30 MASS. EXPERIMENT STATION BULLETIN 261 



Since the average temperature is somewhat lower than that of the Upper 

 Austral, which ordinarily does not have excessive heat, it leaves the problem 

 of determining if the temperature is high enough to favor reproduction. The 

 mean monthly temperatures for July and August (fig. 9) for the Transition 

 Zone are 69.7° F. (21° C.) and 67.4° F. (19.7° C). These temperatures fall 

 near the lower limits of suitability given in Figures 1-5 for the various stages. 

 The beetle successfully overwinters in states that have as low temperatures 

 as this area and apparently the bean beetle can be expected to become a pest 

 over at least the southern part of the Transition Zone in so far as tempera- 

 ture and moisture are concerned, but may be restricted by lack of suitable 

 food plants. As the northern limits of the Zone are approached, the injury 

 will become less. The insect has recently been found in this faunal division 

 in the Housatonic Valley of Connecticut and Massachusetts. 



Caiiadum Zone. The climographs of temperature and precipitation for the 

 portions of Maine, New Hampshire and Vermont in the Canadian Zone are 

 given in Figure 11. The moisture of the environment appears to be satis- 

 factory for the developn.ent of the immature stages. Very little danger to 

 the pest would result from a combination of high temperature and high 

 moisture conditions. However, the temperature alone woidd not encourage 

 rapid developn;ent. The n.ean temperature of the warmest month, July, is 

 6.5.2° F. (18.5° C). This means that the temperature would reach a favor- 

 able position for developn.ent for only a few hours daily and would not be 

 sufficient for the beetle to become a pest. The insect may migrate into this 

 area from the Transition Zone during the summer months and produce a lim- 

 ited amount of injury in local areas. 



Discussion. 



The conclusions that can be drawn from this study are based upon aver- 

 age conditions, and temporary variations from these will, of course, produce 

 an environment either more or less favorable to the pest, depending upon the 

 (direction and duration of the variation. Local areas within the three zones 

 may be found which do not have a temperature and moisture environment 

 comparable to the surrounding region but such will not be suflBcient to in- 

 validate the general conclusions. 



Food AiHiilahiUty in Netc England. 



The principal food plant, beans, is common in Connecticut, Rhode Island, 

 and eastern Massachusetts. This crop is localized in central and western 

 Massachusetts and southern Maine, and is grown to a much less extent irt 

 New Hampshire and Vermont. Part of the Connecticut acreage is used for 

 producing dry beans, but the growers in the remainder of New England 

 market their product as string beans. The non-cultivated plants on which 

 the bean beetle is known to develop belong to two genera, Desmodhim (beg- 

 garweed) and Crotolaria (rattle-box), both closely related to beans (Thomas, 

 1924). One species of the latter, and at least seventeeni of the former, are 

 found in New England. Howard and English (1924) report D. canescens, a 

 species found in New England, as being a suitable plant for larval develop- 

 ment. These weeds may become important factors in the dispersal of the" 

 pest. 



