from the differences in mean development susceptible hosts, all of the same species, P. vul periods (Fig. le) where not only the strains and garis. It is common practice in many studies where hosts were statistically different but the interac putative resistant cultivars are being examined, to tion was also significant. It is therefore essential treat one 'susceptible' host as an adequate com that where development period is used as a pa parator for the experimental seeds. The present rameter in assessing resistance among host seeds, study clearly revealed that such practice is inap the inherent variation among strains of the insect propriate. is taken into account. The most significant consequence of the results Both male and female weights varied consid presented here is that it is clearly impossible to erably between the strains employed and with the identify 'species characteristics'. The discrepan hosts in which they developed. Thus, whilst it cies between strains which sometimes appear very appears to be true that the weights provide a sen small may be of fundamental importance if the sitive measure of differences between hosts, the populations are considered over a few genera interstrain variation and significant interaction tions. Stored products pests such as Z. subfas between strain and host means that the data have ciatus are usually found, by definition, in an abun to be treated with caution. dance of their hosts and there is no evidence, at It is perhaps surprising at first sight that there least where this species is concerned, that their were differences in the way in which the popula- numbers are effectively constrained by biological

a b Population size Weight of seed damaged (kg) 40,000

30,000

20,000

10,000

0 20 40 60 80 100 120 140 Days Days

Fig. 2. (a) Predicted numbers of individuals of the Colombia I (solid line) and Ugandan (dashed line) strains reared in RKB, starting from a single newly mated female, based upon the data presented in this paper; (b) Possible weight of seeds damaged by beetles of the Colombia I (solid line) and Ugandan strain (dashed line) over a three month period, based on. data presented above. Note the rapidly escalating distinction between the two strains of beetles. , factors· such as the activities of parasitoids. At data produce dramatic differences in both popu least in the initial stages of infestation, there is a lation increases and seed damage. large number of pristine seeds which can be uti Two inferences follow from the preceding ar lized, and there is evidence that oviposition is gument. First, apparently trivial differences ii regulated to some degree by host marking by fe bionomic data may be extremely important in cer males (Umeya, 1966); interaction between the tain circumstances. Secondly, the production o progeny of different females may therefore be seed cultivars which diminish fitness to a limite( minimal. Consequently, there are few if any fac extent may still be useful for reducing seed dam tors to inhibit the exponential increase in beetle age. It is therefore suggested that the data pre populations. If it is assumed that interactions are sented not only reveal significant intraspecific avoided and that the number of hosts does not variation in Zabrotes subfasciatus, but also have: constrain population increase, it is possible to wider significance in illustrating, quantitatively estimate, somewhat crudely, that rate at which both the biological and economic importance o two of the populations studied above may in small bionomic differences between populations crease using the data presented. The Colombia I population produced the most adult progeny (52.3) and had the shortest mean development Acknowledgements time (33.35 days) on RKB. Conversely, the Ugandan population produced fewer progeny We are greatly indebted to the Natural Resource~ (30.1) and took longer to develop (35.9 days) Institute, formerly ODNRI, for their considerable on the same host. Making the assumptions financial support and some of the insect stocks. noted, and assuming an adult sex ratio of 1:1, it We are also grateful to Dr. C. Cardona for othe1 can be seen that the population sizes are widely insects and the Calima seeds, to Dr. D. Giga for different after just 3 generations if each started the insects from Zimbabwe, to Dr. Frank Mes with a single, newly mated female (Fig. 2a). In sina for the computer programme used in the cal reality, a few founder females are likely to occur culation of U-values, and to John Val en tine of the which would merely serve to exacerbate the dif Department of Psychology, RHB NC, for his ad ferences. vice on the statistics employed. Noting that the Ugandan strain aggregated its eggs more than Colombia I on RKB (Table 1), it is further possible to estimate the impact of the References strains on stored seeds. Whilst it is probably true that given an excess of available seeds, each fe Bonet, A., B. Leroi, J. C. Biemont, G. Perez & B. Pichard, male will use more seeds for oviposition than were 1987. Has the Acanthoscelides obtectus group evolved in the original zone of its host plant (Phaseolus L.)? In: Labeyrie. noted in Table 2, the relative numbers used by the V., Fabres, G. and Lachaise, D. (eds), Insects-Plants. Junk two strains is likely to remain comparable since Publishers, Dordrecht. Pp. 378. the Ugandan strain always aggregated its seeds Cardona, C., C. E. Posso, J. Kornegay, J. Valor & M. Ser more than Colombia I (Table 1). Using the data rano, 1989. Antibiosis effects of wild dry bean accessions or presented in Table 2, one can then multiply the the Mexican bean weevil and the bean weevil (Coleoptera Bruchidae). J. econ. Entomol. 82: 310-315. number of seeds used by each female, by the num Credland, P. F., 1990. Bio type variation and host change ir ber of females present in each generation. Know bruchids: causes and effects in the evolution of bruchic ing that 100 RKB weighed about 66 g, the weight pests. In: Fujii, K., Gatehouse, A. M. R., Johnson, C. D. of seeds damaged by each generation can be cal Mitchell, R. & Yoshida, T. (eds), Bruchids and legumes culated, revealing the remarkable difference ap economics, ecology and coevolution. Kluwer Academic publishers, Dordrecht. Pp. 271-287. parent in Table 2b. Thus, even if elements of the Dick, K. M. & P. F. Credland, 1986. Variation in the respons( assumptions are not totally valid, it is clear that of Callosobruchus macu/atus (F.) to a resistant variety 01 the small but significant differences in bionomic cowpea. J. stored Prod. Res. 22: 43-48. 47

Dendy, J. & P. F. Credland, 1991. Development, fecundity of the oviposition pattern of Zabrotes subfasciatus inside and egg dispersion of Zabrotes subfasciatus. Entomol. exp. pods of a wild, Phaseolus hmaws, and a cultivated host appl. 59: 9-17. plant, Phaseolus vulgaris. Insect Sci. Applic. 9: 113-116. Diehl, S. R. & G. L. Bush, 1984. An evolutionary and applied Pimbert, M. & D. Pierre, 1983. Ecophysiological aspects of perspective of insect biotypes. Annu. Rev. Entomol. 29: bruchid reproduction. I. The influence of pod maturity and 471-504. seeds of Phaseolus vulgaris and the influence of insemination Dobie, P., J. Dendy, C. Sherman, J. Padgham, A. Wood & on the reproductive activity of Zabrotes subfasciatus. Ecol. A. M. R. Gatehouse, 1990. New sources of resistance to Entomol. 8: 87-94. Acanthoscelides obtectus (Say) and Zabrotes subfasciatus Bo · Southgate, B. J ., 1978. The importance of the Bruchidae as heman (Coleoptera:Bruchidae) in mature seeds of five spe pests of grain legumes, their distribution and control. In: cies of Phaseo/us. J. stored Prod. Res. 26: 177-186. Singh, S. R., Van Emden, H.F. & Taylor, T. A. (eds), Pests Howe, R. W. & J. E. Currie, 1964. Some laboratory observa of grain legumes: ecology and control. Academic Press, tions on the rates of development, mortality and oviposition London and N.Y. Pp. 219-229. of several species of Bruchidae breeding in stored pulses. Taper, M. L., 1990. Experimental character displacement in Bull. entomol. Res. 55: 437-477. the adzuki bean weevil, Callosobruchus chinensis. In: Fujii, Kaplan, L., 1965. Archaeology and domestication in Ameri K., Gatehouse, A. M. R., Johnson, C. D., Mitchell, R. & can Phaseolus beans. Econ. Bot. 19: 358-368. Yoshida, T. (eds), Bruchids and legumes: economics, ecol Meik, J. & P. Dobie, 1986. The ability of Zabrotes subfasciatus ogy and coevolution. Kluwer Academic publishers, Dor to attack cowpeas. Entomol. exp. appl. 42: 151-158. drecht. Pp. 289-301. Messina, F. J. & R. Mitchell, 1989. Intraspecific variation in Umeya, K., 1966. Studies on the comparative ecology of bean egg-spacing behaviour of the seed beetle Callosobruchus weevils. I. On the egg distribution and the oviposition be maculatus. J. Insect Behav. 2: 727- 742. haviors of three species of bean weevils infesting adzuki Pimbert, M., 1985. A model of host plant change of Zabrotes bean. Res. Bull. Plant Prot. Serv. Japan 3: 1-11. subfasciatus Boh. (Coleoptera:Bruchidae) in a traditional Utida, S., 1967. Collective oviposition and larval aggregation bean cropping system in Costa Rica. Biol. Agric. Hort. 3: in Zabrotes subfasciatus (Boh.) (Coleoptera, Bruchidae). J. 39-54. stored Prod. Res. 2: 315-322. Pimbert, M. & M. Jarry, 1988. A non-parametric description